woody

The crack in the case is generally as Tony283 has said, chain jumps off for whatever reason, wraps itself around the sprocket and takes out some of the casing with it. I only managed to ever bend one spindle in all the time I had Ossas back then and like you, I found them very reliable, just dodgy ignitions sometimes. Most problems these days are due to some ham fisted owners home-brewed methods of maintenance over the last 30-odd years, overtightening of threads or ill fitting fastners stripping threads, barrells and flywheels removed with malletts and tyre levers, crankcases prised apart with screwdrivers etc. The actual engineering in the bikes I'd say was pretty good. Still the nicest looking trials bike ever...

Yes I know, saw them a while back. Trying to avoid signing up to that site as when my KTM is sold it is definitely going to cost me large if I do..... They even have the Ossa stamp on them which makes me wonder if they are new old stock. Not bothered whether they are are not, they look the part, that's all that matters

Also worth doing OTF is to check that the threads for the screws that hold the ignition cover on are in good nick. If they aren't there is the chance that they won't hold and will strip when you pull in the clutch lever, meaning you will lever the ignition cover off instead of pushing the clutch push rod. I've come accross quite a few that are in a mess

They did, or at least the Beamish did, similar to the TY250. Pattern sprockets for these two are still made by Talon. On the Ossa the dish is much deeper and no-one makes replacements for these any more. They used to, in the UK anyway, but can't remember who it was.

You're right about them bending but that can perhaps be overcome with a spindle made from stronger material than the original. However I have a spacer that acts as a bearing carrier to enable an extra bearing to be fitted on the sprocket side. It bolts to the sprocket meaning that the length of spindle left unsupported is greatly reduced. This was something that was available back in the 70s but not in great numbers it seems, just a few were made by Keith Horsman for a few customers. The dished sprocket is so much nicer and as the bike won't be used week in week out, so with the extra bearing and stronger spindle it should survive ok.

Ossa MAR was fitted with a fibreglass tank originally from the factory. In UK the law changed around '73/74 which outlawed fibreglass fuel tanks (maybe just for road use or completely - don't know, doesn't matter anyway) Therefore all Spanish bikes imported to UK after that had alloy fuel tanks made, Montesas had a fibreglass cover which looked like the original which fitted over an alloy tank underneath. Bults and Ossas just had alloy tanks made in Wlverhampton by Homerlite. All other countries continued with fibreglass tanks - Ossas did at least This change in law coincided with the MK2 Ossa coming out in '74. Ossa themselves didn't change the shape of the fuel tank on the MK2 but all MK2 Ossas onwards in the UK had an alloy tank and the '74 - '78 models are what the Sammy Miller shape is based on. It is exactly the same except for the vent pipe. It is narrower than the Spanish Fibreglass tank. The last Green UK bikes had tanks which were shaped differently by the headstock. As far as colours:- The MK1 Ossa 250cc had a white tank with a broad green stripe accross the centre of the tank from side to side, painted, not a decal. The MK2 and 3 250cc bikes had a new Green stripe like the one fitted to your Miller tank (although the Miller decal is the wrong shape - see later, don't know where they got the pattern...) The new MK2/3 decals had to be re-shaped for the UK alloy tank due to it's differing shape from the original fibreglass tank. The factory stripes fitted to the fibreglass tank won't fit the alloy tank so don't buy any from abroad..... The UK stripes probably ended up a little darker than the original decals. I have an original (they are water transfers....) and they look darker compared to brochure pictures. Who knows what the original colour was, personally I'm not bothered and think a lighter green looks better than the darker. Unfortunately, the Miller decals are not exact copies, they are shaped wrong and are too fat on the horizontal section. The green is near enough but the size is hopeless. There are two suppliers I have seen selling MAR decal kits:- www.classicbikedecals.co.uk/ and Anglia Vinyl Art (not sure if they have a website - ebay seller) I've only seen pictures of the kits, the shape is good enough but the green looks on the dark side although they may look different in reality. The green on the 350cc MAR decal kit sold by Classic Bike Decals looks closer to original If you want to see brochure pictures of the original bikes look here, but remember these are the factory fitted tanks not the UK versions. Gallery Photos If your bike had the Cheney frame from new it could have had either the original fibreglass or a UK tank fitted as I'm not sure what year Cheney started making the Ossa frames. I'm no expert in fibreglass repairs but wouldn't it be possible to bead blast most of the paint off with plastic bead which should be gentle enough to avoid ripping it to pieces and then finishing with a sander. You'd then need to seal the inside with a product whose name begins with a C but which escapes me at the moment although it has been discussed in Bultaco topics so someone will remember. Just remember if you are able to use your original tank it would have been painted with the broad green stripe as per the MK1, if you want to put decals on it like the MK2 you will have to get them from abroad or just get them painted on. Hope you are able to get it finished either way

