The Synchroflex / Gates / Megadyne AT10 polyurethane belts have trapezoidal tooth form teeth. Testing done by a major belt manufacturer has shown that the trapezoidal tooth form is far more prone to 'ratcheting' (jumping pulley teeth and thus failing) than the later deeper more modern HTD tooth form introduced by Uniroyal in the late 1970s. I have quoited the test results in the belt section of my vast boring epistle that someone (NOT ME) has put on the web ......... ..............................
http://a20b767e.magix.net/#xl_xr_page_1
My version of belt history is given as are the reasons why I personally would never use trapezoidal tooth form belts for power transmission on a motor cycle. Harley did not use an HTD tooth form Gates Polychain belt on the rear of their bikes for no reason!! Ever read the S.A.E. paper series paper 800972 'The Development of a Belt Drive Motor Cycle' which also tells the tale of the Harley supposed shock absorber...I often wonder how badly the so called shock absorbers on our old motor cycles work........... I dread to think how much a copy of that S.A.E. paper costs these days.
The Gates Polychain belt of course has a low friction tooth facing as do neoprene belts UNLIKE the AT series of belts and I was recently told that testing has shown that not only did Polychain belts greatly outlast equivalent sized AT10 belts but did so carrying vastly more 'grunt'.
Exactly why anyone would employ AT10 belts for primary or secondary drive use on our old motor cycles baffles me when, in my opinion, much better more modern belts are available to us..... UNLESS they do not realise that Norton Mod 50 / ES2 / Dommy and Commando clutches were DESIGNED to be employed DRY and think that because the clutch is within the oil bath chain case that it must be designed to be run with oil on the friction interfaces...AT10 belts being more oil proof than STOCK neoprene construction belts so to continue to lubricate the clutch they must think they had better employ an oil resistant belt...... The oil / oil mist upon reaching the dry clutch friction interfaces reducing the Coefficient of Friction acting between the clutch friction interfaces to 1/3 -1/4 of its dry value and reducing to 1/3 -1/4 the amount of torque the DRY fully engaged clutch will carry before slip occurs which is the cause of the Commando clutch slipproblem IF an owner actually uses the throttle and especially if they overfill the chain case, probably with more than 200cc /7 fl oz, along with using oils with friction inhibitors....... Oil also results in stiction causing the plates to stick together and not free off correctly......and the clutch in your car works correctly and frees off instantly without drag doesn't it.......It does in mine and so should the clutch fitted to a motor cycle if it is to be called a clutch or as I refer to the Mk3 Atlas Mk3 / Commando so called 'clutch' ....a gearbox mounted vastly overweight unbalanced gearbox breaking flywheel' Ssuch devices are supposed to possess the LIGHTEST rotating weight reasonably possible not the heaviest ....so I was taught and have read in books.
As for that pulley shown......I 'suspect' the pulley was DECORATIVELY anodised and NOT correctly hard anodised, decorative anodising being MUCH cheaper than even incorrect hard anodising!!. Decorative anodising gives a very thin hard surface probably no thicker than 1/2 the width of a knats cock!! Hard anodising IF and I repeat IF correctly carried out gives, on pure (99%) aluminium, a surface hardness of the order 800 Vickers. For comparison 100 ton tensile strength steel has a hardness of around 440 Vickers. As you add impurities to the aluminium to manufacture the aluminium alloys employed for pulleys (He15TF or HE30TF) the hardness value reduces but it is still something like that of 100 ton tensile strength steel and it will be about 0.002 inch thick, 0.001 inch being into the original material and 0.001 inch being growth so one has to allow for the growth if ending up with pulleys of the correct size. Even a couple of thou oversize to a clutch pulley diameter and a belt will not fit the pulley correctly. Oh it will fit BUT NOT CORRECTLY.
With the pulley shown I suspect the belt has been incorrectly tensioned because it looks to me that it has been riding up the pulley teeth and not making full contact with them. Centifugal forcesand torque cause the problem especially if a belt is employed loose. That is the fault of the user. Belt tension is critical if good belt life is to be achieved as Uniroyal found when testing belts decades ago to see what effect on belt life incorrect belt tension had. When I asked a Gentleman if he could give me some indication of how belt life was effected by incorrect belt tension...the reply went something like .....'Oh I can dd better than that because we conducted testing on this subject many years ago....the results will be in deep hold store which I can probably find for you if you want but basically we found that a correctly tensioned belt will have a life 3 to 4 times greater than that of an incorrectly tensioned belt'.
Of course exactly the same will apply to chain and in my very limited experience of putting away into stock lots of second hand primary cases with chain wear grooves showing many British Bike owners are incapable of tensioning a chain correctly !!! Mind you I wonder how many follow the Renold chain instruction books and remove the secondary chain every 1,000 miles, wash it in paraffin and boil it up in chain lube grease?? See the 'Renold Motorcycle Chain Maintenance' booklet. My copy was printed in 1953. ...................
.......OR at lower mileages in bad weather. Personally I probably changed my rear chain for a freshly cleaned and greased one every 3,000 miles but in those days of youth defying death flat out just about everywhere was more important than maintenance!! Ah for those LONG LOST days of youth which, let us not forget, cost so many their lives........which I guess is why they named a section of the A20 a few miles from Brands Hatch DEATH HILL all those years ago!! Its now named ' Gorse Hill' with 'Formally 'Death Hill' in smaller lettering beneath.... well it was the last time I drove past in my 4 wheeled dry warm very comfortable box before amusing myself on that little back road down the side of the North Downs leading to Ightham...
Plus I suspect the belt employed on that pulley was a Megadyne tooth form belt and not a Gates HTD tooth form belt although I understand that testing showed the Megadyne belt to run better on HTD tooth form pulleys than it did on its own tooth form pulleys.....so I was told. Plus please remember that everyone in the World is now producing HTD tooth form belts and in my experience the quality can be nothing like as good as a genuine Gates HTD belt. I believe one major belt manufacturer had a factory 'out east' shut down and stopped from producing counterfeit belts. Of course if many dealers can obtain cheaper belts and sell them at their full original manufacturers price ....... And please do NOT assume that the people who sell you replacement belts know anything about belts / tooth forms etc. Yes mate it will fit your bike is something I have heard a lot more than once......as i cringed and managed to keep my mouth shut.
Oh and I wonder how many belt system manufacturers have the odd pulley light source profiled to ensure their pulleys are correctly toothed in the first place?? Incorrect toothing can (will?) result in premature belt and pulley failure. Suggested reading being the document now found on the web by inserting 'Synchronous Belt Failure Analysis Guide' .
Its very easy to blame the bit that fails, belt or chain etc, but a lot harder to investigate the cause of the failure and determine why it occurred. It's amazing how much you can learn from investigating failures one thing being how little one actually knows!!
