after 5 months of waiting for my motor to be built my mechanic just got everything together yesterday. he said its has a bad vibration. i was driving it around and it vibrates bad the more gas you give it. even in park or neutral while reving it. the motor is a 383 built by s k speed in lindenhurst with a le2 heads and cam package computer tuned by madz28, full exhaust nothing touches the headers or y pipe, the motor is internally balanced, also installed is a pro torque 2600 stall converter . the motor sounds great seems like its got the power but also last night my friend who has a lightly modded srt 4 was keepin up with me.

this morning i unbolted the converter to see if it was possibly not put in properly. started it up and still had the same vibration when reving it.

what could be the problem could it be the flex plate or was the motor unproperly balanced?

please help

 

Unproperly ballanced is my first GUESS. It could be the ballancer or the flexplate. Maybe they didn't ballance it right. Are the motor mount good?

 

if its internally balanced, i HOPE you dont have the stock flexplate. You will need a neutrally balanced flexplate. Dont race anyone until the vibration is gone, if its a balance issue that will be hell on your bearings. Hope you find out whats causing it.

 

i believe it is internally balanced from what the builder told me he also said the stock flex plate is fine. i am currently using the stock flex plate. someone told me that if you remove the weights from the flex plate it will be fine but i dont know about that. how do you get a neutrally balanced flexplate can u just buy one?

 

ahh and also is the lt1 motor stock externally ballanced or internally balanced?

 

Since the engine is now internally ballanced (like mine) you MUST remove the weight from the flex plate. I've done this twice now. You have to be careful taking the weight off and not damage the flex plate. Just take your time with it.

 

so the tranny has to come back down im assuming to get it off, how is it attached

 

Sorrry to tell you this , but your motor is in danger the more you drive it. The front part of the stock LT1 crank in internally balanced and the rear of the crank is external balanced. So that's why you need to remove the counter weight on the flexplate and then have that rebalanced aswell, if you go with an internally balanced set up.

Did you say you disconnected the convertor and started it up with the same vibration problem? If you did not, try it and if it does not vibrate you could have a drive train problem.


I would give your builder call and ask him if he balanced that flexplate after pulling the counter weight off. Because I had that done to my flexplate when I had my 383 assembly balanced and he had to add a little more weight to the flexplate even after removing the counter weight.

 

The flexplate has about 4 rivets holding the counter weight in place, like sleep_z28 said take your time when removing weight.

 

ive drivin the car 30 miles since the rebuild and confirmed that it is not a drivetrain problem because i unbolted the converter and still had the vibration. so i should pull the tranny and remove the weights and have the flexplate rebalanced, or just remove the weights? also how hard is it to pull that tranny with no lift and just a floor jack with a decent amount of tools

 

Yes, go head and pull the tranny ASAP and remove that flex plate. If I where you I would get the flex plate balanced because anything that's going to be attached to a internally balanced crank has to well balanced!!!

If you have any access to lift use it. It'll make the job alot easier, but it can be done in your driveway with a buddy. The car has to be at least 18 inches of the ground.

 

Update

well i got the flexplate off the car and noticed it was cracked severly around the torque converter bolt holes. the builder got me a new one thats sfi approved and balanced that one. its on the car now i just picked up the car last night and its alot better

i just want to thank everyone for your help

Frank

 

I'm glad to hear you figured it out. Is the vibration totally gone now? Let us know if you get any track numbers, I'd like to see your results.

 

Dang I feel like an idiot for not even thinking about that when I installed my buddys 383. It was internally balanced I put the stock flywheel on but it has no vibration and about 1500 miles on it. Should we pull the tranny and remove the weights?

 

No problem man. That's what this web site is for.