Alloy Diff Cup Bearing Wear

[Butters]

Hey guys,

I am having my diff cups assembly turned so I can use an 8mm x 16mm bearing instead of the 10mm x 16mm. While cleaning I noticed some wear marks on the HPI alloy cup. After everything was cleaned and dried, I went and took a new bearing (10mm x 16mm) from my roomate fresh shipment and fitted it onto the diff cup. I noticed the ring gear witch is made of at least 1020 steel has retained the proper shaft size and has a light press fit to install the bearing. The alloy cup on the other hand on both diffs has actually worn away just enough for it to spin inside bearing. The bearing does catch an spin but the fit is no longer there, I now have perpendicular play to the shaft. These bearing should have a .0002 to .0005 press fit between the inner race and the shaft(ring gear shoulder/alloy cup shoulder). Has anyone else had this problem where there seems to be to much play between the bearing and alloy cup?

 

[ntenc1]

Thats why most guys shim the diffs. If you turn the cup, the chances are it will not be true. If you take a part off the lathe you can not get it perfectly centered again. You can try it on a 3 axle mill, but still run into the same problem. I think you will create a balancing problem personaly

 

[Blazer X]

I would have to say it was like that when you put it together. I find it hard to believe, not impossible, that those diff cups have worn that much. I would call hpi and see if they had any quality issues with the diff cups. Why are you wanting to thin down the parts to run a different bearing?

 

[oregonmud]

The diff bearing is small and weak. I see why he want to get rid of it.

 

[HopIt]

When I assemble mine I always use some loctite bearing retainer. This prevents the bearing from rotating on the aluminium and causing wear. You only need a very small amount !

 

[Butters]

Ntecn1,

Acutally I wont be creating a balancing problem. If I had both parts turned individualy this I would see a problem since I don't have a datum surface to work from. The couter sink hole in the ring gear actually locate the ring to the alloy cup.Trying to pick up axis of the bolt cirlce would be a pain and do to tolerancing and error I could create a miss match as you speak. Now since I am turing these together as a matched set and assembled I won't have this problem. As long as the diameters have a run out of .0005 from the ring gear bearing surface to the alloy cup surface I won't have an issue. I understand why most people shim the diff but shiming the bearing won't create the proper fit between the bearing race and the cup shafts.

Blazer,

Unfortunatly the diff cup had the proper size when it was first bought. The proper fit between the bearing and the cup is only .0002/.0005 which isn't much. These diffs were only in service for 3 months of racing. Now pending on track condiditon the bearing could of froze. With the power of these new engines and the fit tolerance being so small, I don't see an issue of the alloy cup breaking free in the bearing if frozen. With that happening the bearing eventally came apart in the diff. Thankfully I didnt destroy the ring and pinnion gear.

To awnser your second question, yes i would like to run a beefier bearing similar to the Cen Diffs (8mm x 16mm 5mm). This won't be a problem since their will be enough material for the new bearing to ride on. And since the diff is contained on both sides their is no real load direction load (front to back).
The only load I see is the weight of the diff when it actually hit the ground from a jump.