Can you use a lathe to machine a motorcycle wheel?

[t120rmike]

Thanks in advance, I'm not a machinist, I'm an auto tech by trade. Motorcycling is my hobby. I recently replaced the rear rotor on my bike. Unfortunately, I think that when I was cleaning the mounting surface where the rotor mates to the wheel I must have put a low spot in it because now there is a terrible pulsation. I was able to mount a dial indicator to the frame of the bike and rest it on the hub of the wheel with the rotor off and there was some runout, however the dial indicator I was using was probably not accurate, it seemed to have a lot of play. (It was a shop tool that I'm sure has been terribly abused.) Would there be a way to put the rim on a lathe in order to cut the rotor mounting surface flat again? Ideally it would need to be exactly perpendicular to the centerline of the axle? Is this possible? Do machine shops usually have lathes capable of working on such a large object (the wheel is a 17")? Is the lathe even the right tool for the job? Is there a machine that could have the wheel held down flat the cut the mounting surface, like a flywheel?

Thanks,
Mike

[nitrosnfr]

Yes it could be done on a lathe.Care chucking it up so not to egg shape it but not a problem.I would do it and indicate concentricity and the faces in no problem.17 inch really no big deal.

[t120rmike]

Another friend recommended a milling machine, which I'm not really familiar with. Any thoughts? I'm worried that asking an automotive machine shop which is used to machining blocks, heads and flywheels to work on something out of their comfort zone may not go smoothly. Is this an unreasonable worry? How tricky will getting this done be? Am I making mountains out of molehils?

[ViperTX]

Well are you sure it's not the rotor that is the problem.....have you tried running without the rotor.....some runout on the wheel is most likely due to the bearings not being torqued......how much is some runout??

[NC Cams]

Re: mountains and molehills -

It all depends on the machine shop. Some guys might be fully capable of truing up the hub and/or the rotor with a flat file. Yet, some people could screw up chasing a thread with a quarter million dollar VMC.

Chances are a car parts chain with a brake drum/rotor lathe would NOT be the place to take it - they just aren't trained for "wierd" machining operations.

Similarly, a "pound and grind" jobber machine shop, too, might not have the where with all to do it because it wasn't part of the recommended useage they were taught how to use their machines for.

If the machinist knows how to "indicate" surfaces in and/or mount and find the proper axis of rotation and qualify axial/radial runout to do just that, they could true up the mounting flange and/or rotor on a mill or lathe and perhaps even on a flywheel refacer or grinder.

Find somebody who does GOOD racing engine work or a good motorcycle shop. See who they'd recommend for custom machining. Take it there and pay the price.... might try to find a way to get them to show off some work ahead of time - good machininst will gladly do so....

If the shop is a trash bin, find someplace else - if they can't keep the place clean, their work usually is of comparable quality.

[t120rmike]

It's definitely a rotor/hub mounting problem. The pulsation is felt only when the brakes are applied, just like a car with warped rotors. I just put 1500 miles on the bike last week and as long as the rear brakes aren't applied the bike rides normally. The rotor is brand new, and was also machined before I installed it, I've had too many bad experiences with new rotors pulsating out of the box. Since motorcycle rotors are so thin to begin with, they are very hard to cut on an automotive lathe because they "sing" and there is no good way to quell the vibrations. Even the local motorcycle shops don't cut them; they just recommend replacement. I had the rotor cut on a flywheel machine by a machine shop, and they seemed hesitant to do that.

I've been able to roughly mark where the high spot and low spot causes the rotor to drag on the inside and ouside brake pad, so I could also probably try a flat file, but removing the wheel, removing the rotor, filing the wheel, reassembling and repeating is a fair amount of work to do over and over, and with no real way to measure the effectiveness without remounting everything, could take a while. I suppose I could also try using thin washers to shim the low spot and judge it's effectiveness, then if I mic'd the washers I would have a rough idea of how much material I would need to remove.

The dial indicator I was using seemed to have a lot of play in the zero mark, but I'd have to say it was .004-.006". That kind of runout on your car would shake the fillings out of your head from 60 mph.

Sounds like I need to do some legwork, thanks for the info everyone.

