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Author Topic: K75 rattle  (Read 8046 times)

Offline andrej_gr

  • Motobrick Curious
  • Posts: 13
K75 rattle
« on: July 28, 2019, 12:59:49 AM »
I've got this periodical rattle sound on my 1995 K75. Seems to be coming from alternator area. Pulled clutch doesn't change anything. Can't hear it on higher rpm, but that might be due to engine sound becoming louder. Ideas?

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  • Sydney, Australia
  • K75

Offline Martin

  • ^ Quintessential Motobricker
  • Posts: 4475
Re: K75 rattle
« Reply #1 on: July 28, 2019, 01:17:22 AM »
More than likely the monkey nuts in the alternator. Use a stethoscope or alternatively a long screwdriver to confirm the source of the noise. Place the blade end of the screwdriver onto the engine and an ear on the handle then move it around until the noise is at it's loudest.
Regards Martin.
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  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Offline The Mighty Gryphon

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  • Posts: 6857
Re: K75 rattle
« Reply #2 on: July 28, 2019, 11:59:30 AM »
Rattle between 1200 and 2000 rpm is loose fit between output gear and balance shaft.  Nothing you can do about it.     
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  • In my garage in Marilla, NY
  • '91K100RS White/Blue
Current:
'91 K100RS16V "Moby Brick Too"

Past:
'94 K75RT "Ilsa, She Wolf of the SS"
'92 K100RS16V "Moby Brick" (RIP, deceased in a vehicular assault)
'94 K75S Special Edition Dakar Yellow "Cheetos"
'89 K100RS Special Edition "Special Ed"

Offline Laitch

  • Faster than a speeding pullet
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  • Posts: 11645
Re: K75 rattle
« Reply #3 on: July 28, 2019, 12:57:19 PM »
Quote from: andrej_gr on July 28, 2019, 12:59:49 AM
I've got this periodical rattle sound on my 1995 K75.  Ideas?
Sonic Defenders.
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  • Along the Ridley in Vermont.
  • 1995 K75 102,000 miles

Offline K1300S

  • ^ Quintessential Motobricker
  • Posts: 1295
Re: K75 rattle
« Reply #4 on: July 28, 2019, 03:01:17 PM »
what gryph said.....if it goes away at idle and above 2k rpm.

one of my K75S's does it, the other does not.


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Project Thread "K75s Midlife Refresh"
http://www.motobrick.com/index.php/topic,7810.0.html

Offline stokester

  • ^ SuperNatural Motobricker
  • Posts: 850
Re: K75 rattle
« Reply #5 on: July 28, 2019, 04:50:59 PM »
Quote from: mlytle on July 28, 2019, 03:01:17 PM
what gryph said.....if it goes away at idle and above 2k rpm.

one of my K75S's does it, the other does not.
Ditto:
My '93 has no rattle, the '94 rattles like hell at low RPM until warmup.
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  • Yorktown Virginia
  • '94 K75S Dakar Yellow - '93 K75S Seiden Blau - '91 R100RT Bermuda Blue- '78 R100S Smoke Red

Offline The Mighty Gryphon

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Re: K75 rattle
« Reply #6 on: July 28, 2019, 09:28:47 PM »
I've had some luck with carefully adjusting the valves to the same clearance, cleaning the injectors with Techron, and adjusting the throttle body balance.  Makes it better, but it's still there.

I did have some temporary relief for a year or so by tightening the clutch nut on the output shaft after cleaning all the oil off the face where the balancer contacts it.  The trouble is that you need to take the clutch apart to get at it, so it's not something you want to do every year or so. 

The sloppy fit between the parts seems to have been built in.  When I had my engine apart I inspected the parts and the fit very carefully, and the gap is not the result of any wear, the parts were machined to fit like that.  I thought about tightening the fit by welding some additional metal, but held off due to not knowing how I would be affecting the hardness of the parts.

It's just something you have to live with.  It's a harmless part of the K75 engine's charm.
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  • In my garage in Marilla, NY
  • '91K100RS White/Blue
Current:
'91 K100RS16V "Moby Brick Too"

Past:
'94 K75RT "Ilsa, She Wolf of the SS"
'92 K100RS16V "Moby Brick" (RIP, deceased in a vehicular assault)
'94 K75S Special Edition Dakar Yellow "Cheetos"
'89 K100RS Special Edition "Special Ed"

Offline Laitch

  • Faster than a speeding pullet
  • Administrator
  • ^ Quintessential Motobricker
  • Posts: 11645
Re: K75 rattle
« Reply #7 on: July 28, 2019, 09:36:09 PM »
It sounds like a cat purring in its sleep. Don't disturb it.
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  • Along the Ridley in Vermont.
  • 1995 K75 102,000 miles

Offline andrej_gr

  • Motobrick Curious
  • Posts: 13
Re: K75 rattle
« Reply #8 on: July 28, 2019, 11:07:20 PM »
So as per Martin's advice took off the alternator... Bingo!

* 20190728_211000.jpg (63.24 kB . 768x576 - viewed 1066 times)
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  • Sydney, Australia
  • K75

Offline Laitch

  • Faster than a speeding pullet
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Re: K75 rattle
« Reply #9 on: July 28, 2019, 11:15:31 PM »
:cheers:
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  • Along the Ridley in Vermont.
  • 1995 K75 102,000 miles

Offline Martin

  • ^ Quintessential Motobricker
  • Posts: 4475
Re: K75 rattle
« Reply #10 on: July 29, 2019, 12:29:35 AM »
Good result.
Regards Martin.
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  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Offline aussiebeemer

  • Motobrick Curious
  • Posts: 10
K75 output shaft end play
« Reply #11 on: April 25, 2020, 12:43:17 AM »
HI K75s Vin WB1056306P0213381 I am replacing the rear engine output seal but notice there is 3+mm of endplay on the output/balancer shaft? (The shaft is disconnected from the clutch assembly)
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Offline aussiebeemer

  • Motobrick Curious
  • Posts: 10
Re: K75 rattle
« Reply #12 on: April 25, 2020, 04:25:36 AM »
attached video of shaft movement* output shaft.MOV.zip (1850.14 kB - downloaded 281 times)
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Offline daveson

  • ^ Quintessential Motobricker
  • Posts: 1318
Re: K75 rattle
« Reply #13 on: April 25, 2020, 06:34:33 PM »
That's a huge amount of endplay, but that's normal with the clutch nut removed.
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  • Victoria, Australia
  • Current; '85 K100RT~100,000km; four other bricks. Past; Vulcan 1500, V Star 650, KLX 250(dirt bike) TT250(dirt bike)

Offline aussiebeemer

  • Motobrick Curious
  • Posts: 10
Re: K75 rattle
« Reply #14 on: April 25, 2020, 07:29:26 PM »
 112350 Happy to read that. thanks.
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Offline Martin

  • ^ Quintessential Motobricker
  • Posts: 4475
Re: K75 rattle
« Reply #15 on: April 27, 2020, 08:12:10 PM »
I'm still running on a lot of my original parts including 170,000 KM monkey nuts. I've had spare nuts and cup in my spares inventory for years awaiting the dreaded sound of my nuts disintegrating. 44271
Regards Martin.
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  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Offline aussiebeemer

  • Motobrick Curious
  • Posts: 10
Re: K75 rattle
« Reply #16 on: April 28, 2020, 03:54:36 AM »
Thanks for the info. I am giving the 75s a big freshen up after me being off the road for several years. My talented brother has repainted all body parts. Photo to come.
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