BBC wrist pins

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kyleracer
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BBC wrist pins

#1 Post by kyleracer » Fri Jan 20, 2006 10:03 pm

Hi, I have a question about pressed wrist pins. I had a set of pistons fly cut to clear a bigger cam. The shop that did the work also reinstalled the rods. After about 10 miles of driving the motor started to smoke with bad blow by. I thought that a piston broke so I tore the motor down and found that #1,2,6,8 pins have moved in the rods and rubbed big grooves in the cylinders. I pushed the pins out without having to heat them on those 4 rods. The shop says that I ran the motor to hot/ lean from bigger cam and that is why this happened. The shop that did the work also did a race balancing in 1991 and it has not been changed/apart until cam change started this mess. . Does any one know if thay are right ? Should I only use pins with locks? Any ideas? This is looking very expensive to fix. The block needs 4 liners and oversized pins. If I rebuild I do not want a repeat. The motor is an original LS-6 with standard bore and had 0 problems until now. Thanks-Kyleracer

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John_Heard
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#2 Post by John_Heard » Sat Jan 21, 2006 7:30 am

To me it doesn't sound like whoever worked over the rods got the press fit sizes right on the holes - or the pins were undersized, something was wrong there. I doubt this had anything to do with heat unless there was a press fit problem to begin with. I've seen small blocks dang near melt down on the dirt track becuase they were too hot (mud in the radiator/coolant leaks, etc.) and they didn't have problems with the wrist pins coming out. Somebody got something wrong on that press fit on your motor it sounds like to me.

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CoMax Racing
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BBC Wrist Pins

#3 Post by CoMax Racing » Sat Jan 21, 2006 11:06 am

I agree with Beyond. The heat that would be required to make a proper pin fit come loose would melt the engine down. I also agree the machinist who reworked your rods must have altered the interferance between the pin and the rod to the point where they came apart. If a pin is press fit to the proper tolerances there shouldn't be any reason to go with floating pins and retainers. I would shop around for a new machine shop. If you do go to floating pins use spirolocs not tru-arcs. I've had a few failures with tru-arcs in the past.

kyleracer
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Location: waynesboro pa

pins

#4 Post by kyleracer » Sat Jan 21, 2006 1:55 pm

He says the pins were the originals that were taken off when he fly cut pistons. Can the rods ends stay too big/loose after heating ?

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CoMax Racing
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BBc Wrist Pins

#5 Post by CoMax Racing » Sat Jan 21, 2006 2:27 pm

Unless he heated them to cherry red. Metal will come back to its original size after heating. The whole thing sounds very suspicious to me.The only way you would pound a pin out of a rod is if you are hitting the engine with massive blower boost 30 psi+ or lots of nitrous.

kyleracer
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Joined: Fri Jan 20, 2006 1:22 am
Location: waynesboro pa

#6 Post by kyleracer » Sat Jan 21, 2006 3:13 pm

The ends of the rods are very blue! Would that do it ?

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CoMax Racing
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wrist Pins

#7 Post by CoMax Racing » Sat Jan 21, 2006 10:49 pm

No, blue color is pretty normal for the amount on heat needed to put the pins in. About 350-375 degree F if I'm not mistaken. If the rods were a straw color(yellowish) then they got way to hot.

It looks like they didn't put to much heat in.

Can you measure the rods and the pins to see the interferance? Or are they too damaged?

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