Heavy Vibration Issue

baz said:

I'm left wondering what a "urist" is exactly

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A person who installs and maintains urinals…

A thousand apologies Dellis, we’ve killed your thread here… we are having a larf tho…!

baz said:

I'm left wondering what a "urist" is exactly

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...well, "avin the piss" isn't it what you all say?

Right so this morning I was up at 6.00 got the KTM out to go to Crossgates to retrieve the gloves I left there when Rog rescued me. I had an interesting start to the day, I got the bike out, went inside for a coffee then came out for a ‘smoko’ and was met by an intruder and I asked what me was doing and he replied I’m looking for somewhere to sleep for the night, as this was 6.45 I didn’t quite believe him, buggered him off and advised the Police. Next on the list was that I got nicked for speeding, 83 mph in a 60 mph limit luckily I’d spotted him and had knocked it off…

Back to my vibes issue. When I got back from Crossgates I nipped out on the Commando and the vibes are still there, went home adjusted the chain and tried again and they’re still there. I have an idea though, I tried to tighten the clutch centre nut without the shims and the nut bottomed on the main shaft threads, it was almost nipping up the clutch centre but not quite so I reinstalled the smims and it tightened. I’m now thinking I need some additional shims but what I intend to do is matchine a new clutch spacer about 0.040"- 0.060" thicker at the recess than the standard item (will measure to ascertain the correct size) and that will ensure the nut doesn’t bottom out. I’m also going to reduce the slack in the belt as I have about 1" slack when hot (the previous measurement was an estimate at the side of the road the 1" is with the bike hot and on the bike lift). I’ll let you know how I get on.

Dave

Is the vibration changed by having a pillion?

I have fixed the vibes issue… the primary belt was too slack!

Now my theory as to how I didn’t notice it when I first rode the bike is that when I ride any bike from cold I nurse it along until it’s reached normal temperature, so I’m guessing as I’m nursing the bike along and all was getting warm the belt took on enough tension to be within tolerance so no heavy vibes. I stopped in Rhayader for about an hour and in that time the bike had cooled enough for the belt to be slack again and when I set off I’m into the day’s ride so didn’t nurse it and the vibes were apparent. Then assuming that I have a bigger problem nursed the bike to Crossgates but if at that point if I’d have opened it up the expansion would have again masked the problem. At least I know what was wrong and I have worked out why it only showed up after I’d stopped. I’ve reduced the cold free movement by about 1/2” and have ridden the bike until fully warm and I still have plenty of free play, that’s with the primary cover off so I still need to check the hot free play with the cover on but I think I have enough slack, if not it’s just a case of a little more adjustment.

I searched before I fitted the belt drive but the only reference to cold free play I could find suggested 40mm + but in my recent experience that’s too much.

Anyway all is good now.

Dave

Dellis said:

I have fixed the vibes issue… the primary belt was too slack!

Now my theory as to how I didn’t notice it when I first rode the bike is that when I ride any bike from cold I nurse it along until it’s reached normal temperature, so I’m guessing as I’m nursing the bike along and all was getting warm the belt took on enough tension to be within tolerance so no heavy vibes. I stopped in Rhayader for about an hour and in that time the bike had cooled enough for the belt to be slack again and when I set off I’m into the day’s ride so didn’t nurse it and the vibes were apparent. Then assuming that I have a bigger problem nursed the bike to Crossgates but if at that point if I’d have opened it up the expansion would have again masked the problem. At least I know what was wrong and I have worked out why it only showed up after I’d stopped. I’ve reduced the cold free movement by about 1/2” and have ridden the bike until fully warm and I still have plenty of free play, that’s with the primary cover off so I still need to check the hot free play with the cover on but I think I have enough slack, if not it’s just a case of a little more adjustment.

I searched before I fitted the belt drive but the only reference to cold free play I could find suggested 40mm + but in my recent experience that’s too much.

Anyway all is good now.

Dave

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Thats great Dave
My "method" is to nearly achieve 90 degrees twist (in the middle) with a very firm hand/fingers.
I think I got that from Bob Newby
Cheers

oldmikew said:

*Is the vibration changed by having a

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robs ss said:

Thats great Dave
My "method" is to nearly achieve 90 degrees twist (in the middle) with a very firm hand/fingers.
I think I got that from Bob Newby
Cheers

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Thanks Rob, I’m just glad I found what was wrong and understand why it manifested itself when in did so all is good.

Dave

I initially set up the RGM belt so that it could manage a full 90 of twist, same as my two bikes with Newby beltdrives.
That did not work with the RGM belt drive as it would slip on kickstarting.
I do recall a couple of early rides where there was a lot of vibration happening, in addition to some other minor start up problems. I attributed the vibration to the new isos possibly getting stuck in the alloy housings I had made. The iso rubbers were coated with a special grease before assembly, so the stuck iso idea was a bit of a longshot.
After reading of your findings Dellis, I'm wondering if the vibration I experienced was also due to the loose belt.
I had forgotten all of this until reading your post. The vibration was fairly intense and only increased with rpm, as I recall.
I was more concerned about the Kickstart slippage than the vibration.
Once the belt was tight enough to prevent slipping on kickstarting, the vibration problem went away completely, which is to say it now vibrates much like a standard Commando, virtually no vibes above 3000 rpm.
I attributed the fix to the iso rubber breaking free after some higher rpm running. That probably wasn't it, at all.
How much total movement cold slack are you running now?

Thanks
Glen

As worntorn indicates, the way to measure your belt slack is by twisting the top run, not by up and down movement like you do with a chain.

'Correct' setting is generally considered to be 90 degree twist, but some seem to be better with only 45 degrees!

