Heavy Vibration Issue

So here goes, I have just fixed an RGM belt primary to my ‘74 850, yesterday I took it for a ride to test the belt tension and confirm everything was ok, I had previously run the bike with the primary cover off to check alignment and whilst out yesterday day I stopped a couple of times to check the belt tension when the bike was at fully operating temperature, all was well there is no tension on the belt when it’s hot and it still has over 1/2" of free play.

Now to my problem, I had covered around 150 miles in Wales on a mixture of roads from single trackers, hilly minor roads and a few main roads all with the aim of making the bike work to generate heat and test the belt tension. I stopped for a late breakfast in Rhayader, vey goos it was too, then fired the bike up for the 110 mile run home feeling very pleased with myself that all was well. Anyway all was not well, under moderate load I was getting a really heavy vibration through the foot pegs this was present in all gears so I stopped at Crossgates, whipped the primary cover off and had a look assuming it must be to do with the recent work. What I found was that the belt was still at the correct tension, there was no evidence of the belt tracking either in or out and no marks on the outer edge of the belt (I’ve stripped it this morning and can now verify that there are no marks on the inner edge of the belt either.) My assumption while sat at the side of the road was that either the clutch centre nut had come loose or the retaining circling had failed or deflected but obviously couldn’t get to this as I didn’t have my diaphragm spring tool with me. I came to this conclusion as I could feel a very small amount of play in the clutch basket. I called aa pal who picked my trailer up and made the 200+ mile round trip to collect me. Thanks Rog, you are a star.

We move on to this morning and the strip down. I took the primary cover off and as with yesterday all was well, the tab washer was still in place and the play I could feel yesterday has all but disappeared probably due to the change in temperature. I had torqued the centre nut to 50 ft lbs, less that the 70 ft lbs in the workshop manual which is generally considered to be too much. I undid the centre nut which was snug but certainly nowhere near the 50 ft lbs I’d tightened it to, I removed the clutch basket and centre checked the location of the circlips (bearing and clutch centre) and checked the bearing which is perfect. The clutch retaining circling on the main shaft looks ok but obviously will be replaced when I reassemble. In addition to this I have checked:

1. Checked gearbox mountings top and bottom - all good there
2. Checked for play in the main shaft - all good there (the gearbox was rebuilt about 5,000 miles ago by Norman White before I acquired the bike)
3. Gearbox oil level - all good
4. Belt alignment - all good there as also indicated by the belt
5. Wheel bearings - all good there
6. Engine mounts including those to the gearbox plates
7. The spacer behind the clutch that encapsulates the main shaft circlip was where it should be

One thing that I noticed today was that the drive chain was a bit loose, I has to replace this when I fitted the belt drive as the existing chain was too short, the slack is just the chain bedding in but I’m wondering if a bit of chain slap might have created the heavy footpeg vibrations? (I am not going to adjust the chain until I have reassembled the primary and tested it otherwise I’m not going to know where the issue was assuming it disappears).

What I intend to do is reassemble the clutch with a new circlip, torque if up, leave it for 24 hours and re-torque it, I’m not sure if this will achieve any thing but it will allow any deflection in the circlip to be identified (if there is any movement to achieve the same torque), test ride and see if the vibes have gone, if not I’ll adjust the chain and test ride again.

So my questions are;

Do yo think I’m on the right track?
Is there anything else I need to check?
Is 50 ft lbs too little or too much torque on the clutch centre nut?
Any other ideas?

I’ll order some circlips today and they’ll be with me on Tuesday so I’ll be back into it on Tuesday evening.

Edit - Just to add after posting I had another thought and have just checked the drive chain for tight spots or bad links and it’s fine.

Dave

50 ft lbs is good but needs loctite as safety factor.

Other things to look out for after removing and then replacing all the items needed for belt install is clearances from primary case to frame as they are small to begin with and the work may have moved something enough so there is contact when the engine is moving in the iso's the most ie low revs.

kommando said:

50 ft lbs is good but needs loctite as safety factor.

