79 clutch noise

airheadDan · Post by **airheadDan** » Sat Oct 24, 2009 10:24 am

Gentlemen, You are probably wondering why a guy calling himself airheadDan would be posting on a CBX website. Yes I am a fan of and owner of old airhead BMW's. Simple and low tech bikes. Perhaps the oposite of the CBX. A friend recently purchased a ' 79 CBX, and since he is computer illiterate I am going to try to get help for his clutch noise problem. He had previously owned a ' 79 CBX with the well known clutch rattle. The bike he has now has a similar noise, maybe louder, more like a knock. pulling in the clutch lever does not make the rattle/knock go away as it did with his first CBX. If you put the bike in gear and ease the clutch out til it just starts to engage, taking the freeplay out of the drivetrain but not moving the bike, the noise goes away. Other than this rattle/knock the bike runs and shifts great. Any help fixing this problem would be greatly apreciated. Thanks,airheadDan

Simple by choice

Don · Post by **Don** » Sat Oct 24, 2009 11:02 am

You may have more problems than just the clutch basket

So far as the clutch goes, probably the best, most permanent solution is to replace the clutch basket with one from an '81/'82 CBX - Honda had it all figured out by then. Even the '80 model basket is better than the one they used in '79

Alternatively (and much cheaper) is to buy a set or replacement rubbers from SixCenter in Holland and rebuild your '79 basket. For about $75 and a few hours of work your clutch rattles will be gone . . . . and then any other problems you may have will be easier to diagnose

http://www.sixcenter.nl/

Don

alimey4u2 · Post by **alimey4u2** » Sat Oct 24, 2009 12:25 pm

Welcome to the site airheadDan.....

Clutch rattle is aggrevated by carbs being out of synch. "They all do that Sir" under this scenario..... As Don suggested it may be more than that, possibly primary chain tension ( or lack thereof.) This is automatically adjusted by a hydraulic tensioner, oil being supplied by the cooler circuit pump. Strobe the timing when off load & then under load ( rear brake on, feed the clutch softly & in gear.)

If the timing chain is loose you will see the timing drift ( flutter) when off load & stable when loaded. Try to do this with the engine idling....

airheadDan · Post by **airheadDan** » Sun Oct 25, 2009 8:52 am

Thanks for the response. I will pass along the information. Is there a site with a "how to" on the clutch noise fix ? Thanks for the tip on checking the timing to determine if the primary chain is loose. Are problems with the primary chain tensioner common? We have the engine out of the frame at this time, and when we removed the sump cover to deal with a stripped drain plug. I saw that the bike used a primary chain and had a susspicion that this could be the source of the noise. The owner of the bike is not eager to split the cases. He is a good mechanic very experienced with older Kawasaki 900's and 1000's, but is a little put off by the complexity of the CBX. Thanks again for the help, airheadDan

alimey4u2 · Post by **alimey4u2** » Sun Oct 25, 2009 9:38 am

Several people have "upgraded" their clutch to the later Prolink model some to good effect but it isn't a guaranteed fix. There is someone in the UKCBX club that does a modification if I remember. Maybe Mel could advise... There are also peeps in the States doing it too.
As for the primary chain tensioner, these old girls are getting a little long in the tooth & their suspender rubbers are also. Having said that, mine is fine. I think it depends if the engines were laid up dry at some point in their history...Fuel/oil contamination & other ill effects like using non specific motorcycle oil... Gonna catch hell for that one..

Problem is Honda don't make the rubber seals anymore ( I think) but enterprising peeps are hard on the case...

I have to ask this one... Have the cams been worked on recently ??

EMS · Post by **EMS** » Sun Oct 25, 2009 10:22 am

Together with the clutch in the later models, Honda also changed/improved the primary sprocket, which could be another source for the noise. They omitted the spring and replaced it with a lock nut.

Dave Hansen · Post by **Dave Hansen** » Sun Oct 25, 2009 2:42 pm

I sure hope this isn't the issue but a rod bearing in the early stages of failure can make a knock that goes away with a little loading. The wrist pin joint too. Have you tried a stethscope to locate the origin of the noise?

airheadDan · Post by **airheadDan** » Wed Oct 28, 2009 12:33 pm

Thanks for the suggestions. The engine is out of the frame currently as the frame is being painted. Once we get it back together we can try to diagnose the problem. Thankfully it doesn't sound like a rod or wrist pin knock, but the primary chain is a possible culprit. Using a timing light to check this out is a great idea. The owner is looking to clean up the bike, paint it and resell so it will probably be sold as is, with the noise, unless we come accross an easy fix. Thanks again, airheadDan

daves79x · Post by **daves79x** » Wed Oct 28, 2009 6:13 pm

If the carbs are really out of adjustment or partially plugged, the bike can sound like it is knocking also. You'll need to go through the carbs completely to be sure they are clean and adjusted properly, or the bike will never run or sound as it should.

Dave

les · Post by **les** » Mon Nov 01, 2010 6:40 am

Hi to all from brisbane australia i have a 1978 and 1979 cbx twin shock that have both been restored.Both bikes have the dreaded clutch rattle after having carbs balanced.There are at least half a dozen CBX owners i know personally with the same problem. One has even fitted a brand new prolink clutch and the noise is still there.Are we looking in the wrong place for the problem? I have a mate who is an engineer who also owns two CBXs and he cant sort out the problem! Some of these bikes have been restored to better than new in appearance but sound like they are about to self destruct at idle. The common fix seems to be just turn the idle up to around 1200 rpms but i would rather a better solution. Both bikes have around 70,000 klms on them. Can anyone help? Thanks Les.

EMS · Post by **EMS** » Mon Nov 01, 2010 7:42 am

As I said above:

EMS wrote:Together with the clutch in the later models, Honda also changed/improved the primary sprocket, which could be another source for the noise. They omitted the spring and replaced it with a lock nut.

NobleHops · Post by **NobleHops** » Mon Nov 01, 2010 1:08 pm

les wrote:Hi to all from brisbane australia i have a 1978 and 1979 cbx twin shock that have both been restored.Both bikes have the dreaded clutch rattle after having carbs balanced.There are at least half a dozen CBX owners i know personally with the same problem. One has even fitted a brand new prolink clutch and the noise is still there.Are we looking in the wrong place for the problem? I have a mate who is an engineer who also owns two CBXs and he cant sort out the problem! Some of these bikes have been restored to better than new in appearance but sound like they are about to self destruct at idle. The common fix seems to be just turn the idle up to around 1200 rpms but i would rather a better solution. Both bikes have around 70,000 klms on them. Can anyone help? Thanks Les.

Sorry I'm no help on this issue Les, but welcome to the site, very glad to have you here.

N.

Jeff Bennetts · Post by **Jeff Bennetts** » Mon Nov 01, 2010 1:48 pm

Worn cam joins can also be source of motor noise.

EMS · Post by **EMS** » Mon Nov 01, 2010 2:33 pm

Any multi-cylinder, multi chain-driven cam engine will make noise if the idle speed is too low and the effect of rotating mass balance is not there. That being said, the spec in the Service Manual calls for an idle speed of 900 +/- 100 rpm. Don't expect this motor to run smooth and quiet at 800 rpm or lower.

The International CBX Owners Association

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