Combustion chamber erosion?

[Grizzly]

Hi all.

Is anyone clued up on how to repair Combustion chamber erosion?

I've just been inspecting my twin cam head to see what it needs before it can be fitted and noticed quite a bit of Erosion in no1 combustion chamber, even though i've not got the valves out yet the Exhaust doesn't look to healthy and is also burnt away around the edges.

Not the best pics, makes it look better than it is.




Obviously i will have to take the valves out and have a proper look at it but i'm thinking i may have a problem with that Dcoe? (maybe running lean) its odd how its only on that cylinder.

As for repair, i am thinking its going to need valves and seats (possibly Guides) but how could i repair the pitting? (assuming it is not bin food) could it be welded up and skimmed or clean it up and match the others to it?

Any idea's?

Cheers
Chris

[RogerFrench]

I'm not sure that's erosion - it looks like it could be mechanical; damage, as though something small got in there and rattled around for a minute or two before leaving via the exhaust .
In any case, with new bits as you suggest, I don't think it's much to worry about. Clean it up, and it'll be good to go. The difference in combustion chamber volume will probably be negligible and as long as there aren't any sharp edges to burn it should be fine.

[oldchieft]

That is water erosion/corrosion, the engine has been drawing water in and burning it.

Basically the steam and water gas cleans off all the oxide coating and then attacks the metal.

It makes a mess to steel piston crowns and heads in ships engines, so aluminium takes a hammering.

Jon the Chief

[Grizzly]

You can't really see it in the Pictures but the Exhaust valve looks burnt round the edges which is why i thought it could be running lean or Det damage?

I'm hoping there is some thing obviously wrong with the carb when i strip it because i hate having damage i can't account for.

[Grizzly]

That is water erosion/corrosion, the engine has been drawing water in and burning it.

Basically the steam and water gas cleans off all the oxide coating and then attacks the metal.

It makes a mess to steel piston crowns and heads in ships engines, so aluminium takes a hammering.

Jon the Chief

Does that mean possibly bad head gasket? I will have a word with the previous owner and see if it was using water, thinking on i noticed the rad had recently been re-cored so maybe the Head gasket could have been bad??

What sort of time scale would do that sort of damage?

[oldchieft]

My guess would be it would be a fault that happens when the engine is hot, and stops when it is standing,

It is likely to have been over a long time and slight leakage or it would have been noticed on a cooling system that small.

I have seen that sort of damage in other engines, but I have no hands on experience yet with Lotus twin cams.

The usual suspects would be gasket or cracked head, I would pressure test the head first before I spent any money overhauling it.

Jon the Chief

[Chancer]

+1 for water damage.

Its usually an infinitesimal small amount, often from a cracked head or block and hence does not worsen like a head gasket leak would do.

no question in my mind.

[Elanconvert]

interesting....I've seen similar, but not so bad, damage on an Imp head......
how do the speed freaks who use water injection avoid it?
fred

[rgh0]

If its water erosion / corrosion and not mechanical damage it was some time ago as water in the cylinders strips all the carbon off and its still present in the indentations so the engine has run for a while after it occurred and without it occurring again so the head is probably OK.

It would be easier to diagnose if we could see all the head chambers not just the damaged one so the difference could be assessed.

The valves do need replacing

cheers
Rohan

[Grizzly]

Sorry not the best Pictures but you get the idea of what its like. Bear in mind that i have not cleaned this up at all but it does look like the previous owner has scratched some of the loose carbon off the valves (has been off the car 25 years now)

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I have just put a straight edge across the head and at first impressions it looks flat. I had a good look for the old head gasket (the previous owner kept absolutely everything) but sadly it seems to have been misslayed some where along the line which is Unfortunate.

[rgh0]

Combustion conditions look pretty consistent across all the bores for a substantial period when it was last run. The damage in the one cylinder is definitely old and the engine ran OK for a substantial period after it occurred

cheers
Rohan

[Grizzly]

I have just spoke to the original owner (he had if from new) he told me late 70's it had the head gasket replaced by a Lotus main dealer, he also said that he doesn't remember it being smoky of running rough but he said he could make it pink quite easy. But it never used water and the rad was re-cored due to stone damage and it never got hot.


So i guess the question is do i just get new valves and seats etc and leave that erosion or get it welded up and refaced? Would that sort of thing cause any running problems if it was left? from what the Previous owner said he's done over 20k on that damage but i never heard it running so i don't know if his standards are lower then mine

[Galwaylotus]

If it has a history of running ok for that many miles I'd leave it as is rather than risk damage by welding and grinding.

[oldchieft]

Yep, leave well alone

Jon the Chief

[rgh0]

My greatest concern with the head would be how hard it is. The indentations in the face from the fire rings look significant in the photos (though always hard to tell just from photos). What do the head bolt indentations on the top look like.

I would get the head hardness checked before doing any significant work on it. Assuming it is still hard enough then at least a good chemical clean to remove corrosion from the water jackets, a skim to clean up the face surface if the fire rings have caused indentations, new valves and potentially new seats and guides and cam follower sleeves depending on wear.

I would just smooth out the ridges in the rough area in the head combustion with a dremel and suitable carbide cutter to ensure no sharp areas that could heat up and cause pre-ignition, no need to get it perfectly smooth or need to weld it up

cheers
Rohan