31 replies to this topic

[Jon937]

Hi I have a 1275 A+ bare block to build up.

 

i wanted to know what length crank would be best to fit. i want to fit the KAD 16V head and keep it under the bonnet so need to drop the top of the engine by atleast 12mm (i think).

 

I can obviously get that scimmed off the top of the block but would the 76mm crank be too short, as higher reving but not as much torque.

[Spider]

Being a 16 valve head, you'll get the best from that with higher revs, so a shorter, but not too short, stroke would give the best life. Perhaps de-stroking a Big Journal Crank down to a Small Journal.

[Alex_B]

I am thinking about de-stroking the engine I am building to 1071 spec. My build will be using a BMW K-series head and I want something thats a little more free-revving. However I doubt I will be chopping 12mm off the block, thats a huge amount so I don't think you will achieve this, also destroking the engine to reduce the height of the engine isnt really the right way about it imo. I would be looking at lowering the engine in the subframe (which will bring about its own issues; driveshaft angles, sump to floor clearance, etc however this would likely be a better option. 
 

[Spider]

I know all the pre-A+ 1275 Blocks, you can take 3/8" (~10 mm) off the deck no problem. When they made the Cooper S Blocks, they all had an extra 3/8" 'slab' on the deck. If the block was being machined for a 1071 or 970 Engine, they would machine this off to reduce the block height, only to get the pistons nearer the deck (to maintain CR), further to this, for the 970 engines, they had a longer rod for the same reasons.

 

From a production (and engineering) point of view, it always seem a daft way to go to me, when all they really needed to do was use 3 different pistons, each with differing pin to crown measurements. Anyways, that was BMC's call.

 

When they did the 1275 'solid tappet cover' block, that extra 'slab' was maintained. They did also carry this over to the early A+ blocks, however I think in later years, it was thinned.

 

Alex, I can see a lot of merit in lowering the engine in the subframe, but also a shed load of work to do it!  I'd want to look at it in more detail, but I'd probably be inclined to start off with an Auto Subframe, that will get the engine sitting about 1 to 1-1/2" lower off the bat, you can always raise it from there.

[Jon937]

Would the 76mm crank be to short for a 1275 block with KADs 16v head?
I again would like to have a 16v engine using KADs head under a standard bonnet so could you please comprise a list of the alterations that would need to be done if I was to lower the complete engine.
I initially thought about skimming the 12mm off the top of the block but would the cam belt then be to long or would the tensioner be able to take up that slack?
Any help greatly appreciated.

Thank you

[carbon]

Before skimming 12mm off the top of a 1275 block I would check on the forum to see if anyone has taken this much off and made an engine that works reliably.

 

Getting the head gasket to seal after lopping half an inch off the top of the block could be a real challenge as deck could be very thin and prone to distortion?

[Spider]

I doubt you'd be able to take 12 mm off any 1275 (or any other) block.

 

Many of the earlier Blocks you can usually take 10 mm from, but I'd suggest measuring 3 times and cutting once.

 

Or you could always try a full wet deck approach!

Edited by Moke Spider, 11 June 2015 - 08:57 PM.

[Alex_B]

I have no experience with machining the a-series other than research I have done, however I wouldn't want to be taking that much off the deck face. As mentioned you are likely to get into some trouble with getting a decent gasket seal and or breaking into the water jacket. 

Have you considered another cylinder head thats shorter than the KAD head? For instance the BMW k1200 head will fit under a mostly standard round nose (may need to modify the bonnet support bracing.) 

 

[Jon937]

I looked at the BMW head but didn't want to block and redrill all the holes. If I could skim some of the top of the block what would be the maximum sort of figure? I could skim the head also to lower the top height. But what would I need to do to lower the whole engine without any machining work done on the head/block deck?

[Jon937]

I looked at the BMW head but didn't want to block and redrill all the holes. If I could skim some of the top of the block what would be the maximum sort of figure? I could skim the head also to lower the top height. But what would I need to do to lower the whole engine without any machining work done on the head/block deck?

[Jon937]

Would I be able to use the 78.3mm Stoke crank sold by med, skim 3mm off the top of the block and then lower the complete engine atleast 9mm?
If so what would be required to lower the engine in the subframe, obviously move the side engine mounts further up on the engine/box?

[nicklouse]

Would I be able to use the 78.3mm Stoke crank sold by med, skim 3mm off the top of the block and then lower the complete engine atleast 9mm?
If so what would be required to lower the engine in the subframe, obviously move the side engine mounts further up on the engine/box?

Not really you make new mounts.

Don't think you could take 9mm of the top. Try measureing the thickness of you deck now.

Oh then you have issues with the water pump and the head.

But why.

[CobraV8]

Wouldn't it be better to make some humps in the bonnet?

[adcyork]

Use an auto front subframe, they're wider at the engine mounts. It's then just a case of redrilling the mount holes and making up spacer plates to suit the required position in the subframe

[Jon937]

I will be using a titanium subframe from force would this be wide enough or would I need to ask them to tweak it when building?