Project finished, cylinder head rebuilt.
Photo by Iain Barker
More Social Distancing, Workshop Style
by Iain Barker
Part 4 — Rebuilding a Cooper S cylinder head
With the “short engine” completed, and the COVID lockdown well into its second month, I figured I would turn this project it into a full engine build.
Original cylinder heads used for the Mk1 Mini Cooper S were rather notorious. They were engineered in low quantities for the knife-edge of “works” race/rally performance as opposed to reliability. Even in period, the manufacturing quality was quite variable.
The main problem with the original design was the excessively over-sized exhaust valves, which at 31mm were so large that they did not fit into the combustion chamber without the valve seat physically overlapping into the area of the (also oversized) 35mm inlet valve. The area between the two was machined so thin during manufacture that it easily overheated and burned through the iron casting, cracking from one side to the other and rendering the head unusable.
In 1969, Daniel Richmond of Downton Engineering redesigned the whole head assembly to improve reliability, increasing the head thickness to aid cooling and reducing the exhaust valve size slightly to 29mm. It may not seem like much, but that extra 2mm radically improved reliability — with the result that starting very soon afterwards BMC Service would retro-fit the new head design onto Mk1 and Mk2 Cooper S cars when the original head failed. The new-spec Cooper S heads were stamped with “S” behind the thermostat housing and part number 12G1805, versus the early AEG613 and the generic 12G940 used on later 1275cc engines.
The passage of more than 50 years has made availability a challenge. Finding a good condition Cooper S head is especially difficult in the USA, where there were historically many fewer cars sold. Shipping is also a problem, as the head assembly weighs around 25 lbs. so it’s not the easiest thing to mail across from Europe. But I had a cunning plan…
Used S heads are occasionally available on eBay U.K., and we had already booked an Easter vacation to visit my family there. I would simply have the head delivered to Mum’s house and carry it back as hand luggage on my return flight.
You can see where this is going. Unfortunately the whole COVID-19 thing happened a few weeks before Easter, and it was obvious that our trip would be cancelled. Not wanting to burden Mum with breaking isolation, I engaged a local courier to do a “contactless” pickup-and-then-forward via DHL to me here in the U.S. All told, it was still cheaper than buying a modern performance head from one of the U.S. vendors, but not by very much. C’est la vie — at least I had the head and could start working out if it was going to be usable for this project.
I knew from the eBay advertisement that it had been extensively worked, polished and ported, then left unused for about 20 years. An ideal match for the cylinder block that I used for this build, which was also machined and left unused for a similar period!
With the head safely delivered, I set about stripping it down. The double valve springs, collets, caps and valves were soaked for a week in carburetor cleaner, and the head was given the same treatment as the cylinder block — a few hours soak in CLR (Calcium Limescale Rust remover), followed by internal and external wire brushing.
Lapping in the valves.
Photo by Iain Barker
Amazingly, the head looked as good as new after cleaning, requiring just a light polish using 2500 grit wet and dry paper by hand on a sanding block to re-dress the flat cylinder face. I filled the water galleries with boiling water and let it stand for 20 minutes or so — no seepage into the valve chambers, so at least porosity would not be a problem. I also re-lapped the valves into their seats in the traditional way that Dad taught me years ago — coarse carborundum paste for the first hand lapping, followed by fine for the final pass, until no chafing could be heard when rotating the valve against its seat while being pushed firmly into its guide.
This head does not have hardened inserts fitted, so for unleaded use I’ll need to use a fuel additive — but considering the low mileage my Mini does each year, seat recession is not going to be much of a problem.
The springs all looked good after their cleansing soak, so reassembling the valve assembly was straightforward.
The “extensive work” listed in the eBay description was certainly evident. The inlet ports were massive, and the head thickness measured 40 thou below standard, so they had been skimmed, then the combustion chambers opened back up using a die grinder. Before I could use this head, I needed to know whether the combustion chamber volume was standard, or if someone had modified it for high compression during the skimming. This is usually done by fixing a flat piece of Perspex to the face, fitting a spark plug, and then measuring the volume of fluid needed to fill the chamber.
I didn’t have any Perspex handy, and with the isolation lockdown, going to a hardware store wasn’t an option. After some searching around the house for a substitute, I settled on the clear 6” square plastic of a CD jewel case. With a few holes bored through for bolts to be fixed and using axle grease as a sealant against the block face, I slowly filled the void. In total it took a little under 22cc of fluid I used WD40 to avoid promoting further rust. The standard combustion chamber volume of a Mini head is 21.4cc, so allowing for some seepage and my not-so-scientific method, the result is nominal.
