Author Topic: drive belts  (Read 10559 times)

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Offline clee

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drive belts
« on: 25 Oct 2006 at 02:14 »
G'day all from sunny Queensland,  i have a question on drive belt's for my 2.75 hp Douggy. Has anyone shortend a drive belt and by what means was it rejoined. I have seen over the years people using a bont over nail and wondered if this was the go or if some other means worked better. It is a rubber v-belt that was picked up some time ago but is a few inches too long.  Hope someone has an idea.   Regards Col
colin lee

Offline Ian

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Re: drive belts
« Reply #1 on: 25 Oct 2006 at 03:57 »
To do this most use a joining link which is bolted on to the belt and has a hook arrangement

I have attached a photo of mine and also one of some new linked belt we are trying - horrible colour but can be blackened with raven oil apparently. I am just about to use on my TS and a couple of veterans - the old 7/8" TS belt is finally dead.



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« Last Edit: 25 Oct 2006 at 13:09 by alwyn »

Offline clee

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Re: drive belts
« Reply #2 on: 25 Oct 2006 at 04:55 »
Thank's again Ian, I will make something similar to what you have. I do have some link belt very much the same as you, but it is a real pain to shorten links as each pin goes through 3 links each. When i bought it the bloke who sold it to me could'nt undo it either so he just cut it.  Good luck and let us know how you go with it.  Regards Col
colin lee

Offline graeme

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Re: drive belts
« Reply #3 on: 25 Oct 2006 at 05:54 »
Col,
For a much lower price than that of the link belt, you can get endless belt from bearing shops. I just bought a 77" C section belt for the 3 1/2hp for $38. The brand is Opti, bought from an SKF shop. To fit it requires undoing the frame at the bottom of the rear stays, but once fitted the belt should never stretch. The difficult part is working out just what length belt you require - I took in the old link belt for measurement, which came out as 71". Way too short. I measured the diameters of the pulleys and the distance between the centres, the measurement for the belt came out at 83". Way too long! Turns out that 77" is mid-way between the two measurements. What length is needed for a 2 3/4hp I wouldn't have a clue!
Cheers, Graeme

Offline Chris

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Re: drive belts
« Reply #4 on: 25 Oct 2006 at 09:25 »
Drive belts all stretch with use, some types more than others so a means of adjustment is essential. Endless, machine belts apart from the difficulty of fitting (I have photographs of a 2.3/4hp where the rear frame has been cut and fitted with fish plates so as to enable endless belts to be fitted) are not of the same construction as solid belting designed to be joined. They have reinforcing fibres in the outer section of the belt only and are designed to transmit a certain amount of horsepower and generally under constant load conditions. Multiple belt pulleys are often provided to ensure these loads are met with ease. They are also designed for use in dry and usually oil free conditions and invariably, adjustment for wear and stretch is provided by means of slotted feet on the electric motor or engine driving.

Motorcycle drive belt conditions are much more stringent with the need to drive under constantly varying load condition in wet or dry weather and often contaminated by oil from total loss lubrication systems, lack of effective main bearing and gearbox seals etc.

There are various designs of belt in common use. In the distant past a variety of manufacturers solid belts were available in many sizes. Most Douglas models with belt drive specified 3/4" size but for some reason this size virtually disappeared and 7/8" became the norm. This in turn has been largely replaced by the modern 22mm. ("C" section) A current manufacturer of this is Optimat and this differs from the original solid belt in that it has ready pierced holes throughout its length at about 10mm intervals. It is joined by means of their own design of clip available from Optimat stockists comprising an inner tapped plate, an outer wider plate with countersunk holes and two instrument type screws. Adjusting belt length for correct tension is simply a matter of using a junior hacksaw to cut at the next hole and replacing the clip. This make of belt is also available in the 17mm size, more suitable for the very early machines with a very small engine shaft pulley driving the rear wheel directly.

I had a very good life from a "Pirelli" made belt of similar design to the Optimat on my 1910 veteran but have been unable to find a current source. I also have a very good solid belt that came new in a cardboard box with one machine I purchased. This is the original 3/4" size and made by Dunlop, has the words "Dunlop - Made in England" in raised letters repeated around the circumference. This is joined by the hook type fastener shown in Ian's photograph. The holes for these fasteners to be applied to the belt are pierced by means of a patented tool still commonly available from auto-jumbles ( I even found an original brand new one in its original packaging last year). They are available in sizes to suit each size of belt and comprise a cast roughly triangular body in which the belt is a good fit. A screwed hollow punch is provided guided by a boss on the outer section of the triangular body. The belt is placed in the tool in the position where the hole is required. The hollow punch is then screwed all the way through the boss and belt until it reached an anvil. It is then retracted leaving a hole in the belt and a "worm" of belt material issuing from the punch. The tool together with a junior hacksaw and a small spanner (for the square headed fastener screws) held in the tool kit enables a very simple roadside belt adjustment.

The other most common type of belting is the segmental belt usually termed "Brammer" belting. This was originally made from very strong canvas reinforced sections. It was notorious for extensive initial stretching and one solution  I was given years ago was that before use, it was a good idea to secure one end to a high beam in the workshop and then to hang a 56lb weight on the other end for a week or two. This woudld reduce the amount of early adjustment necessary upon fitting to the machine. (It can literally stretch 6") This design of belt is more flexible than solid belting and is therefore better for very small pulleys. Disconnecting and connecting the links seems impossible at first glance but special tools were available originally and do appear from time to time but I have not, so far, been able to find one, However, a pair of circlip pliers and a screw driver of the correct blade width make the operation quite simple with a bit of practice. The object of the exercise is to open up the slots sideways in each section while bending the belt to permit the rivet heads to disengage.

Original Brammer belting is again now very scarce and expensive (Last year I did find a length of original new 3/4" Brammer that I have installed on my current restoration) but modern versions are available in different colours/grades and appear to be polypropylene coated which may be more oil resistant but I have doubts about its friction properties compared with the original. Another later version of the segmented design also currently available has little "T" bars instead of the round head rivets. These permit easier adjustment as the bars can be turned to align with the slots for removal of links.

I hope that the above gives some insight to the problems of driving your old flat tanker. The best solution is the one on the CW model where Mr Douglas sensibly provided chain drive although still churning out belt drive on the TS and SW models.  Chris.

Offline graeme

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Re: drive belts
« Reply #5 on: 25 Oct 2006 at 22:58 »
Chris,
I can certainly confirm your experience of stretch with Brammer belting - on the 3 1/2hp outfit, I would think that in the first couple of hundred miles we must have taken out at least a dozen links before the stretching slowed up! Even then we had to occasionally take out a link until the belt eventually snapped after a few years use. Another foible of Brammer belting is that when it gets wet it shrinks - tightening up to an unbelievable degree. I can tell you there is no way you can get the belt off the rim to try to fit some more links in when it is wet. When it dries out the belt slackens off, and because of the tightening, it has stretched - so more links need to be removed!
Here in Australia, the majority of veterans that are ridden much now have continuous belts fitted. They really don't stretch at all. Their only down side is that they can slip badly in the wet - so riders usually carry rosin powder in the tool kit.
Cheers, Graeme

 

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