2.8 engine vibration

[mickman055]

Hopefully someone knows the answer to this problem (likely it will be alot of someones). I have a 87 pickup, spun some rod and main bearings. I also had another engine, year is kinda unknown-was told by the guy that it was out of a 89 4x4. Anyway I pulled the "89" down measured all clearances with plastigage-all on the lower end of tolerances. Honed cylinders and reassembled engine-of couse with an engine gasket set. Now at idle and up to 2000 rpms it feels as though a motor mount is grounding out or something of that sort. I used the flex plate and balancer from the old engine on the new one. Mounts all looked good, I dont know if the vibration acually goes away or is just covered up by the rpms. It does this at idle, in any gear, and at speed, any gear. Noticable at stop lights or parked. Help. Thanx for any info and tips

[Ed Mc]

Most likely the cause of your vibration comes from using the flex plate out of the '87 motor, which is probably balanced differently than the replacement.

Older motors were balanced externally with weights on the flywheel or flex plate. Newer motors were internally balanced, with a "zero balance" flywheel/flex plate.

So, you're gonna need to change out the flex plate to a later style. If I recall, '88 was the transition year so if you were to pick up a flex plate for an '89, it'd definitely be the correct one.

Don't run it with that vibration, it'll wreak havoc with the engine's innards.

HTH........ed

[mickman055]

Still got the flex plate from the 89, they looked the same but maybe I missed something on it. Just really hate to swap them if you know what I mean, its a real bummer in the pickup. But I guess Ill try it anyway.

[mickman055]

I had read somewhere that the "zero balance" motors had the one piece rear main seal, both of these motors had that. Am I wrong in this assumption?

[mickman055]

Yea!! It is fixed, thanks to your suggestions. After 3 or 4 days of hemmin and hawing about if it was out of balance or valves too tight or vaccuum leak, I decided to just at it. Pulled the inspection cover off of the converter housing and guess what...... I spyed a weight on the back side of the flex plate. So then out comes the trans, not all the way but just enough to unbolt and replace the flex plate. Started it up and it runs as smooth as can be. I guess thats what I get for second guessing myself when I put the motor together, the flex plate off of the 87 was cleaner. According to one site I read, GM went to an internally balanced engine in '88, and the build date on this truck is 8/87, late 87 or early 88?. Once again, thanks for all your help. Im sure I'll be using you guys and gals somemore in the future. Mickey

[betterthanyou]

Don't feel bad, your not the first one to do it. Glad you got it fixed without pulling your hair out.