Ironhead Question about sprocket shaft bearing design

[bobber58]

Something I'm not understanding. What makes the dual Timken stronger than the flathead style needle rollers? I understand the double opposing Timken handles thrust loads better, but there really shouldn't be that much thrust load in the flywheel assembly should there? Do they handle high bearing speed better? If so, why aren't all the bearings in the engine and trans tapered rollers? I'm just not understanding how changing to the Timken in my project adds any strength to the assembly. Thoughts?

[thefrenchowl]

Hi Bobber58,

The Timken is not there to handle side trusts, it is there for quicker factory assembly since the crank end play can be done at the Timken factory rather than opening and closing the cases several times while inserting the right amount of end shims in the HD factory...

Nevertheless, it is much stronger than any other bearing at the cost of more friction.

Don't know why people feel they have to change it, I have never had to replace one in 40 years of Sportsters ownership...

Patrick

[ryder rick]

I had to replace one. I pulled this down off the wall of shame.



This is what happens when you assemble a double timken WITHOUT the spacer!
It split the outer race and spun the race in the cases, had to send the cases out and get the insert in the left case replaced to fix it.

[Chuckthebeatertruck]

I think you are referring to a big twin conversion.

Long story short

Double row sprocket bearings as used in pre-54 big twins do not handle long strokes or sustained high speeds very well.

It's not about strength, it's about flex.

Just google broken panhead cases and note almost all are pre-54 and many split right through the vin pad

[ryder rick]

You mean I can't shift my 5" stroke Pan at 7500rpm?

[Iron Mike]

Sure you can. Shift from inside to outside the cases!

[bobber58]

This is actually for my stick stroke Magnum motor. Trying to figure out if if really necessary to change to a Timken.

[mrmom9r]

It's only necessary if you want it to live.

[Chuckthebeatertruck]

Originally Posted by mrmom9r

It's only necessary if you want it to live.

+1000

If (and I mean "if") you actually want to run the double row in a magnum, open the mains clearance towards .002.

To quote someone much wiser than me:
That kind of bearing isn’t tolerant of crankshaft flex.
When the wheel assm flexes (it will)the bearing needs to have enuff clearance so bearing don’t "jam".
If the bearing does jam it takes the outer race for the ride too. That means the ccase flexes, and cracks.

You are seriously overpowering a 45 by turning it into a magnum . . . so take that into account.

[Ferrous Head]

Norton went to "Superblends" to help with the problem.

The smart Norton guys have billit cranks and the Superblends.

(But then Norton cranks make cooked Spaghetti jealous with their flexibility)