do do do detonation neat pic inside
Thread Starter
Melting Slicks
Joined: Apr 2002
Posts: 3,019
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From: down that one road next to that big tree
do do do detonation neat pic inside
i still can't figure out exactly what caused this but when i tore my old engine apart the other day i found 4 broken rings in 4 different cylinders. however this is the real prize winner, it's a stock 108k mile 1990 L98 piston. 
[Modified by gtsyellow, 6:22 PM 8/28/2002]
[Modified by gtsyellow, 6:25 PM 8/28/2002]
[Modified by gtsyellow, 7:10 PM 8/28/2002]
[Modified by gtsyellow, 6:22 PM 8/28/2002]
[Modified by gtsyellow, 6:25 PM 8/28/2002]
[Modified by gtsyellow, 7:10 PM 8/28/2002]
Thread Starter
Melting Slicks
Joined: Apr 2002
Posts: 3,019
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From: down that one road next to that big tree
Re: do do do detonation neat pic inside (87Beast)
quite, i've spent a small fortuine doing this rebuild details are in my sig, with any luck it will be done in a few days and i can install it :) i went with some pretty strong stuff so hopfully this engine lasts many years. :jester
Thread Starter
Melting Slicks
Joined: Apr 2002
Posts: 3,019
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From: down that one road next to that big tree
Re: do do do detonation neat pic inside (tkrussell)
amaizingly enough NONE< the block is getting a line bored and .040 overbore in the cylinders & being decked to zero. mobil1 really does wonders for preserving a engine the block was in better shape than many 30k mile cars i've seen.
Pro
Joined: Aug 2002
Posts: 702
Likes: 1
From: the corner of walk and dont walk
Re: do do do detonation neat pic inside (gtsyellow)
Is that a flat top piston or optical illusion? Do all the L-98's have flat top pistons, or only 1990/newer? Are there holes behind the oil ring, or just a slot? :confused:
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Thread Starter
Melting Slicks
Joined: Apr 2002
Posts: 3,019
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From: down that one road next to that big tree
Re: do do do detonation neat pic inside (bogus)
well as you can see the ring land is destroyed and there's even a hole in the top where it all blew through. the hole you see i think is the wrist pin. other than that there's just locks and standard rings. only the VERY late L98's used flattops as all others are dished for lower compression. when this started i'm not sure but i think only 90 and 91 used flattops.
Thread Starter
Melting Slicks
Joined: Apr 2002
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From: down that one road next to that big tree
Re: do do do detonation neat pic inside (Maximus9000)
a few bad tanks of i wannabe 92 octane gas, a few hundred miles with bad spark plug wires that were crosstalking and knocking at idle, a few miles with my knock sensor rigged not to detect knock. my lead foot, a engine GM designed with 10:25-1 compression to start with, heads that have low swirl rpm at low lifts, a cam with pretty low duration that loves building cylinder pressure at low rpms. detonation usually happens in lower rpms not higher if anyone wasn't aware of this. end result? see above pic :lol: the best part was the serious cloud of smoke that came out of it, it reminded me of spy hunter. the car later was driven 100 miles in the above condition, closely tailed by corvette0096 who later had to degrease the vehicle he was driving. :D
Burning Brakes
Joined: Feb 2000
Posts: 824
Likes: 2
From: Camden SC
Re: do do do detonation neat pic inside (Tom/99)
Disconnecting knock sensors can contribute to this type failure. When you factor in your other problems, an operating spark retard system becomes a near necessity. Had a couple of pistons do the same thing on a mid 70's engine, before knock sensors. Made a believer outa' me. Any ping is really a bad thing.
Hope your repairs turn out OK.
dlmeyers 90 coupe zf6 3 speed shocks
Hope your repairs turn out OK.
dlmeyers 90 coupe zf6 3 speed shocks
Race Director
Joined: Dec 1999
Posts: 16,945
Likes: 9
Re: do do do detonation neat pic inside (gtsyellow)
Looks like you had a little too much detonation there, that's what usually causes the ring lands to break.
Marck
[Modified by Twinnie, 10:41 AM 8/29/2002]
Marck
[Modified by Twinnie, 10:41 AM 8/29/2002]
Safety Car
Joined: Dec 2000
Posts: 3,767
Likes: 5
From: Jacksonville Fl
Re: do do do detonation neat pic inside (gtsyellow)
Looks like the piston pounded the roof of the combustion chamber.
I definitely would not reuse those same connecting rods.
I don't think it's detonation... detonation usually beats the rod bearings to death and puts holes in pistons...that piston slapped the combustion chamber roof. A little different scenerio don't you think?
[Modified by BBA, 11:48 AM 8/29/2002]
I definitely would not reuse those same connecting rods.
I don't think it's detonation... detonation usually beats the rod bearings to death and puts holes in pistons...that piston slapped the combustion chamber roof. A little different scenerio don't you think?
[Modified by BBA, 11:48 AM 8/29/2002]
Thread Starter
Melting Slicks
Joined: Apr 2002
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From: down that one road next to that big tree
Re: do do do detonation neat pic inside (BBA)
maybe but there was a explosion in the ring land, the aluminum is melted basically the detonation happend below the top ring. my best guess is i already shattered the top ring {like 3 other cylinders} then it kept detonating and ignited the oil on the side of the piston and blew it's self to pieces. the silver area you see where the chunk is missing is also melted, you can see where the explosion happend & it was so hot it seriously melted the piston. the engine going in it is in my sig. i saw no reason to reuse ANYTHING in this engine besides the block and my d-port head castings. i managed to score a set of eagle SIR I-beam 5140 forged rods with ARP bolts for $199 new in the box. where you see the piston all torn up on top is from the chunks of metal comming up and slamming into the quench area. this also gouged one of my heads pretty good. i'm hoping .020 off the head will smooth up most of it. i also polished the combustion chamber to a mirror this time around & used forged pistons. :jester
[Modified by gtsyellow, 3:32 PM 8/29/2002]
[Modified by gtsyellow, 2:34 PM 8/30/2002]
[Modified by gtsyellow, 3:32 PM 8/29/2002]
[Modified by gtsyellow, 2:34 PM 8/30/2002]
Race Director
Joined: Dec 1999
Posts: 16,945
Likes: 9
Re: do do do detonation neat pic inside (BBA)
Detonation will cause these kinds of piston failures, a guy I know running a supercharger on a stock cfi bottom end busted his forged pistons in the exact same spot because he forgot to retard the timing on his freshly rebuilt engine :)
Marck
Marck
Thread Starter
Melting Slicks
Joined: Apr 2002
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From: down that one road next to that big tree
Re: do do do detonation neat pic inside (6spd.89)
i could mail you this piston with a little pink bow around the skirt if you'd like it to show up on your door :jester