Cylinder Head - How is it?

[UncleLol]

I'm a little concerned about some scratches on the cylinder head. I think it may also be a little warped because when placing it on a mirror, i can slide a feeler gauge under one side, but not the other, however this may just be some buildup from the valves i was unable to remove with a rag. Please have a look at these pictures and post your opinions

ps this is my first engine rebuild so please bare with me

[beero]

Don't think the scratches are too much of a worry but when you say you put it on a mirror to test for warping, how can you be certain the mirror isn't warped?

[MarkyB]

Quite unusual for a cast iron head to warp, in this case getting it skimmed will kill at least 2 birds with one stone.
Raising the compression ratio brings benefits too.

[bmcecosse]

You can't be sure of the mirror. Put a good straight edge across it - 12" or 18" steel rule (Poundland!) , or even the back edge of a NEW hacksaw blade, and look under it as you move it around with a light behind the rule. The scratches aren't a worry -although shouldn't be there....... DO NOT under any circumstances attempt to rub them away with any abrasives..........

[JOWETTJAVELIN]

If it ran fine like this before it will run BETTER after a decoke.

[bmcecosse]

De-coke won't help at all - but grinding in the valves WILL !

[JOWETTJAVELIN]

Which is, of course, part and parcel of a proper decoke!

[les]

You say you only wiped the surface with a rag, that won't remove any stubborn deposits such as carbon build up. It's bound to show up gaps if you don't clean it properly. Rub the face over with some emery paper with a block of wood and check again.
It might well be warped but give yourself a fighting chance!

[bmcecosse]

I strongly advise against the emery paper - even on the block of wood.....

[JOWETTJAVELIN]

Whenever I perform a decoke I use a wire brush attachment in the drill to get into all the nooks and crannies - I remove the valves very first thing and treat them separately, putting them in a drill chuck held in the vice, setting the drill going and getting to work on them with an old screwdriver and then emery cloth (avoiding the edges where they seat, of course!)

Nowadays I reckon you can expect to benefit from a decoke every 50,000 miles, as modern bang-water seems to burn cleaner.

[les]

Emery is designed for iron/steel it's using on aluminium that is to be avoided, one assumes of course that the head is going to be washed before assembly, if that was your concern.

[bmcecosse]

No - the concern is that the emery will rub away metal between the combustion chambers - leading to blown gasket.

[kennatt]

its a while since I had a head skimmed,but seem to remember it not being that expensive,if you have doubts about warping,then just get it skimmed,it then takes that doubt away,and as said slightly increases the compression.If you don't you will allways wonder if a head gasket is going to blow.

[les]

No - the concern is that the emery will rub away metal between the combustion chambers - leading to blown gasket.

Hence the block of wood! I'm not anticipating someone rubbing away all day, just enough to remove any carbon traces.

[bmcecosse]

Even with the block of wood....... There is no need - a careful clean using a small paint scraper or the square tail end of a 12" steel rule does the job.

[les]

Ok I give in

[David W.]

How much can you skim off a 948 head before bad things happen?

[bmcecosse]

Bad things?? Ideally you need to measure down the oil feed hole to the rocker shaft - and compare that distance with the thickness of the head. They all start life at 2.750" thick, but check in case someone has already had a go at it! . I would say that 60thou is ok, 80 thou may be possible, and 100 is a bit risky. Why do you want to skim it?

[David W.]

It's off, and on the bench. I'm replacing valve guides, and it'll never be easier to have it done.
Also, while it's out, I'm going to plug the coolant bypass.