460 cracked piston
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Joined: Jan 2002
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From: berkeley usa
460 cracked piston
I have and 83 f250 with a 460. It has 130k on the clock, and at 120k (last spring) I freshoned it up with a holley 750, performer manifold, performer cam kit, etc. soon after this I had what sounded like valve train noise at freeway towing speeds (55mph) OH< BTW, I only use the truck to tow horses...6000lbs at a time.
I had a faulty radiator cap which popped and overheated the truck towing on the freeway. It still ran after a Pegged-to-the-H overheat, although it has less power now. I performed a compression test, and all cylinders were about 150lbs and withing 5% of each other. So I took it to my mechanic and he drives it and says" Its got a cracked piston"
Questions:
Are cracked pistons common?
Can they be caused by overheating?
And why would this not show up as a low compression cylinder?
Thanks in advance for your input.
Rob
I had a faulty radiator cap which popped and overheated the truck towing on the freeway. It still ran after a Pegged-to-the-H overheat, although it has less power now. I performed a compression test, and all cylinders were about 150lbs and withing 5% of each other. So I took it to my mechanic and he drives it and says" Its got a cracked piston"
Questions:
Are cracked pistons common?
Can they be caused by overheating?
And why would this not show up as a low compression cylinder?
Thanks in advance for your input.
Rob
Mountain Pass
Joined: Apr 2000
Posts: 241
Likes: 2
From: Holland, Michigan
460 cracked piston
[updated:LAST EDITED ON 07-Jan-02 AT 04:15 PM (EST)]Overheating is a very good cause of cracking a piston. My question is, when the temp gauge was rising....Why didn't you stop? Getting a cracked piston is not a common problem. Something must've been wrong.
TBirdGuy
TBirdGuy
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From: berkeley usa
460 cracked piston
My wife was driving the truck, towing 2 horses on the freeway at the time. I've got her checking the gauges quite often as she drives, and she swears that she saw o.k. temp pressure just a few minutes before...then the radiator cap blew so she looked down, and the temp gauge was already pegged on H. She slowed to 20 mph and pulled off and stopped at the first exit, about 1/2 mile down the freeway.
This all happened within 6 miles from our barn, so she was only driving for 15 minutes and only 2 minutes on the freeway before it blew.
As for something else being wrong to cause the crackec piston..I can't find anything obvious. Compression is still quite good and even across cylinders and the truck runs o.k., albeit with less power.
I'll post more info when I tear it down later this month.
Rob
This all happened within 6 miles from our barn, so she was only driving for 15 minutes and only 2 minutes on the freeway before it blew.
As for something else being wrong to cause the crackec piston..I can't find anything obvious. Compression is still quite good and even across cylinders and the truck runs o.k., albeit with less power.
I'll post more info when I tear it down later this month.
Rob
Post Fiend
Joined: Nov 2001
Posts: 6,748
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From: Tallassee, ALabama
460 cracked piston
[updated:LAST EDITED ON 09-Jan-02 AT 12:04 PM (EST)]I'd find me a new mechanic. Pistons are generally 'not' known to crack in a case like this. They are mor prone to breaking/cracking the skirt when the engine is cold and rev'd excessively. Generally what happens in an overheat situation is you loose the tension on the rings and it allows blow-by of the compression rings. But, you say you have 150 psi cranking cylinder pressure, how close are they to each other? Are they all around 150 plus/minus 10 psi? What happens if you squit a little oil into the cylinder? Does the pressure go up? A cylinder leakdown test would tell you if any of the cylinders have bad rings or bad vavles/seats or blown head gasket.
When you replaced the cap and filled it with water, does the engine lose water now or is it okay? Is the lost of performance just your imgination so you can talk wifey into letting you hop it up?
When you replaced the cap and filled it with water, does the engine lose water now or is it okay? Is the lost of performance just your imgination so you can talk wifey into letting you hop it up?
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