Trials Australia Forums

Tony T wrote:Hi all,
I'm just starting my first trials bike (and first Ossa) resto so I've got a few questions to start me off.
FYI it's about a '74 Explorer (not MAR) and I'm not really stressed about using OEM parts as long as they're reasonably period correct.

1. I've been trawling the internet for the last week or so and found a couple of suppliers with potential. Mainly in the U.K. Is there any one that stands above the rest? In Motion (UK) are very good as far as customer service goes, but are not OSSA specialists. SM Products (UK) are good too but also are not OSSA specialists. Keith Lynas in San Diego USA is a gold mine of OSSA knowledge and is also a parts supplier.
2. Is there a way of working out whether I have a '73, '74 or '75 model? And does it even matter when ordering parts? Look at the rims, fork bottoms and the carby mounting to work out which year. The first OSSA MAR (1972?) had a flange mount IRZ carby, then followed a MK1 (flange mount) AMAL, followed in 1975 by a spigot mount carby and I can't remember which type of carby that was, probably AMAL MK2). Early OSSA trials bikes had shouldered Akront both ends and by 1975 they were shoulderless Akront both ends. Fork bottoms started out cut-off square at the bottom, by 1975 the axle clamps were waisted down. Also only from memory, the Explorer came out first in 1974. The very early MAR came with a swingarm that is shorter than later MARs and Explorers and some people reckon that MAR triple clamps are different to MAR triple clamps but I doubt it. The motors did not change mechanically in that period (1973 to 1975) apart from the previously mentioned carby atachment method.
3. Are the engine bearings and seals a special item or can I get them at my garden-variety bearing supplier? Don't know - am yet to rebuild mine. The primary chain is same as one model of BMW car engine cam chain.
4. Are Gonelli or other generic guards available in Australia? Yes Don Newell in Brisbane has them but maybe not the full range of colours. There is now a longer rear Gonelli that works a treat on OSSA and Bultaco trials bikes
5. What's the deal with the rear sprocket? Are they difficult/expensive to replace? SM Products makes a kit that has a spacer with an extra bearing and a flat sprocket. This helps with one of the weaknesses of the OSSA. The standard rear axle bends easily, and the outrigger bearing design in the SM Products design reduces the bending moment the axle is subjected to.
That's about it for now, but give me a couple of hours and I'll be in need of more help......

Thanks in advance for any words of wisdom.

TriCub wrote:David forgot that 72 MAR's had a fiberglass bash plate, but as you have an Explorer that is not an issue

David Lahey wrote: He has also been mercilessly teasing me since 1977.