13 replies to this topic

[Racey754]

I have recently bought an Ossa having decided I needed a project and fancy a go at twin shock trials. How do I find exact pictures of the bike, details age etc. I noted from a member earlier that the frame and engine numbers should match and date the bike. They are different but similar: B-234300 & B-231300, I didn't know if I'd miss read it but am fairly sure they are different. Can anyone help?

[Woody]

The 23 prefix is generally a MAR from 1974 - 76, in other words the MK2 MAR. They would have matched from the factory, I'd say you've mis-read one of them in view of the fact that they both end 300, but obviously, a 35 year old bike could have had an engine swap and as a coincidence, they could be similar.

Look here - http://www.ataq.qc.ca/galerie/index.php?fo...=/Mus%E9e/Ossa/

Yours would be the 1974 model as produced by the factory - for the UK the fibreglass tank was changed to an alloy one by the UK importers as fibreglass was outlawed by then. One of the nicest looking trials bikes ever made.

Lots of info on this site too http://hem.passagen.se/ossa/

[MotoVintage]

http://www.ossaplanet.com/

[AMO]

Nice choice!!
I think you may have misread the numbers as the engine numbers start with a M, also the stampings were not done very well on some bikes so could be possible to confuse a 1 with 4

Are you planning on a stock looking restoration or with a few mods for riding? pictures would be nice
I've got 7 of them to do when I've finished my yank car

Plenty of suppliers in UK, USA and spain, dont think there's any problem with building one to as it left the factory condition if thats what you want

AMO

[Racey754]

I believe from the help recieved from people on here I have a 1974 MAR, non of the pictures I've seen have a flat hub/sprocket, mine does. Any suggestions?

[Woody]

The bikes had a nice dished sprocket as standard. An alternative aftermarket conversion was to fit a spacer to extend the hub and a flat sprocket. This was generally a Sammy Miller conversion, not sure if anyone else did it (in the UK)

With the dished sprocket, there was a long spacer between the sprocket and swingarm and as the spindles are only 12mm and a bit soft, the pull of the chain could bend the spindle slightly where it was unsupported. I don't know whether the flat sprocket conversion was to cure this or because it was cheaper to produce than a dished sprocket - or both, although pattern dished sprockets were produced as well by some companies.

Dished sprockets have been unavailable for years now, but finally they are being reproduced in Spain

[B40RT]

Was there not a conversion with an extra bearing within the spacer ?

[monoped]

B40RT, on Nov 20 2009, 08:47 AM, said:

Was there not a conversion with an extra bearing within the spacer ?

Yes there was, I had one on my Cheney Ossa, fitted on the outer edge of the dished sprocket. By the way dished sprockets have been availble for some years www.ossacels.es Senior Joan Cells Grau in Spain a nice guy to deal with and a good selection of parts.

[pedronicman]

Woody, on Nov 20 2009, 08:02 AM, said:

The bikes had a nice dished sprocket as standard. An alternative aftermarket conversion was to fit a spacer to extend the hub and a flat sprocket. This was generally a Sammy Miller conversion, not sure if anyone else did it (in the UK)

With the dished sprocket, there was a long spacer between the sprocket and swingarm and as the spindles are only 12mm and a bit soft, the pull of the chain could bend the spindle slightly where it was unsupported. I don't know whether the flat sprocket conversion was to cure this or because it was cheaper to produce than a dished sprocket - or both, although pattern dished sprockets were produced as well by some companies.

Dished sprockets have been unavailable for years now, but finally they are being reproduced in Spain

Talon make a flat sprocket with spacer conversion , www.inmotiontrials.com have them.

[Woody]

monoped, on Nov 20 2009, 08:57 AM, said:

Yes there was, I had one on my Cheney Ossa, fitted on the outer edge of the dished sprocket. By the way dished sprockets have been availble for some years www.ossacels.es Senior Joan Cells Grau in Spain a nice guy to deal with and a good selection of parts.

Yes, whilst dished sprockets were still around Keith Horsman made a very neat bearing carrier that bolted onto the dished sprocket which gave support to the spindle. You ended up with 4 bearings on the sprocket side of the wheel.

The spacer used with the flat sprocket conversion also acts as a bearing carrier.

[Heavydabber]

Flat Talon sprocket is part no TR 241 - No of teeth required, Steve Sell at Marlimar-UK has loads of stuff, some NOS, some S/H, try him at steve@marlimar-uk.wannadoo.co.uk or ossa.mar@ntlworld.com, sometimes he takes a while to get back but he's very helpful. Further afield, try Keith Lynas at Ossa planet (website), KLynas@aol.com , what he doesn't know about and have for Ossas isn't worth talking about, loads of NOS and repro parts too, his Wiseco pistons are the mutts nuts, he's in California, parts take about 10 days, postage not much more than UK rates really. There's a Spanish website, Ossa Cels with a lot of stuff on but I've never tried them personally, Hope this helps

[AMO]

Just to illustrate;
The one on the left is the flat sprocket spacer, the one on the right is the extra bearing carrier/spacer for dished sprockets



Also a few things I've noticed lately;
If you stand a bare frame on a surface plate (flat table) with both front down tubes and the bottom of the frame resting on the table (the side of the headstock tube is at 90* to the table) then measure from the table to the footrest brackets the left footrest is 6mm higher (or lower, cant remember which) than the right footrest
I have done this with 3 TR77 frames and 1 MAR, all the same
Whats that all about???

Also;
Tried using a set of TR77 yolks on a mk2 MAR for temporary use, it doesn't work the MAR yolks are 10mm wider on the centres of the stantions
Was scratching my head for a while wondering why the wheel would not fit again
You can tell the TR77 yolks from the MAR yolks as they are a lot flatter and deeper when looking at the front of them

Dont want anyone to lose sleep over these points just thought it may be of use to somebody

[B40RT]

AMO, on Nov 21 2009, 04:25 PM, said:

Just to illustrate;
The one on the left is the flat sprocket spacer, the one on the right is the extra bearing carrier/spacer for dished sprockets



Whats that all about???

The original jig was out ?

[Woody]

B40RT, on Nov 22 2009, 12:34 AM, said:

The original jig was out ?

Magical has one leg longer then the other...