To complement this original head, I purchased a set of used rocker gear — again, the Cooper S specification is different from the regular Mini engines and uses stronger forged rocker arms, rather than the pressed steel of a standard A Series engine or the sintered steel of the later A+ type.
Tapping for a new bypass valve.
Photo by Iain Barker
One other job was to renew the bypass hose spigot. The rubber bypass hose is an Achilles heel for the Mini engine — difficult to replace once the engine is installed, and prone to leaking due to passing hot coolant from the head to the water pump, bypassing the thermostat.
In the case of this head, the original mild steel bypass hose spigot was intact but had clearly seen better days. Rather than risk failure down the road, I decided to replace it now. But of course it was rusted solid into the head, and all my efforts using vise grips, impact driver, etc., only succeeded in creating an increasingly shorter length of tube. Frustrated, I drilled out the hole and re-tapped it to fit a new spigot. This being a 1950s-designed engine, the required thread is an obscure Whitworth 5/8-16, but fortunately a UNS tap of the same thread pitch was available from Amazon.
With a fresh coat of etch primer, and MOWOG mid-bronze green paint to match the block, all that remained was to fit the new stainless steel studs for the heater take-off, thermostat housing, and manifolds, then fit the head onto the block — usually quite straightforward on a Mini. I chose a Payen BK450 composite head gasket. I had lightly sanded both faces to clean them up its additional compliance should seal any micro-scratches. The harder surface of a copper-faced gasket is more suited for use with freshly machined surfaces.
Well, I say usually quite straightforward. In this case, I encountered a problem with the set of used MG Midget standard pushrods I purchased off eBay (same spec as Cooper S, of course). The rod would not fit through the #4-cylinder inlet valve hole in the head. Fortunately, I had not yet torqued the head down, so I lifted it back off to investigate the problem. It seems that during the porting work, whoever did the grinding had broken through into the pushrod hole and a sleeve had been fitted to remedy the problem. All I had to do was drill the central hole of the sleeve a little larger, so that the pushrod could pass through cleanly. Another sign that the head had most likely not been used since the machining work was carried out.
With the head torqued to 45 lb.-ft. the top end assembly was complete. Next time, clutch and flywheel...
British cars mustering for the parade, Mini KK in the back row.
Photo by Iain Barker
Mini Drives in the Pandemic
by Iain Barker & David Schwartz
Social-distancing car parade, May 10th
Nuala and I joined the Arlington Classic Car Club (ACCC) for our first run of the year. Our car, “Mini KK,” had zero preparation after the winter. All I had a chance to do was pump up the tires, top off the oil and water, and fill up with fresh gas. The ignition was rough and the points gap didn’t look correct, but I didn’t have a spare set on hand. I did have spare distributor and spark plug leads in the trunk, so I quickly fitted those and off we went with fingers and toes crossed.
In compliance with the ACCC’s “ad hoc, no rules, no structure” anti-charter, the event was organized without much in the way of prior coordination. We assembled on parade day in a church parking lot. I counted 35 cars in total, nearly all pre-’80s classics with a few modern muscle cars and other interesting vehicles.
Mini KK had a bad misfire, really struggling to get up the Route 2 hill to Arlington Heights, and I couldn’t get her to go over 30mph. Once we arrived at the parking lot, I opened the bonnet and pulled the spark plug leads one at a time with the engine running. Cylinders 2 and 3 were not doing anything so I swapped the plug leads over and she was back to life. Well, at least cylinder 2 was working. Number 3 has low compression, which is why I spent the winter building a replacement engine!
The projected driving route was around 30 miles in two hours, but it took over three hours as there was a fantastic spectator turnout. Every street in Arlington seemed to have at least one family having a picnic on their front lawn, with social distancing being respected between each property. We sounded our horns as we waved to everyone.
Beatriz the Bulldog — how does she reach the pedals?
Photo by Alex Jones
It was a nice showing of community spirit and a welcome morale boost in these strange times.
At one point I tapped out Morse code on the car horn for “ACCC” (dit-dah, dah-dit-dah-dit, dah-dit-dah-dit, dah-dit-dah-dit) and “MINI” (dah-dah, dit-dit, dah-dit, dit-dit), and thought I heard someone beep “MM” in response (dah-dah, dah-dah). Anyway, it was all good fun and a great afternoon out in the sunshine. —IB
Chasing Mini Classics Run redux, May 24th
MINIs of Boston held a repeat of their May 16th Lexington-to-Sudbury drive, again organized by Josh Amato, this time including both Minis and MINIs. There were five classic Minis scattered among 15 modern cars. We used two-way radios to communicate, which came in handy when part of the group didn’t make it through a few traffic lights.
