Time Sensitive Deterioration of Airhead Parts

Okay, Airheads are great. BUT. These motorcycles are 25-40 years old now.

What items should be suspect for replacement simply because of age and not necessarily mileage?

Seals, especially engine seals like the rear main seal- how likely are they to become hard with age?

Clutch plates, do these retain their properties with age?

Rubber parts, obviously.

What else?


If I pull my gearbox of my '91 to fix the retainer clip problem, should I also replace the rear main seal and the clutch plate even if it looks good???


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I don't do that kind of maintenance typically...replace something just because of time. I replace for cause...which can translate to miles. Or possibly "since I'm already here...".

I would think things like clutches could safely be replaced due to miles...my estimate would be around 75K and above, depending on type of driving. If city driving mostly, fewer number of miles...if mostly highway miles than maybe more miles say 100K or above. Generally, the clutch gives you a bit of warning as slipping in high gear or running out of adjustment range. The other thing is it's relative easy to get back to the clutch...doesn't require a great deal of disassembly.

The rear main seal might be a different story. If the seal has low miles and it's not leaking, I might let sleeping dogs lie. But if the miles are up there, it could be a lot more miles before you're back in there. Plus, note the extra caution is needed to block the crankshaft from moving when the flywheel/clutch carrier is removed.

As for seals, especially the external ones, they usually "leak before break" so you have some warning.

I think you need to find a balance between usage and maintenance. While not necessarily the same thing, the USAF optimizes their maintenance schedules to give the best chance at safety but also to keep those darned mechanics away from the airplane! Stuff just "happens" when tools get near the wing, fuselage, etc. The more times maintenance is done, the more chances that something will go wrong.

leafman60 said:

Okay, Airheads are great. BUT. These motorcycles are 25-40 years old now.

What items should be suspect for replacement simply because of age and not necessarily mileage?

Seals, especially engine seals like the rear main seal- how likely are they to become hard with age?

Clutch plates, do these retain their properties with age?

Rubber parts, obviously.

What else?


If I pull my gearbox of my '91 to fix the retainer clip problem, should I also replace the rear main seal and the clutch plate even if it looks good???

Click to expand...

I may take a different approach than Kurt, but if I had expended the labor to get the transmission out, I would certainly replace the rear main seal and oil pump cover seal if I didn't know when/if either had been previously replaced. The OE rear main seals always eventually leak (particularly, it seems, if the bike has been out of regular use for awhile), and there's not much virtue in chancing its continued good behavior, even if it looks good now. There's a spec for clutch friction disc thickness, and, depending on your riding style, it may be perfectly fine (when my airhead mechanic last lubed the transmission input splines on my '84 RT, he asked when I had replaced the clutch, because it was essentially the same thickness as new---even though the bike had 70K miles on it, and the clutch is the OE item it left Berllin with).

Beyond tires and tubes, the list of rubber parts that deteriorate standing still with age is fairly extensive, and distributed around the machine. Any seal that is constantly immersed in oil, or is exposed to heat cycling (like pushrod tube seals) or UV, etc. can be expected to have a finite lifespan, and some are mission-critical to the bike's operation. These would include: fork bumpers and other fork internal bits and seals, carb o-rings, float needle tips, petcock discs, fuel lines, flexible brake lines, caliper piston seals, speedo cable boot (it keeps rain and wash water out of your transmission), and the seals that keep oil compartmentalized and contained in the swingarm and final drive.

Another bit that seems to deteriorate with time, rather than strictly mileage, is your fuel tank's lining. Alcohol fuel and some fuel stabilizers may hasten the lining's deterioration itself, or otherwise attract & phase-separate water, causing internal corrosion problems there. The lining eventually starts to flake off, or come off in sheets and wads. I've recently had to have the tanks on both my '84 RT and my '91 R100 Classic professionally re-lined (to avoid DIY-bunging up (with etching acids, solvents, or re-lining material), the OE pearl white paint on my RT, and the less-complicated, but rarer, classic black metallic on the '91). The tank lining may be a sleeping dog best left alone for some, but, at least for me, the dog will wake up and take a bite out of your wallet.

I'm sure I'm missing some things, but other more-knowledgeable folks will surely chime in.

Replacement

leafman60 said:

Okay, Airheads are great. BUT. These motorcycles are 25-40 years old now.

What items should be suspect for replacement simply because of age and not necessarily mileage?

Seals, especially engine seals like the rear main seal- how likely are they to become hard with age?

Clutch plates, do these retain their properties with age?

Rubber parts, obviously.

What else?


If I pull my gearbox of my '91 to fix the retainer clip problem, should I also replace the rear main seal and the clutch plate even if it looks good???


.

Click to expand...

Lots of people never consider the old, brittle, corroded wiring system.

I've restored several Airhead's and always found that to be one of the best approaches to prolonged reliability. It's nice to go for a long ride on my old R90s and know that at least the electrical system will get me home.