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Author Topic: K75 Engine noise  (Read 22797 times)

Offline bgcameron

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K75 Engine noise
« on: April 09, 2021, 01:12:31 AM »
Hey guys,

I have a '90 K75S with 53,000 kilometers on it. I am getting a loud, intermittent clacking noise, possibly coming from the front of the engine. It only happens in motion, under a light load at any speed or gear. It seems to happen around 3500 rpm, but it is not a consistent "chatter". It is more like a "clack!...clack clack, clack!". At first I thought it was some noise from the fairings when going over the odd bump. I can even feel it through the handlebars when it happens..

I searched forums and didn't find anyone with a similar issue. It is difficult to isolate exactly where the sound is coming from because it only happens when riding. Help!

Thanks!
Branden
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  • Vancouver Island
  • 1990 K75S

Offline daveson

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Re: K75 Engine noise
« Reply #1 on: April 09, 2021, 05:07:48 AM »
I guess that means you can't reproduce it on the centre stand at 3500rpm in gear or neutral. Can you reproduce it while riding at 3500rpm in neutral, or disappears with the clutch pulled in?

A bit of wishful thinking, sometimes it's as simple as a loose spark plug lead, or old plugs or leads. What brand are they?

What about the history, like is it a new problem, or had it for years, or developed suddenly after some repairs, or something like that?

It wouldn't hurt to clean and gap the plugs and leads.
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  • Victoria, Australia
  • Current;'85 K100RT~100,000km; four other bricks. Past; 1500 Vulcan, V Star 650, KLX 250(dirt bike) TT250(dirt bike)

Offline Laitch

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Re: K75 Engine noise
« Reply #2 on: April 09, 2021, 11:06:20 AM »
Quote from: bgcameron on April 09, 2021, 01:12:31 AM
. . . under a light load at any speed or gear. It seems to happen around 3500 rpm . . .
If you go full throttle in first or second gear up to 5000 rpm there is no noise?
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  • Along the Ridley in Vermont.
  • 1995 K75 89,000 miles

Offline bgcameron

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Re: K75 Engine noise
« Reply #3 on: April 09, 2021, 12:34:21 PM »
Quote from: daveson on April 09, 2021, 05:07:48 AM
I guess that means you can't reproduce it on the centre stand at 3500rpm in gear or neutral. Can you reproduce it while riding at 3500rpm in neutral, or disappears with the clutch pulled in?

A bit of wishful thinking, sometimes it's as simple as a loose spark plug lead, or old plugs or leads. What brand are they?

What about the history, like is it a new problem, or had it for years, or developed suddenly after some repairs, or something like that?

It wouldn't hurt to clean and gap the plugs and leads.

It is so sporadic when riding- I'll be going down a straight stretch of pavement and get a single "CLACK!", sometime more- so it is hard to determine what might mitigate it. I'm sure the problem has existed since i've owned the bike. I have not ridden it much- less than 3000kms. I recently changed the plugs and leads, which did not make any difference.


Quote from: Laitch on April 09, 2021, 11:06:20 AM
If you go full throttle in first or second gear up to 5000 rpm there is no noise?
No, nothing under full throttle as far as I can tell. Light throttle and maintaining a speed seems to do it.

Is it possible that I have a failing cam chain tensioner?
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  • Vancouver Island
  • 1990 K75S

Offline The Mighty Gryphon

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Re: K75 Engine noise
« Reply #4 on: April 09, 2021, 12:53:43 PM »
Cam chain slap is a real possibility if the chain is stretched.  Probably will happen on closing the throttle when under hard acceleration.  Pull the cam chain cover on the front of the engine and check the chain and the guides.
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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 daveson

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Re: K75 Engine noise
« Reply #5 on: April 09, 2021, 04:44:08 PM »
Unlikely but quick to check for some loose bolts up front, like if the mud guard is loose you might get a clack from it, or calipers, or steering head.
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  • Victoria, Australia
  • Current;'85 K100RT~100,000km; four other bricks. Past; 1500 Vulcan, V Star 650, KLX 250(dirt bike) TT250(dirt bike)

