I had my motor rebuilt, the shop said they put in a forged balanced rotating assembly.

I also put a new clutch in (no new flywheel).

Now I have a bad vibration at 3-4.5k rpm.

Do I need to buy a neutral balanced flywheel to fix this or did the shop I used to remove/install motor & clutch possibly install the flywheel wrong? I'm lost, any help would be appreciated.

 

Bump, let me ask this in a different manner.

I had all forged internals installed weighted within a gram.

The only thing left stock was the crank.

Also a new clutch.

Now, since the bottom end (crank) wasn't messed with, my previous flywheel should be good, correct? Was my problem not balancing the flywheel PP and clutch together before install? I know there's only one way the flywheel and PP can go on. So, no vibration before, vibration now. ALL RPM related. Same range, through all gears. NOT speed related. I'm not the best when it comes to engine rebuilds and certain things you do to make it right, but common sense is telling me this is a balance issue. So, pull the t56 and get the flywheel and pressure plate balanced together or neutral balance flywheel? Also, let me add that this vibration is present with clutch engaged & disengaged, in every gear, and in neutral. Same RPM ranges, driving, or sitting still.

 

OP

ask your machine shop if they balanced the "rotateing assembly" neutral aka zero balance. Many rebuilds are done this way. stock motors are "external" balance so there is a cast in weight on the back of the FW.

if your motor is now internal balance than you need to have your FW neutral balanced at a machine shop or buy a neutral balance FW. The billet aftermarket ones usually have weight that unscrews making it zero balance (you should put back 3 of the 4 retaining screws though)

your car will vibrate like a dog shiating razor blades otherwise and it will kill bearings if you continue to drive it.

I have a internal balance 383 and i send any FW out with my clutch to a machine shop to have first the FW neutral balanced, then the PP neutral balanced on top of that.

 

OK so please be clear, Im in the same boat, if I had all forged internals from eagle, rods that were balanced to +1/-1, crank the same and JB pistons,
is it considered internally balanced? Im about to do my clutch and flywheel swap and had my engine done 3 years ago? So should I assume its internally balanced and get my flywheel nuetral?

 

You need to talk to your engine builder. Normally if the rotating assembly was externally balanced in the rear they should have provided the flywheel used to balance the rest of the assembly.

 

what SS says above. If the rotateing assembly was not balanced with your stock FW it "should" be zero balanced aka neutral

You should check with the shop that did it to confirm. with that said if you don't know it would be odd for any machine shop to balance a rotateing assembly without a FW if they were trying to match a stock "external" balance moto, They would need the FW to do this.

the pic shows a aftermarket (F1) FW with a removeable weight. For a neutral balanced motor you would remove the weight....BUT it is always best to have a machine shop onfirm this as you see by the pic 2 spots where machine shop removed material after removing the weight to make it "zero" balance. Don't take the word of a manufacturer. My McLeod Billet was 25 grms off because the holes where the weight was screwed on amounted to 25 gr of missing material 3 of the retaining bolts = the weight with washers amounted to that and I used lock tite on those threads, to bring it into exactly neutral balance. You then want the shop to attach the PP and balance that also.

you can have the stock cast FW neutral balanced. they would grind off the cast in weight and then put pins in the hols on perimiter as needed to balance (2nd pic). shop could also just drill out material to balance but ideally they use pins in holes on the edges

This again is for "internal" balanced motors

 

If the internals are well balanced the weights on the stock fw need taken off...
The stock fw may never reach 100% neutral balance but taking the weights off should put you in the ballpark.
Just my 2 copper.

 

Ehh i just realized that on engines with the one piece rear main seal the weight that should be on the end of the crank was put on the fw...This is still considered internal balance.
Like SSRRR said asking the builder about the fw they used is a good idea.

 

well they balanced it with the flywheel i gave them which was an aftermarket that i had from a stock set up so then I would say it is externally balalnced and once i get the old flywheel off I should see if the weight is there or not

 

Thumbs up on that.

 

No it's not.

 

I apologize for my lack of knowledge.
Just trying to help.

 

if they balanced the rotateing assembly WITH the FW you have on the car now than the FW should not be the issue. If they used a donor FW, your FW would need to be balanced to whatever the donor one was.

The "weight" on a stock FW is cast in so it would have to be ground off. In doing so just grinding it off would not make a stock FW neutral, it would have to be correctly done at a machine shop as after grinding off the weight they would have to add/remove material where needed during the balance process