Talk Morgan Forums Morgan Sports Cars Morgan Three Wheeler & Super 3 belt squeal on downshifting

I have mentioned this issue before but now the car is back on the road, I need to get this resolved. In previous discussions the fingers were firmly pointing at rear wheel alignment and I have researched various threads and also the Bulleting articles by Ian Brett (January 2018 page 6) and Phil Bleazey (March 2019 pages 9 and 10) so the actual alignment mechanics I am not too overwhelmed by,

The first picture shows my rear sprocket with the belt reasonably tight up to the wheel side.



This second picture shows the BB sprocket with the belt right to the opposite outside edge.



This pictures shows the unused part of this sprocket



To adjust the rear wheel alignment looks simple to me. If I pull back the tensioner on the (UK) drivers side that will realign the rear wheel meaning the (UK) passenger side edge is closer to the BB and so the belt should drift away from the tyre. But this action would I think mean the belt at the BB sprocket will also want to drift to the outside of the car where it is already at its limit tight up to the edge of the sprocket.

So I guess my questions would be;

1. Which sprocket most likely causes the squeal?
2. Is my understanding of cause and effect on playing with the rear tensioners correct?
3. If the rear tensioners deal with the rear wheel sprocket, does the BB mountings have adjustment to re align the BB sprocket or is all dealt with at the rear?
4. How much adjustment on the tensioners is needed to actually see a positive amount of movement in the belt? Currently I only dared try a one sixth turn of the tensioner bolt, went for a test drive and no improvement at all in the amount of squeal on downshift as the belt remained in the same places on both sprockets.

Unfortunately my laser is not of a type to place on the rear so am working on the principle of if the belt runs centrally on the sprockets at both ends then the squeals should disappear.

But one bit of good news is that about 15 years ago I picked up a 36mm ring spanner off the road oustide my house (must have dropped of a lorry I guess) and have never used it until today! Knew it would come in handy one day.....

Sorry to hear of your squealing drive belt. Since writing the bit about laser aligning the rear wheel for The Bulletin I have found that 100% straight rear wheel alignment isn't everything with belt alignment and sometimes it has to be sacrificed a little for belt alignment. I have found that if you remove the LH rear shock absorber you can get a long straight edge (1 meter) along the edge of the bevel box sprocket and the rear wheel sprocket. With that in place you will see what needs moving where to get everything aligned perfectly.

The rear swing arm LH pivot seems to need to be adjusted to almost touching the bevel box pinion to get good alignment and some belt clearance to the BB pinion guide plate when running. This was to the extent that the plastic bung was often left out of the LH swing arm pivot at manufacture. You may need to replace the corroded swing arm bearings if this was done on your car. If the belt alignment dictates a large deviation for wheel alignment, the bevel box mounts will require repositioning, not so difficult with Phil Bleazeys mount but more of a task with an NVH mount.

It really isn't a simple task to get the wheel aligned and the belt running true, usually some compromise is required. When laser aligning my rear wheel it is about 1/4" off to the right over the length of the car on the front number plate target to get everything running right with the belt, acceptable I think. The guide plates are just that and shouldn't have the belt running hard up against them under any conditions, front or rear.

Just a beginner, and not experience in car mechanics, so really don't give my view much credence, but having just gone through taking out the rear wheel and sticking in the Bleazy Bevel mount kit and replacing the wheel, I'd say for point 4) on the tensioners a turn or so would make a difference once up to tension.
This was based on just jacking up the rear wheel at spinning the wheel forwards to see where the the belt tracked. Adjusting the LH tensioner it was fairly easy to get the belt to sit such that it wasn't touching either side plate on the rear sprocket.
As for central alignment, I decide it didn't really matter if it crabbed a bit. With one wheel at the back and two at the front, I reckoned any possible non optimal wear patterns would be inconsequential compared to all the other things that will go wrong on it.
That said, given the variability in chassis dimensions that I noticed when fitting new shocks, I could imagine what works on one works less so on another!

A question as not clear from the pictures - is the big sprocket a steel one or a worn aluminium one? The latter can give different noises under power/on over-run when worn as most wear occurs on the drive side of the teeth. Also is the hub silver or black annodised...if the former, it will be an early hub that is much harder to get properly aligned and the belt clear of the tyre.

