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Old 08-22-2010, 06:37 PM   #1
nic.wiggins
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Default #4 pisten mystery

My dad and I own a 1929 82A pickup. We replaced the worn out 30A block with a 32B block, winfield head, brinley 3/4 cam, balanced crank, ansen down draft, demon carb and mallory centrifugal advance distributor, mallory coil - professionally built.

Now the mystery - at about 500 miles, driving from a car show the #4 piston fails (rod stripped of babbit, damage to piston skirt). Sounds like a cement mixer.

This has happened now 4 times!

I really need some help.
Any ideas welcome.
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Old 08-22-2010, 06:42 PM   #2
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Default Re: #4 pisten mystery

fail; #4piston mystery
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Old 08-22-2010, 07:17 PM   #3
cannon
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Default Re: #4 pisten mystery

it very well may have been a bad pour on the rod.
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Old 08-22-2010, 07:19 PM   #4
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Default Re: #4 pisten mystery

must have read out of your post: didn't see failed four (4) times! YIKES
check the journal size for roundness and taper......
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Old 08-22-2010, 11:19 PM   #5
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Default Re: #4 pisten mystery




Somebody said something about an off set. What do you have?

skip. Left click the curser, let it blink on the drawing and Hold the Ctrl key down and tap the + key to enlarge.
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Old 08-23-2010, 12:40 AM   #6
Tom Wesenberg
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Default Re: #4 pisten mystery

Check the block for junk in the coolant chamber in the rear. That will make number 4 overheat and seize the piston, thus ruining the skirt and putting undue pressure on the rod and babbit, though I wouldn't think the added pressure would ruin the rod.
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Old 08-23-2010, 12:52 AM   #7
J Franklin
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Default Re: #4 pisten mystery

Has it been broken in as described in the owners manual? At what rpm does this failure happen.
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Old 08-23-2010, 03:43 AM   #8
Mike V. Florida
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Default Re: #4 pisten mystery

Was the number 4 piston put in with the correct orientation to front?
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Old 08-23-2010, 05:30 AM   #9
BRENT in 10-uh-C
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Default Re: #4 pisten mystery

Your Dad asked this same question earlier on here, ...and it is being asked on HAMB too. Early on, I wrote that I suspected that it is detonation that is hammering out the babbitt. Based on all that has been written, I still stand behind my initial comment. Let me add additional thoughts...

Since the block has been replaced twice, the thoughts about multiple incorrect bore or cooling issues are unlikely between two different blocks. The same mindset applies to an oiling issue within two different blocks.

Now lets think this next thought through regarding crankshaft. Just "how far" would a crankshaft need to be out of round to cause this? Many engines out there have slightly out of round crankshaft journals and they survive more than any 500 miles. If it was severely out of round, the rod would be so stiff in one area of rotation that this after the 3rd or 4th time of assembly would throw up a 'flag' to the rebuilder. While we can be critical of some engine rebuilders, shouldn't one must assume that after the 2nd or 3rd time of doing it over, that ultra care during assembly would be taken where obvious issues would be corrected?

The only other possibility in my mind is the question that was posed in #14 of the other post about whether the crankshaft has been drilled for oil pressure. If it has and the dipper has been closed off, this could be a logical explanation if there was an obstruction in the galley hole. Outside of that, the #4 rod area has the most amount of oil due to the inclination of the engine. If oil is prevelant in this area, then the chances of it being splashed up to keep a piston skirt from gaulding is very likely.

Therefore it is still coming back to a situation where detonation can easily be caused by too aggressive timing. Its effects appear in different ways but one needs to realize the extra forces that it can cause. It can cause ring land issues, it can cause a piston to rock in the bore, and it can cause rod bearing (babbitt) issues too. I wish I could see many of these parts as the engine is being disassembled to determine the true culprit.

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