The weather was perfect, so I drove my ’68 Mini Traveller. NEMO members Wendy and Tom Birchmire attended in Wendy’s MINI convertible.
Mauricio Zambrano Vergara’s 1992 British Open Classic carried two bulldogs, usually in the back seat. Beatriz the Bulldog enjoys taking an occasional turn at the wheel. How does she reach the pedals?
The drive ended at the Wayside Inn Grist Mill, where attendees enjoyed the mill and beautiful grounds. —DS
Truly NOS! This came complete with period wrapping and a genuine BMC computer punch card from the ’60s.
Photo by Iain Barker
More Social Distancing, Workshop Style
by Iain Barker
Part 3 — External assembly
With the hard work of the engine internals completed, it’s time to turn my attention to the exterior of the block.
Usually this is just a case of cleaning up the old parts and bolting them back on. Since I am building this engine from scratch, I need to source all the correct parts first. In years gone by, this would entail schlepping around swap meets, and making many phone calls to used parts dealers to find just the correct piece of obscure metalwork. These days, it’s much easier — the main vendors have on-line indexes, and the eBay global shipping program takes care of the rest.
The Mini engine owes much to its predecessor, the Austin A30. Launched in 1951, the A Series engine has been steadily improved from a tiny 803cc (26bhp) up to a massive 1460cc (180bhp) on some turbocharged race engines. But despite this wide range of performance, the basic design is essentially identical, with a cast iron block and head, hardened steel crank, rods and camshaft, and alloy pistons.
Although exotic materials were used for the race-bred Cooper S engine, the external ancillary components are surprisingly mundane. Pressed steel ‘tin-ware’ is used for the front and side engine covers and relatively inexpensive castings such as the oil filter head, water pump, etc.
As with most things on the Mini, the design of these castings was improved (or, ahem, “cost-reduced”) over the years since the original Mk1. The oil filter is a good example. Later cars use a simple spin-on oil filter head with disposable cartridge filters, just like a modern car. But the original Mk1 uses a design that originated from the MG TA engine way back in 1936 and has a disposable paper filter within a reusable canister. This is much messier to change, but just as effective, and visually very different.
I chose to use original parts where possible. New parts are no longer available for the oil filter housing and canister, but similar 1960s era cars used almost identical components to the Mini, so it was relatively easy to find an equivalent part — in this case, a good used item taken from an MG Midget.
Used parts always need a close inspection for wear or abuse, and this one was no exception. The canister was dented, the filter head was clogged with 50 years of gunk, and it was missing the internal pressure plate. Fortunately, the pressure plate is the one part that is easily purchased new, since unknowing owners have a tendency to accidentally throw it in the garbage when changing the inner paper filter!
This filter housing needed a good clean before being fit for use, so it went for a weekend “spa break” in a bucket of carb cleaner, followed by some judicious wire brushing. It came up pretty well, and after hammering some dents out of the canister, and applying some etch primer and satin black paint, it was more than fit for the job.
Then I realized I didn’t have a gasket for the filter head to the block. Not wanting to wait another two weeks for USPS delivery from the West Coast, I cut one out of thick construction paper using an X-acto knife. I always use Permatex Aviation gasket sealant on all metal joints, so the gasket is really just there to carry the sealant.
I do have an original 1960s cast iron water pump, but after 50-plus years it needs new rubber water seals — not something I can do myself in the basement, as a fly-press is required. But I was able to locate a NOS alloy pump with the BL “plughole” logo cast into it, a sure sign that it’s a ’70s original part.
(British Leyland had commissioned an experimental alloy cylinder block to see if they could reduce the weight and improve performance of the engine. Although the engine worked well, it was not put into production due to projected development costs. The aluminum alloy water pump from the new design was re-worked to fit with the existing cast iron engine block, and A Series water pumps have been cast in aluminum ever since.)
Tin-ware on the Mini includes the front timing chain cover and two valve follower/tappet chest side covers — one of which contains an oil vapor condensing breather. Again, the 1960s version of these is different from the later Mini models but was used on similar cars of the era, including the Morris Minor and the MG Midget. I obtained and refurbished the correct “convex” type covers with MOWOG stamping. The cover with the breather was actually an original part that was supplied in its 1960s-style BMC waxed protective wrapping and with a dealer stock-control punch card!
Transmission and block mated.
