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RA462 · 04-10-2003, 05:44 AM

Last night I went to assemble my 455 and I have a huge problem. The number one piston would not go back in the bore! I found one of the piston’s skirts was bent out by .008”! It’s just one side at the bottom quarter inch; I checked it with a straight edge and mics. This is the same cylinder that it came out of. I can’t understand at all this how this could happen. I was thinking that I could chuck the piston in the lathe and clean this up. Has anyone ever seen this? They are TRW forged +.030 pistons. I don’t know what to do and I need this solved to finish assembling the engine. I know I didn’t drop it or anything, could the shop have done anything pressing the pins in? Please help!

RA462 · 04-10-2003, 05:44 AM

Last night I went to assemble my 455 and I have a huge problem. The number one piston would not go back in the bore! I found one of the piston’s skirts was bent out by .008”! It’s just one side at the bottom quarter inch; I checked it with a straight edge and mics. This is the same cylinder that it came out of. I can’t understand at all this how this could happen. I was thinking that I could chuck the piston in the lathe and clean this up. Has anyone ever seen this? They are TRW forged +.030 pistons. I don’t know what to do and I need this solved to finish assembling the engine. I know I didn’t drop it or anything, could the shop have done anything pressing the pins in? Please help!

PONTIAC DUDE · 04-10-2003, 05:56 AM

Did they heat the rods or press them in?

I have seen pistons distort when pressing as you are then pushing against the other side with the rod when install the pin.

Pressing pins is a No No in my book. Also sometimes the inside of the piston isn't 90 degrees to the rod and can cause binding and twist in the pin area.

Build it fast, build it right, build a Pontiac.

http://PontiacDude.cc

RA462 · 04-10-2003, 08:28 AM

I could not see any discoloration at the small end of the rod from heating it up. They are CAT rods press fit. They did say that they put a small chamfer on the pin bore to help get the pins in. The pin slides nice and smooth in the piston. By the way does anyone know what the rod bolts get torqued to? I lost the paper that came with them.

PONTIAC DUDE · 04-10-2003, 08:59 AM

65 ft/lbs.

They color quickly because of the material and smoothness. So I would venture to say that they pressed them if there is "No" color at all.
It is "Possible" that the rod distorted the pin boss area which affected the skirt, as there isn't much lip for the rod to ride on the inside of the piston to press.
If you squeeze the sides the skirt has to go bigger. And at it's weakest point. The lower skirt area where there isn't a lot of support.

I never liked the press deal. You take a chance of gauling the piston pin boss area or ending up with a tight rod/piston deal. Then the shop has to take them apart and hone the piston pin boss. Then you have a slight knock when it warms up due to a looser pin fit.

Build it fast, build it right, build a Pontiac.

http://PontiacDude.cc

PONTIAC DUDE · 04-10-2003, 09:04 AM

Btw; You need to replace the piston, don't grind or mill. It can distort back to size or go where it wants to after it's fired.

Build it fast, build it right, build a Pontiac.

http://PontiacDude.cc

RA462 · 04-10-2003, 10:36 AM

Do you have any individual pistons or a GOOD used one? You have know idea how much this stinks!

Now I'll have to get a new piston, have the valve relief's opened up, and it ballanced to the rest.

Bartman · 04-11-2003, 05:49 PM

From what you described it sounds like it got dropped after the rod was pressed. Your best bet is to replace the piston.
Bartman

Ponies run but Birds fly

Gooatee · 04-11-2003, 07:29 PM

Pardon me, if I am out of place! Wouldn't it be the shops responsibility to find you a piston and replace it if they damaged it fitting the rods? Even if they dropped it I would think they would be there to right the wrong! Now if it is due to your own error that is another thing.

ron thorne · 04-12-2003, 10:36 PM

sounds like somebody dropped the piston/rod assembly and the rod hit the inside of the skirt. is there a telltale mark on the inside of the skirt where the rod would have hit it? usually this only happens on thin skirt/lightweight pistons. since it is a forged piston, it may be salvageable by sanding, peening, etc.

RA462 · 04-14-2003, 06:12 AM

I know that I did noting to damage this piston. There was no sine of damage to the piston from dropping it, no nicks or anything. The guy at the shop said that he had to put a small chamfer on the small end of the rods to help allow the pins to go in. This is the number 1 piston that is messed up. I think he was working on them in order had problems with the first one, and then chamfered the rest. I do believe he cold pressed the pins in that also could have caused something to bind. This shop has a good reputation but of curse doesn’t work on Pontiac engines much. I’m going to talk to him this afternoon to see if he is willing to work something out on this matter. Not sure if he will do anything because I took his advice a straightened the skirt out myself. I was very satisfied with his work up to this point and have sent a friend of mine to have work done there also. Now were wondering about his parts. I should have just made the drive to KRE!

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