Hot rear hub.

[Roguetek]

Bike: 1977 R75/7

Problem : rear hub overheating.

the rear hub is overheating, and I cant seem to find the source. the hub is uniform in temperature, but only just cool enough to touch. it's the same temp across the final drive housing, and the bearing on the other side.

the final drive has fresh oil in it.

the brakes are not binding.

the wheel has no wobble to it ( bearings are not loose )

Is this normal? or is something not right?

and while I'm thinking on it, who's bright idea was it to have -two- positions that the ignition key can be removed in? one of which drains the battery overnight.

also, the kickstarts is the most -useless- frigging kicker I've ever had the misfortune to kick.

[20774]

Bearings are not too loose, but are they too tight? If you've not gone through the process of setting the preload, you don't really know the answer to either. I believe that the hub has to heated to a pretty good temperature (spit sizzle) of say 225F so that the bearing stack can be driven out. At least this is what was done on my /7. I had help doing this at a Tech Day...I'm glad I had more experienced people holding my hand.

Beyond that, it sounds like the drive needs to come apart so that the gears and how they mesh can be looked into. Has this been a long time problem, new to you, or just showed up recently?

As for the kicker, you should think of it as a "get me home, please, since my starter has died" feature. The electric starter should be your friend here, not the kicker. It was the only way to start /2 bikes, but its utility and robustness has gone downhill since the introduction of the /5.

[rpeckham136133]

The two-position-removable key is a holdover from European bikes, that could have the "parking" lights left on with the key removed. Your battery may not be much good if it is drained overnight by a couple of parking bulbs (or less).... or perhaps the middle position is wired wrong?

The hot-final drive: if you have access to an infrared thermometer, ride the bike for five minutes or so, and shoot the hub to see where the temperature differential might be..... most likely it is bearings, perhaps drive bearing and not wheel bearings. Take a look at the fiche to see the construction of the final drive: there is a needle bearing at the driveshaft input, and another one outside the ring gear, and a roller bearing on the inner side of the ring gear/drive.


:idea


Just a thought, and I have never done it, but you might be able to slide the axle through the removed wheel assembly and tell how the wheel bearings themselves are... wheel bearings tend to get rumbly and feel gritty when they go bad. That would be MUCH easier than doing the rear drive bearings....

[GeorgeRyals]

"just cool enough to touch" Can you put your hand on it for more than 15-20 seconds? If so it is below 120F...not all that hot as far as damaging anything.

[Funride]

I have a new RT and if I go for 20 or 30 miles on the highway at 65 mph and then stop the FD hub is warm on mine. About like my coffee cup after about 5 minutes. Not really hot. I can put my hand on it all day if I want.

Put it this way the valve covers are warmer than the FD hub and I can put my hands on the valve cover without burning (not the cylinder or exhaust pipe).

If you burn your hands on the FD hub I would start worrying.

[Roguetek]

temp is shy of a 1st degree burn, but not by much. I can hold my hand there, but it's just into the threshold of pain, and just below the threshold of burn.

I can hold my hand there for about 20 seconds, easy.

[RandyB]

Just a thought, and I have never done it, but you might be able to slide the axle through the removed wheel assembly and tell how the wheel bearings themselves are... wheel bearings tend to get rumbly and feel gritty when they go bad. That would be MUCH easier than doing the rear drive bearings....

Clean the axle well first. There should be a bit of grease on there if the bearings are correctly greased. Dry is not good. This is an easy (relatively) fix as long as the preload is still good.

[mneblett]

Before getting into a lather about this, keep in mind that the drives naturally get warm.

The use of ring and pinion gears inherently is accompanied by a 2-3% power loss. The energy from that power loss has to go somewhere -- from the gear teeth to the gear bodies, then to the gear oil, then to the housing, and finally rejected from the housing to the environment by convection and radiation (and a small amount of conduction back up the swingarm). After sufficient time, the steady application of power (i.e., steady-state cruising) results in temps which settle into a stable, elevated state.