Photo by Iain Barker
The timing chain cover oil seal is notorious for leaking on a Mini. The usual cause is that the oil seal is not centered on the crankshaft fan belt pulley, resulting in deformation of the seal and consequential weeping of oil. The easiest way to avoid the problem is to fit the new seal to the timing chain cover first, then fit the pulley into the seal before attaching the whole cover-plus-pulley assembly to the front plate. This guarantees that the crankshaft pulley will be centered in the seal. Some prefer to use RTV paste on the timing cover, but I like to use the same Permatex sealant as for the rest of the paper gaskets.
Unique to the Cooper S engines is a two-part Metalastic damper, and a star-shaped locking tab. This is designed to cut down on crankshaft vibration at the high revs at which the S engines were designed to run. The special locking tab is used in place of the soft fold-over tabs on regular Mini engines, which can work loose over time.
Fitting new core/freeze plugs was straightforward. The Mini uses the pre-formed cup style, so they don’t need peening after installation — just a lick of gasket sealant and then drive them home with a suitably-sized parallel dolly or a socket wrench and hammer.
An original Cooper S large cast iron fan belt pulley was trivial to clean up. The larger size reduces the water pump speed at high revs and avoids caviation (formation of small vapor-filled cavities). I painted the pulley bright yellow, which is the original factory color for the pulley and fan of a 1967 Mini.
(Note: Austin cars used yellow pulleys and fans, early Morris cars used MG Maroon, but both changed to yellow after the first rationalization around 1962.)
The last parts to fit are the distributor housing, oil pressure gauge takeoff and bypass valve. The current engine in my car uses an adjustable bypass valve, with a ball bearing and stronger spring. I’m trying the plunger type this time around as it’s supposed to regulate the pressure better.
For the distributor housing, I initially couldn’t find the proper A Series type for a Mini. I tried the B Series from an MGB as it looked to be the same size, but unfortunately the nose tube was too long. I considered cutting it down with a grinder but managed to locate a used one on eBay, thus avoiding a bodge.
With the external assembly completed, the engine can finally be mated onto the gearbox (which I also built up from scratch last year). Working at waist height on a table, and doing this singlehandedly was a challenge, because the rubber half-moon/crescent seal for the front main cap needs to be held in position for the duration. The factory lowered the gearbox onto the inverted engine, rather than lowering the upright engine onto the gearbox. So, I did the same this time around. It’s certainly much easier than trying to manhandle the heavier engine block into position over the gearbox.
Incidentally, the crescent seal is the only place on a Mini where I use RTV. Just a thin bead on both sides of the rubber seal to hold it in position, then let it cure for 15 minutes before joining the gearbox to the engine. This seal is now available in a composite rigid neoprene/metal version that was developed as a warranty replacement. It is much higher quality and stays in place better than the original simple rubber type.
With all the studs and bolts replaced and torqued up correctly, the major assembly is done. Next month, rebuilding an original Cooper S cylinder head!
Left to right: The Alex, Iain and Josh Minis on the Sudbury Run.
Photo courtesy NEMO
On the Road with Minis
by Iain Barker & David Schwartz
Mini Classics of Boston Sudbury Run, May 16th
The MINIs of Boston (MOB) Facebook group has a related group, “Mini Classics of Boston.” Josh Amato, one of the MOB organizers, invited classic Minis on a back roads drive from Lexington to Sudbury.
We met at the Paul Revere capture site on Rt. 2A near Hanscom airfield. There were three classic Minis (driven by me, Alex Daly and Michael Gonsalves, and Josh), plus another Mini owner (Mauricio) who came in a Jag F-type because his Mini had died the day before.
We drove in a convoy, stopped at a pop-up pizza van near Lincoln to pick up lunch, then continued on to the Wayside Inn Grist Mill in Sudbury. There is a nice open meadow next to the river where everyone sat in appropriately socially distanced groups to eat. —IB
Wedding postponed, but...
May 16th was also to have been Alex and Michael’s wedding day at the Larz Anderson Automobile Museum and Park, but with the pandemic it had to be postponed. It was disappointing they couldn’t host the event, but they made up for it with a classic Mini rally, a game of golf, and a surprise fancy dinner for Michael (special thanks to family and friends for stealthily making this happen). The quotes below are shared with permission from Alex’s Facebook page.
Alex: “Today is the day I was supposed to marry my best friend, my partner in crime, and sometimes my adult supervision... I can’t wait for the day when we can actually get married, but until then we have a fun day of adventure planned!”
