K75 – rattling noise post engine-swap

[FLATout?]

Hey Motobrick, got an issue with my K75 I’d like your input on. It’s recently undergone an engine swap performed by my local shop, RideWest BMW. The bike itself is from 1988 (only 30k miles, imported from Germany in 1990), and the swapped-in engine is from 1994 (25k on it).

The issue is a loud rattling noise that occurs when the engine is under load. Here’s a link to a couple movies where you can hear it. In the video I am holding the rear brake, and slipping the clutch in first to apply a load on the engine.

I noticed the noise almost immediately after hopping on the bike after the swap, and brought it back. Ben the shop master at RideWest rode it, listened to it, and gave it back saying that it will not cause a failure; it’s a just a result of an incorrect year engine mating to an older transmission. As such he suspected the noise was originating from the output shaft, and any more work looking for the noise would be exploratory, meaning $$$.

Other than that the bike runs phenomenally, no noticeable lack in engine response/power. My auditory intuition is screaming at me telling me it's just a loose washer somewhere I can’t find. Help me Motobrick…your my only hope.

[Laitch]

Welcome to the forum. Thanks for providing the video. Why was the original engine swapped out? How long have you ridden this bike?

My bike would sound like that if I did to it what you're doing to yours, so I don't do it. Did the other engine make that noise when treated that way? I'd be surprised if it didn't.  Give the engine revs and don't lug it. It wants to run phenomenally.

I don't know what to make of your tech's explanation if that's what he actually said—maybe compost.

This site is your only hope?  :giggles :hehehe :laughing-on-ground:

[johnny]

greetings flatout?

needs more rpms and less brake... you must live up to your name... flatout...

j o

[FLATout?]

Thanks for the warm welcome! I bought the bike in relatively rough shape about 2 years ago. It had flat spots throughout the rev range. Eventually discovered that cyl 1 had good compression, cyl 2 had 60% of cyl 1, and cyl 3 had 30% of cyl 1...and it wasn't the valves. Evidently the PO had run it a distance with a coolant leak, and warped the cylinders. The engine swap fixed the issues, but introduced an atrocious rattling sound.

I should clarify the noise. It occurs throughout the rev range whenever the engine is under load. So when you're in 2nd going up a hill, or pulling 3rd on the freeway, or really whenever you're accelerating. It's loud enough to notice even on windy days. This noise was non-existent on the old engine. The only way to get a video of it is to force a load while the bike is stationary; can't take a video while moving!

Honestly the shop spent a long time debugging the bike until they deemed an engine swap necessary. I got the vibe they wanted the bike out of their shop, so I take what they told me with a grain of salt.

Yep, finding a brick guru (or Jedi) on this forum is my only hope as of now. *puts tongue in cheek*

[Elipten]

I agree stop abusing it like that.  Give us a video under normal riding conditions and rpms. 

[Laitch]

. . . can't take a video while moving!

It's a sound. Video is overdoing it, a little.

[Laitch]

To clarify, zip tie an audio recorder to the handlebar, frame, exhaust pipe, your jacket etc. What's worked for me is changing the file name to .mpg then uploading using the Attachments and other options feature.

[Scott_]

With the swap, did they use the old intermediate housing/assy or did the replacement engine come with it.
I'm thinking noise from the intermediate gearing, backlash spring assy.

[FLATout?]

OK! Ask and ye shall receive. The bike is in the shop ironically undergoing a water pump rebuild to fix the same coolant leak that killed the previous engine, but when I get it back the first thing I'll do is set my girlfriend up on the backseat with a cell phone camera and try to capture the sound in action throughout various engine loads, and report back here. We'll see how well the camera picks it up, then depending on that I'll look into renting a decent microphone for an audio recording. I'll just throw the files into the linked OneDrive folder as I've done previously.

Scott, I'm not sure which intermediate housing/assembly was used in the swap, I'll ask today tomorrow or the next day when the current service is finished and I pick up the bike. Could you possibly help me with the best way to phase the question I should ask them?

Thanks y'all for your interests in this issue.

[TimTyler]

Engine oil level looks a little low, but not crazy low.

Have you checked the gearbox oil level?

[FLATout?]

Yep oil is fine. Recent change. In the video I'm position on my inclined driveway, off the centerstand.

[Laitch]

A well-done recording should tell the story here. Try recording solo, too, if possible.

[hartodeks]

Hey, that sound like no alternator damper. Check it