No, Brian Cotterill who won it a few years ago now, can't get an entry, so it's not automatic for all previous winners

ok, thanks for the info Tim, I had thought that after cutting off the last bit that is angled down, I could weld on a straight extension piece to the same length as the 49 pipe and then get it rechromed - last resort obviously. I'll keep looking. I can get by with what is on it at the moment but the fit is not ideal. However, it works so I can at least use the bike - just want to get out and ride it... it's quite a pokey motor from the quick spin around the garden I've had.

I emailed Romeros and he was able to have enough English to reply and told me that they have the type 49 exhaust in stock, 75 euros which I thought was very reasonable with today's prices, but then I nearly peed myself at the next sentence which was 35 euros postage, but I guess still not too bad at an overall cost of about

Thanks for the suggestion but tried both of those as well, no luck

I need the chrome front pipe for a Bultaco Sherpa 49 - the original horizontal type not the kit version as fitted to type 80 for the downward pointing silencer. There are none available in the UK at the moment, I've tried the US with Hugh's, Hogans and a couple of others but no luck. I've found a website in Spain for Romeromoto and they have them but I can't speak Spanish and his English is not too good - communications have failed after a couple of e-mails.... He has them but I just can't order one... Does anyone know of anywhere that has these exhaust pipes for sale? Mr Greeves - do you know of anywhere in Spain that I can get one from? They must be available somewhere as they are fitted on restored bikes Maybe if you know anyone coming from Spain to the Classic Offroad show in February, they could bring one with them and I could pay them there - or send the money to them first.

Why not ask Nigel Birkett who knows Yamahas like the back of his hand, is the Scorpa importer too and has stocks of spares for both. He is an honest bloke and won't rip you off.

Craig Mawlam who bought the Majesty stock from Shirty has one of Mick's original 360 big-finned motors and was using it in the Classic series a few years ago. Those bikes in the pictures are from Mick's initial spell with Yamaha, one is the cantilever, the other when he reverted to twinshock. Craig also has a 6 speed small finned 250 motor fitted in a mini-majesty frame to make a very nice Yamaha Majesty - is this the motor you mean Sam? Were there two different types, the early big finned 360 and a later small finned 250? I know you have probably forgotten more about Majesties than I'll ever know but I think the bike that Salty rode had the same type of 6 speed engine that Craig is now using but they are 250 (according to Salty) The one Salty rode had the special frame, forks, hubs - completely different from the normal Yam Majesty (similar to the forks/hub on the twinshock picture) I was told there were only 3 of those made. There is a picture of one in John Hulme's twinshock book with Shirt Snr riding it (in SSDT?) in the early 80s. It was pretty much a prototype Yam mono with twin shocks wasn't it? Nice bike anyway, I remember him riding it for a few seasons in the ACU Classic series and both he and the bike well. Anyway, back to the bikes in the pictures, Mick showed me one of the 'fuel injection' throttle bodies they used on those bikes once, made from magnesium it weighed nothing. He also had a magnesium carb and when you held it in one hand with a conventional carb in the other, the difference in weight was amazing. He also showed me some hand prepped factory gears that were very much lightened. That's how the weight was shed I guess, exotic materials and all excess metal dispensed with.