Michael: “Well, Alex got me good. Coming home from an afternoon of golf to this table set-up, warm dinner in the oven, and dessert in the fridge was a complete surprise. In the face of a postponed wedding, I can’t think of a better way to conclude what ended up being a phenomenal day!”
We wish Alex and Michael many happy years together. —DS
Wendy Birchmire’s collection of miniature Minis and MINIs was revealed during the meeting!
Photo by Wendy Birchmire
NEMO Members Zoom into Meeting
by David Schwartz
At least 10 members participated in an on-line NEMO meeting hosted on Zoom on Saturday, May 2nd.
The technical aspects were mostly glitch-free. One person had audio problems and there were occasional video freezes, but it worked well overall. Zoom has become a de facto platform for simple video conferencing, despite some security concerns. You can download Zoom to your computer, phone or tablet.
Most people connected from home offices, family rooms, or in the case of Faith and Bruce, the super-secret British Marque headquarters. Bill Fralick broadcast from his garage and treated us to a view of his Cooper S restoration project. Amazingly, it is the very car that was the first Mini Dave Black ever rode in and the car that inspired him to become a lifelong Mini enthusiast!
Some experienced Zoom users had fun with custom screen backgrounds. Wendy Birchmire was one of them. She also posted a photo of her collection of 92 red Minis and MINIs, in a variety of scales.
Ken Lemoine gave us a tour of his diecast vehicle collection, as well as Mini and MG stained glass windows he created. The Mini windows were done some time ago and are sized to fit in the rear doors of Ken’s Mini Traveller. The MG logo was recently completed and is a birthday present for Ken’s son Brett. His latest project is a window hanging of the Jaguar logo.
Ken Lemoine’s stained glass projects include a representation of the NEMO logo, a classic Mini superimposed over an outline of the New England states.
Photo by Ken Lemoine
Iain Barker displayed his green Lego Mini Cooper, and yours truly showed off a 3-foot-tall Lego model of the Apollo Saturn V moon rocket. This was a quarantine project assembled by me and my daughter Laura.
Please post photos of your 1:1 scale cars and diecast vehicles on the NEMO Facebook page (www.facebook.com/NewEnglandMiniOwners). I will pin a photo link to the top of the page. Click “Comment” and the camera icon.
If you don’t want to post to Facebook, you can share them with the NEMO Google Group. Send an e-mail to email@example.com and ask to join the group. You can also e-mail firstname.lastname@example.org and I will post on your behalf.
It was great to catch up with people we hadn’t seen since the 2019 car show season, or the Holiday Party in December. Given that more events are being cancelled, we will definitely hold another on-line meeting. Next time I promise more advance notice.
Looking forward to “seeing” you soon!
Getting it done — with a timing protractor and an improvised locking tool.
Photo by Iain Barker
More Social Distancing, Workshop Style
by Iain Barker
Part 2 — Engine timing
This little project to build a 1960s Mk1 Cooper S engine started on 12th March. It’s mid-April as I write this, and we’ve just entered the second month of ‘social distancing’ (a.k.a. workshop lockdown!).
At the end of the previous installment, the pistons and rods, crankshaft, camshaft, oil pump and bearings had all been installed. Next up, the front of the engine – front plate, cam retainer and a shiny new AE ‘performance’ timing chain set, to tie it all together.
The engine front plate design has changed several times since the 1960s. On the mainstream ‘small bore’ Mini engines of 1098cc and below, a single row (simplex) timing chain was deemed sufficient for the Cooper S (970cc, 1071cc and 1275cc engines), however, an improved double-row (duplex) chain drive was introduced to cope with the higher demands of a racecar engine. For later 1980s cars the configuration was modified again with the A+ engine to incorporate revised engine breathing.
Original A Series front plates are getting harder to find, and a quick on-line check showed there were none available from the usual U.S. vendors. eBay to the rescue! I managed to locate a good used front plate in the U.K. It’s a 998 version, which means countersinking the two main bearing screw holes to fit the flush-mounted hex ‘Allen key’-style screws, so that they don’t interfere with the wider duplex chain. But it’s the correct style for A Series rather than A+, with an added bonus that the seller had already painted it with engine enamel, saving me the job.
The triangular cam retainer is fitted next. This holds the camshaft in position and needs to be aligned in no less than three different directions! While apparently symmetrical, it is important to get the cam retainer right way around — one side is coated with white-metal bearing material to provide the thrust surface for the cam, whereas the other side is just plain steel. The first alignment is with the camshaft sprocket fitted and the nut torqued. The end-float (in and out movement) needs to be very tightly controlled, the factory tolerance is 3 to 7 thousandths of an inch (‘thou’).
