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Old 03-20-2011, 11:49 AM   #1
lloydunknown OP
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Oddometer: 78
Airhead Valve Question

Greetings,

I recently acquired an '83 r100rt. It is in pretty rough shape cosmetically, but seems to pretty average mechanically.

I think I am experiencing the dreaded valve recession. Here's what I got:

36,565 Miles:
Left Intake okay at 0.10mm
Left Exhaust okay at 0.20mm
Right Intake NOT okay at 0.05mm reset to 0.10mm
Right Exhaust NOT okay at 0.10mm reset to 0.23mm

37,839 Miles:
Left Intake okay at 0.10mm
Left Exhaust NOT okay at 0.178mm reset to 0.229mm
Right Intake okay at 0.10mm
Right Exhaust NOT okay at 0.178mm reset to 0.229mm

Thats 1,274 miles and 0.022mm movement on the left and 0.052 on the right.

Thoughts? The PO told me that the bike probably has 50,000+ miles on it and that the odo does not represent the true mileage. Also, the title does not have an odo disclosure on it. It looks like it has seen high mileage. For example, the rear disc is almost worn out.

Ideas?

Thanks,
Lloyd
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Old 03-20-2011, 12:04 PM   #2
Boon Booni
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Location: Richmond, Va
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Quote:
Originally Posted by lloydunknown View Post
Greetings,

I recently acquired an '83 r100rt. It is in pretty rough shape cosmetically, but seems to pretty average mechanically.

I think I am experiencing the dreaded valve recession. Here's what I got:

36,565 Miles:
Left Intake okay at 0.10mm
Left Exhaust okay at 0.20mm
Right Intake NOT okay at 0.05mm reset to 0.10mm
Right Exhaust NOT okay at 0.10mm reset to 0.23mm

37,839 Miles:
Left Intake okay at 0.10mm
Left Exhaust NOT okay at 0.178mm reset to 0.229mm
Right Intake okay at 0.10mm
Right Exhaust NOT okay at 0.178mm reset to 0.229mm

Thats 1,274 miles and 0.022mm movement on the left and 0.052 on the right.

Thoughts? The PO told me that the bike probably has 50,000+ miles on it and that the odo does not represent the true mileage. Also, the title does not have an odo disclosure on it. It looks like it has seen high mileage. For example, the rear disc is almost worn out.

Ideas?

Thanks,
Lloyd

I think a few more data points are needed. Ride it another 1000 miles and see what's up.

How long did the bike sit before you picked it up?

and change that rear brake pad.
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Old 03-20-2011, 12:04 PM   #3
SOLO LOBO
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Well, the creep you see could be measurement error, and it small enough wouldn't do anything now but ride and continue to measure.

Some will say that is the soft valve seats wearing, but I would say to wait until you need to replace them before making a change. I believe Airhead Wrangler saw some similar number on his ST, and then rode 15K miles to somewhere in South America and back from Seattle with no issues.

How's the compression?
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Old 03-20-2011, 12:11 PM   #4
lloydunknown OP
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Oddometer: 78
Thanks, I'll ride it and get another data point. I had adjusted the valves before and not written down the info. I'll do that from now on.

The bike had been a daily driver before I bought it.

It has a very sad history. I think someone bought it new in '83 and let it sit forever. The logs I have on it show it had low mileage around 2004 and was well cared for. Well, except for the PPPO buying mirrors every year from knocking it over.

Then it was sold to the PPO who kept no records. I imagine it was wrecked under his ownership since now the paint is not original or matching. Also, the fairing is tweaked and the valve covers ground up.

The PO rode it as a beater for daily use. Now I'm the O.

This would have been a great bike if the PPO didn't hose it all up.

This is certainly a poorman's BMW. I can't afford head work so I really, really hope it is okay.

Anyone know a good cheap source for a rear brake disk?
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Old 03-20-2011, 01:15 PM   #5
squiffynimrod
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Quote:
Originally Posted by lloydunknown View Post

Anyone know a good cheap source for a rear brake disk?
Motobins in the UK.
About $125 US if you can't source a good used one.
http://www.motobins.co.uk/bmw-parts....20valve%20Twin
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Old 03-20-2011, 05:11 PM   #6
supershaft
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Did you torque the heads?
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Old 03-20-2011, 07:08 PM   #7
Wirespokes
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Please fill out your profile so we can see where you're from. It'll help us answer some of your questions as well.

Valve recession is due to the seats being too hard, not too soft. And normally if they're changing slightly it's not a big deal. With your larger gap of .008" they should do fine.

But, if they're not, and they keep receeding at .oo4 or .oo5" a thousand, then it's probably time to consider replacing or repairing the heads. Don't push it, or run it hard in hot weather and you'll do fine till you've saved up the cash to renew or replace.

It's been speculated that broken valves could be the result of worn valve guides, so keep that in mind.
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