Other things to look out for after removing and then replacing all the items needed for belt install is clearances from primary case to frame as they are small to begin with and the work may have moved something enough so there is contact when the engine is moving in the iso's the most ie low revs.

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Thank you, I’ll check the clearances for any witness marks.

Dave

This is a long shot but perhaps the cable adjustment on your carbs went catawampus when you parked it for breakfast. Worth a check.

Best of luck. You are not alone. I have a RGM belt clutch on a pre-Commando and it does the same thing.

I can torque my center hub nut to 70ft lbs, but stop at 65ft lbs. Pre-Commando mainshafts don't use the little mainshaft circlip that can't take the higher torque. It's not a Commando example, but my point is more torque than 50ft lbs doesn't make any difference with that vibration.

I run my drive chain at the max end of a loose drive chain. Have done so since discovering decades ago the standard chains last a lot longer run on the loose end of the typical spec. I'm very confident that the drive chain has nothing to do with that particular type of vibration.

I often think the AT10 synchronous polyurethane belt could probably be run tighter, more along the line of 3/8" free play fully heated up drum, whatever free play really is with a belt. When I first put the RGM belt clutch on, I ran the belt at 1" total up and down movement cold, and it was smooth running, but I only ran around the block that way thinking I was in heaven. Ever since using the closer to correct 1/2" of free play with the drum heated up I get vibration from the clutch. Feels like those big AT10 widely spaced teeth on the belt are going in and out of sync with the drum pulley. I get no belt slip, but still maybe I could run the belt tighter. I've been hesitant to tighten it up, but it is probably next on the list of things to try.

Please report back if you figure it out.

I don't think this is of relevance but with a standard set up I have a smooth 80kmh (50mph) in fourth but ride at 100kmh (62mph) I also feel vibes in the footrests which I have put down to the secondary drive chain. It is not drastic but it makes itself known. I have considered renewing my chain, it is the last one on the list now.

John

Perhaps a stand is flopping about? Have you checked for side stand bumper condition/presence and centerstand spring connection hole erosion?

I have an rgm belt drive on the 920. It's a smooth running bike.

Glen

Maybe your new belt drive clutch basket's splines are not right. I recall someone had bought a clutchbasket from waldridge and the splines didn't fit well with the clutch plate spines and caused problems. I only vaguely recall that the issue was the "new" part. It only makes sense that because you recently fitted a belt drive, the old triplex clutch basket was replaced by a belt drive toothed basket. I would say that you should also check the hub spines to see if they are notched from previous wear and the plates are hanging up on the notches. Clutch plates hanging up intermittently can cause a lot of odd issues. Good luck Dave, just another thing to add to your list to check.

I've had the circlip pop out on my mainshaft and the witness marks inside the inner primary case and between the swingarm and back of the inner primary case are the signs of that issue...

I just went for a little 20 mile last shake down ride before the sun disappears for 3 months. The RGM clutch did feel smoother and a little quieter once warmed up, so the belt probably does need a slightly tighter adjustment.

The vibration I feel on a bike without isoelastics is not heavy, it is merely noticeable. The single row chain clutch ran smoother, but it never worked as well as the RGM belt clutch does.

seattle##gs said:

This is a long shot but perhaps the cable adjustment on your carbs went catawampus when you parked it for breakfast. Worth a check.

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I don’t thing that’s the issue, but I’ll check.

Dave

Tornado said:

Perhaps a stand is flopping about? Have you checked for side stand bumper condition/presence and centerstand spring connection hole erosion?

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No not the stands, spring is good on the centre stand and the stop on the side stand is still there so no change before and after.

