Broken balancer key, need your advice please!

gbak

gbak

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Mar 24, 2008
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It started with a little rattle when accelerating, the sound came back a couple of times.
Two hours later my balancer and pulley was hanging on the crancshaft bolts last threads.
Last night I pulled out the balancer and found the key was broken.

What caused the broken key?
Can it be my 20 years old 6 1/4" fluiddamper that have finely giving up?
Or just a bad key?
If replacing the balancer; is it ok to use a low buck balancer, or do I need a high quality balancer?
Max rpm is 7000 rpm.

My old balencer looks exackly like the one on the photo below:

flu-620101.jpg
 
Any thread damage?? for for that matter damage to the key slots??

if everything is kosher, I would replace the key and use some locktite to put that bolt back in with....should use a balancer tool to put it on with,

is that a flip fit balancer?? or one like stock, you have to press on???

:gurney::drink:
 
The bolt threads have minor damage, so I will get a new bolt.
Key slots are ok!
There is not any pressfit anymore, as the balancer rotated on the crankshaft.
I just hope that the crank snout still is ok and that the balancer took al the damage but I'm not shure......
 
gbak said:
I just hope that the crank snout still is ok and that the balancer took al the damage but I'm not shure......
Click to expand...

The crank is hardened, and that hub is not. Your just going to have to buy a new one and see. I would buy a good one for 7,000 RPM use.
 
big2bird said:
gbak said:
I just hope that the crank snout still is ok and that the balancer took al the damage but I'm not shure......
Click to expand...

The crank is hardened, and that hub is not. Your just going to have to buy a new one and see. I would buy a good one for 7,000 RPM use.
Click to expand...

That's good news!
Any balancer recomendation, they all look nearly the same but the price tag differs a lot....
 
No personal experience but I have read some nasty stories about cold weather and fluidamprs...now given your location that there may very well be part of the problem. I think I read something about a broken crank snout somewhere. I don't use fluidamprs, only ATI.
 
Car was standing in low temerature (below 0*C) for a couple of weeks last winter, before I could get it into a warm garage.
 
Last edited:
The logic behind the fluidamper working weird at low temp is very sound. Silicone goes pretty solid around freezing.

The key sheared because the balancer was not moving with the crank. GM pressed these on because the interference fit tranfers the tortional vibration. The bolt is only to keep things together when you add engine accesories driven off the crank. There is no bolt on small journal cranks from GM. If your press fit is gone toss the balancer or it will eject again.

New balancer and a good ARP bolt should fix you up. Dorman and Pioneer make reasonably priced units but they are imported from China. I use ATI.

Make a quick check that your torque converter or clutch pressure plate bolts are tight. If these are loose the vibration can cause the balancer to come off.
 
I agree, if the press fit is not there, the key takes the forces, it's not designed to be that way (although many others are, pontiacs, fords, mopars....)

If however the balancer was once fitted with a good press fit (some need a little honing because they are too tight) there should be no reason for it to get loose after a while. Who did the install? Has it been removed since and maybe has someone honed it so it goes on very easily?
 
I agree, I use ati, never had one fail, you can find a good rebuilt one pretty reasonable, I see them on ebay all the time.
 
redvetracr said:
Fluidampers are JUNK, ask anyone who balances cranks for a living.
Click to expand...

OK, then maybe you know what say a old Poncho engine can do a slip fit balancer but the SBC does not?? same firing order, I would think the Poncho with a 4.21 stroke would need the press on far before the SBC at much shorter strokes....

so what gives??? anyone??

:hissyfit:
 
There have always been a loose slip fit between crank and balancer. Explains why the key collapsed. What diam should the crank have?
 
[tr][td]Crankshaft Snout Diameter[/td][td]|[/td][td]Recommended interference[/td][/tr][tr][td]1.0000" - 1.2500"[/td][td]|[/td][td].0009" to .0012"[/td][/tr][tr][td]1.2510" - 1.3750"[/td][td]|[/td][td].0008" to .0011"[/td][/tr][tr][td]1.3750" - 1.6000"[/td][td]|[/td][td].0007" to .0009"[/td][/tr]

GM cranks are typically to tolerance +/- .0001". If you are using an OEM GM crank you can hone the damper hub as follows:
Big Block: hone to 1.5993" +/- .0001"
Small Block: hone to 1.2460" +/- .0001"

On all other cranks, the crank must be checked with micrometers and the hub with a dial bore gauge to verify fit. Most OEM cranks are held to +/- .0002" while most aftermarket cranks are held to +/- .0005." Hub bores are tight to accommodate aftermarket cranks and most steel hubs will require honing.
 
The professional products one is a POS, check the ATI page for a nice exploded one.

I would go with the TCI and 2nd the trick flow one. They are is steel, the Pioneer one is nodular iron. They kind of look the same though.
 
Do I need a install tool, or will I rip of the threads if I use the balancer bolt when installing the balancer on the crank?
 
Always use the install tool. ATI has a very nice tool but it's rather expensive. it works awesome though. I have seen that summit offers what looks to be exactly the same tool in exactly the same case for a whole lot less. It's made by ProForm. I have never used the proform one so can't comment on quality but since it's identical to the ATI one judging by the pics it will work just like it, dunno about the quality of the parts. I just now noticed they sell them under summit and other brands too...even cheaper. DAMN!!!

The ATI one:
http://www.summitracing.com/parts/ATI-918999/

Proform
http://www.summitracing.com/parts/PRO-66514/

Summit:
http://www.summitracing.com/parts/SUM-G1025/
 
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