Inner primary bearing failure:

Possible causes, flip a coin:
Alignment (Primary to Trans shaft)
Too much tension on chain (Automatic tensioner)
Oil starvation (Oil feed hole not capturing enough oil, may also be starved if idled on the kickstand for too long)
Inferior bearing material


2005 And Earlier No Dowel Bushings Manual Chain Tensioner



2006 No Dowel Bushings Automatic Chain Tensioner



2007 And Later With Dowel Bushings Automatic Chain Tensioner

 

None of the above.. The problem stems from them swapping the position of the ring gear and primary chain.. Running a bike hard can ratchet the tensioner too tight which doesn't help. The early primaries don't have an oil hole for the IPB..

 

Appreciate the info!!!

 

You brought up some things that I didn't know about the 2005 and earlier Dyna's;
Primary chain ran closer to the bearing
No oil feed hole to bearing

What do you think of Harley Davidson's fix of adding alignment dowels?
If your theory is correct, then all the 2006 and up Dyna's, and all the other 2007 and up Twin Cam's are going to have inner primary bearing failures.


2005 And Earlier



2006 And Later


2005 And Earlier


2006 And Later

 

Great job on the visuals guys - nicely done!

 

Correct.
The tech told me late model '06+ Dynas had doweled cases.. Mine was mfg late '05

 

I suspect that with the alignment dowel, they might have moved the bearing towards the back a little. Maybe a thou or 2. IMO the shaft flexes under load. If centered it can flex enough to keep the roller bearing from seeing an even load across the bearing.. Load on the edge of the bearing causes it to destruct.. If you look at the dowels, they are split and pretty thin.. You can spring them a little with your fingers. I suspect that they did that so there was a slight preload toward the rear so that the inner bearing was resting on the forward side of the bearing race. This is just enough to allow the bearing to have a more evenly distributed load across the rollers as the chain pulls the mainshaft forward.. The dowel pins them selves only provide alignment during assembly since you can squeeze then with your fingers. There is enough support from the clamping force of the outer case to the tranny and motor to keep things from shifting once assembled..

As far as bearing survival on later bikes, I suspect that it is better because of the dowels but could still possibly happen.. Increasing the oil dribble size is a good idea. I did it.. Still, there have been some reported fixtures. My 07 EGC failed but it was sort of a special circumstance that exacerbated the failure.. Corrosion under inner race caused the bearing to swell slightly.. Some might pooh pooh that but you'd be surprised what a chemical reaction can do.

This is all my theory so take it for what it cost you..

 

I wonder if guys with belt primaries (open or closed) have IPB issues. I'd suspect the belt would flex more than a chain, and help prevent the shaft from flexing and wiping out bearings. Hhhmmm....

 

I've owned an evo with internal belt. Bearing needed replacing at 20K and 40K.. Own a evo bobber with BDL 3 inch open.. It has about 36000 miles on it and the IPB is still good. It uses a dual row 3205 bearing. Point to remember is that these are sealed bearings since there ain't any lubricant to keep em wet. The closed primary uses basically the same bearing Baker TQ bearing, 6205, The only real difference is that the inner part of the bearing is sized a few tenths larger than normal to allow a slip fit on the shaft. Heck the stock wheel bearing from 08 up on the big twins are 6205..

 

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