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Old 09-21-2010, 09:40 AM   #1
spartanman OP
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who makes high-performance pre-81 airhead clutch?

The stock unit seems marginable for my 77RS. Anybody make a stouter clutch for these bikes?
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Old 09-21-2010, 10:40 AM   #2
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Quote:
Originally Posted by spartanman
The stock unit seems marginable for my 77RS. Anybody make a stouter clutch for these bikes?
I think marginal is accurate. BMW makes the best high performance clutch for them. It's a '81 on clutch. It is the best solution.
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Old 09-21-2010, 11:04 AM   #3
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Quote:
Originally Posted by supershaft
I think marginal is accurate. BMW makes the best high performance clutch for them. It's a '81 on clutch. It is the best solution.
Yeah, but you have to change the input shaft. And I like the heavy flywheel. I really want a drop-in replacement that uses a better diaphragm spring and clutch material.
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Old 09-21-2010, 11:46 AM   #4
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Worn bits?

Unless your engine is a fire-breathing monster, a stock clutch should be up to the task. Your spring and pressure plates may need freshening. I think Snowbum had some tips on shimming to increase pressure when necessary.
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Old 09-21-2010, 11:56 AM   #5
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Originally Posted by mykill
Unless your engine is a fire-breathing monster, a stock clutch should be up to the task. Your spring and pressure plates may need freshening. I think Snowbum had some tips on shimming to increase pressure when necessary.
Stock engine. New spring, pressure plate, friction disk and flywheel have about 2K miles. New rear main seal and oil pump o-ring. No sign of oil leakage. Didn't overdo the spline lube. Clutch is adjusted to spec. I've noticed some slipping at high loads in high gear. I figure the diaphragm spring isn't up to the task.
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Old 09-21-2010, 11:59 AM   #6
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I don't think worn bits is the answer. I remember when these bikes were brand new. The clutch is marginal.

Siebenrock and the other place sell early clutch stuff. It makes for a STIFF clutch pull and still doesn't work that well in my opinion. A late model clutch IS the best option. I can understand wanting some flywheel on a CR500. Maybe even a 250 but why on an airhead? IMO, they are WAY better without it. And the clutch is WAY better to boot!
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Old 09-21-2010, 12:00 PM   #7
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Quote:
Originally Posted by spartanman
Stock engine. New spring, pressure plate, friction disk and flywheel have about 2K miles. New rear main seal and oil pump o-ring. No sign of oil leakage. Didn't overdo the spline lube. Clutch is adjusted to spec. I've noticed some slipping at high loads in high gear. I figure the diaphragm spring isn't up to the task.
a defective pressure plate maybe?
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Old 09-21-2010, 12:47 PM   #8
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If you want to throw your $$$ away, Motoren Israel can probably help. They manufacture good stuff for racers and the high performance crowd but the prices are insane. Look em up via Google and rest easy in the knowledge that they take credit cards.

You can easily shim your spring to get more pressure and then add an 'easy clutch' system but you'd better keep an eye of the ancillary parts.

The late model clutch is the way to go.
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Old 09-21-2010, 01:44 PM   #9
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Originally Posted by mymindsok
The late model clutch is the way to go.
Educate me: Why is the later clutch better than the pre-81 version? I owned an '82 RT. My recollection was that it revved faster and the clutch was easier to pull, both good things. But the engine vibrated more than my '77 RS or old '78 S, which is what I'd expect with a lighter flywheel. The RT also took more revving to get underway from a stop, again due to the lighter flywheel.
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Old 09-21-2010, 03:22 PM   #10
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Quote:
Originally Posted by spartanman
Educate me: Why is the later clutch better than the pre-81 version? I owned an '82 RT. My recollection was that it revved faster and the clutch was easier to pull, both good things. But the engine vibrated more than my '77 RS or old '78 S, which is what I'd expect with a lighter flywheel. The RT also took more revving to get underway from a stop, again due to the lighter flywheel.
Why is the later clutch better? Because they don't slip with a lighter pull at the same time.

I suspect leaving from a stop is the best place to appreciate the earlier flywheel. I guess I just don't worry about that one small parameter. Hellfar, I read that some want a lower first gear so they don't have to slip the clutch so much with their 2.91:1 FD. I have a super tall close ratio first gear that is close to taking off in second with a regular tranny and no flywheel AND I live in San Francisco! 99k miles on the original late model clutch at it STILL doesn't slip. I do wheelies and ride over the ton ALL the time. Same story with my other late model and it has more miles than that.

Vibration? I don't think it was the flywheel.
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Old 09-21-2010, 04:06 PM   #11
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Quote:
Originally Posted by mymindsok

/snip

You can easily shim your spring to get more pressure and then add an 'easy clutch' system but you'd better keep an eye of the ancillary parts.

/snip
There's a couple of other ways to get the spring closer to the plate too, but that's probably the easiest and cheapest way to increase the pressure using the older parts.
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Old 09-21-2010, 04:21 PM   #12
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Quote:
Originally Posted by supershaft
Why is the later clutch better? Because they don't slip with a lighter pull at the same time.

I suspect leaving from a stop is the best place to appreciate the earlier flywheel. I guess I just don't worry about that one small parameter. Hellfar, I read that some want a lower first gear so they don't have to slip the clutch so much with their 2.91:1 FD. I have a super tall close ratio first gear that is close to taking off in second with a regular tranny and no flywheel AND I live in San Francisco! 99k miles on the original late model clutch at it STILL doesn't slip. I do wheelies and ride over the ton ALL the time. Same story with my other late model and it has more miles than that.

Vibration? I don't think it was the flywheel.
Assume you have the same engine. Install a heavy, then a light flywheel. The heavy flywheel setup will run smoother because there is more rotating mass (inertia) to maintain constant engine speed between firings and absorb combustion pulses. It's all a moot point right now because I fixed the problem.

I had adjusted the clutch cable by the book with the bike cold. it turns out the clutch adjustment changes slightly when the bike warms. No suprise, really. I rode it for a few miles, then added a tad more free play at the lever. No more slip.

spartanman screwed with this post 09-21-2010 at 04:30 PM
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Old 09-21-2010, 04:31 PM   #13
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Thanks everyone for the help. I appreciate it.
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Old 09-21-2010, 05:11 PM   #14
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Quote:
Originally Posted by nella
There's a couple of other ways to get the spring closer to the plate too, but that's probably the easiest and cheapest way to increase the pressure using the older parts.
Right-O!
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Old 09-21-2010, 07:24 PM   #15
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Motobins do a heavy duty clutch spring.

http://www.motobins.co.uk/bmw-parts....20valve%20Twin
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