Talk Morgan Forums Morgan Sports Cars Morgan Three Wheeler & Super 3 Drive belt tooth jumping? maybe a solution...

The belt squeal had been an issue to varying degrees since I got the third chassis. It's a bit of a hybrid chassis, it's got the welded in braces at the front but has the earlier solid mounting for the bevel box. They possibly took a standard later model chassis and welded in the older style bracket for the front end of the box; the bracket's certainly not quite as far forward as it should be for easy fitting and I suspect that the output shaft and the swing arm pivots are slightly further away from co-axial than the earlier chassis so a bit more variation in belt tension with suspension travel and with all the other variations I don't think that the swing arm was ever as close to the sprocket as it should be even if it was adjusted as far over as it could reasonably go.
The machine gun banging was only since I took out the swing arm to clean and repaint it, that's when I discovered the lack of a dust seal and that the unprotected bearing was utterly shot so changed the bearings too. What I did was set up the bearings like I would any other taper rollers; take them up tight then back off slightly and lock the adjusters when what they really need in this application is to take them up tight, then tighter and tighter again until the problem goes away. Luckily mechanical sympathy was something I had to try to learn rather than being born with, so was able to get there in the end!
Hopefully I now have the two issues either solved or at least under control. Wonder what will go next?

I've got the swing arm out and back in round trip down to a bit over four hours if you don't count the time to make, measure and fit new things. The trouble is the number of times I have now done the seats out, bulkhead out, adjust the bearings and put it back together to see if anything has changed.

I say Calum, you have that down to the science and speed of a good pit stop. I wonder how many hours MMC allows for their warranty work?

I tend to agree with Phil Bleazey that the banging on acceleration is from the Bevel Box nodding and hitting the chassis but it could be related to swing arm pivot bearings as well? I had this noise when I had the NVH mounting and some witness marks on the chassis to back this up but it went with the fitment of Phil's BB mount. Maybe the hybrid chassis BB mount isn't so secure as the Bleazey and still allows some BB nodding? It doesn't have the upper third stabilising mount as the Bleasey one does. The early and hybrid chassis type of mount has been known to bend and distort, Austin Smith had this problem on his M3W racer.

I have always done the swing arm bearings up tight enough to eliminate any play of the swing arm, when wiggling the axle fork end, then about an extra 1/4 to 1/2 turn preload. Not been a problem at that. If you load it more the swing arm tubes appear to deflect in, much more than I expected considering it is fairly chunky box section. I would be concerned about distorting the swing arm pivot points with the loading you describe. That said, if it works for you........

I like the new bearing bung and guide plate with the countersunk screws, another couple of critical mm adjustment available. Just a gnats .... clearance, similar to a "baw hair" only a smidge tighter 😁. Enjoy the non clunking and squeak free motoring.

I think there are (at least) three main causes for the acceleration banging;

1) Drive belt loose...probably needs to be very loose and may well need dodgy sprocket alignment to go with it.
2) Rubber mounted bevel box nodding and battering off of the chassis.
3) Inadequate load on the swing arm pivot bearings.
and of course, any and every combination of the above!

I don't reckon there is significant movement of my solid mounted bevel box though the top mount would certainly take some of the load off of the original mounting brackets which might well be a good idea for the long term health of the chassis. Might be a winter project.
Must admit that tightening the adjusters as far as I have did not feel "right" but with all the other variables I could think of sorted and/or not having any effect it seemed the way to go.

Reading Callum's interesting post and suffering the same machine-gun rattle from the belt got me thinking about a way to reduce this.
To get an idea of what’s going on I set up a GoPro and did some test runs, the first was with the belt set at what I would call normal tension and the second with the belt set so tight that you could play tune on it.
What the videos show is the belt is gaining some slack and flapping up and down a remarkable amount even on moderate throttle openings.
Although I have the NVH fitted now I have had a solid bevel box mount previously and could still get the belt to rattle against the aluminium mudguard mount, even with this cut back enough to clear the belt its still flapping about a lot.
There must be some very large forces at play on the belt and some strong resonance from the engine. Maybe the slack is a combination of the Bevel box moving, the swingarm and chassis not having enough strength to stop the taper bearings spreading and maybe the belt stretching a bit, I really don’t know.
I have been trying this roller set up using a Rosta belt tensioner which works in the same way as a trailer rubber Indispension axle system.These are great as they come in different strengths, have a damping effect and the load they apply can be altered by rotating the mount. Its set in the video with not much pressure on the belt and can be easily pulled off the belt by hand but the resistance ramps up the further its deflected by the belt.
The main problem was noise from the roller with the back of the belt being ribbed, I have tried several types going up in diameter and material softness and have ended up with a 80mm diameter 78a skateboard, actually a longboard wheel, with some groves cut in it and is now quiet enough not to notice. Not sure of longevity as have only run 500 miles but with no visible wear, if the wheel can stand doing 70mph going down an alpine road with someone standing on it sliding round the corners i’m hopeful it will be ok, anyway have got 3 spares as you have to buy them in fours.
Just thought I would share this and no doubt you will think I’m mad and its a waste of time🤪
https://www.youtube.com/watch?v=57ykqvhAyLQ
https://www.youtube.com/watch?v=ir3peVEBFoc
https://www.youtube.com/watch?v=ZFbMGPhZVt0

Quite amazed at just how much the belt jumps about with "normal" (and tight) tension. The tensioner certainly seems to control that but it does reduce the ground clearance quite a bit and looks vulnerable. Impressed with the engineering. Has it made any noticeable difference when running? I am sure that you are correct when you say there are some very large forces at play, the drive belt has very little flex in it when setting it up but looks like it jumps about in use. That little wheel will be doing some serious revs when sat at 70+mph..... Interested to see how things go with it.

Interesting videos - this section of the belt is the "slack" side when the car is being driven so will no doubt get all of any slack available and flap around no doubt creating noise.

The difference in feel when driving is you don't get that vibrating feeling through the seat you get when accelerating through 3000 rpm especially in 4th gear.Whether its enough to bother doing I'm not sure though, must have too much time on my hands🤣
Ground clearance is exactly the same as the bell housing on my car.
Have worked out the r.p.m but maths is not my strong point so happy to be corrected. Ive got wheel radius with load as 11.5" so 877 revolutions to the mile, 1,023 rpm @ 70 mph, pulley rotates at 3.5 times per wheel rotation so is doing 3,580 rpm at 70 mph which is not excessive. If the same wheel (1.634" radius) was on a longboard doing 70mph down hill it would be doing 7,204rpm, as I've said if this is wrong please someone correct it!