GTL gearboxes have the tapered end with keyway, and new sprockets for them are as hard to find as new crank bearings.
Until I have found a commercially viable method for alternatives for GTL sprockets, I have diverted efforts into the SD/GTV gearboxes as these have the “regular” 6 spline shaft like the pantah. Again, ploughing through the JT Sprockets catalogue an alternative was found, although it was a 520 chain rather than original 530. The thinner chain is not so much an issue as modern 520 chains are extremely strong, but it does mean sprockets for the GTL have to be modified. SD/GTV wheels have the same sprocket carrier as the pantah/750Paso/Sport 16″ wheels, and those sprockets are still readily available.
the front sprocket was found to be the same as a Yamaha 250 dirtbike, and available in Z12 and Z13, just like the 350 and 500 models. A distance bushing is required to ensure correct chain alignment.
front sprocket 520 (SD/GTV): JTF431.12 (350) and JTF431.13 (500).
rear sprocket 520: JTR491.38 and JTR491.40
rear sprocket 530: JTR1022.38/40/41/47
fitment 520 front sprocket: place the collar to the outside so front sprocket backside is flush with rear sprocket backside.
spacer required for 520 sprocket: 22(+0.2/-0) x 28(±0.2) x 6.7(±0.3) mm
advised: strong belleville spring washer DIN2093 22.4 x 45 x 1.25 with loctite 242/243.
We are currently in negotiations to get GTL sprockets manufactured in 530 chainsize
(5/8″ x 3/8″) for both 350 and 500 models, z=12 and z=13 respectively.
been doing these bikes since 2004 with some gaps inbetween for other bikes (ktm LC4 for example) but the fun really kicks in when you’ve found a workable alternative thats readily available, too!
the challenge for me with the chaindrive is the conicle part, and personally i’m not a fan of machining down and welding on other sprockets, as there’s definite end to when it cant, or increasingly difficult to be done.
i estimate its probably easier to have standard blind sprockets to be machined and grinded conically and keyway broached and then possibly even hardened afterwards, than having to have them custom made.
most industrial power transmission suppliers (conveyor belts, belts, chains and the like) have catalogs for standard parts, so perhaps i might dig in that and get some info and quotes for modifying these sprockets.
i’ll post results when i have them, unfortunately i’ve also got a full daytime job (oil+gas) and family at home so time is scarce most of the time.
Thank you, Arthur for publishing the results of your work. Just a few weeks ago, I started to rebuild a 350 GTL, which was buried in a barn for 25 years. I’m facing a lot of problems and already found some good solutions and impulses reading this site. In the first place I’ll just do cleaning everything and replacing rubber parts. But the days are coming, when I have to rework the chain drive as well. Hoping, you’re not losing the fun for it.
My Best Regards