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-   -   Airhead Valve Question (http://www.advrider.com/forums/showthread.php?t=670164)

lloydunknown 03-20-2011 11:49 AM

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

Boon Booni 03-20-2011 12:04 PM

Quote:

Originally Posted by lloydunknown (Post 15464466)
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.

SOLO LOBO 03-20-2011 12:04 PM

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?

lloydunknown 03-20-2011 12:11 PM

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?

squiffynimrod 03-20-2011 01:15 PM

Quote:

Originally Posted by lloydunknown (Post 15464624)

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

supershaft 03-20-2011 05:11 PM

Did you torque the heads?

Wirespokes 03-20-2011 07:08 PM

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.

lloydunknown 03-20-2011 07:14 PM

Thank you all for the prompt responses.

"Please fill out your profile so we can see where you're from."
I am in Delaware, USA.

I'll keep an eye on the valves. I've been nursing a weeping fork seal since last summer. Today I noticed the leaking is accelerated and in danger of fouling the brake surfaces. I won't be riding until I replace those fork seals.

Luckily, I have all of the parts in the garage and the oil.

lloydunknown 03-20-2011 07:17 PM

"Did you torque the heads?"
I've torqued the heads at two valve adjustments so far. I don't have the numbers from those adjustments because I didn't think to write it down.

I heard that you shouldn't torque the heads at every adjustment in fear of pulling a stud through the case. The last two times I did not torque the heads.

Myro 03-21-2011 06:26 AM

Personal experience, 82 R100RT, mileage at approx 40K miles. Valves needed adjustment every 600 miles. Pulled heads to rebuild and discovered that the seats were perfect but the valves were toast, almost ready to pull through the seat they were so thin and curled. Sorry it was a long time ago so have no pictures. The valves were poor quality metal and so was the final drive spline. This is apparently a known issue with this vintage of Beemers.

fishkens 03-21-2011 06:36 AM

You can pull the spark plugs and rotate the engine to view part of the exhaust valves (use a flashlight) to check their condition.

kraut.burner 03-21-2011 09:20 AM

Kind of abstract, but could there be a chance that it might be bad tappet adjusting bolts?

I had ones that were stripped and kept throwing the valves out of adjustment. I'd usually end up with measurements similar to yours.

supershaft 03-21-2011 10:04 AM

Once I have checked the torque properly, I just check the torque versus re-torquing them. In other words, I don't loosen the nuts and then re-tighten. No need to really and I think it puts unneeded wear and tear on the components. Once a year or so is enough IMO but now you know that you do not have a stud pulling.

Sometimes the seats are too hard and the valve gives and sometimes it is the seat that gives. Very often it is a combination of both.

bmwloco 03-23-2011 07:54 AM

Elaine (Vech's SO/Wife/Partner) has her own web page on how to adjust /2 valves. You can find it here:

http://benchmarkworks.com

No direct link as they have finally updated their web site! Look under "Tech Advice" on the left and then "Technical and How To". There is a wealth of knowledge and information there.

danedg 03-23-2011 12:17 PM

How timely.
I adjusted my /2 R60 valves last nite.
Probably for the first time in 8 - 9000 miles.
In the first 10K after rebuild, I checked 'em every 500 - 1000m, and gave up after 12K, cause they hadn't budged.
Didn't check 'em at all last year. Another 8000 miles. Bike ran fine. There is one little tap, however.
So, being completely bored, I pulled covers yester, and whipped out the feelers. Guess what?
Dead on, both sides.:clap
Then I read this thread, and went back to Elaine's Tech Article.
I'd been doing right all along, but didn't realize that a push rod could be bent...and that might be the source of the unidentified tappety tap...
How badly could the rod be bent and still operate? And if it IS bent, how long will it continue to operate in that condition?:ear
Another 68,000 miles?:evil


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