Knocking in the primary case

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Nortorious

Nortorious

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I noticed a knocking noise in my primary case today as I was intending to tune my carbs. When I got the bike recently the primary case was overfilled with oil, so I took off the cover, cleaned it out, put on a new seal, replaced the cover and filled it with automatic transmission fluid up to the level hole.

So now I hear a knock. I can't say if it was there before my work since the bike is so new to me.

Some pictures are attached of when I had the case apart a few weeks ago in case that holds any clues.

Any recommendations on what to check? I'm going to take it apart (again) next chance I get to look it over. It seems like this could be serious and I don't want to miss an opportunity to avoid disaster.

Here is a link to a video in case you can hear it. It's difficult to hear on a video but it's there.. https://photos.app.goo.gl/7ovX8oLWDtoUC3ob9

PXL_20210515_213146254.jpg

PXL_20210515_213149435.jpg


PXL_20210515_213205886.jpg


Thanks for any advice!
 
Last edited:
your primary chain looks a little loose. Sometimes it takes 3 or 4 times to get it right. When ever you adjust it take it for a short test ride for a few blocks and then check chain tension again. It could very well go either way. If all is well check it again after a short ride.
 
When does it happen? With clutch in / out? When accelerating / decelerating? Etc?

When you’ve got it down like that, check that the centre stud is spaced off correctly and its not being pulled in when tightened.
 
Stator nut has come loose, main / gearbox bearing on way out. . . . . . .
Try holding a long sctewdriver with the tip on the chaincase and end of handle to your ear next time engine is running to determine if louder noise is coming from front or rear.
 
Automatic transmission fluid in the primary? Isn’t that a bit thin. What do you guys run in there anyway!
 
Not "very" likely, but POSSIBLE that the alternator rotor is loose on it's hub...

 
I agree with some others that it looks like your chain is loose. Even a belt can slap the primary case if it's too loose:



Have a look inside for witness marks on the bottom of the primary. If your primary can be made as clean as your first photo you can run the engine at idle with the outer cover removed for diagnostic purposes. Any oil on the chain however will fling everywhere.
 
seattle##gs said:
your primary chain looks a little loose. Sometimes it takes 3 or 4 times to get it right. When ever you adjust it take it for a short test ride for a few blocks and then check chain tension again. It could very well go either way. If all is well check it again after a short ride.
Click to expand...
Thanks! I was looking at that chain and it looked ok, but watching the video posted by @maylar it seems like even a little slack can cause that noise.

Great suggestions here! I'll report back what I find for posterity.
 
Nortorious said:
Thanks! I was looking at that chain and it looked ok, but watching the video posted by @maylar it seems like even a little slack can cause that noise.

Great suggestions here! I'll report back what I find for posterity.
Click to expand...
I would remove the rotor from the engine while you are about it and try and move the centre collar, it should be solid.
A Broken clutch plate can do all kinds of mysterious knocking, so, it's worth a strip for a look- see.
 
gortnipper said:
your primary chain is loose.

Check it at half a dozen places around its circumference.

Section C41
Click to expand...
I confirmed the chain is loose and out of spec. Then I got a bit mystified on how to add tension.

So I busted out my 3 manuals and I'll be damned if I can't find the primary chain adjustment process. I looked in the Clymer BSA Twin/Norton Commandos/Triumph book, the Haynes workshop manual, and the Chris Rookie How to Restore a commando book. They're all great for assembly & disassembly inatructions but not chain tension.

I finally figured out the adjustment bolt on the opposite side of the chain case and it appears I need to pull the whole gearbox back towards the rear of the bike to create more tension. Is this right? Does anyone recall a section of the manual with more guidance,.or have any tips on how to do this process well? Thanks!
 
Nortorious said:
I confirmed the chain is loose and out of spec. Then I got a bit mystified on how to add tension.

So I busted out my 3 manuals and I'll be damned if I can't find the primary chain adjustment process. I looked in the Clymer BSA Twin/Norton Commandos/Triumph book, the Haynes workshop manual, and the Chris Rookie How to Restore a commando book. They're all great for assembly & disassembly inatructions but not chain tension.

I finally figured out the adjustment bolt on the opposite side of the chain case and it appears I need to pull the whole gearbox back towards the rear of the bike to create more tension. Is this right? Does anyone recall a section of the manual with more guidance,.or have any tips on how to do this process well? Thanks!
Click to expand...
Section C41


Note this covers both 750/850 models.
 
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