It may seem like a poor design to allow the camshaft to wander in and out of the block. But in fact, the lobes of the camshaft are machined at a slight angle, and a matching contour ground onto the base of the camshaft followers ensures that when rotating, the cam is always thrust toward the front of the engine against that white-metal bearing surface, and away from the oil pump. The tolerance is actually to allow sufficient slack so that the oil pump is free to rotate, since it is driven directly from the rear end of the camshaft.
The second alignment is to ensure the camshaft sprocket and the crankshaft sprocket are parallel to each other, with no offset that would cause the chain to drive against the sprocket teeth at an angle. The crankshaft sprocket is deliberately machined under-sized, and steel shims are fitted behind the sprocket in increments of 5 thou. The alignment is measured using nothing more than a straight-edge engineers’ ruler and feeler gauges. In all, I used three shims to bring the sprockets into alignment, for a 0.015” total offset.
The only snag during assembly was that I didn’t have the correct tool to lock the camshaft pulley when torqueing down the nut. Rather than break cover to visit Harbor Freight during the Covid-19 lockdown, I made my own crude approximation of a camshaft locking tool from a bit of old steel bed frame. Whatever works to get the job done!
Woodruff keys, used to fix the offset between the crank and camshaft and thus adjust timing.
Photo by Iain Barker
With the timing gear fitted, next was the tricky third dimension — the dreaded camshaft timing. When the timing gear is manufactured, a ‘dot’ is stamped in each sprocket so that the teeth can be correctly aligned ‘dot to dot’. However, with 40 teeth on the camshaft sprocket, and 360/40 = 9° per tooth, and two rotations of the crankshaft for one rotation of the camshaft, each tooth on the camshaft is equivalent to 18° of crank rotation. The timing specification for each camshaft is given by the manufacturer based on the point of maximum opening of the inlet valve, in this case that figure is 107° after top-dead-center (ATDC).
Phew. What does all that mean? Way too much math and engineering.
To make it simple: the four cycles of the Mini engine are suck, squeeze, bang, and blow. The ’suck’ is the inlet stroke, where the pistons draw the fuel and air mixture into the cylinders via the valves in the head. The ‘blow’ is the exhaust of the burned gas through the head and out to the tailpipe. These inlet and exhaust valve openings need to be precisely timed so that they occur when the piston is at the correct point of its rotation via the crankshaft, i.e., when the piston is moving down the bore to suck in the inlet charge, or as it’s moving up the bore to blow the exhaust gas out. So 107º ATDC simply means that the inlet valve reaches its point of maximum opening after the crank has rotated 107° from when the piston was previously at the top of the bore.
O.K., engineering lesson over (for now) — back to the build.
The offset between the crank and camshaft is fixed by Woodruff keys. These are little tongues of steel that slot into a groove machined into the front of the crank and camshaft. To adjust the relative position of the two sprockets, offset keys are available in steps from 1° to 9° of crank rotation. So, fitting the key pointing to the left delays the camshaft and causes the timing to be retarded. Fitting it pointing to the right advances the timing, causing the valves to move earlier relative to the movement of the piston.
Basically, all that needs be done is to measure the point at which the inlet valve reaches its maximum opening and look to see where the crankshaft is pointed. Simple! Well, maybe for a modern electronically-managed engine with hydraulic or pneumatic valves. The engine management system on a Honda VTEC does this hundreds of times per second. But there are no such luxuries on the 1950s-design Mini engine. The camshaft is opening the valves mechanically, by pushing the followers using lobes that have a curved top. So, the point at which they reach their ‘peak’ is really more of a ‘flat’. To get an accurate reading, we have to measure the valve lift at the same point on the slope for the leading and the trailing edge of the curved lobe, and then average it.
Nuala does the math.
Photo by Iain Barker
Arrgh, more math. But I have a secret weapon! My daughter Nuala is 7 years old, and on ‘home school’ due to the Covid lockdown. This seems like an ideal time for an applied math lesson!
I have to say, she did a pretty good job. She read off the Dial Test Indicator (DTI) and timing degrees at the front of the engine, while I rotated the crank from the flywheel slot at the rear, and together we measured the lift using a DTI at 5 thou before peak on the leading and trailing edge of the inlet lobe. The values were 88° and 116° one adds these together, then divides by 2 for a median value. Ours was 102° after TDC for inlet valve peak. The target is 107°, so it needed a 5° offset Woodruff key to retard the cam pulley.
