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OPEL-LESS!!!
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Discussion Starter · #1 ·
piston swap

hi everybody, i'm rebuilding a motor for my 70 GT. i have a 2 1972 motors, one was in the car when i got it and had bad compression and weak oil pressure. the other was rebuilt before it was blown up ( broken rod) the motor that was origionally in my car when i got it has the best block out of the 4 motors so i'm taking that one and putting the head and timing chain/gear componets from the blown up motor onto the 72 with the good block. i hear that 1970 has 9:1 compression pistons instead of 7.6:1. is this true and if it is can anybody tell me if i can use these pistons in the 72 motor?
 

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They fit right in, if both bores are the same size. In other words, if neither block was ever bored out to an over size, or if both were bore the same, such as 20 over, etc. Nice easy way to pick up some compression.
Good luck,
James
 

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OPEL-LESS!!!
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Discussion Starter · #3 ·
so are the 9:1 pistons just flat tops then? i seen the pistons out of the 71 and both 72 motors i had were dishes when i tore them down yesterday
 

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Yes, the 9.0:1 pistons are flat top. The dished pistons are 7.6:1.

It is clear from all of your posts that all of your engines are VERY "tired". So... do yourself a favor while you have the engine apart. As a minimum, have the cylinder honed and put in new piston rings. Have the crank checked and pick the best one. I think I read that you are getting new bearings... do both the main and rod bearings. Also, you should have a good valve job done on the head. I know this is going to cost some extra money but doing it all again will cost more money... and a lot of aggrivation. More aggrivation is the last thing you need. You've already had more than your share of that.
 

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OPEL-LESS!!!
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Discussion Starter · #5 ·
ya i'm getting all new bearings and rings and we have a valve grinder in the barn so i planned on a valve job. we honed the cylinders last night (2 in the morning) pops is gonna show me how to check to make sure they are still in specs, hopefully they are.
 

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my friends dad had a camero that he bored .10 over and used stock pistons with new rings, and the ring end gap was in specs but once he started it up it was on its way to the junk yard. so the moral of this story is to use the correct over sized pistons for what ever it was bored to.
 
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