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USD conversion bearings available again

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dont you have to shim the bearings possibly because of length differences in the stem/bearing heaight

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There are two considerations for shimming. The first is that the conversion bearings are slightly shorter (I think it's 12mm high vs. 15mm stock), and so a thin shim comes with each bearing to make up the difference. The shim can be put either within the headstock, beneath the bearing race, or outside of the grease seal.

 

The second consideration is the difference in length of the stems. A second, thicker, shim comes with each bearing. They're probably better sized to go outside the grease seals.

 

These are generic converion bearings that are used for many swaps, so the shims are not specific to XRs USD swaps.

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There are two considerations for shimming. The first is that the conversion bearings are slightly shorter (I think it's 12mm high vs. 15mm stock), and so a thin shim comes with each bearing to make up the difference. The shim can be put either within the headstock, beneath the bearing race, or outside of the grease seal.

 

The second consideration is the difference in length of the stems. A second, thicker, shim comes with each bearing. They're probably better sized to go outside the grease seals.

 

These are generic converion bearings that are used for many swaps, so the shims are not specific to XRs USD swaps.

Me myself would go with turning stem and not the conversion bearings that way when you need new bearings a they dont have them then you are F--ked they will allways be XR bearing avl!

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Me myself would go with turning stem and not the conversion bearings that way when you need new bearings a they dont have them then you are F--ked they will allways be XR bearing avl!

  Well, IF that happens, you can always spend the money and have the stem turned down.  I haven't heard of any failures posted here or any of the sites I read.   ;)

Edited by MindBlower

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I've been mocking up a set of these conversion bearings on a spare frame.  There are no provided instructions specific to this swap.  The bearing outer race is much thinner than normal, but it is still strong enough to be pressed in without cracking.

 

 I've been trying different configurations of spacers.  Each bearing comes with two shims, one thick and one thin.  They are the same ID (a sliding fit on the CRF steering stem) but different OD.  The thinner shim's thickness almost exactly makes up the difference in overall height of the shorter conversion bearing.  I put these two thin shims within the headstock, to the inside of the bearing races.  This positions the outer surfaces of the conversion bearings in the same place as the stock bearings.  These thin shims required having their OD turned down slightly on a lathe to be a tight sliding fit within the headstock.

 

Another conseration is the steering stops.  The CRF lower clamp's stops do work with the XR's frame stop.  The lower triple should probably be as high up as possible on the bike (as close as possible to the bottom of the head tube) to give the best contact between the triple's and the frames stops.  So putting shim spacers under the lower bearing isn't ideal. 

 

I ended up with both thick shims between the top bearing's grease seal and the tensioner nut.  One thick shim alone wasn't enough and the tensioner nut bottomed on the CRF steering stem's thread shoulder before tensioning the bearings sufficiently. With two thick shims there, the tensioner nut does just barely have full thread engagement, so it's (just) satisfactory.  Also, then, with the top triple in place, the top nut just barely has enough thread engagement.  I think the ideal would be to slightly reduce the thickness of one thick shim.  I could remove one of the thin shims from within the bearing outer races, but I don't want to chance damaging a race by pressing it back out and then in again.

 

So, for someone without a lathe, the best configuration is probably to put two thick shims and one thin shim under the tensioner nut, and otherwise assemble as normal.

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I've been mocking up a set of these conversion bearings on a spare frame.  There are no provided instructions specific to this swap.  The bearing outer race is much thinner than normal, but it is still strong enough to be pressed in without cracking.

 

 I've been trying different configurations of spacers.  Each bearing comes with two shims, one thick and one thin.  They are the same .

hey heart ever figure this out

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I have four or five rides on the USD forks and everything seems to be working well.  I've done some higher speed blasting and some tight technical single track, I've taken a few spills, and the bike has become one with a pine tree after blowing through a berm.  The turning stops are holding up and there aren't any interference problems with the xr600 factory plastic fuel tank.

 

My final arrangement of spacers was to put the two thin spacers to the inside of the bearing races, within the headstock.  That puts the outer surfaces of the bearings, and the grease seals, in the factory XR location.  The thin spacers are the correct thickness to compensate for the slightly shorter conversion bearings.  The outside diameter of those thin spacers did need to be trimmed down slightly; it took 30 seconds on a lathe, or could be done by hand easily enough.  Then the two thick spacers were stacked together between the tensioner nut and the upper bearing's grease seal.  That gave full thread engagement to the tensioner nut and the top nut.  The steering stem/bearings/grease seals/headstock arrangement is basically the same as factory XR, and the upper and lower triples hold the forks in the factory CRF locations and distance apart.

 

I tried putting one thick washer under the lower bearing's grease seal, but that spaced the lower triple's steering stops too far downward for good contact with the frame's stops.

 

The CRF steering stem is a little longer than the XR stem.  The lower triple is in the same location as stock, so the top triple is now slightly higher than stock.  I forget the exact amount, but something like 1/4" or 1/3".  It's not enough to affect lengths of cables.  But it's something to remember when talking about how high the forks are raised in the clamps, which is measured relative to the top triple's upper surface.  I would guess that the Emig conversion stem is probably the same length as the XR stem.

 

For fork length, remember that in 2005 the CRF forks got 6mm shorter.  So I measured these 2007 forks as just about 0.65" longer than the XR6 forks.  If using earlier CRF forks, they'd be just under 1" longer.  XR650L or XL600 forks are probably slightly different lengths than XR6 forks.  The triple clamp and axle offsets are different, but the end result seems to work fine.

Edited by heart_of_darkness
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Heart of Darkness, can you provide a link where I can purchase the conversion bearings? I tried searching for them and I can't seem to find them. I want to mock up my USD's in my new (street legal :goofy: ) frame before I get it powder coated to check the steering stop situation out. Thanks in advance.........

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