A week later the offset Woodruff key arrived in the mail. After I assembled and checked the timing again, it came in at 106º before top dead center (BTDC). There is always some slack in the chain after a few hours of running, so this should settle down to the target of 107º without further attention — it’s definitely close enough, the factory tolerance is within 2° — and much better than the ‘dot to dot’ initial setting.
That’s it for this month. Next time, we’ll take a look at the external engine assembly. Everyone, stay home and stay safe!
The block before cleaning.
Photos by Iain Barker
Social Distancing, Workshop-style
by Iain Barker
The engine in my 1967 Mini Cooper S is worn out. I threw it together quickly a couple of years ago with what I thought were ‘good enough’ tolerances. The cylinders were overbored by 20 thousandths of an inch (+20 thou) and measured wear at around 3 thou, so I just de-glazed them with a honing stone and re-ringed the original pistons. In retrospect, that was a mistake. I really should have had the block rebored while it was stripped down. Sure, the engine ran and the initial compression was good. However, cylinder bore ovaling soon caused excessive oil consumption, producing an embarrassing amount of blue smoke while driving.
I didn’t want to lose a driving season while I stripped and rebuilt the original engine over the summer, and my rented storage lock-up has no electricity nor any heat, so working over the winter is not viable, either. I decided the best option was to try and build up a spare S block in my basement slow-time, so that when completed it would be ready to drop into the car along with my recently rebuilt gearbox. This would minimize the time my car would be out of commission.
Due to the COVID-19 mandatory lockdown in Massachusetts, I now have rather more time on my hands than expected. So, I guess there’s nothing for it but to start a new build.
My goal is to build up a complete 1966/67 specification short engine (everything below the head gasket) for an Mk1 Mini Cooper 1275 S, using all new old stock (NOS) or original manufacturer/reproduction parts. Not an easy task, considering that engine specification had a unique cylinder block and was only in production from 1964 to 1967. So spare parts are not available off the shelf.
Part 1 — Internal engineering
An early break enabled me to source a thin-flange S block in good condition from Seven Enterprises (7ent), the exact same AEG312 type as the original in my car. Apparently, it came from Doug Peterson, Mike Kearney’s racing partner from the Fortech Mini days. It was machined +0.030” oversize, and then put aside as a spare for the racecar. Fortunately, it was stored indoors for 30 years and retains the original main caps. It appears that it was also lightly skimmed to increase compression.
The block had just a little surface rust, but needed a good clean-up and camshaft bearings fitted before it could be used. A good scrubbing with a brass wire brush was followed by soaking in a gallon of CLR (Calcium/Limescale/Rust) dissolving solution. I also removed the rusted freeze/core plugs and all the brass screw plugs on the oil/water ways for access.
Then I used a gun/rifle barrel cleaning kit to pull helical wire brushes through all the drillings to clean out the rust and muck. It was pretty filthy, but there was no significant rust penetration. The water jacket only had some loose rust flakes behind the core plugs, which were easily dislodged and flushed out.
The new camshaft.
With the block now in usable condition, it was time to hunt for the rest of the Cooper S-specific parts. Since we aren’t actually living in 1967, ordering from BMC isn’t an option. So, I hit up the main USA and UK Mini parts vendors, plus eBay and the Mk1 Mini Forum for the harder to locate items.
My shopping list:
Crankshaft — A good EN40B S crank, courtesy of Nick at min-e-bitz UK.
Connecting rods — A used set of original S-type AEG521 con-rods off eBay.
Camshaft and followers — Sourced from Mini Spares UK.
New bearings (cam/main/big end/thrusts) — Sourced from 7ent and Mini Mania.
Front plate — Sourced from eBay UK (surprisingly hard to find Stateside).
Tinware — Sourced from eBay NOS and 7ent used parts.
Duplex timing gear — From Mini Spares UK.
I already had a set of +30 “County Brand” pistons (an AE Hepolite clone) on the shelf, in preparation for a rebore for my original engine. Gudgeon/wrist pins attach pistons and con-rods using an interference fit, also known as a press fit. The tricky part would be fitting the new pistons to the used con-rods without having access to a hydraulic press.
A technique I’ve used before is to put the new pins in the freezer overnight in a sealed bag with some uncooked white rice. The cold makes the pins thermally contract and the rice absorbs any water vapor from inside the bag. Then, I use progressively shorter bolts to wind the pins through the piston from one side, into an over-sized impact wrench socket used as a die on the other side.
For the camshaft, I really wanted to stick with the same AEG510 profile that I used in the previous engine. But Mini Sport has stopped selling their ST510/CA1 reground camshafts, so instead I went for the Mini Spares “Evolution 1” camshaft, which has a reputation as being drivable with good torque.
