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Ossa MAR ..restoration advice please!


ScottyA
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Hello again everyone, 

A good while back I asked some questions regarding my 250 MAR . I got some great info but as expected I’m going to need more help! 
 

Ive only just got round to working on it now . I was too busy but like most people I’ve suddenly got a lot more time on my hands these days ! 
 

So far I’ve cleaned and painted what I can, I’m not sure the silver and green  I’ve managed to get is quite right both are a bit too bright . I’m not too fussed on that, I just want a working bike that I can ride.  I’ve got a rolling chassis , i need some parts ( see below ) but in general the build is fine apart from the engine. 
 

I’m up for learning, and I’ve got some manuals but I think this engine has had a rough life and some unsympathetic  previous owners. Because of that I think this job is going to be a bit trickier.

One thing that I’ve noticed is that there seems something amiss with the clutch.  As you all know, the clutch cable attaches onto a lever which turns a vertical shaft and it in turn acts on a horizontal shaft that runs through the sprocket . This little rod or shaft just shoots in and out with zero resistance. It goes in so far that you can’t see it, but if you turn the engine on it’s side it falls right out again. So as far as I can see there’s no way that can transfer any pressure through to the other side of the engine.any ideas? I’m assuming that there’s something not right internally and so the engine will require to be split to investigate. I will try to attach pictures of the shaft I’m referring to 

I was up for having a go at the more standard stuff and change gaskets, seals, clutch plates etc but if there’s likely to be damage that requires experience to resolve it might be time to leave the engine into a professional .

when I got the bike it was in bits already , on removing the head I noticed the piston rings are missing. I know the bike had been in bits for decades and the head was only on loosely . The piston and bore look in good shape. Piston is stamped with a 72 and a 4 . I’m not sure what that means in terms of piston size as my manual refers to the sizes in letters . Would you think it’s possible to order rings to fit this piston? Or is it a no brainer to just fit a new piston ? 
 

The engine number is M342 454. Which makes it a MK1 with a smaller crank apparently ? It was mentioned when I looked and engine rebuild kits 
 

Aside those queries my plan is to order up

a gasket kit 

crankshaft seals 

brake shoes 

brake and clutch levers ( They are missing) 

chain and sprockets 

shocks or springs.. I have working shocks but the springs are cosmetically damaged. If I can just change the springs I will 

Ive found all of the above online, just thought I would ask here before ordering incase there’s something else I should do ! Or otherwise ! 

 

Thanks in advance! Scott 

 

 

 

 

 


 

 

 

 

 


 

 

 

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The rod you're holding is a pushrod. There should be two pushrods in the Ossa with a ball bearing inbetween them. If you only have one that's the problem, it's not long enough to engage with the clutch on the other side of the engine. There should also be a seal in the end of the final drive shaft that the pushrod passes through, it might be there but I can't tell from the picture but if the pushrod just falls out it's either not there or so worn it needs replacing as the friction from the seal should stop the pushrod just falling out

The standard bore is 72mm with 72.20,  72.40 and 72.60 oversizes, so maybe the 4 you can see is 40 for +40 oversize.  You should be able to source rings from somewhere

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Thank you Woody,

 

I’ve had a look at the exploded engine diagram and can see that there should be another pushrod on the other side.  It has the same part number so at least I know that what I need is identical to what I already have. 
 

I will see if I can get my hands on some rings that are suitable too

Thanks for taking the time to get back to me, without having people to ask I would probably give up. I’m in over my head and it would be impossible without some advice ! 
 

Cheers Scott  

 

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As you're in the UK the only place I think you will get rings from now in the UK is In Motion but I don't remember what sizes they have left. You may have to try abroad for rings. Join the vintage Ossa group on facebook and ask on there if In Motion can't help 

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