Offline Laitch

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Re: K75 Engine noise
« Reply #6 on: April 09, 2021, 05:38:29 PM »
One person's clack might be another's click. Check the header bolts for tightness and the exhaust heat shield for looseness.
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  • Along the Ridley in Vermont.
  • 1995 K75 89,000 miles

Offline rbm

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Re: K75 Engine noise
« Reply #7 on: April 09, 2021, 09:18:44 PM »
Are you 100% certain the noise if from the front.  If you are, then ignore this suggestion.  If not, a similar noise might be possible from the alternator region if the monkey nuts are kaput.  To check, remove the alternator and run the engine briefly to see of the noise abated.
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1987 K75 - Build Blog @http://k75retro.blogspot.ca/

Offline bgcameron

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Re: K75 Engine noise
« Reply #8 on: April 10, 2021, 12:08:26 AM »
Thanks all,

I've checked everything for looseness and no luck. I am going to see if I can replicate the sound with it in gear and on the center stand. I'll check those monkey nuts too.. does anyone have a video/audio clip of the sound it makes when they are bad?

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  • Vancouver Island
  • 1990 K75S

Offline daveson

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Re: K75 Engine noise
« Reply #9 on: April 10, 2021, 04:43:10 AM »
There's an example in the workshop section called "k75 rattle" by Andrej. Sometimes it sounds a bit different, and sometimes there are other causes. Dunno how to do links, near the top of the sixth page at the moment.
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  • Victoria, Australia
  • Current;'85 K100RT~100,000km; four other bricks. Past; 1500 Vulcan, V Star 650, KLX 250(dirt bike) TT250(dirt bike)

Offline Laitch

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Re: K75 Engine noise
« Reply #10 on: April 10, 2021, 08:15:48 AM »
Here's the video from daveson's video reference. Because bgcameron's description mentions only a random rattle in a narrow rpm range, its source is unlikely to be this.
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  • Along the Ridley in Vermont.
  • 1995 K75 89,000 miles

Offline bgcameron

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Re: K75 Engine noise
« Reply #11 on: April 10, 2021, 02:49:04 PM »
^ Definitely not that. The noise I am getting is significantly louder, and will present as anything from a single "Clack!" to a series of "clacks". I'll investigate more today.
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Offline Martin

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Re: K75 Engine noise
« Reply #12 on: April 10, 2021, 04:28:59 PM »
A bit out of left field, are you sure the noise is coming from the engine? Front shocks have been known to emit the occasional noise. Try bouncing the bike with the engine off.
Regards Martin.
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Offline bgcameron

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Re: K75 Engine noise
« Reply #13 on: April 10, 2021, 07:55:48 PM »
trying to capture some of this on video. It is hard to hear among the engine and wind noise, but some can be heard around the 12 second mark. It seems louder on the left side of the engine.. maybe coming from the head? I don't know. Is pinging a possibility? I am using 91 octane without ethanol.



And I am not sure if this is related but it can be heard at idle.

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Offline Laitch

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Re: K75 Engine noise
« Reply #14 on: April 10, 2021, 08:26:52 PM »
That was an excellent effort at recording!  177381 

In a previous thread, you noticed "movement of the tensioner" during valve clearance inspection. Does that mean there was slack taken up during rotation of the camshaft? Do you know approximate number of kilometers this engine has traveled and if it has been conscientiously maintained?

Will the engine create that sound when the moto is run on the center stand in neutral at 3500rpm or does it need to be under load?
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  • Along the Ridley in Vermont.
  • 1995 K75 89,000 miles

Offline bgcameron

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Re: K75 Engine noise
« Reply #15 on: April 10, 2021, 08:46:21 PM »
Haha, it was a little tricky to record. I started recording on my phone, put it in my pocket and then hung it down when I got up to speed.

Regarding the tensioner, if I remember correctly- there was some slight movement if you were to turn the cams in either direction. I seem to recall the tensioner taking up the slack when turning the cams the correct way.

The bike has 53,000 kms and the for the first 45,000 or so it may have been somewhat neglected. The last owner seemed to be on top of things and did a number of maintenance tasks during his short time of owning it.