Anyway, once you have a setting that works cold and hot and doesn't put too much pressure on the shafts.....it is completely repeatable. So fix it in place!

Fixing the primary adjustment is discussed in recent threads.

If it is getting too hot inside your primary, consider some ventilation, but do make sure you don't create a stone entry point.

worntorn said:

I initially set up the RGM belt so that it could manage a full 90 of twist, same as my two bikes with Newby beltdrives.
That did not work with the RGM belt drive as it would slip on kickstarting.
I do recall a couple of early rides where there was a lot of vibration happening, in addition to some other minor start up problems. I attributed the vibration to the new isos possibly getting stuck in the alloy housings I had made. The iso rubbers were coated with a special grease before assembly, so the stuck iso idea was a bit of a longshot.
After reading of your findings Dellis, I'm wondering if the vibration I experienced was also due to the loose belt.
I had forgotten all of this until reading your post. The vibration was fairly intense and only increased with rpm, as I recall.
I was more concerned about the Kickstart slippage than the vibration.
Once the belt was tight enough to prevent slipping on kickstarting, the vibration problem went away completely, which is to say it now vibrates much like a standard Commando, virtually no vibes above 3000 rpm.
I attributed the fix to the iso rubber breaking free after some higher rpm running. That probably wasn't it, at all.
How much total movement cold slack are you running now?

Thanks
Glen

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I can just twist the top run to 90 degrees with firm pressure, previously I could twist it past 90 degrees with little effort.

Dave

SteveA said:

As worntorn indicates, the way to measure your belt slack is by twisting the top run, not by up and down movement like you do with a chain.

'Correct' setting is generally considered to be 90 degree twist, but some seem to be better with only 45 degrees!

Anyway, once you have a setting that works cold and hot and doesn't put too much pressure on the shafts.....it is completely repeatable. So fix it in place!

Fixing the primary adjustment is discussed in recent threads.

If it is getting too hot inside your primary, consider some ventilation, but do make sure you don't create a stone entry point.

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I’ll give it a little time and if I’m happy I’ll fix it in place.

Dave

Thank you all for responding, it was good to have other views on what may be the cause.

Dave

Well you fixed it. In an effort to help early on I did mention the AT10 polyurethane belt RGM uses could be run tighter in post #5 on the first page of this exercise. Also mentioned the vibration issue had nothing to do with a loose rear chain. Just saying.

Twisting the top run is sort of meaningless with that stiff belt in my experience with it. You have to find what works with the RGM belt. Roger's instructions mention it can take a while to dial it in. He does give that 1" movement in the top run at fully heated up, but it's only a starting point.

Schwany said:

Well you fixed it. In an effort to help early on I did mention the AT10 polyurethane belt RGM uses could be run tighter in post #5 on the first page of this exercise. Also mentioned the vibration issue had nothing to do with a loose rear chain. Just saying.

Twisting the top run is sort of meaningless with that stiff belt in my experience with it. You have to find what works with the RGM belt. Roger's instructions mention it can take a while to dial it in. He does give that 1" movement in the top run at fully heated up, but it's only a starting point.

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You did indeed

Dave

Do you have any issue with the belt rubbing on the stator studs? That has been a problem with mine. Now belt is at the 45 degree twist when cold. Kenny at NYC Norton told me he sets his to
just be able to slide on the clutch wheel. BNR that is. Problem is the belt has a lot more slack at cold.

Onder said:

Do you have any issue with the belt rubbing on the stator studs? That has been a problem with mine. Now belt is at the 45 degree twist when cold. Kenny at NYC Norton told me he sets his to
just be able to slide on the clutch wheel. BNR that is. Problem is the belt has a lot more slack at cold.

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No, the belt isn’t rubbing on the stator studs and even when it was looser there was no contact. However, a P. O. had at some time run the primary chain very slack and there are some telltale chain marks on the top stud.

Dave

Dellis said:

No, the belt isn’t rubbing on the stator studs and even when it was looser there was no contact. However, a P. O. had at some time run the primary chain very slack and there are some telltale chain marks on the top stud.

Dave

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I had to remove quite a lot of metal from mine to stop the Maney belt from contacting the stud mountings. Well over a mm, and the leading edge well rounded off. Other people say that they have had no need for this, so there's a lot of variation between castings.
When I fitted the first belt, on checking I found the primary case full of black swarf from the outer belt face, even after having removed quite a lot of material. Bit scary that....

Hi, some years ago i recogniced heavy vibration under ++full++ load on my newly restored commando with the conti atf belt.
the reason turned out to be to much slack. the teeth klimb the tooth..
turning the belt on a given degree with disired force is not ease to reproduce. i keep to the "slack" procedure. the red conti atf belt with metal inlays ist very stiff. 18mm slack did it for me the last 12000 miles with no change. see pictures

Finally got around to tightening the belt up on the RGM clutch. I'm trying out .937" total up and down movement cold. It doesn't vibrate as much at idle which is where mine was vibrating excessively. Clutch is still a little noisy idling cold, but I just tell myself it is a dry clutch. I did remove material at the bottom of the lower fill hole in the outer primary cover. Different location from a Commando. The stator is in the outer cover so no stator standoffs to deal with. I am using a 25mm wide Continental AT10 Gen III belt 890 length. I started with a 20mm, but decided to go a little wider. Needs to be test ridden to see how it shifts after tightening it up. Not sure when that will happen.

All of my observations are somewhat irrelevant other than being an RGM clutch that works better on the tight end of the spec. Supposed to work with just slightly more than 1" of movement when warm, but mine doesn't without vibrating at idle.