1275 cooper s block

Any topics pertaining to the BMC A-Series engine.

1275 cooper s block

Postby TFR1 » Tue Feb 12, 2013 9:56 pm

Just hoping someone has a thick flange Cooper S block that they will part with.

I am planning to have a 970 short stroke in line crank made for the block and vintage race in the small bore class.

Let me know if you can help.

TFR1
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Re: 1275 cooper s block

Postby Charlie Tolman » Thu Feb 14, 2013 1:38 am

With a Cooper S transverse engine block and a special inline crankshaft, is it possible to connect an inline transmission to the block ?

Charlie T.
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Re: 1275 cooper s block

Postby TFR1 » Thu Feb 14, 2013 10:46 pm

Charlie,

The back side of a Spridget block is the same as the transverse Mini block in most respects. The rear main bearing cap and the 'scroll' seal Spridget arrangement is not the same on a Cooper block. The scroll seal rear main cap assy can be fitted, but it is a tedious job.
The rear engine plate is easily fitted.

The only other challenge is tapping the un tapped hole in the Mini block so that the Spridget oil pick-up pipe and screen can be fitted.

I built one of these a number of years (20) ago with some technical help from Richard Longman. Richard provided me with a cylinder head and cam similar to what he was using for a 1 liter class in the UK.

The little engine would turn 9500rpm.

I sold it with a race car in the 90's. It still sits unused after all these years in an old friends collection. I have been trying to buy it back for a very long time. Finally decided I would just have to build another.
TFR1
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Re: 1275 cooper s block

Postby Charlie Tolman » Fri Feb 15, 2013 1:19 am

Why not start with a Sprite or Midget 1275 inline block? The stock bore is the same size as the transverse Cooper-S blocks.
Reduce the deck height a little, offset bore the cylinders as much as possible, machine a new crankshaft with the correct stroke to keep the displacement just under one liter, and use some forged aluminum pistons (Venolia ?) with a special wrist pin height ( or find or machine longer connecting rods ).

Sounds like an interesting project, especially if one can find a good camshaft and valve train for the high rpm performance.

Charlie T.
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Re: 1275 cooper s block

Postby TFR1 » Mon Feb 18, 2013 6:52 pm

Charlie,
You have probably forgotten more about engine building than I will ever know. So forgive me if I seem a little slow about sorting out these details.

The reason for using a Cooper block is apearance only! The goal is to build an engine with less than a 1000cc so that my Bugeye can run in the small engine class. A Cooper block with tappet covers looks very much like a 950 block.
Many years ago(1985) I had Dave Tabor build an "all you can do" 948 engine that was "vintage legal", not SCCA legal, .060 over bore, larger valves, DCOE 40 webber carb. Engine dyno tested at 103hp @ 8300 rpm. Displacement 995cc I think.

The Cooper S based engine I built in 1992 used .040 over sized Omega 6cc dished pistons, 6" carillo rods, special 970 stroke Farndon crankshaft, along with the Richard Longman special bits. Engine dyno tested at 115 hp @ 9500 rpm. (998cc if I remember correctly)

So you are right, the best way to do this would be to start with a stout A+ block, offset bore it, install a 970 stroke crank and twist it as high as we dare.

One problem I did have was finding a proper rear end ratio. 4.55 was almost to tall at most tracks.

Thanks again for the input. I still have much to learn.
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