Talk Morgan Forums Morgan Sports Cars Morgan Three Wheeler & Super 3 Drive belt

Good evening everyone,

Had my M3W MOT'd the other day, which it passed with no advisories. They did mention the drive belt needs adjusting and possibly a new belt. I'm not too bad with a spanner, is this something dealer only or would I be able to adjust or fit a new belt?

Cheers,
Martin

How would an MOT inspector know anything about belt tension or condition on a M3W which is a very unique application? Unless you are at very high mileage the belt is likely fine as is. The belts are very durable and long lasting as long as the tension and alignment are both in a reasonable range. The original alloy rear sprockets were a different story and wore fairly quickly and were later replaced with steel. It is possible that a very worn alloy sprocket can do damage to the belt teeth, so look for that if you have or had an alloy rear sprocket fitted.

To answer the replacement question, if you have a jack and a couple of stands you can do a belt R&R yourself (search this forum for details). It does require removing the rear wheel and swing arm, so it's a bit involved, but can be done in a few hours. Belt alignment takes some nuance, but again not too difficult. You might wait and evaluate all things belt related until the rear tire needs replaced, unless the belt is manifesting problems at present.

Also see:
https://www.mtwc.co.uk/wp-content/uploads/2018/01/M3W-Rear-Hub-and-Sprocket.compressed.pdf

which will give you an indication of the amount and type of work to be done.

Maybe they were interested in the way the belt probably overhangs the edge of the drive sprocket by about 4mm...this is the approved configuration.

Hi, it was mot'd at Brands hatch Morgan , they do know what's what ! Thanks for the reply and the link though, I'll get the car up on stands and take a look and decide whether I can do it or leave it to the experts

Had a look at this today, when spinning the rear wheel forwards, the belt overhangs the rear sprocket by around 4mm, when I spin the rear wheel backwards, the belt migrates a further 3 or 4 mm off the sprocket, is that normal or does it need a tweek? it also seems that the belt is slightly rubbing on the frame crossmember just behind the front sprocket, I cant see a way to avoid that? both sprockets are in excellent condition as is the belt. I di put a bit more tension into the belt as it seemed a bit too loose.

My personal method for centering the belt is to lift the rear of the trike with a jack while the engine is running and second gear is engaged, then adjust the tensioners to position the belt in the middle of the rear sprocket.

Does the 'front' pulley (assume bevel box pulley) still have its outer flange in place? If it does then the belt cannot touch the chassis - or when you say frame do you mean the NVH kit running across/behind the chassis - normally galvanised silver in colour?

Yes, still got the flange and pulley looks to be in good condition, its only done just over 3K miles, it doesn't have the NVH kit, I'm assuming the belt has been really loose at some point

The drive belt should run fairly much on the sprockets if they have guide plates on both inner and outer faces, front and rear. Not easy to achieve but it can be done, a straight edge along the sprocket faces helps a lot when setting this and the bevel box and/or swing arm may need adjustment to get it all in line.

Early cars didn't have the belt guide plate on the rear wheel sprocket outer face but they also had a different spacing for the sprocket on the rear hub, silver hubs, later cars had a black hub with different offsets. If you have the early set up then the belt will run about 3 or 4mm off the outer edge when set up correctly.

For later cars the guide plates should be just that, guides, not restraining plates. Once aligned and tensioned correctly the belt should stay within the guide plates without any excessive side loads. You should also have about 3mm clearance between the belt and the tyre sidewall, although some tyre brands are a bit "fat".

I can only assume that the belt touching the "frame crossmember" is the chassis tube that is under and slightly aft of the bevel box pulley lower run? That is usually because the tension is too low and the bottom side of the slack belt "grows" with speed and increased load as tension is put on the top run and the slack is on the lower run and rubs on the tube, sounding like a turbine.

The drive belt is usually bullet proof and hard to damage. When correctly set up it requires just the occasional clean with soapy water to keep it working perfectly and lasting thousands of miles.

Just for clarity, the only difference between early 'silver' hubs and the later 'black' ones is the position of the wheel mounting flange - with the later one (theoretically) giving 5mm additional clearance between the belt and tyre. The sprocket mounting flange is identical between the two.

On my early 2012 car, I run a 1/4" spacer between the sprocket and the hub flange and my belt tracks quite nicely. This is with a black hub and Fabian sprocket. The inner diameter of the spacer does need to be machined out slightly for fitment to the Morgan hub. This isn't necessarily a recommendation by the way because we all know that each car is different!