Engine Knock Under Load

Thanks for that. That was an issue on many of the 81-84 models.

I got a stethoscope and determined it was on the left side so I pulled it apart again and everything was in spec and I still have the noise. I have an idea of what it might be after talking with my friend Bob that built the motor over 10 years ago.

Befriend someone with a Dyno.

--Bill

Good idea Bill. I have removed the sidecar which would make that a lot easier and I do have a friend with a dyno.

Fill us in. What did you figure out?..

JH

Glad I found this thread, sort of. My 77 r100 is doing the same exact thing after a high rev pull through a tunnel. Lots of good insight here, even if I do hope that it isn't a bearing, I have a funny feeling it is...

Problem solved. It seem to be a combination of things. Once I got a stethoscope I could here a noise in the carburetor like the slide was rattling. I replaced the carburetors with another set of 40mm Bings and the noise mostly went away. Secondly I rejetted the carbs to a European R100GS spec, retarded the timing and now I have no strange knocks at all.

Actually your dipstick rattles against the inside of the case. I think you'll need the scope to hear it though.

Spending some time with the scope listing to this and that (valves, timing chain, transmission, rear drive, instruments, etc.) can be very useful. You gt a feel for what it all sounds like when it's running well. Then go around at the same spots come tune-up day and give a listen again and see what has changed and might warrant further attention. I mention 'tune up day' simply because you are getting greasy and irate anyway.

[Did I propose you use a stethoscope on the problem back on post #3 about 2 months ago???]

My 40mm rh bing did the same thing a couple of years ago but I could tell straight away where the noise was coming from.
A few drops of oil on the slide stopped the noise. It's never been back.

Good to know. Thx

Chris,,never saw if this was a new build or if you had some miles on the engine?

Greg this was a motor that Bob G built many years ago and has not had the best life since he sold the sidecar it was in.

So it was pinging after all? A rattling slide inside the carb could not produce a mechanical sound like the knocking under load you describe. Since you changed 3 parameter (different carbs, rejet, retard) at the same time, you still don't know what your root cause was exactly. That wouldn't satisfy my curiousity. How do you know it's not coming back?

A rattling slide can make noise under load. I got a buddy with a BSA chopper that never had a filter on the carb since it was built in 71. That slide is so loose you can push it from side to side and front and back, and it makes hella noise throughout the range.

I woudn't have thought that, given the size of the "resonating" body (aka carb body). I assumed a knock being lower frequency emitting from a larger body (e.g. engine block). Glad you got it finally sorted.

That part of the problem; the word "knock".

One mans knock is another mans rattle is another man buzz is another mans ping, etc.