When we change the rear tyre, we have the car up on stands and run the engine for a while to check the alignment is stable.

My belt hangs about 3mm off the edge of the rear sprocket both going forward and in reverse.

The best way I have found on my car to align the belt is to jack the back end up so the rear wheel is just off the ground, remove the boot liner slacken the axle nut just enough so it can move in the swing arm forks with a little force. Then slacken off the adjuster lock nuts.

Use the adjuster bolts to align the wheel so the belt tracks in the same place whilst rotating the wheel forwards and backwards. The belt will find its own best place, mine has always been about 3mm off the edge of the pulley. Tighten the adjuster lock nuts and then the axle nut. That should do it.

What makes me think yours is out of true is the witness mark on the bevel box pulley. It should only be the width of the belt, yours is much wider than the belt which would suggest the belt is wandering from side to side.

Hope this helps.

If the rear sprocket is the stock aluminum one then the squealing will only get worse over time until it is deafening. The bevel box sprocket is steel so will not make that kind of noise. Another tell is the copious amounts of black dust in that area. That will be the powdered aluminum that the belt is removing from the rear sprocket. Steel won't do that.

Which colour is the central rear hub - this will make a difference.

It looks like its an earlier car as its a minilite type wheel? If so they normally had the silver hub - later cars had the black hub which meant that the sprocket part/belt was pushed away from the wheel. Some early cars have been updated to the black hub.
If the belt is wandering as per Dab of oppo comment, then this may help resolve that issue with more accurate alignment.
You can get a spacer to move the sprocket away rather than purchase a new black hub.
Its not easy to move the bevel box mounting positions, as that all depends on how close the BB output sprocket flange retaining bolts are to the swing arm in the first place. We have had a car here where the BB sprocket flange failed (I think due to poorly aligned rear wheel) as 3 of the mushroom headed bolts had sheared and then the flange bent outwards and thus caught the swing arm....the remainder bolts failed (not surprisingly) and the flange then went AWOL and wrapped itself around the belt...bit of an (expensive) mess.

Got dragged to the beach yesterday with the family but back on it now!!!!!

Thanks for all the replies, much to think on.

I think my rear sprocket is aluminium. Looking at the flange on the tyre side of the sprocket, that is a little dirty so whilst the belt is close to that side it is not really hitting that flange, leaving the dirt in situ. There are wear marks on the teeth but interstingly not equal wear marks along the length of the each tooth. There is more wear on the outer end of the tooth than the inner end of the tooth. Can only think this means more belt pressure on the outer end of the tooth.

The hub (or what I think you mean as the hub) looks silver to me so fits in with my car being a 2012 car. Yes it has a minilite type wheel and yes there is black dust a plenty.

On the BB sprocket, having jacked the car up a bit higher, there does not seem to be any belt wander but in fact the belt looks to be very tight up to the outside edge flange as the inner face of that flange is highly polished by belt contact. At this end the belt is not wandering at all imho as the dirt build up on the BB sprocket is too much to indicate belt wander.

I ran a straight edge between the sprockets as best I could and the contact points all seemed to make contact equally. If out of alignment I would have expected an air gap between the straight edge and the sprocket at one contact point.

So from your comments and observation today, I think the uneven wear on the rear sprocket teeth says that there has been some alignment at the rear to try and make the belt wander at the BB sprocket away from its outside flange. But it is now not sufficeint, if it ever was.

So it seems I need to consider a steel rear sprocket upgrade and to look at the mounts on the BB if I wish to get a realiable and quiet running belt alignment. Not comfortable with playing with swing arm adjustment on a DIY basis yet. Guess I will need to live with this squeal a while longer until I can sort the items needed.

I assume you don't have many miles on your 2012 car? I would have expected all early M3W's to have had their alloy rear sprockets replaced by now but there must still be a few left. Low mileage early cars can require a lot of work and money to make them useable if they have quietly sat in garages for several years. The alloy sprocket will be the reason for the noise and will require replacement with a steel or poly overlay sprocket. It's not worth the effort trying to make a worn alloy sprocket run quietly.

Sprocket options for reference

Morgan Steel Sprocket


Lightweight Steel Sprocket (Made to order - see other threads on here)


Supermax Polyurethane Overlay - Morgan Aluminium sprocket reworked