I was able to slightly recreate the sound on the center stand , in 1st gear with the brake applied. Now for some confusion- I just had it out and I was going up a slight hill. It did its noise at 3500. I pulled the clutch and held the revs at 3500 and the noise continued to a lesser degree.
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Offline Laitch

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Re: K75 Engine noise
« Reply #16 on: April 10, 2021, 11:39:49 PM »
When I check valve clearance, all rotation of the camshaft seems direct—no slack or hesitation. Because you can reproduce the sound when the moto is on the center stand, you might be able to rig the first gear-and-brake technique in a way that will allow you to use a mechanic's stethoscope—or a screwdriver tip against the timing chain cover with its handle to your ear—to determine if the source of the noise is within there. At least the stretching to achieve it will be good for your ligaments.  :laughing4-giggles:

If that won't pinpoint the source, you might need to fall back to using my favorite method—ear plug wearing, until the sound gets loud enough to track or goes away. How's the oil level?
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  • Along the Ridley in Vermont.
  • 1995 K75 89,000 miles

Offline bgcameron

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Re: K75 Engine noise
« Reply #17 on: April 11, 2021, 12:42:15 AM »
Oil level is good. I may just pull that front cover off to inspect the timing chain.

Is it possible that it's pinging? I'm doubtful because of the cool temperatures and light engine load, but at this point I am open to the possibility!
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Offline daveson

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Re: K75 Engine noise
« Reply #18 on: April 11, 2021, 12:52:49 AM »
Yep it's well time to remove the front cover.

"it seems louder on the left side"

That reminds me a bit of the clicking sound when a spark jumps on the outside, although it doesn't seem to effect the revs. Maybe remove the spark plug cover and look for any sparks, especially if it's night time.
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  • Victoria, Australia
  • Current;'85 K100RT~100,000km; four other bricks. Past; 1500 Vulcan, V Star 650, KLX 250(dirt bike) TT250(dirt bike)

Offline Laitch

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Re: K75 Engine noise
« Reply #19 on: April 11, 2021, 09:14:31 AM »
Quote from: bgcameron on April 11, 2021, 12:42:15 AM
Is it possible that it's pinging?
That's why trying to listen to action within the case was recommend, before removing the cover.  :thisplacewhack
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  • Along the Ridley in Vermont.
  • 1995 K75 89,000 miles

Offline The Mighty Gryphon

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Re: K75 Engine noise
« Reply #20 on: April 11, 2021, 12:49:35 PM »
Doesn't sound like pinging to me.  Pinging only happens when opening the throttle to accelerate under heavy load at lower rpm, and goes away as soon as the throttle is backed off, not at a steady speed.  It's been a long time since I've heard an engine ping, and never on a brick, but my recollection is that it is more of a crackling sound than the clack you are hearing.
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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 bgcameron

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Re: K75 Engine noise
« Reply #21 on: April 11, 2021, 07:25:32 PM »
Thanks guys. I figured I would rule out the monkey nuts, even though they are an unlikely cause. It's an easy enough job to check them so why not? They are starting to deteriorate/crack so they are worth replacing.

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  • Vancouver Island
  • 1990 K75S

Offline daveson

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Re: K75 Engine noise
« Reply #22 on: April 11, 2021, 08:18:33 PM »
Anyway have you ever had the rocker cover off? There's spose to be a spring pressing against it to provide a path for earth.
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  • Victoria, Australia
  • Current;'85 K100RT~100,000km; four other bricks. Past; 1500 Vulcan, V Star 650, KLX 250(dirt bike) TT250(dirt bike)

Offline bgcameron

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Re: K75 Engine noise
« Reply #23 on: April 11, 2021, 08:24:27 PM »
Quote from: daveson on April 11, 2021, 08:18:33 PM
Anyway have you ever had the rocker cover off? There's spose to be a spring pressing against it to provide a path for earth.
Yes, it is in place.
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  • Vancouver Island
  • 1990 K75S

Offline daveson

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Re: K75 Engine noise
« Reply #24 on: April 11, 2021, 08:44:30 PM »
I spose you didn't find any stray sparks from the leads behind the plug cover or coil cover in the dark?
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  • Victoria, Australia
  • Current;'85 K100RT~100,000km; four other bricks. Past; 1500 Vulcan, V Star 650, KLX 250(dirt bike) TT250(dirt bike)
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