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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: scoobs on July 05, 2014, 10:55:39 AM

Title: 92 k75RT goes "Clunk" when passing through 4000 rpm !!
Post by: scoobs on July 05, 2014, 10:55:39 AM

I've recently installed a replacement engine in my bike with 55k miles on it- runs smoothly with ~50 mpg but when accelerating/decelerating through 4000 rpm there is a distinct "clunk' that can not only be heard but also felt through the frame/handlebars. I've checked for any loose fasteners that may have been causing a resonance at that particular engine speed but have found nothing obvious.
Any thoughts on this ?
                              Cheers,
                                         Ian.  :dunno

Title: Re: 92 k75RT goes "Clunk" when passing through 4000 rpm !!
Post by: TimTyler on July 05, 2014, 04:03:03 PM

With the bike in neutral gear on the center stand, you get a single clunk at 4000 rpm?

Title: Re: 92 k75RT goes "Clunk" when passing through 4000 rpm !!
Post by: scoobs on July 05, 2014, 04:19:41 PM

I haven't tried it in neutral- only on the move. I'll give it a test and report back.
Thanks,
          Ian.

Title: Re: 92 k75RT goes "Clunk" when passing through 4000 rpm !!
Post by: Bokobob on July 06, 2014, 09:06:30 AM

Also could try to run it through the gears on the center stand, in addition to the good idea of running it up past 4K rpm in neutral on the center stand...

Title: Re: 92 k75RT goes "Clunk" when passing through 4000 rpm !!
Post by: jessez on July 06, 2014, 04:46:26 PM

Is this what some call the 'K rattle', a distinct quick vibration accelerating past 3k rpm?

Title: Re: 92 k75RT goes "Clunk" when passing through 4000 rpm !!
Post by: scoobs on July 06, 2014, 09:36:08 PM

Okay, after setting up on the centre stand I warmed the engine up then ran it up through 4000 rpm in neutral with no clunk, then did the same up through all gears with the same result. Took it for a 50 mile test run and everything appeared to be smooth, however when returning home later the distictive clunck had returned- noticable in 4th and 5th gears.
I'm wondering if it may be clutch-related, I replaced the clutch plates etc. while the bike was dismantled for the engine transplant. It changes gear smoothly enough but ......
Any further thoughts welcomed,
                                           Ian.  :dunno

Title: Re: 92 k75RT goes "Clunk" when passing through 4000 rpm !!
Post by: Motorhobo on July 07, 2014, 06:09:53 AM

Quote from: jessez on July 06, 2014, 04:46:26 PM

Is this what some call the 'K rattle', a distinct quick vibration accelerating past 3k rpm?

No, that's more like a fart than a clunk. It's probably trying to say "hey, if you're going to give me that much throttle, how about some more rpms? Kbikes like rpms.

Chuck out this recent thread -- maybe it's the same thunk...

http://www.motobrick.com/index.php?topic=5811.0 (http://www.motobrick.com/index.php?topic=5811.0)

Title: Re: 92 k75RT goes "Clunk" when passing through 4000 rpm !!
Post by: scoobs on July 09, 2014, 10:47:19 PM

After a bit of thought I checked the final drive and Lo and behold the splines are shot, as are their buddies on the output end of the driveshaft.
If anyone out there has any spares for sale please give me a shout.
Cheers,
           Ian. :falldown:

Title: Re: 92 k75RT goes "Clunk" when passing through 4000 rpm !!
Post by: Motorhobo on July 10, 2014, 06:25:24 AM

Where are you and what year/model....you might consider putting that info in your profile signature.

Check k-bikes.com and ebay -- at least you'll find something that'll hold you over till you can get yours rebuilt.

Title: Re: 92 k75RT goes "Clunk" when passing through 4000 rpm !!
Post by: Bokobob on July 10, 2014, 07:06:23 AM

Bummer on the splines...probably much too expensive considering cost of shipping much of your drivetrain, but I saw somewhere on these forums that a BMW dealer in California addresses this problem by welding the grooves and teeth "shut" with a special welcmen and then cuts new grooves/teeth into the "fattened" female and male parts..