Dave

o0norton0o said:

Maybe your new belt drive clutch basket's splines are not right. I recall someone had bought a clutchbasket from waldridge and the splines didn't fit well with the clutch plate spines and caused problems. I only vaguely recall that the issue was the "new" part. It only makes sense that because you recently fitted a belt drive, the old triplex clutch basket was replaced by a belt drive toothed basket. I would say that you should also check the hub spines to see if they are notched from previous wear and the plates are hanging up on the notches. Clutch plates hanging up intermittently can cause a lot of odd issues. Good luck Dave, just another thing to add to your list to check.

I've had the circlip pop out on my mainshaft and the witness marks inside the inner primary case and between the swingarm and back of the inner primary case are the signs of that issue...

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I don’t think that’s the case mine are a good fit and the fit is the same now as before the issue developed.

Dave

Schwany said:

I just went for a little 20 mile last shake down ride before the sun disappears for 3 months. The RGM clutch did feel smoother and a little quieter once warmed up, so the belt probably does need a slightly tighter adjustment.

The vibration I feel on a bike without isoelastics is not heavy, it is merely noticeable. The single row chain clutch ran smoother, but it never worked as well as the RGM belt clutch does.

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It’s not the ‘normal’ vibes it really is heavy and definitely a problem.

Dave

worntorn said:

I have an rgm belt drive on the 920. It's a smooth running bike.

Glen

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yes mine was before breakfast…

Dave

A too loose rear chain will cause vibrations in the foot pegs if its too loose, I be adjusting it then take it for a ride see, a belt should run smoother but I ran a RGM belt drive for a few years then had troubles with it trying to run off so have gone back to a primary chain and really not much difference with running smoother well not noticeable to me.

Ŷ

ashman said:

A too loose rear chain will cause vibrations in the foot pegs if its too loose, I be adjusting it then take it for a ride see, a belt should run smoother but I ran a RGM belt drive for a few years then had troubles with it trying to run off so have gone back to a primary chain and really not much difference with running smoother well not noticeable to me.

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I suspect it might turn out to be the chain but before I adjust it I’m going to build the clutch back up and ride it, if it goes away then it’s not the chain, if it doesn’t then I’ll adjust the chain and try that. I only want to do one thing at a time so I can properly identify where the harshness is coming from..

Dave

Like Ash, I feel the vibration (as well as snatch) from a loose chain on the Commando.

concours said:

Like Ash, I feel the vibration (as well as snatch) from a loose chain on the Commando.

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And now I’ve had it apart I tend to agree but will find out when I put the clutch back together which should be tomorrow evening if the new circlip arrives on time.

Dave

Dellis said:

Ŷ

I suspect it might turn out to be the chain but before I adjust it I’m going to build the clutch back up and ride it, if it goes away then it’s not the chain, if it doesn’t then I’ll adjust the chain and try that. I only want to do one thing at a time so I can properly identify where the harshness is coming from..

Dave

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Dave
Not wishing to teach egg sucking but....
Be careful the loose rear chain isn't because it is pulling the gearbox rearward - over tensioning your belt.
My first 9000 miles with the belt primary(cNw) were characterised by that phenomenon.
I checked belt tension every 500 miles. Seems to have settled down now.
I have put it down to a "slippery" newly powdercoated cradle.
Cheers - and good luck!

The recovery was a bit of a faff. I stopped at midday to investigate the issue and as I said above I was concerned that I could feel some play, albeit very slight, in the clutch drum so I called the RAC to arrange recovery, this was about 12:45. While I was waiting I called a pal of mine, Rog, who offered to come and get me, a round trip of 200 miles and I said don’t worry I’ve called the RAC… The RAC patrol arrived at 16:00 and called for a recovery vehicle and at 17:00 I was called and told recovery would be after midnight, not ideal so I called Rog back, who I really didn’t want to inconvenience when we were chatting earlier but he ended up coming to get me and I was home with the bike at 23:00. The RAC cover is included in my bike insurance. Not great service but at least I was at a cafe/garage. If it ends up being chain slack I’ll be eating a bit of humble pie with Rog. He’s coming round next Saturday night with his wife and I’ll be cooking for them as a thank you with a few beers to wash things down.

Dave