Can someone explain this on my head?

[Alphabettispaghetti]

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 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?

 

[zbloke]

I'd suspect the reason for the one chamber being different is, its had a valve, valve seat or a spark plug failure and the chamber has been ground back to remove the dings and nicks left by whatever was bouncing around in there after it broke.........I could be wrong though.......

Personally, I strip the head and do a pressure test, if that come back ok check the chamber volumes and perhaps take it to a head specialist who could weld the damaged chamber and reshape the undamaged ones to equalise the shape and capacity?

All IMO of course

 

[rallymanDP]

I have a mint condition E31 Cylinder head - unmolested and untouched, if you are needing one.

Also the Piper 285 Cam - new.

 

[Alphabettispaghetti]

I'd suspect the reason for the one chamber being different is, its had a valve, valve seat or a spark plug failure and the chamber has been ground back to remove the dings and nicks left by whatever was bouncing around in there after it broke.........I could be wrong though.......

Personally, I strip the head and do a pressure test, if that come back ok check the chamber volumes and perhaps take it to a head specialist who could weld the damaged chamber and reshape the undamaged ones to equalise the shape and capacity?

All IMO of course

That's sort of what I was thinking, my car came with a complete rebuild kit, rings/valves/bearings etc and a packet a half used gasket set, some new gaskets on the top end of the engine...... I couldn't until now workout why. Zero marks on the piston either, so its had a quick fix but they didn't either skim the head flat or fit/torque the head down properly.

 

[Alphabettispaghetti]

Some more pics..

side by side

after I removed the damage around the thread and casing splinter

 

[morbias]

Was the engine sitting for a long time?

Maybe that cylinder was open to the elements and the head corroded which could have been ground down by a previous owner. Mine had corrosion in one cylinder, coincidentally cylinder 6.

 

[jonbills]

I'd have thought the cost of repair to that head would be more than cost of replacing it. But then I don't know what E31 heads cost

If you're doing all that work, why not go for a lot more capacity and start with a later head with 44/35 mm valves?

 

[Alphabettispaghetti]

I'd have thought the cost of repair to that head would be more than cost of replacing it. But then I don't know what E31 heads cost

If you're doing all that work, why not go for a lot more capacity and start with a later head with 44/35 mm valves?

I did consider doing that but after thinking about it i'd prefer to use the original engine and keep it at 2.4ltrs(ish). A 240z without a 2.8 is a rare car now

Also i'm running some real world gearing with a subaru 4.4lsd and s14 gearbox so a nice 2.4 should be good fun, i've had cars with 500bhp/tonne before and came to the conclusion for me I can have more fun with less poke.

 

[jonbills]

Fair enough!
I'd guess that the removed volume is probably no more than 1cc, so by my calc, when the rest are at 10.5:1 CR, this one is going to be something like 10.3:1, which isn't going to make a lot of difference.

Given that building it up again would be skilled & expensive & runs the risk of warping the head, I'd be inclined to live with it as it is.

 

[Alphabettispaghetti]

Fair enough!
I'd guess that the removed volume is probably no more than 1cc, so by my calc, when the rest are at 10.5:1 CR, this one is going to be something like 10.3:1, which isn't going to make a lot of difference.

Given that building it up again would be skilled & expensive & runs the risk of warping the head, I'd be inclined to live with it as it is.

Thats where I got to also, I just need to measure it properly. I could just match the others but i'm hoping to get compression up a little to work with the cam

 

[zbloke]

Just an observation, but on the chamber that's been ground back there looks to be quite a lot of spark plug thread visible, when things start warming up these could glow red hot and may lead to some pre-ignition

If your going to grind the other chambers in the same manner you may have to use copper washers to backspace the plugs so they are flush with the inside of the chamber when installed

IMO of course

 

[Alphabettispaghetti]

The bit above the sparkplug was already ground back, leading to my thoughts about earlier damage, all i've done is remove the sharp edges.

 

[zbloke]

The bit above the sparkplug was already ground back, leading to my thoughts about earlier damage, all i've done is remove the sharp edges.

I know, I'm not having a pop at you or what you've done

Its when you mentioned matching the other chambers in post #10 that I assumed you where going to remove material in the same manner and area as has been done to No.6

 

[Alphabettispaghetti]

Possibly, or from around edge of the combustion area, I've got some research to do I think.

Zbloke- thanks for your input, its appreciated

 

[Throttleton]

Francy, My head was the same .
The same pot had some strange damage/ pitting. I assume coincidence????
I took the head to the Z farm for diagnosis and while the particular pot was scruffy and pitted I was advised it was probably something that had been rattling around in there that shouldn't have been.
However I was also advised by Duncan to get the head checked out properly as it will be a waste of tome and money to rebuild the motor if your guessing all will be well.
There is a thread on here somewhere showing how to mildly improve the head by taking off the sharp edges around the valves/spark plug etc. It looks like the job has been started on your head and someone 'gave up' after the first pot.
Hopefully if you can find out there are no cracks or distortion your head will be fine.

 

[SKiddell]

Combustion chamber balance is important to the continued running of your engine, a couple of CC's differance is comparable to a significant weight imbalance....you need to get it sorted.

As ZBloke said, it looks like something might have been clattering around and someone has made a poor attempt at fixing it, or they tried some chamber mods and got bored.


Personally I would put a better head on as that one is pretty ugly, seeing as its an E31 which are uncommon, I would consider the cost of repair, but I wouldnt get too precious about it.