Hi all

I have been battling a engine miss. I've ruled out electrical so I pulled the head off. Because I suspect a burnt valve.

The valves look ok.

I made up a plate with a rubber seal to blank off the combustion chamber. I put 100psi in the spark plug hole. I then tested each cylinder.

The first cylinder was leaking into the inlet valve the second cylinder was the exhaust valve and a little into the inlet. The third one was leaking out both valves and the fourth was leaking mostly from the exhaust.

There is no obvious cracks or dAmage. I just assuming the valve seats need a lap.


This brings me to my question....

Is this a fairly common thing to happen?

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If the valve faces are concave at all they need refacing, not just lapping. Ditto the seats in the head if marked.
Strip and clean the head then take to an engine reco shop, they have the gear to face valves and seats. Shouldn't be too expensive.

But if the valves are getting thin I'd just replace them, they are cheap these days. But do get the seats in the head recut.
You had better check the valve guides too, if worn I'd replace them first.

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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.

Worn guides

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"Show me the Mini!"

Okie dokie. I will get it looked at. I will see how they are worn. It really hasn't done that many kms. I will check the guides.

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That valve is an inlet valve. They kinda all looked like that. There was no thinning or real damage. All I found was the nic and corresponding mark on an inlet valve. The seats although dirty were pretty flat still. If I can get the valve and the seat cleaned up everything should be sweet?. There was no side to side slop in the valve guides either..... The exhaust valves were in better shape and cleaner than the inlet valves... You can see by the top photo how grubby they were.

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I tiny bit of oil weeping down a guide may result in clouds of blue smoke, every now and then on start-up, especially after the car has been sitting for a few days...

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"Show me the Mini!"