Last night driving home i stop at the traffic lights... engine nice and smooth... go to drive off when they go green and sounds like a volkswagen. Obviously one or possibly two cylinders not firing and it isnt ignition related. Thisafternoon i did a compression test... 205 PSI in 1st and 2nd cyls. 3rd and 4th gave 100PSI max. There also seems to air coming back out the carb on the right hand throat (back not in!!!) every revolution... Im pretty sure i have a blown gasket between cylinders 3 and 4... am i right? Blown head gasket after 3000km... why?

Sounds blown to me.

Did you retighten the head next day after fitting? Or check it after 1000KM?

Don't believe anyone who says they don't need retensioning. Most head gaskets do, the `copper' ones particularly.

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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.

Mate sounds like you are right, head gasket is pretty likely. Without knowing the history of your engine is a bit hard to say why. Here are some common causes, perhaps you can pick one that suits the history of your car. Head not skimmed to ensure it is true the last time it was fitted, similarly block not skimmed, head studs need replacing as they become stretched after a while, compression too high (200psi is pretty high for a road car to begin with), when fitted make sure head stud sequence is followed. What bore is your engine, as the gap btw the bores reduces so does the ability to seal, believe it or not timing can affect the burn and can reduce the life of the gasket especially on high performance engines. Hope this is a start. G.

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1970 Cooper S ex-Bathurst & ATCC
1964 Austin Cooper S ex-Group C race car
1967 Morris Cooper S ex-Group B
1962 Mini Speed sports sedan
1968-71 ex-Peter Manton Shell car

Last time i had the head off was when i did the cam change (rocker shaft has to be taken off and so ofcourse i replaced the gasket). I do recall checking the head tension once after replacing the head... i cannot recall if it was with this gasket or the one before that. Ive always used the copper gaskets mainly because they come off clean. I think ill lap the valves on the 12G295 and put it on instead.
I checked the coolant level and it seemed a little too low. Could overheating have caused the gasket problem?

Overheating, yes. But a bit low coolant won't do it alone, unless it overheats.

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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.

Chris, just stop for a minute....was the head working OK before it blew the gasket?? Were there some symptoms before it blew??

While you have the head off do the flatness checks others have recommended (head and block).

Is there any evidence of burning or blowby on the gasket to indicate where the problem might lie??

If you blow a gasket you can lose coolant obviously so don't necessarily go looking for problems that might not be there!

Hurry slowly!!!

Heres one from left field: if you have a blown gasket, and you are checking compression, can there be a path from other cylinders falsly pumping up the cyl under test?? (Doc!! do I need help in the head dept??? )

As always, make some calls and get some old "heads" working on the problem - thats what they are there for (Richard, Barrie, Ray K, Wayne P etc NOT poor old Pete at the moment tho)

Good Luck

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"Show me the Mini!"

99% of the time, if compression is low in 2 adjacent cylinders, the gasket is blown between them.
Small bores blow between 1-2 or 3-4 because the gasket is narrower there. 1275s go between 2-3, same reason.

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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.

Yeah im convinced its blown between 3-4. especially since it blows back into the carb (obviously when one is on compression and the other on its inlet stroke and the leak is causing the gas to flow back into the carb). The 12G295 seems to have been skimmed at sometime. It was running on a flattop 998 when i got it so i think some extra skimming might need to be done. Is buretting the best method for this? i tried once but found that the valves didnt quite seal 100% so i was loosing fluid and i couldnt get an accurate result. I found that the radiator cap wasnt sealing on its seat properly and so the system wasnt under pressure... that combined with me seeing how fast it could go probably didnt help... (it can go 95mph on flat btw). oh well 12G295 should add a few extra horses anyway

Chris and Anto,

Had a quick talk to Barrie B at Eastern Creek today and the first thing he recommended was to use the Metro Turbo gasket "like we all do" (racers).

Cheers, Mick

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"Show me the Mini!"

A smear of grease on the valves will make them seal.
I put the head in the vice, tilted slightly so plug hole side is highest, level it lengthways. Then put a sheet of perspex on top with a 3/8" hole in it.(smear underside with grease)
and fill to bottom of hole.
I use water with 25% metho in it, ATF is also good. I use a 30cc syringe which I can read to about 1/2 a mL (cc) .

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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 kev- great but simple idea. Where did you get the syringe from?
Ive put the 295 on for now... just lapped the valves, cleaned the face and put new stem seals on. The car is running fine and no more blue smoke... so much for that 'reconditioned' head i bought let me see 3500kms ago!!! i wont mention the place in sydney i bought it from because that would be defamation. Now my car revs alot happier, a little less bottom end tho but what can you expect. I think its running a bit on the lean side (bigger main jets?). And yes my gasket was blown... rather well a chunk 3-4mm wide missing in the narrow bit between 3-4.

Go buy some main jets & air correctors and play with it.... there's HP hiding in there.

With my 45 I've just gone back up from 170 air jets to 180- it's sooo much better over 6000 now.. gotta buy some 185s...

<edit> Vets will sell you a big syringe, or the chemist down the road.
You want a 30cc one.

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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.

How much do mains and air correctors etc cost? ive got a few pairs of chokes already 32's are in atm i think they are right for 1100 with head and mild cam.

At Carburettor Service Co, I paid $99 total for 2 air correctors, and 8 main jets.

Cheapest way though is to import them from Eurocarb in UK.

Website is www.dellorto.co.uk

Email is sales@dellorto.co.uk.

Air correctors there are 3.25 GBP, main jets also 3.25 GBP.

Email and they will post you a price list.

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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.

Yesturday i picked up some idle jets at $8 each from the local dynotune.