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Modifying A-Series Engines
You want me to tell you everything there is to know about modifying Morris Minor engines, don't you? Unfortunately for you, I'm NOT going to do it!
For one thing I DON'T KNOW IT ALL! (don't tell anyone I admitted that!). For another, there's just too much to know. The easiest thing to do, for all of us, is for you to go out and buy the BMC Engine Bible, a.k.a 'Tuning BL's A-Series Engine', by David Vizard. This is simply a 'Must Buy' if you want expert advice on hotting up your Minor engine. Sure, Mr. Vizard is a Mini-freak, but he's also a Wizard ('scuze the pun!) on any A-Series engine; Minors, Minis, Sprites, Allegros, etc, etc.
What I'm going to tell you here is what I learned building a race-spec 1098 Minor engine taking Vizard's book as gospel (which it is).
1220cc Race/Fast-Road Engine Build
My first attempt at any engine building whatsoever was going to be a rebore & tidy-up of the standard 948cc engine of my 1962 Minor 1000. What came out of the garage two months later was a Minor that climbed hills like they weren't there, accelerated like a scolded cat and cruised oh-so-happily at 85mph! I even got 100mph out of it down the back straight of the local racetrack!
The following is a few of the things I learned whilst building a Race-Spec Minor Engine!
Find yourself a nice, leak-free 1098cc engine from as late a model Minor that you can find or afford. Nah, forget that, just get the latest one you can find; earlier blocks are more likely to have bad wear in the rear main bearing shells (more on that later). If you can find a (nearly) leak-free one running in a car, grab it! Any more than one or two drips of oil off the back of the block after a good run is a good sign that the either the rear engine gasket is stuffed (easy to fix), or the rear main bearing shell is worn (not easy to fix!). If it's the latter then there'll be some extra engine-shop machining work to be done. Either that or you'll need to find a rear crankshaft oil-seal kit.
If you happen to come across a genuine Midget or Sprite 1098 engine, with an engine plate number starting with '10CC' then this is the best one to get. It is a much stronger casting than the Minor engines and uses bigger bearings. I have never seen one so you're probably not likely to find one very cheap!
- Next, you'll need the following bits :-
- 4 x STD size Hillman Imp flat-top pistons.
- MG1100 or Mini Cooper 998 head (casting code is 12G-295).
- 1 1/2" SU Carburetor on Austin Allegro 1300 manifold. The manifold will have to be cut at the 'hot spot' join between the inlet and exhaust pipes. Cut through the exhaust pipe in preference to getting too close to the inlet manifold to avoid putting a hole in the inlet pipe. Throw away the exhaust manifold.
- A set of extractors/headers. If possible get a set which exit the Minor engine bay through the standard exhaust aperture. Some extractors exit down the side of the block past the gearbox. Avoid these if you can as the pipe width is restricted and generally results in sharp bends in the pipe which constricts gas flow.
- A set of double valve springs to suit the head (Mini Cooper).
- A re-profiled camshaft - I used an original Formula Junior race-cam, but for general road use this is a bit hairy! I ended up using a modern version of the BMC 731 camshaft - this is a much better bet for the road.
- Double row (Duplex) timing chain and sprockets. Try finding a set from an Austin Allegro. These chains are stronger and less likely to stretch and therefore result in a quieter engine. You may be able to find a set which includes a chain tensioner - this is a good thing as it theoretically eliminates all timing chain rattle.
- Lightened flywheel. This allows the engine to rev more freely, but does affect the torque available to pull up hills etc, however, this is easily offset by the increase in horsepower. Note that flywheels should be lightened on the inside face (facing the block) and avoid cutting into the surface that bolts to the crankshaft. This can cause serious vibrations if this surface is not perfectly flat!
Some Engine Building Tips
Before you start dismantling your new engine/boat anchor, make sure the outside surface is as clean as possible. Get rid of 30 years of road grime before it gets anywhere near your workbench! The key to successful engine building is CLEANLINESS!
Strip the engine back to a bare block (keeping track of all the bits and where they came from!). I highly recommend following a DIY manual such as the Haynes Morris Minor 1000 Workshop Manual or something similar.
Dismantle and clean everything! I use kerosene (a.k.a paraffin) in an old (washed!) plastic cat's litter box; it's about 5 inches deep and big enough to take a Minor engine block.
Remove all plugs and taps from the block and have the head and block steam cleaned, making sure all waterways and oil ways are flushed as well. Have the head and block checked for cracks; if the head is cracked you'll probably want to get it fixed since the 12G-295 heads are getting pretty scarce/expensive.
The block now has to be re-bored to take the Imp pistons. Unfortunately the wall of the number 2 bore is very close to a water jacket so it has to be offset slightly. You may have to hunt around for an engine reconditioner who can set this up accurately. This is why you have to use STD-size Imp pistons; the Minor block wont take oversize Imp pistons, plus you can still use standard 1098cc head gaskets using STD-size Imp pistons.
I had the block skimmed by 0.115" to raise the compression ratio to 9:1. See David Vizard's book to find out how this is done.
When fitting the Imp pistons to the Minor con-rods I replaced the gudgeon pin circlips with custom made Teflon bushes. I had to do a rebore after one of the original circlips broke and the pieces scored up and down the bore! Teflon bushes mean no more broken circlips! If not Teflon, then you should at least fit new gudgeon pin circlips.
When fitting the duplex timing chain, you have to replace the two bolts behind the crankshaft sprocket with countersunk Allen key screws. I simply used an oversize drill bit at slow speed to countersink the holes in the front engine plate.
Make sure you prime the oil pump with some heavy grade or engine rebuild oil as you do the rebuild. If you don't, there will be an air blockage and the oil pump won't be able to do anything when it comes to starting up your new engine for the first time. If you forget (as I did the first time!), then it is possible to inject some oil down the oil gallery at the back of the block on the exhaust side. This oil gallery is located just in front of the oil pump, so (hopefully) it will drain into the pump and get things moving.