how to check TDC for timing change on a 3.1
August 16th, 2014, 2:10 PM
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how to check TDC for timing change on a 3.1
Hi I replaced a timing chain and gears on a 3.1 in my 94 corsica. took forever to start and stuttered when done. I tore it back apart to check timing, the cam gear looks fine it's right at the 12 oclock point and the crank gear is right lined up to the mark on timing cover and also it's right on it's mark straight up inside on the timing tensioner too. I had a big problem finding TDC before I took this apart.I didn't have any help to turn motor over and sparkplug hole was too far down to feel when compression was building up. I'm worried I might have had the number 1 piston up on it's exhaust stroke instead of up at TDC on the compression stroke. To know if I'm right now when the crank is up on the mark I checked where some of the other pistons are now, the number 2 piston is all the way down and the number 4 piston is all the way up. Does this confirm that I'M FOR SURE at TDC now? AS number 2 is next in firing order so it sould be at BDC when number 1 piston is at TDC? Also number 4 piston is up the same time as number 1 is up at TDC also right? Thanks
Last edited by turbotim23; August 16th, 2014 at 2:25 PM.
August 18th, 2014, 12:48 PM
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August 18th, 2014, 3:31 PM
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Thanks I knew I could check TDC by knowing what the valves were doing when it was coming up to TDC but didn't know what they were supposed to look like at TDC. I also just didn't want to have to pull the rear valve cover. Looked like a hassle but if I have to I have to. Thanks for your help. Some motors[interference fit] will bend valves if you break timing belts or timing chains, causing the valves to hit the pistons [in my case from maybe putting it together wrong]. Are 3.1 motors like this and could I have damaged the valves?
August 18th, 2014, 3:46 PM
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Thanks I knew I could check TDC by knowing what the valves were doing when it was coming up to TDC but didn't know what they were supposed to look like at TDC. I also just didn't want to have to pull the rear valve cover. Looked like a hassle but if I have to I have to. Thanks for your help. Some motors[interference fit] will bend valves if you break timing belts or timing chains, causing the valves to hit the pistons [in my case from maybe putting it together wrong]. Are 3.1 motors like this and could I have damaged the valves?
I did a quick search and found several internet discussions.
Not sure on your corsica, but 92 lumina had a dogbone on the front of the motor, You could rock/rotate the motor forward a little, and lock it up further in the eye slot if I remember, enabling easier plug access to the back of the motor.
this one says yes:
Is GM 3.1L V6 in 1991 Lumina an interference engine
August 19th, 2014, 2:49 PM
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