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Enlarging bearing seat

I'm installing uprated forks (newer model) into my motorcycle. The steering stems are the exact same length, the only difference being the bearing sizes. The new stem has larger bearings, ID and OD. I checked if I could get a bearing to adapt to my smaller outer race but the sizing only went the other way.

So I first thought of turning up an adapter to use my old stem in the new triple tree. The old stem would NOT come out. I started bending all sorts of things but it would not seperate! I do have an extra old stem & tree.

The only feasable method I can see is to enlarge the bearing seats in the frame. It is aluminum and there is a lot of material around the seats. The old outer race was 47mm in diameter, and the new one is

52mm. This is the upper bearing; the old lower one is 52mm and the new lower one is 55mm.

This leads me to my question. Would this be safe to do with a hand reamer? Is there a better tool? The hand reamer is pricy at $180 (McMaster-Carr). I was also looking at possibly using a ridge reamer for a small engine. I was thinking of rigging up the reamer with some all-thread and a tapered cone so as to ream the seats concentric with the opposing side.

Any ideas welcome,

Ryan

Reply to
Ryan
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Ryan, The only way to do this without replacing the frame head by cutting and welding in a new one is to make a boring tool that can be driven by a large drill motor. In order to make this tool, you need access to a lathe. You must first machine a shaft the diameter of the ID of the frame. This must fit very close. No more than .001 clearance as this will be your boring head guide. Without seeing this in person, I cannot be specific, but you may have to make 2 tools, 1 for the top boss and the second for the bottom boss. If the inside of the tube cannot be used as a boring bar bearing, you may have to create one by using the existing bearing boss as a guide to position a pair of guide bushings in the tube. You machine on the lathe the OD of the new bushing loose, coat the bushing with epoxy and let it set while being held concentric to old bearing boss with a plug, also turned on the lathe. This plug must pickup the ID of the boss and the OD of the temporary bush. Once the frame head tube has bearing bushes installed, you can then make the cutter head using only a single lathe cutter held by set screws. In this light, you should be able to use the same cutter with different adjustment for both upper and lower bosses. It will be tricky to feed the cutter at a very slow state, but I have done it before. The cutter will act as a fly cutter, but tool loading is actually quite low. When both bosses are finished, just use a hammer and a drift to knock out the epoxied bushings. Steve

"Ryan" wrote in message news: snipped-for-privacy@posting.google.com...

Reply to
Steve Lusardi

Does the new stem fit through the steering head of the old frame, or will you have to be enlarging the inner diameter of the entire steering head?

If the stem is long enough, you could consider turning up a steel part that fits into the existing steering head, and has a bore for the newer larger, bearings, above and below the existing bore in the aluminum frame.

Other than seeking bearings that do what you need, ie smaller rollers with the correct ID and OD (there are a

*lot* of bearing houses and manufacturers out there) I would NOT modify (enlarge) the seat for the steering bearings in the existing frame. There is a tremendous amount of stress in this area and a failure can lead to a crash and the rider's death.

Jim

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Reply to
jim rozen

Hi Steve,

I've bodged something up that resembles what you have described. I asked the guys at work and they think it should do the job. I'll try it in a couple days and let you all know how it went. If I start to booger it up I will stop and just yank the frame and some guys at work will make a fixture to hold the frame and bore it on the mill.

Thanks to all that responded, and I will proceed with caution. This is my motorbike as well. I also have an extra frame too (thanks to my parts bike) so if it's iffy I won't chance it.

Ryan

Reply to
Ryan

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