86/87 GN Motor?'s Replacement motors


Dec 26, 2005
I have and 87 GN and the motor is .030 over with trw forged pistons, 212/212 comp cam, ported heads, Walbro 340 fuel pump and hotwire kit, 65#PTE injectors, Precision gt6152 turbo, and turbo tweak 93 chip, vigilante, stock torque convertor in now but I have vigilante non lockup convertor going in. Question is just rebuilt motor and it has 100 or so miles on it and it sounds like it spun a rod bearing? My bore is .385 and I was told that that was right for the pistons. Possible skirts collapsed and not bearing? What are other possibilities, or things to check for? I just bought the car and have had head gasket problem and it took out piston so that is why the rebuid.

Does anyone sell a long block like Jaspers or Marshall? Are they worth buying if they do and any problems known with them out there? Who sells the best long block for the money? How much is a good long block?

Please help, just want to have fun with the car and no more problems. email me at rye_24@hotmail.com Thanks
did you check torque convertor bolts? also what is your oil pressure also could be a cam lobe take off breather on driverside and watch rocker arm and see if it is rocking right
Oil Pressure is around 30psi idel. I have not looked at rocker arm. Torque convertor bolts are tight.
try to take each plug wire off then rev and see if knock goes away then that would eliminate rod bearing the fireing against piston put pressure on rod and will knock. usually rod will knock on deceleration or at idle could be valve train noise
I would be really weary of .005" piston wall clearance. My local machine shop made my clearances about the same with those same pistons. After about 500 miles of oil puking out the breathers, I pulled the heads off to find the pistons were actually rocking in the bores. It caused the rings to never seat, thus I was getting bad blowby. If your machine shop screwed that up, maybe they screwed the bearing clearances up as well. If you want a motor assembled and ready to go, I'd go with Grooms out of Nashville. HTH.
I didnt think .005 p/b clearance would have done that. Stupid machine shops...always giving us Chevy clearances. :mad: