How do you "balance" an externally balanced flywheel on an existing motor without pulling the crank and pistons out?

sorry this is a long post..... but I am running out of ideas....

I have been trying to isolate a vibration in my vette since installing the new motor and TKO600 box. It has only just become an issue as I have now begun to pull higher rpm.

I have managed to attenuate the intensity by lifting my floor slightly at the trans crossmember, eliminating some contact under torque twist, but the fundamental vibration is still evident. It is two-fold....

1/ It occurs at 45~50 mph when under load in any gear.
But if I depress the clutch, or coast in neutral at those speeds, I can't notice the vibration.... but under slight load it is there.
It is a low frequency repetitive drone.

2/ At elevated rpm >4500, there is a very strong vibration that is difficult to isolate its origin.... motor/gearbox/tailshaft.

I never had any issues like this prior to the engine and trans swap.

I have checked the motor/bellhousing/trans for clearance from body/firewall. All OK.
I removed the tailshaft, and had it checked... it was out of balance, and I had it re-balanced locally (at up to 3500 rpm), but that has only provided minimal improvement.
Alignment of trans with diff is good horizontally, but does have a slight vertical misalignment. But how much mis-alignment is too much?

Under hard accelleration, the vibration is quite pronounced...... especially over 4500 rpm.

Several workshops I have visited over the past month for various work have all asked the same question.... do you have the wrong flywheel on?
I have confirmed with my builder that my motor does require an externally balanced flywheel.... I sent pictures of the flywheel that was installed, and received confirmation that it is the correct style.

However, my vibration continues.

I had the vette run up on elevated dyno rollers this morning, so as to get under the car whilst under load, and suspicion is now focussing on the flywheel.

Background info...
I purchased my new stroker with the intention of running an auto, hence it was supplied with a flex plate. (externally balanced)
Prior to installing the motor, I decided to put in a 5sp manual (CC5S Tremec TKO600RR).
It was a pain in the backside fitting a custom clutch pedal/ hydraulic assembly in my RHD vert, but it eventually worked out.
Gearbox install was fairly straightforward, except that insufficient clearance to floor was encountered. Some high density rubber strips wedged between trans crossmember and floor have raised the tunnel by ~5mm. But vibration persists.

So my question is....

HOW DO YOU GO ABOUT BALANCING AN EXTERNALLY BALANCED FLYWHEEL ?
A local engine builder says he can do it, but I am curious as to how it can be done.

Would the original flexplate supplied with the motor be of any use?

Also, could the clutch pressure plate be the culprit? I recall seeing a weight welded to its outer surface, so I assume it was neutrally balanced? Or is it necessary to align the weight on the clutch with the external offset weight on the flywheel?

I am getting pretty desperate for a solution....



All feedback gladly received.

cheers
tom

 

See if you can get your new flywheel "match balanced" to the flexplate that was balanced to your motor when you bought it. A good machinist should be able to do this or you can find one that will. Your other option is to re-balance the entire rotating assembly.

 

Great advice above and take your pressure plate with the flywheel. Make sure the pressure plate is, in fact, correctly neutrally balanced.

1) Also, how about your motor mounts? A bad one, usualy the driver's side will raise some hell.

2) A bad input bearing on the tranny can do what you describe, under a load.

3) You might remove the driveshaft and run the engine and tranny in your driveway to determine that the DS is not at fault,..or nothing in the 3rd member. Though, it will be impossible to duplicate "under a load" conditions, you may be able to isolate the problem.

4) Was the harminic changed? In addition to externally balanced flywheels, SB-400 and BB-454 have biased balancing in the harmonic as well.

5) Also, a balky U-Joint or a U-Joint that's not seated correctly can cause balancing problems.

Lastly, I once solved a vibration problem by simply phasing my driveshaft 180 degress. Might try it.

Good luck and let us know what transpires.

 

Depending on the type of balancer the shop has, a S-W unit you would spin the flywheel and read how far out of calance it is in inchs. You would only be balancing it to what the OEM says. You can not do it right without your whole rotating unit with the flywheel on it. But you can match it to your auto flywheel for sure. If a shop says they can't do it then find one that will cause it can be done as I have done it many times for people. But Have you tried taking the belts off the engine also to be sure it is not in an asserary? Can you make it shake with out the car moving and just verying the rpm to see if it really is in the engine? I would vote for the drive line as an engine usally will not change how it shakes by load as it sounded it does by your statements. Good Luck finding this.

