K75 Engine noise

[bgcameron]

How's about the noise remaining or disappearing, gradually or suddenly, at some point after your noise at 3,500rpm?

I ask because if it disappears, that might be at a point where the oil pressure finally reaches a high enough point for the tensioner to work properly.

Watchyagot.

The noise seems more sudden. Here's another sound clip. The noise starts kicking in at about 15 seconds. Towards the end I pulled the clutch lever and held revs.

[Laitch]

Try this on for size, bg. Bon voyage!

[bgcameron]

Thanks Laitch. I had a look at that article prior to checking the tensioner and made a point of checking that little piece for wear.

[daveson]

Dunnowaddamake outtada last video.

If it's broke, replace it, if your lucky the noise will be gone.

Its turning into a bit of a Saga.

That's not a saga.

I've seen a thread that was longer than War and Peace, that's right and I'll say it again too, it was longer than War and Peace. There was a noise from the water pump and cylinder four so the engine was opened and the output shaft came out. All sorts of measurements were made, and heaps of parts replaced with new. After it was all stitched up, the noise remained the same.

That's a saga.

[bgcameron]

Oh man, that sucks. I hate noises but I have boundaries! At least with this job I am doing a full spline service. I've been finding other things here and there while I'm at it and learning lots about the bike.

[daveson]

Would you say the sound changes or disappears over a  certain rpm, if so when?

[Laitch]

Thanks Laitch.

[bgcameron]

Would you say the sound changes or disappears over a  certain rpm, if so when?

It seems to disappear after 4000 rpm.

[daveson]

Good link Laitch to Colin Carpenter, so even if it ain't broke, might need replacing due to wear.

[Laitch]

. . .  even if it ain't broke, might need replacing due to wear.

[The Mighty Gryphon]

https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=bmw+k75+engine&_sacat=0

[Laitch]

 

[daveson]

If I had these symptoms on my bike and that part of the chain guide was broken or worn, I would just replace the chain guide. A partial failure there could explain why the noise disappears at about 4,000 rpm.

Why the tin hat? The reference from Colin Carpenter also says it might need replacing if worn.

[Laitch]

If I had these symptoms on my bike and that part of the chain guide was broken or worn, I would just replace the chain guide.

bg has asserted that everything in that timing chain case has been inspected right down to the molecular level by bg's own eyes, and everything is OK. 

[bgcameron]

If the noise persists after I put the drivetrain back together then I might just check that tensioner again for peace of mind. If that piece is cracked then I'll eat my shorts.

[daveson]

I was thinking about people reading the thread, I didn't actually say it needs replacing.

True, I didn't notice wear on mine until after I read the link, and If that piece is broken it may, or may not, have anything to do with the noise, but wants to be replaced anyway.

Bg you won't have to eat your shorts either way. At this point there's still a lot of options, for example it's not surprising it's not worn, it's low mileage, but it's thirty years old. The bonding may have partially failed after you looked at it, while installing, say while the guide rail was clipped to its steel backing, or clipping the tensioner on, and cracked later.

When I zoom in I see a black line between two pieces, with the video I see hinged movement on the right side.

Bg, look at the video on full screen and ask yourself this question "does it look like one piece solidly bonded to its backing?" Show this video to anyone and ask them if it looks like mine (please don't ask them if the timing marks align)

To me it definitely doesn't look like mine. If I'm wrong I won't have to apologise because I already did, so there.

I'm hoping I'm right because that's an easy fix.

[Laitch]

If I'm wrong I won't have to apologise because I already did, so there.

Maybe you should step up like bg and eat your shorts, too. It could be a Zoom event, and posting a link to it here would relieve the tedium. bg's getting adept at video. 

[daveson]

I've already said, on this thread, some of my posts could be crap.

This chip is on the same side as your video, maybe it's just a chip we see.

[daveson]

Hmm I'm not so sure now after looking at it on a computer screen.

