Enigine has just been rebuilt.355/nothing speacial. Mods listed below. Stock harmoinc balancer with 140k seems to be in good shape,not falling apart.does it in neutral as well as in gear.Doesn't get worse in gear. Car feels like it is running great except for this vibration.We checked the motor mounts and the engine is not trying to lift in fwd or reverse. No exhaust leaks either. Any help would be greatly appreaciated as I am planning on going to the track tonight. The only thing I was thinking of doing was maybe checking the valve lash again before I go. Any thoughts? Thanks.

 

Did you do any balancing during the rebuild? If so, did you balance the flywheel as well?

 

yes everything was balanced and also just broker the 500 mile mark after rebuild. forgot to mention that fact.

 

So, your crank pulley and flywheel/clutch were all balanced with the crank?

 

no they were not. I was mistaken. called machine shop after that post just to verify and they did not.they measured the weight of each piston and conecting rods to make sure there would be no piston sling from one being heavier than the other. But they did not balance the crank to the balancer to the flywheel,etc. Do you think this is the issue? What would be a solution without pulling the engine back out?

 

I went through this same exact issue when I did my 6 speed swap. I had my stock flexplate zero balanced (with the crank) and when I put the new flywheel on, it was factory balanced and caused a horrible low rpm vibration. I had to pull the tranny back out and have the clutch and flywheel zero balanced. After I did that, it smoothed out and everything is good now. If your crank is balanced and the flywheel still has the factory weight on it, that is your problem (vibration). As for the crank pulley, have it balanced as well. They were supposed to come from the factory zero balanced, but I've heard of people discovering that some final balancing (from the factory) was done by drilling weight out of the crank pulley. I wouldn't drive it anymore like that or you'll shake the bearings out of the lower end.

 

thanks for the advise

 

FYI to all with similar problem, changed crank positioning sensor and problem went away. Finally got code pulled and that is what it came back as.

 

Congrats. That's a hell of a lot less work than pulling the tranny back out.