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!
Parts
List
-
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 go see Owen
Burton in the UK for one of his rear seal kits. 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!
-
- 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,
it's too complicated for this Site!
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.
Good
Luck!