Mk2/Mk3 swingarm spindle

OK, So you would need to ream the cradle to fit the oversize pin. I can readily see that the best solution is to do the mod that holds the spindle properly BEFORE you end up at the point where the oversize pin is required. Once the pin is properly secured by the methods discussed earlier, the only place that noticeable wear can occur is the swingarm bushings which are easily replaceable. Have I got this essentially right?

MexicoMike said:

OK, So you would need to ream the cradle to fit the oversize pin. I can readily see that the best solution is to do the mod that holds the spindle properly BEFORE you end up at the point where the oversize pin is required. Once the pin is properly secured by the methods discussed earlier, the only place that noticeable wear can occur is the swingarm bushings which are easily replaceable. Have I got this essentially right?

Click to expand...

you got it

A very small amount of movement at the spindle/cradle will result in significant movement at the wheel spindle. Loss of the center fixing bolt allows the spindle to rotate in the cradle rather than the swingarm to rotate on the spindle. This will rapidly wear out the cradle bore. As batrider points out, the spindle lock bolt can work as a pivot, but this action is much slower than the rotation of the spindle if the lock bolt is lost. I have found a number of machines with the bolt missing. All had worn cradles.

An issue with the oversize spindle is that not only the cradle needs to be reamed to size, but the bronze bushes in the swingarm need to be reamed as well.

I find it interesting that the RGM replacement spindle is both drilled and broached. There were two different length spindles, the older long one and the shorter ones for Mk2A and Mk3. The Mk2A was short but retained the single lock bolt while the Mk3 was the same length but was broached only. The RGM replacement is apparently designed to fulfill both needs.

The deck is stacked against the cradle by having its plates so close together. Any designer would rather have the swingarm mounting points outboard of the bushings and both of them as far apart as possible. Buy being close together they concentrate the stress. Having said that, the plates themselves bear all of the forces and trying to enlist the tube after the plates have been stretched is sort of wishful. I like the idea of cutting the original tube out and putting a very thick tube in its place, with bolt anchors. The large diameter of the weld gives a wider spread of the stress on the plates and the 1/4" thickness of the plate doesn't have to bear the load, which it obviously can't. Heinz's couplings would do it too if they were brazed or welded around their periphery to the inside surface of the plate.

May as well go "all out" and do a Kenny Dreer "big bearing" conversion and do away with the bushings entirely.

Are we far enough off topic yet?

grandpaul said:

May as well go "all out" and do a Kenny Dreer "big bearing" conversion and do away with the bushings entirely.

Are we far enough off topic yet?

Click to expand...

You still talking about the swingarm? Then, no.

Perfectly on topic.

grandpaul said:

May as well go "all out" and do a Kenny Dreer "big bearing" conversion and do away with the bushings entirely.

Click to expand...

the thing is this does nothing to address the problem with the cradle. bob patton IMHO is more on the right track with the weakness. to really fix it in the confines of the design means removing the tube and install one with a LOT thicker wall and put in 2 lock bolts as close to the sides as possible.

I think the ball or roller bearing conversion copes with the forces imposed in a much more efficient manner than the friction imposed on the spindle/bush arrangement.

I can see where Kenny had to go to a rolling element bearing on the swngarm. There must be about a 800lb load there with someone sitting on the seat, static. It would be pointing down where around a 300lb force is pointing up at the rear axle, it's like a fulcrum multiplication. Did he use needle bearings in the linkage?

Couldn't a bushing (properly lubricated) handle more load than bearing in the same amount of mounting space? There would be more supported surface area with a bushing since the entire bushing is a supporting surface. Seems also to me like that sort of rotational movement - back and forth maybe 1/16 of a turn would not be the kind of rotation that bearings are good at. Just a thought - I don't know anything about the actual science involved.

MexicoMike said:

Couldn't a bushing (properly lubricated) handle more load than bearing in the same amount of mounting space? There would be more supported surface area with a bushing since the entire bushing is a supporting surface. Seems also to me like that sort of rotational movement - back and forth maybe 1/16 of a turn would not be the kind of rotation that bearings are good at. Just a thought - I don't know anything about the actual science involved.

Click to expand...

