What could cause this

[2CrX]

My buddy has a B20 block with a 99 Si head. It had 11.5 to one compression. He was driving normal at about 5k rpm when he heard a bad noise and the motor shut off. I went today and helped him pull the head, the motor was fubar. It looked like someone had thrown a stick of dynamite into cylinder 3. The piston was almost compleatley gone, all 4 valves where trashed. It actually put the head of one valve through the intake port of the head into the intake manifold. Bottom half of the sparkplug was compleatley gone. We are trying to figure out what caused it. Any help would be appreciated, sorry so long. Will post pics soon.

[EliteConcepts]

Many problems could have caused this, The first one that comes to mind is clearance. If there wasent enought clearance from head to piston it could have caused this. You have to remember that rods flex at around 5-7000 rpm when hot enough. If it flexed with out enough room(BOOM) there goes the motor.

Thats the first problem that comes to mind.

Tim Court

[5gcivic]

Yeah thats what I would think too. Piston to valve clearance. Or a retainer could have come off of the valve and caused the valve to drop into the cylinder. That sucks good luck with it tho. Post some pics too.

[travagliante]

Possible clearence definatley. How long has he had the car running before this happened. Maybe there was bad detonation. Rod couldof bent, or a valve retainer broke or came undone. Look at the valve retainers, or try to find them. See if they look like there in good shape or broke!

Do you have any pictures?

[EliteConcepts]

You will figure something out. If you do however need to find parts to help the fixing procedure check out the site below (Ec Performance)

[2CrX]

The motor had been running for about 5 months prior. All of the valve stems where still held in by the retanors, but the heads where gone. We only found 2 of them so far(havent taken apart bottom end yet. The center of the piston was almost compleatly gone, but the cylinder walls where hardly scratched. one or two gouges but not to bad.

[Gohan Ryu]

If it was a clearance problem all that would happen is bent valves. Probably detonation - with 11.5:1 compression you gotta run very high octane or else...what kind of gas was he using?

[5gcivic]

Originally Posted by 2CrX

The motor had been running for about 5 months prior. All of the valve stems where still held in by the retanors, but the heads where gone. We only found 2 of them so far(havent taken apart bottom end yet. The center of the piston was almost compleatly gone, but the cylinder walls where hardly scratched. one or two gouges but not to bad.

Could we please get some pictures?

[dmbrisket 51]

sheer guess but i would have to say early detonation, possibly from the dizzy vibrating loose just enough to boom, and that is some good compression he had goin, so i beleve that its possible it was just dumb luck somehow.... but then again what were the pistons made out of, steel??

[2CrX]

I know he uses high octane(93). Not sure what the pistons where made of, Ill find out tommarow and get some pics. Dont think it was clearance, all other cylinders where fine, no problems at all. Possible it was detonation, but he had no problems before. No knocks or anything. It wasent valve float, dual valve springs at 5k, theres no way.

[dmbrisket 51]

could of vibrated the dizzy loose, going fine going fine, loose selfe adjust, boom, if they were steel (doubtful) when the casting was made if they had shrink there is a void hollow space in there, its so distructive that if your bit hits it with cnc or a mill the bit is done for and your testies drop another 3" the first time, the void makes the metal verry verry week, soo if there was a flaw in hard metal like that (aluminum is soft metal totally different) it was just an accident waiting to happen

[2CrX]

I know this isnt a vary good pic, Ill get better tommarow. Its the head of one of the intake valves and the bottom of the spark plug. The entire combustion chamber in the head looks like the bottom of the spark plug. dmbrisket, that is deff a possibility. Ill check with him in the morning and see what they are made of. I took the distributer off myself, It was very tight and still aligned.

[dmbrisket 51]

just a total guess, but at 5 grand, and if thats the bottum of the spark plug, i would say there was a melt down ( a void like i mentiond above), just a little to hot and it gave in and that is what he wound up with, and it would explain the lack of shrapnel found (unless its in the bottum of the block yet)

[2CrX]

Sounds like that might be it. Like I said, almost The entire center of the piston was gone, But the skirt and cylinder walls seem to be Ok. Well find out tommarow when we tear it apart.

[honda_luvr_2000]

sounds like a heat transfer problem. if all the valve heads snapped off, then they likely were getting too hot and finally gave in. could have simply been the wrong spark plugs. also coulda been the seating area of the valves being too thin. by the way, there is no such thing as early detonation.
looking at the pic, it looks like sumthin busted loose and had a chance to dance around. also like mentioned a melt down in the cylinder coulda happened due to over heating. looks like aluminum got splattered around. pre-ignition could wear a hole in the piston, detonation would be more likely to bust the piston skirts. looks like it might have been a combo of bad heat transfer and pre-ignition.