K75 Engine noise

[daveson]

Righto here I go again with another long shot, but since the BMW expert mentioned the starter clutch, and I'm hoping the gear box and starter are still off, try this. Put your finger through the hole for the starter, wiggle the idler gear, see if you can move it forward and back with its shaft, you shouldn't be able to, unless the spring is broken.

It's only a 60 second check.

[The Mighty Gryphon]

As long as we're getting really serious about this, maybe you should tear down the engine and remove the output shaft and idler gear.  You can then take them to a machine shop to have the dogs welded and given a better fit in the slots so they won't bang around.

While it's apart, pull the pistons and rods to make sure you aren't getting any piston slap and that the big end bearings are in spec.  I'm guessing that you will find all is well, but it might give you some peace of mind. 

[daveson]

I've been wondering about this topic when it comes up, dunno the answer. If it was the tabs, why don't all k75's do it? And why are the machine marks still on it? 100 ft/lb is more than enough I'm thinking, and it's more than the k100, so that's telling. I think I found from a previous thread, that the tabs are only there so that the shaft can only be installed one way, so a precision fit isn't required.

It would be interesting if someone gets to the bottom of it.

The biggest bonus for me with this thread so far, this is the first time I actually heard it (the later video, post 61)

[Laitch]

Put your finger through the hole for the starter, wiggle the idler gear, see if you can move it forward and back with its shaft, you shouldn't be able to, unless the spring is broken.

If the gear could be wiggled on the shaft, wouldn't that be accompanied by audible Clicks?

[daveson]

Yeah it was, it was louder than I thought, I spose it's about time I learned how to post videos.

You know what, in that post the sensible part of my brain defeated the biffo part of my brain, which wanted to say "if there's any axial movement there whatsoever, it's because the spring has been under constant compression for thirty years"

[Laitch]

. . .it was louder than I thought, I spose it's about time I learned how to post videos.

Louder than you thought, or louder than you expected? Did you check it for rattle after you replaced the spring?

Go to YouTube. Instructions for posting videos are there, then you post the link here.

[daveson]

It's from a spare engine I have that's been dismantled for years. I checked the gear on one of my bricks and there was no fore, aft movement. I mentioned the wiggle because if there's a bit of jamming going on you could be tricked into believing there's no movement, when there's actually a lot,  about 5mm.

I meant it was a lot louder than I expected,more than a quack, probably deserves the honour of a clatter, dare I say a knock.

I wonder if the noise would have been louder if the microphone was taped to the starter motor?  It's on the left hand side, that's the side that was originally thought to be louder.

[Laitch]

I meant it was a lot louder than I expected,more than a quack . . . 

Was that more than the volume of a startled quack, a courtship quack, a maternal quack, a quack in flight or a quack on a still pond in early morning?

[daveson]

It was desperately loud, like the sound of an African duck attempting to cross the Mediterranean with a coconut tied to its testicles.

[bgcameron]

It was desperately loud, like the sound of an African duck attempting to cross the Mediterranean with a coconut tied to its testicles.

Who are you, who are so wise in the ways of science?

I checked that gear for movement and felt nothing...nadda.. Ni!

[daveson]

Well you have to know these things if you seek the Holy Grail.

One of the jokes lost on young ones watching it now was the intermission. Back in the days you couldn't expect people to remain seated for two hours in a cinema. I remember when the intermission sign came up, people started making their way along the aisle, suddenly the movie started again, and everyone rushed back to their seats.

It's good you have no movement there, it's not easy to replace if Faulty.

[Laitch]

. . . it's not easy to replace if Faulty.

Faulty Towers?

[daveson]

Yeah,  I was trying to be economical with my words,  since that post was way longer than it deserves to be. I almost got away with it, until you noticed that.

I've noticed that attention to detail is one of the items in your tool box. I've been thinking to myself, I should try that. As you can see from this thread, I need more practice with it.

[daveson]

Can you tell us about any non routine work done on your brick, mechanical, cosmetic, anything? Anything by previous owners?

Did your brick come with a workshop manual/s and which?

[bgcameron]

Can you tell us about any non routine work done on your brick, mechanical, cosmetic, anything? Anything by previous owners?

Did your brick come with a workshop manual/s and which?

The only thing I know of is the Bruno-modded rear drive. Speaking of that- in the article I linked to a few pages back, the original owner said that the U-joint mod was done.. but there is no serviceable U-joint on this driveshaft.

[daveson]

Where the frame bolts to the intermediate housing, do you have a shim between the two? I believe you should have.

[bgcameron]

Where the frame bolts to the intermediate housing, do you have a shim between the two? I believe you should have.

Yessir.

I just spoke with the original owner of the bike. He purchased it new in 1990. It sounds like most of the its mileage was done on the highway. He is going to dig up his service history on the bike and send it to me.

[daveson]

OK, it's hard to find fault with a low mileage brick that looks absabloodylutely spotless.

I'm running out of useful suggestions, in case you haven't noticed.

The original owner could be the key to this. I'd ask if he noticed this noise, if it developed gradually or suddenly, or anything about it. You might be able to link it to something in the service history.

[Laitch]

OK, it's hard to find fault with a low mileage brick that looks absabloodylutely spotless.

It didn't seem that hard for bg.   

[daveson]

Yeah I should have said it's hard to find the cause of the fault, I'll bet it didn't leave the factory like that. I have a 1991 K75 S, it doesn't have that noise. Until you get the service history, maybe try the microphone on the starter or a few places to see if you can pinpoint it better, or an Italian tune or something like that.

Where I was going with the previous posts was hoping the frame was removed for painting or something, and not installed correctly. Although that possibility is almost eliminated, it might help someone in the future reading this.

If the frame is attached using the Clymer manual as a guide, the shim location and bolt tightening sequence will be wrong, since the k75 sequence is different to the one given.

Hopefully Gryph might chime in again, at least I'd be interested to know if his noise sounds like your recording.

Gryph, help me out here. Your saying ride, free up the rings, get fuel through the injectors, shake the cobwebs out. Yep, I'm with you there, you know I'm with you there, but your well ridden brick does it too. I'm trying to get something that fits, it's like almost there, but just not there yet.

[Laitch]

. . . the original owner said that the U-joint mod was done.. but there is no serviceable U-joint on this driveshaft.

If there is no zerk, the guy's a jerk, to paraphrase Johnny Cochran.

[Laitch]

Until you get the service history, maybe try . . .  an Italian tune or something like that.

I suggest La Primavera by Vivaldi. It's the perfect time of year for that. 

[daveson]

As soon as you say La, I'm hearing La Bamba I'm off to YouTube land for a dose of it now.

[bgcameron]

UPDATE:

Bike is back together and the noise is nearly gone. Under the same riding conditions it will make the occasional "tap" sound but nothing in comparison to the clatter that was audible before. My best guess is that culprit was the nut on the balance shaft.

[Laitch]

I did the disassembly today. Nothing appears to be out of the ordinary. All the splines are well-lubed, the U-joint feels good. The clutch housing nut seems tight, and it did not move under 100 ft-lbs of torque.

My best guess is that culprit was the nut on the balance shaft.

From your post, it appears like you did nothing to the nut because the nut seemed tight. Maybe the cure was just the laying on of hands. I've seen that work miracles in venues as disparate as fundamentalist churches and South Dade honkey-tonks.