I tore down my stock motor which I thought was unopened due to a head gasket failure. Well it's not unopened, timing set has been changed and I found 3 what look like hot-air pistons with the 3 notches forward and the other 3 pistons just have a sort of "punch" mark on the top of the piston facing forward. They are STD size. Is it possible the factory short block could have been built with two different piston styles? Maybe using up old stock?
Miss-matched pistons
- Thread starter NM Tom
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i can state pretty sure that a factory car would not come with different pistons in the same engine------on the underneath of the piston there is a 8 digit number cast------86 engines had different pistons than 87 engines with different numbers------i have opened somewhere in the range of 100 factory built engines and never seen an engine with different pistons than were normally specified...........RC
86 pistons are # 25526298 87 pistons are 25531060 they are similar but there are changes in the area below the wrist pin holes
Well it gets stranger. I pulled the pan and the bottoms of the pistons with the 3 notches look brand new underneath where as the others have some discoloration. I guess I can assume 3 pistons were replaced for some reason. The cylinder bores still show slight cross-hatching. Could that still be seen at 110k or do I also assume it was at least honed when the new pistons went in. Pulled the lifters and found I had 4 of one style and 8 of another. The lifters and cam all look perfect. I have put 25K on the car so I know it has been this way at least that long. Funny thing is this motor ran great and I can't decide to leave the short block alone or not. I have a 4.1 that's going in so I just need to know what to do with the original block.
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dr_frankenstein
Mad Scientist
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- Mar 17, 2008
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- 5,126
I had an 85 HA block with the same deal.
has 5 same pistons and 1 odd ball.
ran great too? so for a stocker application im sure its just fine... but makes me nervous for any kind of real boost.
just a typical cheepo burnt piston replacement I imagine.....
A.j.
has 5 same pistons and 1 odd ball.
ran great too? so for a stocker application im sure its just fine... but makes me nervous for any kind of real boost.
just a typical cheepo burnt piston replacement I imagine.....
A.j.RmvBfrFlght
Well-Known Member
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- Sep 28, 2007
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- 2,234
This is common for the "rebuilder special" engines. Examples of how the rebuilds are done is that if one bore/piston is bad that one hole gets bored if required, then honed and fit with a piston. The other pistons just go back in with nothing more then new rings.
If a piston is cracked that one gets replaced while the other original ones go back in. These engines can come through with two different cylinder heads, the wrong cam and so on. To the rebuilder parts is parts, use the original stuff unless it needs to be replaced. Then if another used part fits, it goes in.
RemoveBeforeFlight
If a piston is cracked that one gets replaced while the other original ones go back in. These engines can come through with two different cylinder heads, the wrong cam and so on. To the rebuilder parts is parts, use the original stuff unless it needs to be replaced. Then if another used part fits, it goes in.
RemoveBeforeFlight
