A quick story....

I decided to use my L24, it ran well with no knocks but always had a little bit of white smoke even when warm, compression results were all good but I knew something wasn't right.

I pulled the head off and found this.



Looks like a slight leak on between the coolant and bore:unsure: Gasket told the story when looking underneath.



Upon close inspection I found on one cylinder cracks/splinters around the spark plug, No worries I thought, I could grind them back so there's no sharp edges/stress points for cracks to start from. Would we agree this is a fair point? I understand that i'd increase the size of the chamber slightly which i'd try to duplicate on the others, good or bad?


Next I cut back, hardly removing any meat at all. Once given a wipe over I noticed that the chamber on this pot has been altered...





An unmodified chamber



1: the spark plug hole/mount has been cut back
2: the shape isn't the same as others
3: I can feel that the shape isn't smooth and without machine marks the others have.

Is is the e31 head off my 1970 240. I'd like to keep/use it however I'm prepared to listen to some wise suggestions. Subject to pressure testing is it ok to go ahead and use it? I can't work out the effects of having a chamber 1 or 2cc larger compared to others.

Strange thing is that the rest of the head is untouched, its not had any 'porting' or anything I can see done.

I'm also not sure if detonation has been the cause of the problems. Valve sizes are 33/42mm.... I take it that these are the standard size?

My plan was to have have hardened seats fitted, new valves/stem seals build engine with;

10.5:1 - 11.0:1 compression ratio
Piper 285 grind cam
dynamic balance on the crank with ATI harmonic damper
+50 bore with new pistons+rings
triple 40's
nice exhaust
4lb off the fly wheel.
full rebuild, obviously not making new history for 240z engines but a nicely thought out fun engine.

It did involve this head, I'd like it too still if possible.

Failing that has anyone got a e31 head knocking around?

:unsure:

I wonder if that cylinder has suffered from damage (e.g. dropped valve, foreign object) in the past and has been repaired by welding, but not machined/ground back to the correct shape? If you are going to the trouble having new seats fitted it would be worth having the chamber volumes measured and balanced if required.

personally unless it was a really rare head i wouldn't bother, I would just go out and find another one.

quote:

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Originally posted by ashg
personally unless it was a really rare head i wouldn't bother, I would just go out and find another one.

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I'd worry about having exposed threads on the spark plug - how about , if you cut them all back to a similar shape , using either shorter reach plugs or spacers on the plugs ? That original shape , to me , looks less than ideal anyway , with `pockets' either side of the plug ?