964Andrew

Hi,

I noticed my harmonic balancer wobble after rebuild. Searched for similar problems on rennlist and found that it is quite common occurrence.

The manual says to take off the balancer and put it back. Tap it with a brass hammer on the inside if not straight, then torque to spec.

So, I've done that... 3 times. Every time I would tap the balancer straight. The pulley would have no runout before torquing. After it would be 0.6mm (max allowable is 0.5mm).

Here is a video of what 0.6mm runout looks like.


Someone has previously mentioned a machining fault of the crank, maybe it is a case with mine. I think that most likely it is the prolonged pull by the AC belt, specially when the engine is off. My balancer appears to be in excellent condition, better than most I've seen. I don't think my freshly rebuild engine is in any danger having balancer that is 0.1mm out of max runout... still, I would like to solve this issue and I am looking at one of the below 4 options. Any help deciding, much appreciated.

1- Aftermarket pulley, maybe single belt. I know this is a can of worms, as I found several threads about crank exploding because no harmonic balancer.

2- Brand new harmonic balancer, made out of gold - worth the same. This might still not solve my problem and how will the new balancer be any good if it was not balanced to my crank and flywheel?

3- Used balancer. Let's roll the dice! $250 might be worth trying, same as above, it will not be balanced to my crank and flywheel, so what's the point?

4- Send off my balancer for rebuild. I wish this option was available, but I haven't found any place that would do that. And, if there is a machining fault on the crank - again what's the point?

Thanks!
Andrew

J richard

If it goes from zero runout to .6mm (which is a lot) just by mounting it, I wonder if it is seated properly on the crank flange.
is the runout always the same angle on the pulley? Or does it move around? If the same I would suggest it's not seated fully if it moves around I'd get a used replacement, it's coming apart.

964Andrew

The runout is the same, in the same spot. I'm assuming just get any good looking balancer and not worry about balancing it with the rest of rotating mass?

Thanks!
Andrew

J richard

Check the runout of the inner pulley lip to see if the whole thing is bent or if it's all in the rubber bonding.

964Andrew

Inner and outer runout is similar. The whole thing seems to be bent.
I would like to know where the imperfection or flaw is thou, even if I have to buy a replacement it would be nice to know what exactly is wrong with this thing

Also, even thou this is a apparently common occurrence, what sort of adverse effects this can produce in long term?

Thanks!
Andrew

964Andrew

What about changing just the pulley hub?
It would make sense since the runout occurs after tightening so it is possible that it is the hub not balancer that is out of true.

Thanks!
Andrew

ras62

I can't explain the runout figures but just a thought as you say this has become apparent post rebuild. After a major service I found my car was firing on 11 of 12 plugs, tbh you couldn't hear or feel anything. One of the lower plug caps wasn't secured correctly. Once fixed the pulley wobble and slight jumping of the belt completely disappeared.

964Andrew

I am firing on all 12 . The runout was measured with engine off to avoid any inconsistencies due to misfire, lumpy idle, etc.

Thanks!
Andrew

Spyerx

Pointers to the threads? I've talked to some very well respected engine builders about this and they've not seen this.

964Andrew

Snapped 964 crank here: http://forums.pelicanparts.com/porsc...-pulley-2.html

More discussion here: https://rennlist.com/forums/964-foru...-a-result.html

And here: https://rennlist.com/forums/964-foru...ft-pulley.html

Continuing with the notion that each part of the rotating assembly is balanced to itself, I shouldn't need to balance the balancer with the crank and flywheel. So, my previous assessment is incorrect and I should be OK getting any harmonic balancer. But, again... if that is true, why not get any 10lb balanced lump to offset the weight of the flywheel on the other end, and what about single mass flywheel on the 89, how does that impacts the weight offset of the balancer, shouldn't the later years use heavier balancer because of that?

Also, if there is a strong thought in the engine build and racing world that the lack of the balancer on 964 does not cause any adverse effects, I would like to know that too.

Thanks!
Andrew

Spyerx

"Yes, A snapped crank is a possibility, the one in the pic though is a 2.7RS crank."

964Andrew

Correct that was a 2.7 crank. I wonder if that crank was properly balanced prior to the damage. Is 964 crank internally or externally balanced for that matter?

Thanks!
Andrew

964Andrew

So, I took everything apart again and found what I think is the root of the wobble. The pulley hub itself is not sitting straight on the nose of the crank. Take a look at the video.


I have disassembled the balancer and will take it to my machine shop tomorrow. Hopefully they will be able to check just balancer assembly for any runout.



New pulley hub is only $150, so that would be the most cost effective fix for me

Thanks!
Andrew

Spyerx

Rothsport has that part.

http://www.rothsport.com/Products/En...ulleys-964.htm

May need check my hub runout prior to pulley install

964Andrew

So, the Rothsport hub arrived. I have assembled the balancer, put it back on the crank on and measured the same exact runout on the Rothsport hub as on the Porsche hub. Summarizing, if the 2 hubs are measuring the same runout and the balancer parts are all straight it has to be the crank.

Sine it has been like that for the past 27 years, it can be like that for some more.

Thanks!
Andrew