Cracked rings and piston lands Why?

[CHANMADD]

Hey ....this is not a new problem. When they shifted the top ring to a higher ...hotter ...position on the piston, the ring gap needs to be around .035 inch. If you do not have enough gap the ring ends bump and the crack the top land. New pistons and gap them properly . Don't listen to any of the other crap.

[blykins]

Unless it's a Keith Black hypereutectic, that data is not correct.....

I buy pistons by the truck load, gap the rings at .0045/.005 per inch of bore and don't have this trouble.

To the OP:

If you pull the piston out and all the ring gaps are lined up, that's another sign of detonation. Also check out the upper rod bearings and lower main bearings. You can also have some piston/head clearance issues which will hammer on the ring lands.

[DanEC]

[quote=blykins;1358658]

To the OP:

If you pull the piston out and all the ring gaps are lined up, that's another sign of detonation. QUOTE]

Brent - curious, how does detonation cause the ring gaps to all line up? I know rings move around but trying to figure out in my mind the connection between the two.

[blykins]

Young1, if you make no other changes, I would at least pull some timing out. However, maybe you can take some measurements and use a little thicker head gasket, or make some other corrections to help out.

Dan,

Not sure of the science behind it, but it's one of those things that has proven to be a tell-tale....

[Young1]

Just checked. Ring gaps are not lined up.

[DanEC]

Originally Posted by blykins

Dan,

Not sure of the science behind it, but it's one of those things that has proven to be a tell-tale....

Thanks - some things defy logic.

[Topfuelhydro]

[quote=DanEC;1358708]

Originally Posted by blykins

To the OP:

If you pull the piston out and all the ring gaps are lined up, that's another sign of detonation. QUOTE]

Brent - curious, how does detonation cause the ring gaps to all line up? I know rings move around but trying to figure out in my mind the connection between the two.

My guess would be its not necessarily detonation lining up the ring gaps but excessively high cylinder pressures which you would get with detonation. I know on a blown nitro engine after a 3-4 second run almost all the ring gaps will be lined up when I pull the engine apart. I have even ran them on the trailer and had to take them back apart for another reason and several of the ring gaps would be lined up after just a few minutes of idle time. These engines have an insane amount of cylinder pressure and are on the verge of detonation all the time.

Steven

[DanEC]

Well, we've established before that piston rings do rotate around during engine operation. With a blown engine like that I can almost imagine that cylinder pressure bleeding through the ring gaps and seeking the path of least resistance, tends to stabilize the ring gaps in a row after they coincidently line up.

Not sure I explained that very clearly.