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Author Topic: What caused this damage to my pistons?  (Read 10552 times)
RunninHorse
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« on: July 01, 2010, 11:14:51 am »

I'll sum this up best I can.  I bought a coupe with a supposedly "professionally built" 347 stroker.  Dropped a valve driving it home.  When I took off the heads I found a very blown head gasket on the passenger side and two damaged pistons in numbers 6 and 7.  The valve dropped in 5.  I'm wondering what caused the damage to the pistons.  I'm curious if the seller knew about the damage and dumped his problem on me.  I find it hard to believe that this damage went completely unnoticed.  Is it acceptable practice to use pistons for non inline heads with inline heads?  The pistons are the Probes that are specifically for Twisted Wedge heads, but the heads are old High Ports (2.08/1.60).  Probe says the pistons are not for use with inline valve heads.  The cam is around 600 lift with a 1.6 rocker.  The compression was supposedly 10.7:1, but I don't know how much the block deck or head deck surfaces have been milled.  Thank you in advance.   Thanx!

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I'm Rob.  Working on my '93 Reef Blue coupe.  Stock internal 302, 80 MAF, 75 TB, Victor 5.0, High Ports, 30# inj., B303, 1.6s, Tremec TKO 3550, Quicktime bell, Fidanza Al flywheel, stage 3 ceramic clutch, & 4.10s.  12.68 @ 111.69
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jayh
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« Reply #1 on: July 01, 2010, 11:43:17 am »

it looks like those pistons have dual releifs?  Hmmmmm

does it have nitrous on it?

it looks like the ring gap on the 1st compression ring was to tight, the ring gap closed and broke the top of the piston/ring land

in my experience its usually more common to happen on 5&6 or 7&8, only 6&7 seems to be a rareity

if it doesnt have a plate on it now, my guess is it did before you bought it OR there was just too much timing in it
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RunninHorse
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« Reply #2 on: July 01, 2010, 11:47:24 am »

Thanks Jay.

There are dual reliefs, so it makes me wonder if the pistons were designed for both inline and non heads.

Supposedly never had nitrous on it.

Ring gap too tight, never would have thought of that.  I guess I can check that.

"if it doesnt have a plate on it now, my guess is it did before you bought it OR there was just too much timing in it"  Not sure what plate you mean sorry.  Wish I had checked the timing when I had a chance.
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I'm Rob.  Working on my '93 Reef Blue coupe.  Stock internal 302, 80 MAF, 75 TB, Victor 5.0, High Ports, 30# inj., B303, 1.6s, Tremec TKO 3550, Quicktime bell, Fidanza Al flywheel, stage 3 ceramic clutch, & 4.10s.  12.68 @ 111.69
'66 F100 shortbed, 352ci, 3 on the tree - on hold
'65 Coupe rolling chassis - on hold
Parts I'm selling: 
Hardened Push Rods - Trick Flow 6.2" .080 - $60
Misc. Fox Body Interior Pieces
jayh
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« Reply #3 on: July 01, 2010, 11:49:47 am »

nitrous plate
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Joel5.0
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« Reply #4 on: July 01, 2010, 01:10:43 pm »

Dual relief pistons are designed to be used with either inline or TW heads + as long as PtV (which has nothing to do with the total valve lift) is within acceptable tolerances, it doesn't matter what type of piston relief is used.
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« Reply #5 on: July 01, 2010, 01:52:56 pm »

Had an engine do this on a dyno several years ago. No NOS ever on the motor. Lifted the exact same part of 5 pistons where the intake reliefs cut to the edge of the piston. Motor had over 500 miles on the street. The pistons came apart around 2500-3000rpms as the motor was coasting down from a pull. And hello-yes it made a racket. The owner knew that something bad had happened. I'm curious what the heads looked like when you got them off. Should be a trail where the parts of the pistons went, dinged heads, bent exhaust valves, ect. Good Luck!
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Brian Feimster
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« Reply #6 on: July 01, 2010, 01:56:19 pm »

Detonation 4 Eyed
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... it was REALLY revving at like 4K...
If I saw that thing in my rear view Im pulling over to let you by, I be scared of that thing Huh? i dont know wich car is uglier ur or mine?
Javier
Ugly?  Easy now -- that's my baby and it's got lots of unique character!  When I drop that built 445" stroker in it you won't have any time to "pull over to let me pass" because I'll have already blown past you when you figure out what the hell was that loud noise behind you . . .  
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« Reply #7 on: July 01, 2010, 01:58:23 pm »

A lot of detonation will lift the ring lands.....that was a bad tune.
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HIGHVOLTJ
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« Reply #8 on: July 01, 2010, 02:32:15 pm »

Detonation 4 Eyed


My thoughts exactly, nothing to do with valve contact, that piece got rattled off of there!
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RunninHorse
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« Reply #9 on: July 01, 2010, 04:48:51 pm »

Had an engine do this on a dyno several years ago. No NOS ever on the motor. Lifted the exact same part of 5 pistons where the intake reliefs cut to the edge of the piston. Motor had over 500 miles on the street. The pistons came apart around 2500-3000rpms as the motor was coasting down from a pull. And hello-yes it made a racket. The owner knew that something bad had happened. I'm curious what the heads looked like when you got them off. Should be a trail where the parts of the pistons went, dinged heads, bent exhaust valves, ect. Good Luck!

I thought the same thing, but no damage in sight.  The heads are at the machinist now, so maybe they'll find something I missed.

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I'm Rob.  Working on my '93 Reef Blue coupe.  Stock internal 302, 80 MAF, 75 TB, Victor 5.0, High Ports, 30# inj., B303, 1.6s, Tremec TKO 3550, Quicktime bell, Fidanza Al flywheel, stage 3 ceramic clutch, & 4.10s.  12.68 @ 111.69
'66 F100 shortbed, 352ci, 3 on the tree - on hold
'65 Coupe rolling chassis - on hold
Parts I'm selling: 
Hardened Push Rods - Trick Flow 6.2" .080 - $60
Misc. Fox Body Interior Pieces
scott0568
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« Reply #10 on: July 02, 2010, 11:07:55 am »

top ring gaps to tight or detonation cause by oil passing by rings ,by the look of your picture is that oil deposit sitting on top ?
cheers
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« Reply #11 on: July 02, 2010, 11:32:57 am »

Kinda odd two pistons with the same damage, same location.

I've massaged my pistons to relieve all the sharp edges.
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... it was REALLY revving at like 4K...
If I saw that thing in my rear view Im pulling over to let you by, I be scared of that thing Huh? i dont know wich car is uglier ur or mine?
Javier
Ugly?  Easy now -- that's my baby and it's got lots of unique character!  When I drop that built 445" stroker in it you won't have any time to "pull over to let me pass" because I'll have already blown past you when you figure out what the hell was that loud noise behind you . . .  
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