Primary rumbling

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Scout63

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I’m getting a significant rumbling in my primary. 72 Interstate with factory primary chain. It starts around 3,000 rpm and gets worse as rpms rise. I’m going to take off the primary cover this weekend and check everything out. Clutch works fine and the bike starts and runs well. Any thoughts will be appreciated.
 
See how close the header pipe is down near the footrest area. Try it off and on Center stand. Mine was touching until I repositioned with loosening exhaust rose and silencer clamp.
 
Clutch bearing would only rumble when lifted. See if engine sprocket can be lifted a few thou(mains) or could be too much beer (gives me rumbles!)
 
If it the origin factor chain then it could be well worn and need replacing but open the case up and do maintenance on everything in there, it all part of general maintenance on our bikes, pull your clutch apart and give everything a good clean and inspection and replace anything that needs to be replaced, make sure nothing is touching the case from the outside and make sure everything is adjusted right.

Ashley
 
Heard a bit of rumbling when the drive side bearing went. The inner race looked like the surface of the moon.
 
I’m going to take it all apart this weekend. It started as a slight grind at about 3200-3500 then disappearing about 3800. Now it starts about 2200 and just gets worse as rpm increases. I can feel the vibrations when I put my hand on the primary cover. Crank bearings are new and the clutch operates as it should. Drive chain is new. I am hoping it’s just the alternator but. Thanks for the help.
 
Everything inside the primary case checked out fine. Gave me a chance to run the primary cover over the buffing wheel. I adjusted the ISO’s, then went for a ride. Still very bad. Then I noticed that the left muffler mount is touching the swingarm.

Then this morning I thinned the nut and mount bolt so that it wasn’t touching. Didn’t help.

It feels as if the rumbling is directly under the primary cover where the clutch is. I’ll dismantle again and this time remove the clutch and disassemble.
 
The circlip behind the clutch basket is always a consideration for problems in the primary case. If it wears on one side and the basket is tilted, then the basket could wobble. Usually there are witness marks on the inner clutch cover if there's an issue with that circlip. It's common for those circlips to eventually fail. Mine did...
 
One of the great things about a belt drive is that you can run the engine with the primary cover off and not have to contend with oil slinging everywhere. I suppose it's possible with a chain drive too if you thoroughly wash the oil off everything first. Just for a few minutes mind you, for diagnostic purposes.
 
Did you check the clutch centre nut?

Another source of rumble from that area can be the swinging arm pivot ends fouling on the inside face of the inner chaincase.
 
Thanks for three sensible suggestions. When I rebuilt the bike I did not replace the clutch bearing or circlips. I’ve ordered replacements. I’ll check swingarm clearance as well. I lent out my clutch and crank sprocket puller so everything is on hold for a few days. Waiting for my Guzzi heads and Matchless magneto to come back. Now I understand why garages have multiple lifts. Ben
 
Scout63 said:
Thanks for three sensible suggestions. When I rebuilt the bike I did not replace the clutch bearing or circlips. I’ve ordered replacements. I’ll check swingarm clearance as well. I lent out my clutch and crank sprocket puller so everything is on hold for a few days. Waiting for my Guzzi heads and Matchless magneto to come back. Now I understand why garages have multiple lifts. Ben
Click to expand...
Earlier you mentioned everything was fine (inside the primary case), but I kept thinking lazyeye had it right on the clutch bearing. I'll bet THAT cures it!
 
grandpaul said:
Earlier you mentioned everything was fine (inside the primary case), but I kept thinking lazyeye had it right on the clutch bearing. I'll bet THAT cures it!
Click to expand...

But the clutch bearing only comes into play when the clutch is disengaged (as Norton Bob already said)...
 
The last time I had a bike in my shop for a noisy clutch bearing I was able to move the crank enough to see that the main bearing was shot. It too was a '72 which puts it in Combat territory.
 
I should have mentioned before -

Extract your alternator rotor, place it in a vice with a thick washer on either side of the hub, and tighten it in place FIRMLY.

Take a strap wrench, or large-jawed (water pump) pliers and grasp the outer circumference of the rotor; attempt to turn it in both directions, on the hub.

My guess is, you might find it to be loose.

DO NOT RE-INSTALL! It is a time bomb waiting to ruin your day, week, month, or even YEAR if it takes out the crank and./or cases when it fails. It COULD (possibly) take YOU down with it, which could be beyond catastrophic, depending on your speed when it fails.

This malady is NOT readily apparent on a cursory inspection of the bare parts!
 
grandpaul said:
... your alternator rotor...My guess is, you might find it to be loose...DO NOT RE-INSTALL! This malady is NOT readily apparent on a cursory inspection of the bare parts!
Click to expand...
This advice goes for ANYONE who has their primary case open, and especially those who have removed your alternator for WHATEVER reason.

CHEAP INSURANCE!
 
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