[fkaCarel]

Let someone else have a look at it, before you start filing at your wheel. By filing you destroy the mating faces and create a potential dangerous situation. It's a brake! By measuring first the run out of the hub, and after mounting the disc the runout thereoff you get a view of the problem. As a disc is a thermal device, distortion is normal. You say the rotor was machined, I would pay particular attention to that, and measure or let someone else measure consistancy of thickness. I think your problem is in that department. Consider mounting your next rotor out of the box. If your brand has problems with brake distortion, consider a floating rotor.

Carel

[t120rmike]

I have enought experience to understand how the mating faces interact, and I assure you I know how to tell the difference between a warped rotor and a hub issue. I suppose I could have been clearer in describing the progression of work done.

I was getting ready to take a long trip on the motorcycle and during my pre trip inspection, I found that my rear brake pads were almost used up. The bike is a 1990 Suzuki VX800, somewhat of a cult bike, and are known for rear rotor grooves. Since my rear rotor was grooved and 16 years old, I decided to get new pads and a new rotor. There was no pulsation before at this time, just some squeaking from the worn pads and the grooved rotor. I removed the old rotor and installed a brand new EBC rotor with new pads. When I removed the old rotor, I lightly (or so I thought) touched up the part of the wheel that the rotor mounts to with a die grinder and a brown 3M Rolok disc. I believe that was my mistake and by leaving the grinder on one spot for too long on the magnesium wheel I put a low spot on the mounting surface. When the rotor is torqued to the wheel, this puts a slight warp in it. Not realizing that at the time, when I got back, I assumed that the rotor was warped. I took the rotor to be machined and when I remounted it afterwards, I assumed that the hub was distorted. Just to make sure I put the original rotor back on, whidh had never pulsated, and when I applied the brakes on the road test found that it too now pulsated. Based on this I assume that I must have put a low spot on the wheel and now need to rectify the situation somehow.

[Geof]

Originally Posted by t120rmike Another friend recommended a milling machine, which I'm not really familiar with. Any thoughts?...

If you have someone with access to a milling machine (VMC) you could machine the rotor mating face on the wheel. It would require a bit of care because the periphery of the wheel would have to be trued up perfectly parallel to the machine table.

Whether it is done on a lathe or mill it will have to be held carfully to avoid distorting the wheel due to the clamping forces.

[NC Cams]

I you have access to an Ammco brake lathe you should be able to proceed as follows:

1. Mount the wheel hub to the lathe using the tapered mounting sleeves.

2. Be sure to mount them so the sleeves pilot on the bearing race contact points in the wheel hub.

3. Dial indicate the wheel in to see if things are running true axially and radially.

4. Remount and correct as needed to be sure the mounting flange is running true to the axis established by the bearings.

5. Use the lathe to true up the wheel hub surface where the rotor mounts just as if it were a flywheel or disc brake pad surface.

6. Do operation 5 in LIGHT cuts so the if it is an iterupted cut, the tool doesn't start to chatter.

7. IF the shop is really well fitted, they may have the high speed grinder attachment for the b/d lathe. If you can get them to use it, they should be able to true it up very, very precisely and smooth if it is a conventional or interrupted cut.

At this point you should be able to "fix" the runout of the flange when it is reassebled.

NOTE: you might want to stress relieve the rotor. Try baking in while lying flat at 250-300F for an hour or so - oven cool if possible.

Then have it blanchard ground smooth - NOTE: if it is warped after stress relieve, DON"T SIMPLY MAG CLAMP IT DOWN. It will rewarp after you release it even though it was ground smooth.

Lay it down and shim any gaps and THEN mag clamp. You can now grind the surface flat. Recheck for flatness on the ground side after unclamping. You can then fix the other side = be sure the clamping table is flat!!!.

WHen you reassemble the rotor to hub, use new bolts and be sure to torque things slowly and evenly and in small increments (5ft-lb or so at a time).

Torque diagonally if an even number of bolts and tighten every 3rd bolt in a circle if there are an odd number of bolts.

These efforts should give you a reasonable chance of success to true up the mess.

NOTE: you might simply find out where the high spot is now and merely play with bolt torque until you get it straightened out.

[RotarySMP]

6. Do operation 5 in LIGHT cuts so the if it is an iterupted cut, the tool doesn't start to chatter.

Probably not a great idea if the hub really is magnesium!

[t120rmike]

I don't feel comfortable trying to cut the wheel myself, that's why I'd rather know what to look for when trying to choose a machinist. I suppose it's also possible to try to shim the low spot on the wheel and then measure the shims to get an idea of how much material will need to come off.