The steady-state temperatures are determined by (i) the amount of power being delivered to the rear wheel to maintain the desired speed (which in turn depends on the driver's speed demand, the amount of load being carried, the road grade, etc.), and (ii) the ambient atmospheric conditions (i.e., how willing the heak sink is to receive the excess heat being rejected from the housing to the air).

Thus, there is no "correct" temperature. No load, low speeds, light bike, drive barely heats up. A K12LT pulling a fully loaded Bushtec trailer up a long grade at 70+, too hot to touch for any significant period.

Unless you are hearing strange noises, can feel roughness in the bearings as the wheel is rotated (roughness that is not the driveshaft universal joints going bad), or have significant freeplay when shaking the tire at 12 & 6 o'clock, my $0.02 is to assume all is well and move on to some other mechanical issue to worry about. :D

[Roguetek]

preload. you guys keep mentioning this.. .what does it mean.

[skiteach]

Drum or disk? Not sure how quickly a rotor transfers heat. Drums heat up really quickly and the housing is a good heat sink.

[DARRYL CAINEY]

preload. you guys keep mentioning this.. .what does it mean.

When the Rear Axel Nut is torqued down to the proper torque the tapered roller bearings have a preload that is set by a shim between the bearing stack.

This setting should be done by a qualified tech that knows Airheads.

Darryl

[Funride]

Before getting into a lather about this, keep in mind that the drives naturally get warm.

The use of ring and pinion gears inherently is accompanied by a 2-3% power loss. The energy from that power loss has to go somewhere -- from the gear teeth to the gear bodies, then to the gear oil, then to the housing, and finally rejected from the housing to the environment by convention and radiation (and a small amount of conduction back up the swingarm). After sufficient time, the steady application of power (i.e., steady-state cruising) results in temps which settle into a stable, elevated state.

The steady-state temperatures are determined by (i) the amount of power being delivered to the rear wheel to maintain the desired speed (which in turn depends on the driver's speed demand, the amount of load being carried, the road grade, etc.), and (ii) the ambient atmospheric conditions (i.e., how willing the heak sink is to receive the excess heat being rejected from the housing to the air).

Thus, there is no "correct" temperature. No load, low speeds, light bike, drive barely heats up. A K12LT pulling a fully loaded Bushtec trailer up a long grade at 70+, too hot to touch for any significant period.

Unless you are hearing strange noises, can feel roughness in the bearings as the wheel is rotated (roughness that is not the driveshaft universal joints going bad), or have significant freeplay when shaking the tire at 12 & 6 o'clock, my $0.02 is to assume all is well and move on to some other mechanical issue to worry about. :D

Good points and now I understand about the energy 2-3% having to go someplace.

[RandyB]

When the Rear Axel Nut is torqued down to the proper torque the tapered roller bearings have a preload that is set by a shim between the bearing stack.

This setting should be done by a qualified tech that knows Airheads.

Darryl

Snowbum has this on his site. Pack sunglasses and a lunch, but it's great info.

If the preload is correct, you can just service the bearings normally. Don't interchange them, etc. It's pretty simple. Is the front hub getting hot as well? You might just need to grease things up a bit.

[20774]

Snowbum has this on his site. Pack sunglasses and a lunch, but it's great info.

ROTF....:clap That's being diplomatic, but I had a good laugh on that one!

[RandyB]

ROTF....:clap That's being diplomatic, but I had a good laugh on that one!

'bum is such a good guy. I wish I didn't have two Airheads already because I'd buy his RT in an instant. Guaranteed to make it home. It's sad he has decided to quit riding.

[20774]

It's sad he has decided to quit riding.

Huh? When/where did you hear that? I'm still catching up on my Airheads list digest emails, but I've not run across 'bum saying that. I know he had some health issues 5-7 years ago, but that seemed to not be an issue. He does seem to be active in the sidecar world, having just been involved in a major rally in his area.

[RandyB]

Huh? When/where did you hear that? I'm still catching up on my Airheads list digest emails, but I've not run across 'bum saying that. I know he had some health issues 5-7 years ago, but that seemed to not be an issue. He does seem to be active in the sidecar world, having just been involved in a major rally in his area.

One day last week, IIRC, on the List.