"new" ZF - Bad Vibration at idle - Very Concerned

[90idi4x4]

Oh and when torquing the flex plate i found that if done out of sequence or to tight can give a vibration or at least on mine it did.

 

[hce]

I will thrown this in a 305 chevy and a 350 chevy use the same crank. Cranks even have the same casting number. Pistons are smaller on a 305. Put the 305 crank in a 350 and it will shake. The difference is the counterweights are drilled deeper on a 305 to account for the lighter pistons.

Edit: Chevy also could have left the cranks exactly the same and weighted the flywheel and balancer to obtain correct balance.

 

[hesutton]

South Bend will tell you the same mis-information about the flywheels. Listen to the engine balancer. That's all they do for a living, they know the difference between neutral and exteranally balanced. The shop that balanced my 6.9 told me the exact same thing......... 6.9 and 7.3 IDI are NOT externally balanced engines.

By the way, that is the same flywheel casting that I got from South Bend....... As I have said before, lots of clutch companies use that flywheel with their SMF kits. Sucks too as they can't control the qauality of that flywheel.

Heath

 

[hce]

I'm scarred of your machine shops.

 

[hesutton]

Not a machine shop. Race engine builder/balancer (diesel and gas). Don't be scared.

I have had a 6.9 flywheel on my 7.3 for > 7 years and over 100k. No vibration....... never has. Smooth as baby's butt.

Heath

 

[hce]

I would like to see a 7.3 flywheel neutral balanced. My guess is it would look like Swiss cheese on one side.

 

[hesutton]

I would like to see a 7.3 flywheel neutral balanced. My guess is it would look like Swiss cheese on one side.

See post #18.

Heath

 

[hce]

Those little holes are not equal in volume to that boss cast in above the holes.

 

[hesutton]

What does that matter?



It takes what it takes. Every flywheel will be different ............. same when balancing the rest of the rotating assembly. Not every single rod, crank, piston, will be equal.





Heath

 

[hce]

That boss adds about 1.5lbs to that side of the flywheel. Those 3 holes removed about 1.8 oz, leaves about 35.2 oz of imbalance on that. Its the same principle as a teeter totter.

 

[madpogue]

35.2 oz? Try about 22. In any event, presumably that boss is there in the first place to counter some inherent imbalance elsewhere in the rotating assembly.

 

[hce]

35.2 oz? Try about 22. In any event, presumably that boss is there in the first place to counter some inherent imbalance elsewhere in the rotating assembly.

I was just doing estimates from pictures, I am impressed I cam that close. Could not remember the actual numbers when we put my flywheel on the crank balancer.

 

[madpogue]

I was just doing the math based on your post. 1.5lb = 24oz. That minus 1.8 = aprx. 22 oz.

 

[hce]

My first estimate was 2 lbs, my second estimate was 1.5, I forgot which one I was using. Guess thats why the math teachers always said show your work.

 

[junk]

I actually went the other way and put a 6.9 t-19 flywheel on the back of my 7.3 15 years ago. Never any problems or vibrations.

I'm guessing the flywheel manufacturer uses a standard flywheel blank that does have a counterbalance in it and with some neutral balancing and some machining it works fine for the 6.9/7.3 engines. They probably use the exact same blank for other engines that require a weight.

I'm wondering what the tolerance the flywheel manufacturer does for balancing the flywheels? Is it possible their tolerance is open and thus it might lead to a vibration? Makes a guy scared to just purchase a kit and put it on that's for darn sure.