With the block cosmetically clean, it was time to refurbish its internals. I’ve never installed cam bearings before. It is always good to learn a new skill and the tools are available cheap on Amazon.
I bought a set of NOS bearings from eBay and tried installing them. After fitting the cam bearings, I found out the hard way that the original BMC parts require reaming to the finished bearing clearance size after installation. Lesson learned, I drifted them out again and fitted a set of modern repro bearings that I had also purchased for my previous engine build.
The crank was already ground 10/10 and just needed the journals to be lightly polished with 2000-grit emery paper to clean up some small rust marks from years of storage, plus new -10 bearing shells. Likewise, the bores needed minor surface rust removed with a light hone in an electric drill. Then the new pistons and rings could be installed — which, without the use of a ring compressor, takes more time (and fingernails) than one might expect.
The last job for fitting the camshaft was to plug two of the three-hole oil pump threads with 1/4” grub screws and blue Loctite. Then, drill and tap a second mounting hole to fit the more modern ‘A+’ two-bolt oil pump.
All coming together with pistons and camshaft installed.
I dropped the crankshaft into place, taking care that the thrust bearings were within tolerance. There’s an easy way to do this without specialist measuring tools. Put the main shells in the block, and put two +3 thou thrust bearings in place on the center main. Then, try to fit the crank. If it won’t slide in, or feels like it’s tight or binding, change to standard thrust bearings.
(Which is what I did this time.)
I installed the distributor drive and was done with the internal assembly. Time for a lick of MOWOG green paint while waiting for the second batch of parts to arrive from Mini Spares in the UK.
[To be continued…]
Cars & Coffee table!
Photos by David Schwartz
Getting Creative with Virtual
by David Schwartz
With the cancellation of many 2020 car events, clubs and museums have been holding virtual events on-line. Facebook is a common platform, so it may be time for those of you who have resisted social networking to create an account. According to one poll, Facebook reaches 70% of all U.S. adults.
In late March, Connecticut-based Nutmeg MINIacs held a Facebook on-line car show with separate categories for modern MINIs and classic Minis. Members of the group posted car photos, and the judging was based on the number of “likes” each car received. I posted a photo of my ’68 Mini Traveller wearing a clown car costume (red nose on the grille and googly eyes on the windshield) and tied for 1st place.
Larz Anderson, Brookline, Mass.
On April 18th, the Larz Anderson Auto Museum (LAAM) held a Virtual Cars & Coffee on their Facebook page. Participants posted a photo and description of their cars to the event page. They were encouraged to include all relevant details, including why the car was important to them. There was a “People’s Choice” category where winners were chosen by the most photo likes. A winner was also chosen by the staff for a “Museum’s Choice” award.
In-person Cars & Coffee had been scheduled monthly, May through October, so I expect there will be more virtual events. Simply like the museum’s Facebook page, www.facebook.com/larzandersonautomuseum, to receive notifications of future events.
Lane Motor Museum, Nashville, Tenn.
The Lane Motor Museum in Nashville has an active Facebook presence. They have been posting photos of many unique cars in their collection, including driving videos. They held a Facebook March Motor Madness event, with a format similar to a sporting event bracket. The public voted for their favorite car in each round. The Dymaxion placed 1st, with the Zundapp Janus in 2nd.
Enjoy a virtual visit on the Lane’s website (www.lanemotormuseum.org) and daily fun on their Facebook page (www.facebook.com/lanemotormuseum).
David’s ‘Clown Car’ Mini Traveller was a virtual winner, and yours can be, too!
Numerous car club Facebook pages have requested members to post photos of their cars parked in the driveway or garage. Some people have held miniature car shows using their collection of diecast vehicles. Getting creative is a great way to maintain our sanity in quarantine.
I will create new photo albums on the NEMO Facebook page (www.facebook.com/
NewEnglandMiniOwners) for modern and classic 1:1 scale cars, and for diecast vehicle cars shows. I know members have large collections of miniature Minis.
How about holding a virtual Mini Meet East with photos of our full-sized and toy cars? Here are a few other ideas to get you started: share videos of past real events arrange a diecast Cars & Coffee scene share slot car racing videos post a photo of you in costume from the year your car was built create a miniature drive-in movie scene hold a Concours de Matchbox stage a miniature funkhana.
If you don’t want to post photos or videos to Facebook, you can share them with the NEMO Google Group. Send an e-mail to email@example.com and ask to join the group. You can also e-mail me at firstname.lastname@example.org and I will post on your behalf.