would a nicked piston/valve cause detonation?
Thread Starter
Drifting
Joined: Dec 2007
Posts: 1,672
Likes: 8
From: Sumter South Carolina
would a nicked piston/valve cause detonation?
Finally think I have a consistent ignition with genuine gm parts but still not sure. However when I was finding TDC with a piston stop the piston didn't stop because of the angled plug. It just bent it.
I did a quick dry compression test to see if I had bent the valve since dumbass me didn't remove the rocker. Things looked good. I got a bore scope from harbor freight and it was just a bit too big to fit into the spark plug hole but I could still clearly see a mark on the piston reflecting. I'd say it was maybe 1/8 long if even that.
My thought is it is nothing to worry about but I also was thinking could this cut end up gathering carbon build up and causing detonation when it is on the track?
I will be tracking this engine hard for 30 min sessions in the middle of the summer. Just wanted to know if anyone had previous experience and if it is something to worry about or possibly try to take off the head and try rounding off the edges of the scratch?
I did a quick dry compression test to see if I had bent the valve since dumbass me didn't remove the rocker. Things looked good. I got a bore scope from harbor freight and it was just a bit too big to fit into the spark plug hole but I could still clearly see a mark on the piston reflecting. I'd say it was maybe 1/8 long if even that.
My thought is it is nothing to worry about but I also was thinking could this cut end up gathering carbon build up and causing detonation when it is on the track?
I will be tracking this engine hard for 30 min sessions in the middle of the summer. Just wanted to know if anyone had previous experience and if it is something to worry about or possibly try to take off the head and try rounding off the edges of the scratch?
Drifting
Joined: Dec 2007
Posts: 1,647
Likes: 4
From: Argillite KY
It depends how much I guess. There is a lot of polishing done to get rid of stuff like that. Anything that can retain heat and "glow" red can cause detonation. The fuel will think it's a spark. I'd certainly try to get it smooth again. Well, not smooth exactly just get the ridges off it and round the edges. You'll be fine.
Thread Starter
Drifting
Joined: Dec 2007
Posts: 1,672
Likes: 8
From: Sumter South Carolina
Now another question would be how long would it take before it started? Could it happen at idle or would it have to be when the car was turinging a higher rpm. I've got a lot of noise that I think is just valves and a header leak but until I fix them a knock is suspect....
Drifting
Joined: Dec 2007
Posts: 1,647
Likes: 4
From: Argillite KY
Picture a glowing ember on top of your piston. As the piston starts down on the intake stroke, the injector starts to feed fuel into the air. The fuel could ignite anytime it wanted bust most typically when under compression with the proper A/F ratio. Yes, it could happen at idle but more likely at a higher RPM. In any event I'd take car of the nick first and then see what's happening with the knock if it's still present.
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Thread Starter
Drifting
Joined: Dec 2007
Posts: 1,672
Likes: 8
From: Sumter South Carolina
I'll prob pull it to be safe but that is an annoying amount of work. With all the money into this engine at least it will be better safe than sorry. I guess I can varify my initial tdc also...
Race Director
Joined: Apr 2003
Posts: 17,700
Likes: 1,667
From: moraga ca
Now another question would be how long would it take before it started? Could it happen at idle or would it have to be when the car was turinging a higher rpm. I've got a lot of noise that I think is just valves and a header leak but until I fix them a knock is suspect....
Instructor
Joined: Apr 2013
Posts: 144
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From: NW Arkansas - usually winter in FL
rithsleeper - -
You do not have a problem. Like none. Do not worry about this minor scratch. Drive your car - this means nothing.
If this blemish was a problem then it would have shown up in every engine which has valve reliefs in the piston top. And some valve reliefs do have some very sharp edges - some of which are very long and very deep and there are hundreds of million of pistons which have valve reliefs.
Drive your car - this is a non-issue. Combustion by-products - carbon - is a much greater problem than your minor scratch will ever be. This minor scratch will not cause any detonation at all.
Might not be too wise to open your engine and in so doing cause more problems than what you had to begin with.
You do not have a problem. Like none. Do not worry about this minor scratch. Drive your car - this means nothing.
If this blemish was a problem then it would have shown up in every engine which has valve reliefs in the piston top. And some valve reliefs do have some very sharp edges - some of which are very long and very deep and there are hundreds of million of pistons which have valve reliefs.
Drive your car - this is a non-issue. Combustion by-products - carbon - is a much greater problem than your minor scratch will ever be. This minor scratch will not cause any detonation at all.
Might not be too wise to open your engine and in so doing cause more problems than what you had to begin with.
Last edited by jake corvette; Feb 13, 2015 at 08:16 PM.