I think the same .
The dia of the spindle seems too small to use needle bearings .
( .. still waiting for Debby's report on how her needle bearing are doing ...)

Ludwig, I agree that needle bearings on the spindle are an iffy situation. The size of the bearing hosing on the swingarm seems to indicate that it's probably not a needle bearing but a caged roller and/or ball, with an inner race. The 'spindle' be comes a shaft as far as function goes. I have never understood why new designs with a clean sheet of paper chose needle bearings in the swingarm.

ludwig said:

( .. still waiting for Debby's report on how her needle bearing are doing ...)

Click to expand...

It's been 8000 miles since I did the conversion and I have not noticed any problems. I've been thinking it would be a good idea to pull the spindle and check it for wear, but I haven't gotten around to it.

On my 850, I have one of those "universal" spindles as described above. I forget where I bought it, but it came sealed in an Andover Norton bag. I think that's how they're building them now. The slots are positioned incorrectly for the clamp screws on my cradle so currently I'm not using the clamp screws. I thought about flipping the spindle over, but only one end is threaded so that would make future removal more difficult. I should probably take it up to the machine shop and have them thread the other end for me (or drill and tap a new 1/4-28 hole 180 degrees from the current one).

This new spindle does not appear to be hardened, so wear from the needle bearings (or deformation from the clamp screws) could be more of a problem. I'm running the stock bronze bushes in that bike for now.

All modern Ducatis use needle bearings on the pivot although the diameter is quite a bit larger. My 1979 Suzuki GS750 had needle bearings on the pivot and I never had any problems with them. I recall the spindle diameter being similar to the Norton's, but I could be mistaken.

Debby

So...talking about wear in the swingarm/cradle. Should you be able to feel any movement at all at the swingarm-to-cradle interface if (bike on centerstand, rear wheel clear of ground) you grab the rear wheel and shove it back and forth? If I put my fingers against the cradle/swingarm joint and do that, I can feel a tiny bit of movement in that joint. I'm assuming that there should be no detectable movement if everything is as it should be, is that correct ?

Mike

Make sure the 7/16" head bolt fixing the spindle is tight before drawing any conclusions. I check the bolt every time I have the back wheel out--it almost always loosens up half a turn or so. If it's loose you'll be surprised how much play disappears.



Tim Kraakevik
kraakevik@voyager.net
'72 Combat

Tim - That loosening just shows that your cradle is worn. The tremendous perpendicular loads on the spindle when cornering will still cause spindle play in the cradle. The 7/16" bolt only locates the spindle and is only masking the problem when you tighten it.

Russ

I just finished pulling the swingarm and taking a good look at everything after cleaning it up nicely. Now I understand all the issues/concerns and I see the value of those clamps discussed in an earlier post. Contrary to what I thought, I discovered that those set screws/lock nuts on my cradle are NOT threaded into the spindle as per Ludwig's. They are just threaded into the cradle and push against the spindle ...that's it. So either I need to have the nuts welded to the cradle, tap the spindle for the screws, or do the clamp thing. I'm tending toward the clamps.

It also appears that one of the bushings was turning in the swing arm. The bushing easily pushed out by hand and the internal part of the swingarm where the bushing mounts is shiny. The other bushing had to be driven out with a socket as a drift and a hammer - not shiny.

The spindle has some play in the cradle though once the bolts are snugged up, of course, it does not. But from other comments, it sounds as if there should be no play between spindle and cradle. Is that correct? If so, I'm not sure what I'll do about it.

I plan to renew all the parts associated with the swingarm - bushings, o rings, washers, and the spindle. Not sure when I'll actually do that but I'm going to reassemble it so I can ride on Sunday. I plan to use some loctite red on the bushing that was turning in the swingarm and I'm hoping that when the new bushing goes in, it will be a tight fit.

How about taking a Sawzall to the frame/cradle tube that the spindle goes through?

Transversely, cut the 1/4" cradle plates AND the spindle carrier/tube clear across and then weld bosses for two big a** pinch bolts to the cradle plates. The bolts would pinch the spindle at both ends AND it would do it as far outside as possible, moving the leverage points as far out as possible within the space available.

Yeah, takes fabrication . . . . and locating the bosses so they won't foul the swing arm would take some forethought/layout.