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Author
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Topic: Piston broke...
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stang106
Gearhead Posts: 786
From: God's Country!... Port Alberni B.C. Canada
Registered: Jul 2001
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posted 07-05-2002 12:43 PM
   
Was just breaking in my 351W, was running obout 5,500 rpm and had a bad noise and vibration for about a second. Went home, oil milky, water in rad foamy. Valvetrain good, checked plugs, #8 had water on it, pulled head off, a piece about 1 1/4 inches #8 piston broken off and gone so you can see the top ring exposed. What happened here? I can't find any sign of water going past the head gasket. The only other thing that I'm sure is unrelated is that all intake ports were oily, oil was being sucked up past the intake gasket from the lifter valley, no sign of water crossing the gasket, had permatex around water holes. Any ideas appreciated, I'll pull the motor and get it magnafluxed, look at rest of the pistons for cracks, I'm thinking I might turf them all and put some forged ones in that are hopefully the same weight.
Dave------------------
'70 ragtop Stang
351W - ready to race! [This message has been edited by stang106 (edited 07-05-2002).]
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n2oMike
Gearhead Posts: 2831
From: Spencer, WV
Registered: Jan 2001
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posted 07-05-2002 01:20 PM
If they are KB hypereutectic pistons, the rings need extra end gap. (They usually mention this in bold print throughout the instructions several times)What happens, is the rings expand and lock in the bore around the top of the piston's stroke (where it's hottest), and when the rod tries to pull the piston back down, the top ring land gets pulled off. IF you have hypers, that's my guess. If not, who knows. Did you check the end gap? Good Luck! ------------------
Mike Burch
66 mustang real street
302 4-speed 289 heads
10.63 @ 129.3
http://www.geocities.com/carbedstangs/cmml_mburch.html
http://www.fortunecity.com/silverstone/healey/367
http://www.mustangworks.com/cgi-bin/moi-display.cgi?220
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Butch Jennings
Gearhead Posts: 633
From: No. California
Registered: Apr 2000
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posted 07-05-2002 01:53 PM
quote:
Originally posted by stang106:
The only other thing that I'm sure is unrelated is that all intake ports were oily, oil was being sucked up past the intake gasket from the lifter valley,
This isn't as unrelated as you might think, oil in the combustion chamber will cause it to detonate. Mike is 100% correct about Hypers needing more ring gap, but if it had sufficient end gap, then detonation is the next logical reason for this.
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Butch
460 powered 1967 Comet Cyclone
10.271 @ 130.231
Butcher's Home Page
"Friends don't let friends drive Chevys"
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Gearhead
Gearhead Posts: 2177
From: Brisbane, Australia
Registered: Mar 2000
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posted 07-05-2002 02:41 PM
Ouch!!! Sorry to hear that Dave.  Man, I hate hearing stories like that. I hope that you can get it back up and running again really soon! Best of luck.------------------
Cheers,
Ian
M&M Member #395
-------------------
'79 Mustang Indy 500 Pace Car
Ian's Pace Car Website
Vancouver Island Mustang Association Website
Indy Pace Car Registry of Mustangs Official Website "A friend will bail you out of jail after you do something stupid... a real friend will be sitting beside you saying 'That was SO COOL!!'".
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SteveLaRiviere
Administrator Posts: 45869
From: Saco, Maine
Registered: May 99
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posted 07-05-2002 04:23 PM
Sorry to hear that. I bet you had a little detonation and the upper part of the ring land gave away.You couldn't pay me to use hypereutectics. ------------------
'70 Mustang Mach 1, '72 Mustang Sprint, '94 F-150
Pics
MCA Member # 47773
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Rustang
Gearhead Posts: 821
From: Clarion PA
Registered: Nov 2000
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posted 07-05-2002 05:05 PM
Detonation was probably the culprit, bit here's another possibility:
With milky oil and foamy coolant, you may have a coolant leak somehow into the combustion chamber. This could have hydraulic'd a cylinder and easily broke a piston. If this would have happened, you would have seen alot of white smoke out the tailpipe.
That leaky intake gasket could also introduce water into the intake, especially #8 cylinder. Or there could be a cracked cylinder, block, and sometimes a bad head gasket is not real evident upon first inspection. If you were burning coolant the combustion chamber or spark plug might have a green color to it from the antifreeze.------------------
'68 mustang 351 clevor- 10.92@124
'67 Stang, 351W -11.18@118
'69 351C Torino-14.90@100
'78 Pickup 351W-15.56@88
'79 Pickup 460 ET=??
