Hey guys I need some help. We are rebuilding the 3.1 turbo motor and we hit a issue. We put new mains and rod bearings in and the motor and it wont spin by hand and if it does we have to push real hard to get the thing to spin but once it starts it is not bad. But when we stop, it locks up again. I have noticed that the old ones had a .016 marking on the mains and no oil grooves. The new ones have no such markings and has grooves. The new ones are part #7242M. They are the right ones from what I have read. Please help me out guys.
                                                                       Shawn

are you rebuilding it or just replacing the bearings? If you have it all apart did it spin when you installed the crank before you hooked up the rods? New pistons and rings? Was the crank turned and how much. Have you plasticgauged the bearings? Did you put oil on it while installing the bearings, rings?
Tim

We just replaced bearings with old rings. Used assembly lube on bearings. If we loosen crank bearing caps it spins better. We are going to plasticgage tomorrow. I was wondering if anyone ever ran into this problem. We are going to put some oil in it and see what that does if everything gauges ok.

sounds like wrong size bearings, any engine work done before to your knowledge?

Quote from: dogginred90 on April 04, 2008, 07:41:38 PM
We just replaced bearings with old rings. Used assembly lube on bearings. If we loosen crank bearing caps it spins better. We are going to plasticgage tomorrow. I was wondering if anyone ever ran into this problem. We are going to put some oil in it and see what that does if everything gauges ok.

Did you mark your main and rod caps? 

sound like you have some oversize bearings for a cut crank. I just looked up the numbers you posted it listed it as a sealed power set and should be standard size. They listed the oversize with the oversize on the end of the part number. I have seen bearing get misboxed not offen but it does happen. Plastic gauge will help figure this out.
Tim

No more worries we got it fixed. For some reason even with oil on the walls it still froze up a bit. Now it spins good. WOOOOOHOOOO. Thanks guys.

Quote from: dogginred90 on April 05, 2008, 12:58:55 PM
No more worries we got it fixed. For some reason even with oil on the walls it still froze up a bit. Now it spins good. WOOOOOHOOOO. Thanks guys.

Just because it spins does not mean it will last.  Precise clearances are needed to maintain EHL (elasto hydrodynamic lubrication)during engine operation.  Otherwise you are just metal on metal and the engine will wear out very quickly especially under the loads a boosted engine sees.  I would plasticgauge that thing to make sure you are in spec for clearances.  Otherwise get some 2-3 inch and 3-4 micrometers and measure the crank and rod journals and compare to the gm manual.  That is the absolute way to make sure you are in spec.  It is easier to take the time to do it now that to pull the motor later.  Flybynite is right, did you mark your mains and rods?  It is important to keep your rods in the same position on the crank as well as the same rod caps to the same rod you took them off of. 

Ken