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| Engineering/ Technical Ask technical questions about cars. Do you know how a car engine works? |
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#1
08-02-2007, 08:04 AM
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rebuilding gm 3.1L ?
unfortunately I did not notice where the pistons rose to in relation to deck on the block during tear down. after putting in crank and pistons I noticed the pistons rose above the deck. If I set the head gasket on it takes up about half the distance. I'm going to put on gasket and head and torque down to see if piston hits the head. This scares me and I wish someone who knows could tell me if this is normal or not. They milled the block down .006. This is on a 94 grand prix 3.1L "M" code. Thanks for any help.
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#2
08-02-2007, 01:49 PM
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Re: rebuilding gm 3.1L ?
no, not normal at all. You want a bare minimum of .040" piston to head clearance. There is no way that is going to work
Either your stroke has changed, the rods aren't the same length, those pistons are completely wrong.....or someone decked the block waaaaaay too much!
__________________
life begins at 10psi of boost Three turbo'd motorcycles and counting. 
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#3
08-03-2007, 08:10 AM
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Re: rebuilding gm 3.1L ?
I did put it together yesterday and nothing hit. I was told by another that it is an extremely close tolerence. I did set the old crank in without the old bearings, I know I shouldn't have thrown them out so fast, just by guessing it looked awfully close as well. I am using the old pistons and cranks, except for 2 new ones. The only other thing is the decking and the company says they only did .006. I'm still nervous, especially after your response. I'm not sure what my next step should be. Being a backyard mechanic and trying to keep your kids car on the road is not easy
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#4
08-03-2007, 11:43 AM
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Re: rebuilding gm 3.1L ?
just cause nothing hits when you turn the engine over, doesn't mean everythings good. You really should measure the clearance
Use a feeler gauge to see how far out of the hole the piston is, then measure t he thickness of the headgasket fire ring. Subtract it, thats your clearance. if its under .040", its going to hit when it runs
__________________
life begins at 10psi of boost Three turbo'd motorcycles and counting.
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#5
08-03-2007, 01:06 PM
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Re: rebuilding gm 3.1L ?
I'm not familiar with the 3.1, but even if the pistons come out of the block as long as the head is round and has proper clearance then they won't hit. .04" seems like a good spec for a minimum.
Put another way, the clearanc emay all be in the head, not the block.
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