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stang106
Gearhead Posts: 786
From: God's Country!... Port Alberni B.C. Canada
Registered: Jul 2001
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posted 07-05-2002 07:53 PM
I did check the ring gaps and they were about 0.016 I now can see a crack in the cyclinder wall between #7 and 8. I had some detonation when I first started it last week but have backed off the timing. I'm still not sure about the sequence here, will pull the motor and take it apart for further inspection.
Dave
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Butch Jennings
Gearhead Posts: 633
From: No. California
Registered: Apr 2000
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posted 07-05-2002 08:10 PM
.016 is way too tight for a hyper piston, that would be ok with a cast or forged deal. I've seen hypers butt the ring at .020 on a 4.030 bore (when run hard), I would think that .022 to .024 would be more in order.... .016 would be ok on the second ring but not the top. Sorry to hear of your misfortune.------------------
Butch
460 powered 1967 Comet Cyclone
10.271 @ 130.231
Butcher's Home Page
"Friends don't let friends drive Chevys"
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SteveLaRiviere
Administrator Posts: 45869
From: Saco, Maine
Registered: May 99
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posted 07-05-2002 08:18 PM
Ouch, that really sucks, Dave! ------------------
'70 Mustang Mach 1, '72 Mustang Sprint, '94 F-150
Pics
MCA Member # 47773
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smblk t-bolt
Journeyman Posts: 93
From: port alberni BC Canada
Registered: Apr 2002
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posted 07-06-2002 12:36 AM
ewwww...that really sucks!did you even get a chance to tune it up?when you came by it sounded pretty advanced...detonation sounds like the likely culprit.too bad.hope nothing else is beyond salvage.gimme a call if you need a hand.ron
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stang106
Gearhead Posts: 786
From: God's Country!... Port Alberni B.C. Canada
Registered: Jul 2001
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posted 07-06-2002 03:01 AM
Motor is out and apart now. The damage is localized to #8. That piston is also tight on the pin, and has a crack from the oil ring towards the pin. the #1 piston and head is alittle shiny compared to the rest. That iis one of 0.020 above deck pistons. I used the 0.041 gaskets. Now I can fix that problem also... On the brighter side, it sure is nice working on a car where everything is clean or new, I don't have to wash my hands!
Dave
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bfxcomet
Gearhead Posts: 691
From: Port Alberni, B.C. , Canada
Registered: Mar 2001
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posted 07-06-2002 03:13 AM
Hey Dave are you still up.
Roger------------------
65 comet project
84 T-bird
Made in CANADA built for speed
#1145
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the last dive
Gearhead Posts: 147
From: sydney australia
Registered: Dec 2001
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posted 07-06-2002 03:56 AM
i had a a set of kb hypers they didnt like detonation either  never mind i now have srp forged  ........such is life!
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bfxcomet
Gearhead Posts: 691
From: Port Alberni, B.C. , Canada
Registered: Mar 2001
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posted 07-06-2002 04:45 AM
Sorry about the engine Dave, you put alot of thought into all your plans for the motor. It seemed all good and a smooth startup. Hope we can find a fix and get you back on the road.
Roger------------------
65 comet project
84 T-bird
Made in CANADA built for speed
#1145
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clevelandstyle
Gearhead Posts: 1309
From: central Indiana
Registered: Jul 2001
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posted 07-06-2002 10:37 AM
quote:
Originally posted by stang106:
On the brighter side, it sure is nice working on a car where everything is clean or new, I don't have to wash my hands!
Dave
Now there's someone looking on the bright side!  ------------------
Ben
Grabber Green '70 Mach I 351C 4V
Robbin Egg Blue '79 Fairmont 351C 4V
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stang106
Gearhead Posts: 786
From: God's Country!... Port Alberni B.C. Canada
Registered: Jul 2001
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posted 07-08-2002 03:16 PM
I willget a sleeve installed in the cracked cyclinder. Looks like another piston may have a crack, I don't want to use any of them now. What's anyone's opinion if I go to forged and not get the assembly re-balanced? I was wondering if I got a simular weight forged piston, if possible, is this idea viable?
thanks,
Dave[This message has been edited by stang106 (edited 07-08-2002).]
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