Metric Mechanic Pistons

[Bmwb]

anyone know the cause of this? , also thinking that the ARP headstuds weren't tight enough and caused the cylinder head to lift up a bit but this looks bad , engine was still running strong but burning oil so I tore it apart and just swapped in a stock I m20b25 for now

[kronus]

valve float?

[Van Westervelt]

That would be my guess. Just on the one piston?

[Bmwb]

nope on all 6 , and the sides are just as burnt

[LJ851]

What was your valve to piston clearance when you assembled the engine?

[LJ851]

Also, post a better picture of the side/corner of the piston where it is damaged. It looks like some detonation damage right at the thinnest part.

[Bmwb]

that's odd im shocked aswell , it was only the intake side that got beat , this stroker was previously in this car with a 272 cam since 2003 0_o , still got the paper work , is there anyway the head could of lifted under boost at all those valve pockets are pretty deep and I doubt the clearance was close to hitting the piston and all , and I was also running meth to stop detonation like I said engine ran strong burnt oil .

im assuming these pistons are toast anyways?

[kronus]

head lifting wouldn't reduce valve clearance.

[Bmwb]

that's off no clue than , everything was written down for the valve clearance just cant seem to find the papers , only the specs of the motor , either way are these pistons fried cuz if they are I got a 2.8l stroker on the way that im getting for a set of rims im gonna probably do and turbo

[LJ851]

that's odd im shocked aswell , it was only the intake side that got beat , this stroker was previously in this car with a 272 cam since 2003 0_o , still got the paper work , is there anyway the head could of lifted under boost at all those valve pockets are pretty deep and I doubt the clearance was close to hitting the piston and all , and I was also running meth to stop detonation like I said engine ran strong burnt oil .

im assuming these pistons are toast anyways?

Does it have the same 272 cam now? Is the head and gasket the same thickness as before? Is the cam timed the same as before? Are the valves the same size as before?The valve didn't hit the bottom of the pocket so the depth of the pocket is irrelevant. If you run enough ignition timing nothing can stop the detonation, meth isn't a cure all.

[Bmwb]

every single thing was the same spec , as pre before i boosted the engine , everything was redone head gasket wasn't blown block was O-ringed welded jackets were the only different changes i made this hauled ass .272 cam was still in there like i said head was refreshed also used the GOETZ hg it ran clean untill it started burning oil nothing was changed just new gaskets

[kronus]

there are different thickness headgaskets you can get, you should verify that what was in it before the boost rebuild was the same *thickness* as after.

[Bmwb]

the hg used was the stock OEM bmw HG . and same thickness as OEM all written down on the first build of this motor stock thickness ,

[Bmwb]

here is the healthy new motor running just stock m20b25 ARP headstuds stage 3 spec clutch

[whodwho]

Hard to tell by the first pic but to me it looks like it got hot and deformed and the edge of the piston top pushed up and in because of being so thin there from the valve pocket and deformed far enough in the valve hit.

On the last pic if you follow the valve pocket it looks out of round where the burn part is, probably not much metal between the bottom of the valve pocket to the ring groove.

More/clearer pics are needed 8^)