Bizarre cylinder head face marks

Ok ok ok…
Time to get it together already.
S1 XJ6 4.2
Original head

I’ve noticed these strange deep gouged marks just behind #1 combustion chamber on cylinder head.
Very weird. I can’t imagine what caused them.

As you note, they are within combustion area of cylinder head gasket.

The removal of head did require persuasion and patience, however I am experienced and used bottle jacks and pieces of wood only.
Always very aware and careful of head surface and during storage.

I would chalk it up to some weirdness or failing on my part, however I happen to have another original S1 XJ 4.2 head which came with another car I’ve since sold which has same marks/location which makes this very bizarre and curious.

The gouges are deeper on other.
Images attached.
1st 2 images original head
3rd image from extra head

Any thoughts?

There were no head gasket issues, and very fortunately, despite the deterioration of coolant causing some serious corrosion concerns, miraculously the head and block passages/surfaces are all ok.

Upon cleaning and hoping surface requires no machining, considering attempting some brazing and gentle filing.


PS: Checking to make certain images uploaded, note how the combustion chamber edges are out of round at the location of those gouges…weird.


My guess is that some small fasteners made their way inside those engines and got bounced around inside the cylinders by the piston. The piston is moving very fast and anything like a steel nut, bolt, washer or screw that found itself inside the cylinder would make that kind of damage to the soft aluminum. Look for similar damage to the top of the pistons.



Yep small items getting bounced as Paul surmises. I would just clean the head and leave as they are. You would need to bring the head temperature up in a oven/BBQ with a hood and then tig weld with Ali rod but the damage is not big enough to warrent that expense, its not a home handy man job really.

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Thanks very much for your replies.

Yes, must be I suppose.
After writing I began to realize there’s no other reason.
There is no damage to piston or cylinder walls thankfully, which i suppose threw me off.
Also, identical type of marks on 2 completely unrelated heads.

This car had been sitting for years apparently. The exterior condition gave no signs.
Really well preserved.

There were hard green gelled composites throughout system due to old coolant, etc.

It’s been years for me and many jags, but I’d never witnessed.

Thanks for touching on the brazing too.

I’d researched and purchased the rods already a while back, intending to prepare/try my hand at it on header tank pipe ends which were badly corroded…fortunately found a restored one.
Came across past thread where someone recommended just heating area with butane torch.

Anyway, appreciate you saying it isn’t necessary. Was my next Q.
Though it bugs the perfectionist within me.
My main concerns were hot spots that might create pre-ignition.

Anyway, weird.
Thanks again!

Another Paul

In the top picture, the spark plug ground electrode doesn’t look right.
Is it bent over, or maybe a piece of carbon is stuck to it ?

Hi there

They are simply those cheesy, gimmicky dual tip plugs…name I can’t recall.
PO installed.

Left in merely to protect spark plug threads in the head and test for valve leaks.

If you bang the head around on the studs when you remove the head the Aluminum is quite soft enough to show gouges from the top of the studs.

Number 2 and 5 are never ‘out of round’ but the others are as they changed the bore centres on all 4.2s.

I was merely referring to how these marks pushed the surrounding metal outward/inward, into the combustion chamber.

Must have been something in there really hammering.

But it’s weird.
More weird finding identical marks within identical locations on completely unrelated heads.
@larebob I hear ya. Absolutely.But no no, not me.

Anyway, thanks everyone for humoring my dumb question.

Kind regards

I think it’s probably due to the 4.2 hemispheres not being centered over the cylinders because they shuffled the cylinders when they increased the displacement, but didn’t change the head.

I’d put a decent bet on a carb butterfly set screw getting sucked in. I’ve also heard of a carb needle set screw being sucked in but I’d expect the damage from that to be a bit nastier.

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There are ways to calculate the piston velocity based on the stroke and RPM. I haven’t done that but I have read that the piston can move at about 60-100 MPH or more while driving around. (I am too lazy to do the math). So a small steel bit bouncing around at that velocity can certainly damage a soft aluminum head. That bit had to go somewhere so if it isn’t inside the cylinder perhaps it was old damage, or it came out the exhaust. Certainly worth a look at the valve and seat in that cylinder for any additional witness marks.


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Just another opinion, but I’m with Larry on this; it looks like careless handling by someone when the head was being lifted off or on before.
Could even be factory workers, as I recall there were quality control and union troubles in the 1970s and cylinder heads was one of the problems. A lot of cars were getting Chevy lumps a few years later due to dropped valve seats.
Clean them up with steel wool, scotchbrite, fine hand files, sandpaper or what have you, smooth out the damage and see how they look. You may not have to do anything more.

Never heard of a dropped valve on a six. A dropped valve seat on an overheated V12 yes.

Detonation can eat away at chamber/piston edges.


They are absolutely not from detonation and the head studs should leave a head stud pattern (so, a roundish imprint), so these not round and only in the chambers (where due to the offset the pistons are really close to the head) it must have been some metallic debris. Personally, I might leave it.

Agreed. I was adding a supplementary fact, not offering a case diagnosis. Alles hat ein Ende, nur die Wurst hat zwei…

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Dropped valve? Nah, just a nut, bolt, screw, piece of a ring (if you had an exhaust port), cotter pin, lock washer, maybe a plug ground electrode, etc, rattling around. Looks damaged like every 2 stroke engine with a broken ring.

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Might want to do a compression check. My experience says that when a metal object gets loose in a combustion chamber bending a rod becomes a definite possibility.

Boy howdy: odd thing is, how damn long the buggers will keep running!

Looks like Knocking on the hot side and should be also seen on the piston. Broken rings destroy homogen the combustion chamber. Frequently seen on sledges and hot bikes.

It looks like something unwanted got in there from somewhere to me. Are all the marks inside the fire ring area? If so, it would be too much of a coincidence for it to have been caused by someone get a bar in there in the past to lever the head off, for example.