[MeanMike]

It’s a high friction washer. It keeps the balancer from rotating any. Brian Tooley explained it to me at an open house. They used to sell them. They’re supposed to be one time use. I replaced mine on my new motor with my ATI balancer.

GM #12578073. It might come without the rubber but it works the same.

 

[MeanMike]

Thanks for the response. I just looked at the single keyway hub that came with the ATI balancer and it does have the groove like yours. I had to buy the hub that had 2 keyways to match up to the crankshaft. I could swear that it was just tapered on the end but in the ATI pics it shows the groove in it also but I really don't want to pull the balancer just to check it. Since the replacement washer doesn't seem to have the rubber, it doesn't look like you'd need the groove to run it. Either way I would have had to cut the washer for the second keyway. I don't think .005 will impact the alignment enough to matter but time will tell.

Has anyone ran an ATI balancer without the washer and if so did you have any problems?

You'll be fine without the washer. The alignment of your keys probably isn't absolutely perfect and your balancer likely can't move at all. The belt alignment is a non issue.

The balancer is meant to absorb rotational vibration. For the really high frequency stuff, the balancer can move the key. This washer is to prevent that. Being as that we are all running these with a big supercharger and corresponding belt, that adds to the damping ability. Torsional damping on our motors isn't much of an issue.

 

[MeanMike]

Thanks Mike. I'm going to run the Kong 2650 so had the second keyway added.

Someone posted that the rubber was to seal the balancer so that oil wouldn't leak between it and the crankshaft. I wonder if there's any truth to that. I figured since it was so thin (i.e. .005) that it was to hold it in place on the balancer to prevent damage while installing it.

I don't think that's what the rubber does because it doesn't' completely go between the balancer and oil pump drive. I think it just holds the washer on the balancer for assembly.

I always put a little RTV under the head of the balancer bolt to prevent any oil from coming out of that area. My washer doesn't have the rubber and it's a GM part number.

 

[MeanMike]

If it were me, I'd be pulling it back off to put the washer on but I'm OCD like that. But I don't think it will cause any harm to leave it off, especially if it was the original (used) washer.

The ATI balancer comes off with a regular 3 bolt balancer puller that you can find at any auto parts store.