8 replies to this topic

[Hughieboy]

Apologies if this appears to be a silly question but I have very limited mechanical knlowledge. I have amini engine block that was described as a 'short stroke' when I bought it (definitely short stroke - no other description) said to be 1.0L. What are the benefits of short stroke as opposed to normal please? How can I tell where the bloack has originated and research it's history? Thanks to all> JJ

[Cooperman]

Here is what I posted yesterday following the other replies which didn't mention the only true 'Short Stroke' Mini engine, the 970 Cooper 'S'.

 

Of course, the REAL 'Short Stroke' Mini engine is the ultra-rare 970 Cooper 'S' block which is classed as 1 litre, but is completely different from a 998.

The 1098 is one of the longest stroke engines and the 998 is not really short stroke as the stroke is still larger than the bore.

It depends on which block it is before one can tell if the head you have will fit at all. If it is a 970 block, the head should fit, but the compression ratio will need sorting out by skimming the head quite a lot.

There is no point in trying to engineer a really big-valve head from a 1275 engine to go onto a 998.

 

So, first of all you need to measure the bore and the stroke. Only then can we tell you what you have. Presumably the crankshaft is fitted, so take the pistons to Bottom Dead Centre and measure how far down the bore they are. the measure a cylinder diameter. post those dimensions on here for a correct and accurate answer.

If you have a 970 Cooper 'S' block and crank it is worth a lot of money.

Also, does the block have 2 removable rectangular cam chest covers on the back?

Only the 970 is true short stroke where the bore diameter is greater than the stroke. This is also known as an 'Over Square' engine and over-square engines can be revved really high, the 970 in competition tune revving to over 8000 rpm and up to 9000 in full race spec.

[Hughieboy]

Here is what I posted yesterday following the other replies which didn't mention the only true 'Short Stroke' Mini engine, the 970 Cooper 'S'.

 

Of course, the REAL 'Short Stroke' Mini engine is the ultra-rare 970 Cooper 'S' block which is classed as 1 litre, but is completely different from a 998.

The 1098 is one of the longest stroke engines and the 998 is not really short stroke as the stroke is still larger than the bore.

It depends on which block it is before one can tell if the head you have will fit at all. If it is a 970 block, the head should fit, but the compression ratio will need sorting out by skimming the head quite a lot.

There is no point in trying to engineer a really big-valve head from a 1275 engine to go onto a 998.

 

So, first of all you need to measure the bore and the stroke. Only then can we tell you what you have. Presumably the crankshaft is fitted, so take the pistons to Bottom Dead Centre and measure how far down the bore they are. the measure a cylinder diameter. post those dimensions on here for a correct and accurate answer.

If you have a 970 Cooper 'S' block and crank it is worth a lot of money.

Also, does the block have 2 removable rectangular cam chest covers on the back?

Only the 970 is true short stroke where the bore diameter is greater than the stroke. This is also known as an 'Over Square' engine and over-square engines can be revved really high, the 970 in competition tune revving to over 8000 rpm and up to 9000 in full race spec.

Thanks for the info on both posts, very much appreciated. I'll take the measurements you've advised and re-post. Thanks again. JJ

[Cooperman]

I bet you hope it's a 970 Cooper 'S' engine. A 970 block & crank can easily be worth £1200 or more if it is complete with con-rods, depending on whether or how much is has been re-bored and re-ground in the past. I sold a 970 crank for £450 earlier this year.

[Hughieboy]

I bet you hope it's a 970 Cooper 'S' engine. A 970 block & crank can easily be worth £1200 or more if it is complete with con-rods, depending on whether or how much is has been re-bored and re-ground in the past. I sold a 970 crank for £450 earlier this year.

Thanks once again - Fingers crossed here!

[Cooperman]

We now all need to know!!

[Hughieboy]

We now all need to know!!

Not exciting news unfortunately - checked bore and stroke and not short stroke as I was led to believe. Bore is around70mm, stroke is around 80mm. There are no oblong chambers in the side of the block. The numbers on the side of the block are 198 126, 1279 & O1C?. On the end of the block (timing chain side) there is another number - 5935. On the crank shaft there are 2 numbers - 12G1505 & 12C1433E. On bearing cover - 5912G1429. I haven't a clue what these all refer to, Can you identify it from these numbers? All info is greatly appreciated. Thanks for the info so far. JJ

[carbon]

A 1275cc motor...

[tiger99]

To answer your original question, in any engine range the short stroke variants can rev much higher than the long stroke, because one of the limiting factors in any engine is piston speed, and the other is the unbalanced centrifugal force acting on the big end. But, with less stroke the combustion pressure exerts less leverage on the crank, so there is less torque. That is a bit simplified perhaps, but gives a good indication of the tradeoff.

 

So in the A series, if you want high revs, the very rare and expensive 970 is the way to go, but if you want torque the 1098 is best.

Other engines made in a range of sizes, such as Ford Kent series, have exactly the same things to consider. Some of the smaller ones were over-square and could rev really well, but the longest stroke variants actually had a taller block casting.