 

Years ago I built my first engine. It was a 400 pontiac. I started with a 69 GTO engine, used a Trans AM block to fit my 78 TA. The GTO was an Auot and the TA a 4 spd. So, I built the engine and used the TA flywheel. I had exactly the same issue. It ran great but at 4500 rpm wow ... too many vibs. I had the wrong flywheel. I merely got a flywheel that went with my combination of parts and it worked. That is until the torque started bending driveshafts ... then the vibs were back but not as bad. The bent driveshafts and the back bearing the tranny adding up to a similiar high speed vibration. I fiexed it a few times.... then got smarter and had a driveshaft built for the application. Neat car!

carbster

 

You simply take it to a balancing shop and let them know the application. They will externally balance it/counterweight it to the spec for the engine - there is a specific counterweight requirement for the extrernally balanced engines.

 

Thanks for all the replies....

As I have the "correct" style flywheel installed currently, with the counterweight cast in the plate, there is a possibility that it isn't within the specification or that my motor requires a slightly different weight.

I guess matching it against the flex plate balance weight might identify my problem.

The other possibility is that the clutch pressure plate is contributing to the problem ???? I'll have that checked for neutral balance also.

arghhhhh !!!!! the fun of hot rodding!

 

Thanks
tom

 

Stupid question, if it were the flywheel wouldn't you feel the vibrtion at that rpm in neutral as well?

 

Yes.... which is why I think I may have a combination of problems.
I have been trying to isolate one thing at a time.
Clearance issues with trans to body and bell housing to firewall...
tailshaft balance
tailshaft vertical alignment may still be a partial factor
now working on the flywheel/clutch to isolate that as the culprit.

As you can see..... I'm running out of options which is why I'm posting for ideas...

cheers

 

My opinion also. If you have an engine balance problem, the vibration should be present when you run the engine up in rpm in neutral.

Years ago I spent quite a bit of time in Adelaide. I thought it was really a great place to live. Had some very enjoyable times there.

 

If it's worse under increased load, it sounds like alignment and the trans or engine mounts.
I had a camaro with a failing trans mount that allowed the tail of the trans to lift up under heavy loads. It would only vibrate when under enough load to lift up the tail and cause an excessive angle.

 

Just a thought: Alot of drivetrain related vibrations that are attributed to the engine not being properly balanced turn out to be caused by the driveshaft angle being out of spec. Good luck

 

Just my opinion : if a flywheel or vibration damper is neutrally balanced (which depends on the type) this vibration is not coming from it.

Does the vibration increase or decrease with changing gears ? If so I would suspect a bearing in the trans.

 

A friend of mine had a small block vette with a vibration problem, he replaced the balancer, clutch, fly wheel, and it never changed. A engine builder said he had good luck with the Fluidampr working on hard to find vibrations. My friend replaced his with the Fluidampr and his vibration was gone. Might be worth a try at least it's not to hard to do.

 

Just got word back from the shop checking my flywheel/pressure plate balance....

After zeroing the balancing machine with my original flex plate, the flywheel was found to be 55 grams out, and the pressure plate was 17 grams out.....

Sure hope that solves the elevated rpm vibes....

 

WOW!! I think the 454 BB which is externally balanced uses a totally different weight configuration than a 400 SB which is also externally balanced. Could this be your problem?

 

From what I can ascertain, the flywheel is the "correct" style, for an externally balanced single rear main seal chev sb.
What has been done now, is the flywheel has been matched to the counterweighted flex plate that was supplied with my motor from the engine builder......


Work is also being done to improve the driveline angles of my tailshaft/uni-joints.... Getting additional clearance to raise the tranny up has been a chore.

I can only hope that when it goes back together tomorrow, ALL the vibes will be gone.

 

Update:
Elevated rpm vibrations are gone.... although there's still a hint of vibration coming through the gear shifter... I can live with it for now....
but I still have my vibe at ~50mph.
Not as bad as before, but still annoying. This is most likely driveshaft alignment.