Boring Motorcycle Fork Leg for Bushing?

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mcman56
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Boring Motorcycle Fork Leg for Bushing?

Post by mcman56 » Thu Nov 03, 2022 6:15 pm

Has anyone successfully bored a motorcycle fork leg for bushings? Any pictures? I have a damaged bore in the leg and not sure if I can find replacement parts. The ID is just the aluminium with no bushing.

I was thinking of a bolt on arbor to fit the bottom of the leg where the damping rod bolt normally goes. I'm assuming this is on center with the bore but probably does not need to be exact. This could be held in a 3 jaw or 4 jaw.

The bushing/ seal end could be supported in a steady rest because the OD looks machined. However the leg is 45 years old so surfaces are pretty beat up.

If the arbor is not enough to make it spin, a lathe dog could be used.

Is there a better way?
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Bill Shields
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Re: Boring Motorcycle Fork Leg for Bushing?

Post by Bill Shields » Thu Nov 03, 2022 7:17 pm

Good luck with that....I have contemplated similar and passed for fear of making it worse on a very unobtainable BMW leg casting from the early 70's

You are on the right track if that is the machinery available.

I would get the bushing reamed/honed to size, then open the hole slightly oversize and loctite the new bushing into place.

Since the bushing is going to be very thin-> a press fit would most likely alter the ID.

Finish size is critical..too tight has obvious problems. Too loose can make the cycle feel like you are riding on ice.

Do you know the manufacturing finish and limits?

Is Frank's Forks still in business?
Too many things going on to bother listing them.

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liveaboard
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Re: Boring Motorcycle Fork Leg for Bushing?

Post by liveaboard » Fri Nov 04, 2022 6:12 am

It was machined at the factory, and surely they used the same centers as you will. The lower bolt hole and the upper machined collar.

If the collar is too damaged to use in the steady, make a steel cover for it; that would have to be very concentric of course.
I'd remove the lower clamp studs so you can get the work closer to the headstock.

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TimTheGrim
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Re: Boring Motorcycle Fork Leg for Bushing?

Post by TimTheGrim » Fri Nov 04, 2022 11:00 am

A buddy that owned an Indy shop back in the mid ‘80s asked me to install an aftermarket “Wide Glide” conversion kit for his FXEF.
It was really pretty but the lower leg bushings were too deep and too close together to adequately support without a noticeable shake in the lower legs. He got it as a “premium” and couldn’t return it.

I hung the legs off the back side of a Bridgeport table with some quick made aluminum vee blocks and made a good snug plug to indicate for concentricity and angularity. Some copper shims helped with fine tuning.
I swung the turret/ram around to access that area of the mill and bored each one individually for an extra bushing with
a Criterion boring head.
It worked like a charm and the front end was much more stable.

What bike is that leg from ?
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'96 Birmingham mill, Enco 13x40 GH and Craftsman 6x18 lathes, Reid 2C surface grinder. Duro Bandsaw and lots of tooling from 30+ years in the machining trades and 15+ years in refinery units. Now retired

mcman56
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Re: Boring Motorcycle Fork Leg for Bushing?

Post by mcman56 » Fri Nov 04, 2022 11:31 am

It is from a 1975 Yamaha TY175, an old trials bike. The tubes are only 30 mm diameter. What did you use for a bushing? Something like 660 bronze? As is, the tube just rides on the aluminium fork leg.

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Bill Shields
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Re: Boring Motorcycle Fork Leg for Bushing?

Post by Bill Shields » Fri Nov 04, 2022 12:15 pm

660 is a good place to start for the bushing.

I was going to suggest using an HBM -> but if you had one available (as they don't fall out of trees), you would most likely not be looking for assistance.

or an oil country lathe which has a large spindle bore and a chuck on each end of the spindle...would allow you to 4 jaw both ends and get the alignment you need.

getting there with a bridgeport with the head cocked over (as suggested) will most assuredly get you where you need to be.

the entire project is one of creative setup.

the actual metal cutting, while not trivial -> the least of your worries.
Too many things going on to bother listing them.

morsetaper2
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Re: Boring Motorcycle Fork Leg for Bushing?

Post by morsetaper2 » Sun Nov 20, 2022 2:56 pm

mcman56 wrote:
Thu Nov 03, 2022 6:15 pm
Has anyone successfully bored a motorcycle fork leg for bushings? ...<SNIP>
That looks suspiciously like a Yamaha outer fork leg. Maybe RD400 or something about that size that ran a single disc setup?

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Bill Shields
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Re: Boring Motorcycle Fork Leg for Bushing?

Post by Bill Shields » Sun Nov 20, 2022 3:50 pm

4 Nov the model defined
Too many things going on to bother listing them.

mcman56
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Re: Boring Motorcycle Fork Leg for Bushing?

Post by mcman56 » Sun Nov 20, 2022 3:53 pm

1975 Yamaha ty175

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