i have a 998 witch i got a 12g940 head off
the engine number is/ 99h834aj / h7387
the pistons read M2039 A6 there about 65mm
thanks iss it a 998 or a 1275 iv been told some 1275 got stamped 998 thanks

Post a photo and any of us older ones can tell you - A 940 head will not run on a small bore motor without valve clearance relief cut outs on the block.

Mike

That number was a 998 originally.
If the pistons are about 65mm diameter it is a 998 or 1098, not 1275.
Many 998s have had a 1098 crank and pistons put in during rebuild, to get more cc and HP.

To see which it has, put a rule down the bore of #2 cylinder, with #1 piston at TDC.
76.2mm = 998 crank
83.7mm = 1098 crank.

Measurements assume #1 piston is flush with top, if lower these measurements increase accordingly.

BTW a 12G940 head WILL work on a 998 or 1098 but only if:
1. Camshaft is stock lift, with stock rockers,
2. Exhaust valves have sunk into the seats a bit,
3. You don't EVER rev it hard enough to bounce valves.

Too many ifs here really , if building for performance, notch the block like Mike said.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

thanks guys ill pot some pics up and try that dtc on the number cyl thank you

Doc
Who would ever put a 940 on a small bore and not give it a decent squirt to see what it does

Its bit like saying if you jump off the top of Everest and assume a skydivers prone position you will get some lift and be able to perform some acrobatics befoere you go *splat* on the ground.

Mike

Yeah I hear you, but Keith Calver regularly bolts 940s onto 998s without notching... maybe he fits much stronger springs?
No way I would do it though without notching the block.

For those wondering `why not rev it', the 1275's exhaust valves stick out over the block on a smallbore, one good valve bounce and they are bent.
Notching involves milling pockets in the block above the exhaust valves, approx .100" deep, to allow valve clearance.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

the bore looks like its been shamperd on sides near top it all so had a 45 dello on it and a copper head gasket

it`s a 998

& yes we`ve done plenty of 1275 heads onto small bore blocks without "pocketing" the blocks,,, use only std valves & no big lift cams tho

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No offence intended here but--> anyone writing a book about minis 30 years ago may not have experienced such worn or stuffed-with components as we are finding these days.

You should put your heart & soul into everything you do.