what are these pits in my cylinder walls?

[monkfish75]

what are these pits in my cylinder walls?

I discovered them after taking off the cylinder head to replace the gasket. Are they the death of the engine?

The reason i took the head cylinder off is because there was alot of pressure in the cooling system and oil in there too.

HELP

sorry its a 1991 2.0 190E

 

[landover]

Looks bad .Was the car lying about for a while not running before you stripped it. It looks like it is corroded from not running.

 

[mike65]

This article relates to diesel engines but is relevent, skip down to Corrosion section.

http://www.bandgmachine.com/technical/august95.htm

Mike.

 

[bigt]

pits

I too have come across this on occasions in diesels. Are they actually pits or are they porous holes through the bore castings. If they are porous, then it explains the pressure and the oil in the cooling system. The ones I have come across in diesels have been caused by a lack of or weak anti freeze - because Ethelyne Glycol also acts as a corrosion inhibitor it keeps the cooling jacket internals clean. In extreme cases the bore can actually rot from the outside to the inner surface, thus causing what you see. If thus is the case, then it is nothing more than scrap I'm afraid.

If thay are just shallow pits, then they have probably been caused, as londover says, by the engine being stood for a long time with moisture in the cylinder and has corroded the bore faces.

 

[Arnie]

The thing to note is that they are all in a vertical line. So, it could be something related to combustion, affecting one particular side of the bore, or it could be that if you have liners, the corrosion pits are as a result of the weld-seam of the liner.

Anyway, the block can be re-bored or re-lined and new oversize pistons fitted, if required. It's not necessarily scrap.

 

[bigt]

I meant the block would be scrap if the holes were porous. Indeed it can be re-bored providing the pits arent too deep.

Interesting point about the fact the pits are vertical - may also point to a head gasket leak constantly dribbling down the cyl wall if the car has been stood a while.

 

[Arnie]

Pressure in the water-system can mean gasket or leak problems.

Your second picture shows two faint lines. The top one has all the pits scattered along it, bu there is a second line about 1.5" below it, leading to one small pit.

Also, there is a dark ring all the way round the top of the cylinder, but this is lighter between the two lines.

Maybe this is the area of the leak, what does the existing gasket look like in this area?

Are all your cylinders like this?

If these are just shallow pits, I would not worry as they are too small to cause any problems.

However, do make sure that you clean up all the crud that seams to have fallen into the cylinder on the piston head.

Also make sure you re-fill with antifreeze solution.

 

[OlafMaxwell]

Can still see the honing marks on the cylinder walls, was there a recent rebore? Seems like rebore was carried out and engine stood for a while. No sign of any vertical wear on cylinder walls........curious. Line above piston looks like a piston ring stuck to the cylinder wall with rust...with a gap where the pits are....

I used work on old motorcycles.....engines like that seemed to occur when fired up occasionally but not frequently enough to clear them out.....

 

[ant500sl]

Having never laid a spanner on a 4 cylinder the following may well only apply to 6 and 8 cylinder engines.

If the 4's are built in the same way as the bigger engines of the same vintage then they will have aluminium bores which are electrolytically coated with a silicon carbide material (or something along those lines). This leaves a matt grey coating on the bore which your engine seems to have. Porsche perfected this technology in the seventies, MB used it from the eighties and BMW & Jaguar made an almighty mess of it in the mid nineties. Over time and subject to use this coating can eventually be worn out.
I have seen a similar pitting on a v8 where the engine had overheated and the piston had scraped the coating off in the area where the forces from the con rod act on the cylinder wall. Having bores recoated is a very specialised process therefore rather expensive.

If the 4's are not aluminium then accept my apologies.

 

[Arnie]

This is not a "Nikasil" coated bore as referred to above. ...and certainly, such a coating should not be honed. The block is obviously cast-iron, but it is not clear whether it has had liners already fitted.