Cylinder Wall Pre-Ignition Damage?

[ducked]

Damage to cylinder #2 wall. Zooming in to the photo, it looks like lots of superimposed little impact marks rather than a scratch.

forumosauploads-12829.kxcdn.com/original/3X/1/c/1c...g

https://forumosauploads-12829.kxcdn....2_666x500.jpeg

My best guess was broken end of a piston ring dancing around, but I have now taken the piston out and so far can't see anything wrong with it or the rings.

I'll clean it up, check the ring gaps, and maybe smooth off the ends a bit, though I can't see any burrs.

Havn't decided whether to hone the cylinder yet. Probably not.

I suppose this damage could have been from a hard object that has since departed

Alternatively, could it be detonation or pre-ignition forcing impact of the ring ends onto the cylinder wall?

(The top ring gap was probably roughly in the right orientation on removal)

When I first got the car it seemed to have some pre-ignition on idle and had some run-on after switch off, both of which went away after a water decoke.

[maxwedge]

Detonation would be most obvious around the top edge of the piston above the top ring land. Looks like foreign material scrubbed the wall, that should be cleaned up.

[ducked]

Originally Posted by maxwedge

Detonation would be most obvious around the top edge of the piston above the top ring land. Looks like foreign material scrubbed the wall, that should be cleaned up.

Think I had pre-ignition rather than detonation, though I can’t be sure. Was shortly after I got the car, getting on for 10 years ago.

By “that should be cleaned up” you mean the cylinder should be honed?

[maxwedge]

Yes a lite hone to clean it up.

[ducked]

Thanks. Might take a bit more than a light hone though.

Now thinking this might be corrosion damage, with the corrosion pits cleaned out by later engine operation (though if so it seems to have been surprisingly thorough)

There is some rust evident around the edges of the bright metal pitting.

https://photos.google.com/album/AF1Q...ImfxnFGy2hU5wT

It'd be nice to know what caused it, since otherwise it might continue happening

[RidingOnRailz]

Originally Posted by maxwedge

Yes a lite hone to clean it up.

Link to photo in post #5 = 404 .....

[ducked]

Originally Posted by RidingOnRailz

Link to photo in post #5 = 404 .....

Yes, SORRY. was working , now it isn't

ALTERNATIVE

https://forumosauploads-12829.kxcdn....2_666x500.jpeg

[maxwedge]

Yeh, better view, make sure there is no crack behind that area.

[ducked]

Originally Posted by maxwedge

Yeh, better view, make sure there is no crack behind that area.

Not sure how I would do that. I can't see any sign of a crack, but I can try and get a higher resolution picture than this (iPhone) one.

I suppose dye penetration testing would be one approach, but I dunno if I can get an appropriate dye test kit in Taiwan.

Maybe dyed penetrating oil, or just nail varnish diluted a bit further with acetone?

GF probably wouldn't miss a little bit.

[ducked]

Now thinking this might be spalling damage from cavitation in the water jacket, like what you get on the inside of tank armor from a non-penetrating round impact or explosion.

images.app.goo.gl/2MyRtRdW2BwW7prp6

Plenty of discussion of cylinder liner cavitation (mostly in the context of heavy duty diesels) out there, for example

http://www.constructionequipment.com...maintenanc...s

but I have not seen any mention of corresponding spalling inside the cylinder, so that’s just my speculation.

If that IS the cause, there will be corresponding pits inside the liner, and it might have been promoted by my practice of boiling the coolant to clear air pockets. Might have to figure out a vacuum fill method instead, a hassle I could do without.

Probably worth trying a different coolant (I used Shell last fill) and maybe changing the rad cap.

Can’t think of anything else.

There doesn't seem to be any mention of a procedure for changing the cylinder linere in the manuals I have, so maybe its considered a specialist machine shop job.

[ducked]

Or could it be spalling due to thermal shock, from water droplets hitting the cylinder wall?

IIve done water decokes a few times, using a plant sprayer, and for a while I rigged an IV line to suck water in at relatively high revs using the negative pressure generated inside the air cleaner. It seems rather more linear than I would expect, but I dont really know.

This cylinder seemed to have less carbon than the others, consistent with it having got more water

In future (if there is one) ill maybe restrict water decokes to using steam rather than liquid water.