[daveson]

Hey Branden, here is something to consider while the gear box is off. This is my guess, hopefully my last guess.

It's the circlip.

It could be fatigued or partially unseated from its groove, weakening its effectiveness. Your symptoms are a snug fit for this, I think.

Here's the good bit, since your there anyway, with the clutch basket removed you have a small window of view to see if the circlip is fully engaged in its groove, all the way around.

Here's an even better bit, with the seal removed you have access to the circlip, without having to split the engine.

That circlip has been under constant compression for thirty years, it could be fatigued.

The K75 does not have a diaphragm spring, like the K100 does. The side load from the gears, with their helical cut teeth, would put the circlip under substantial compression in emergency braking situations. The K100 has a diaphragm spring to bear that load, which would be stronger. With the K75 that compression could partially dislodge the circlip. I would guess though, it would be more likely to be fatigued after years of accelerating and braking forces.

I would take a photo of the circlip, then check that it makes contact with the bearing and see if it can be pressed further into its groove. I feel that it will make contact but might not at 3,500rpm.

If your able to speak with the previous owners, it would be worth asking about its service history, and maybe if there were any occasions of emergency braking.

If I was that far in there anyway, I would replace the circlip.

It's not the only possible cause of output shaft endfloat, but I think it's an easy access option.

[alabrew]

I've had a Brick since 1990. They rattle and make all kinds of noises.They perform wonderfully. The best accessory is noise canceling headphones.

[bgcameron]

Hey Branden, here is something to consider while the gear box is off. This is my guess, hopefully my last guess.

It's the circlip.

It could be fatigued or partially unseated from its groove, weakening its effectiveness. Your symptoms are a snug fit for this, I think.

Here's the good bit, since your there anyway, with the clutch basket removed you have a small window of view to see if the circlip is fully engaged in its groove, all the way around.

Here's an even better bit, with the seal removed you have access to the circlip, without having to split the engine.

That circlip has been under constant compression for thirty years, it could be fatigued.

The K75 does not have a diaphragm spring, like the K100 does. The side load from the gears, with their helical cut teeth, would put the circlip under substantial compression in emergency braking situations. The K100 has a diaphragm spring to bear that load, which would be stronger. With the K75 that compression could partially dislodge the circlip. I would guess though, it would be more likely to be fatigued after years of accelerating and braking forces.

I would take a photo of the circlip, then check that it makes contact with the bearing and see if it can be pressed further into its groove. I feel that it will make contact but might not at 3,500rpm.

If your able to speak with the previous owners, it would be worth asking about its service history, and maybe if there were any occasions of emergency braking.

If I was that far in there anyway, I would replace the circlip.

It's not the only possible cause of output shaft endfloat, but I think it's an easy access option.

Doesn't the K75 have flat drive/driven gears? Without removing the seal, I was able to look around the edge of the circlip. I used an angled pick to reach the holes in the circlip and verify that they are snug.

[daveson]

Your right, I just googled a photo of it. I never noticed that difference between the k100 and k75, but I've only looked close at a k100. I spose the k75 has straight cut gears because the diaphragm spring was deleted.

So ignore the side load comments. Still, let's say the circlip is fatigued from 30 years of compression, like I said I'll guess it's still snug. A weak spring could be OK while the engine is stopped or at idle, but could fail at 3,500rpm.

I mention this because you're only a seal away from access to the circlip.

I'm 99% sure this comment doesn't apply to you, but to anyone who has a brick with a rattle, an unknown service history and has removed the clutch basket, you should check that the circlip has been installed with the concave side facing the bearing. It's only the slightest bit concave and could be easily missed.
 

[bgcameron]

sidenote: as I am getting ready to put this thing back together I will need some spline lube. What is recommended and what should I avoid? Is Castrol Molub-Alloy Paste TA good?

[Laitch]

Molub TA will do.
Here's an acceptable way to apply it.