Compression, engine noise and spark plug threads

[gungehead]

Hi,
I suppose this should really be two or three threads but lets hope it can be sorted with one.
I checked my compression this morning - 3.8 MOD 8:1 head - and found that No 1 cylinder spark plug hole has had its thread stripped at some point in its 53 year life. It been repaired with a sleeve. The sleeve came out with the spark plug. I have got it all back together ok, but was unable to test the compression in that cylinder.
The readings for the other three were 158, 158, 160, 164, 170. Engine hot, all plugs removed, throttle closed and cranked for about 10 revolutions. All within 10% Is that OK?

Any suggestions how I sort No 1 spark plug hole out?

Also, the reason I was checking the compression test is that the engine gets very noisy above 2500/3000 rpm and not so smooth revving. I do have a few valve clearances that are too big and I have an engine driven fan which seems noisy. Any other suggestions for me to look at?
As far as I know the engine is standard.

I did change the dizzy cap after checking the compression and found that most of the plug wires and the HT lead were corroded as were three of the terminals in the old dizzy.
Unfortunately, I have not had time to road test it since getting it back together. It did seem to be a bit better though when I put it back into the garage (psychological?? - probably).

thanks for your assistance.

Dave

[stuarthardy]

Hi Dave

I think what you have described is that the Helicoil in No. 1 plug hole has come loose. It may well be a replacement for the original Heliocoil and might not have been fitted properly. A decent engineering shop should be able to replace this for you but my advice to you is to remove the cylinder head to have this done as it is all too easy to end up with swarf and/or debris in your cylinder.

If the Helicoil is loose then you will surely get compression leakage that will get progressively worse and may even present a danger of fire so please get it done sooner rather than later. This could also explain the unusual noise levels.

When Helicoils are fitted they are driven in with a tang that is snapped off when the job is done. You could easily end up with this in your cylinder and, since it will probably be stainless steel, you won't be able to extract it with a magnet. Just a word of warning.

Regards