Yes, they did include a twinshock class for a few years but the trial was too hard for twinshocks by then and there were hardly any entries, those that did struggled and the class was dropped. It was hard enough on a modern bike back then, never mind a twinshock...

It already exixts. it's just called the Pre65 Scottish.... Yes it would be fantastic to have such an event but I can't ever see it happening. Twinshocks in the UK are the poor relations by far when it comes to 'prestigious' events. The Isle of Man classic is heavily weighted towards Pre65 with only 40 twinshock places, there is a Pre65 Inter-centre trial but not for twinshocks, several Pre65 championships and several high profile Pre65 events throughout the year. There are many Classic clubs catering for twinshocks but no twinshock specific events. A twinshock Scottish would be a dream come true for me as I'd love to ride my Ossa round the course. I remember on my first entry to the Pre65 Scottish there was a question asking for suggestions about the event etc. I put something along the lines of how it would be nice to be able to ride twinshocks and would there be any chance of a future event catering for them. Perhaps that is why that entry was rejected along with the following 6 until I finally got in in 2006......

I suspect that if they did, there wouldn't be enough entries to make the trial viable.....

Well done OTF - don't worry too much as it won't be anywhere near as bad as you think. The sections aren't killers by any stretch, just tricky enough to steal marks. Best get up to Bracken for a bit of rock practise. I got the rejection letter so won't be seeing you up there. More or less expected it after 'going in the note book' last year, though whether that actually had anything to do with it I've no idea - but I'd guess so. At least now I haven't got to worry about how to put fiddle front forks and yokes on that are acceptable but competitive which would have cost ridiculous money, instead that money can go towards a trip to Robregordo hopefully. Disappointed at not getting an entry but every cloud has a silver lining...

Harpower reed conversions are no longer available on the Ossa - or more accurately the person that did them doesn't do them anymore. Bikes with the conversion come up for sale every now and then and sometimes converted barrells appear at autojumbles but probably not in your neck of the woods.... I don't know who did the Romat conversions but it's in the back of my mind it may have been something to do with Mick Andrews following his return to Ossa from Yamaha. The Harpower conversions were already in existence by then. As far as fitting a reed valve is concerned it is pretty basic for a competent engineer (beyond me unfortunately as I'm not even an incompetent one) The fins are machined off the back of the barrell leaving a flat surface to mate the reed block to - either right accross the barrell or just in the area where the reed block will sit like a TY250 twinshock. Obviously the angle and height at which the reed block will sit needs to be considered here in order that the carb still sits in line with the airbox. The cylinder fins get thicker towards the centre of the barrell so where they have been machined off they can be drilled and tapped to enable the reed block to be bolted on. The inlet port is opened up to a larger diameter. On the cylinders I've seen this doesn't appear to be too scientific and the hole is rarely symmetrical.... No idea what the optimum size is. Sometimes vertical flutes are machined into the liner top and bottom of the inlet port but not always. When I had mine done it didn't have flutes and performed very well. The back of the piston is modified to allow more fuel in, either by cutting a big arch into the bottom of the skirt or by cutting a window into the skirt. The former means there is less bearing surface on the piston so it could wear out quicker, the latter retains the bearing surface as the bottom of the skirt is untouched. As far as getting a reed block to use, you could use a TY250 assembly or one off a modern bike. Some people here have used GasGas reed blocks for recent conversions. Nothing else I can think of at the moment, if there is I'll post it. Hope this is some use to you. It applies to any MAR cylinder by the way, not just MK1.

Yes, the centre crankcase castings are exactly the same on the Gripper/MAR so the Gripper engine will go straight into the MAR frame. I think you're right about the crank being different on the Gripper, it's the same assembly but the woodruff key position may be in a different place. The positioning of the cylinder studs is different too. The 250 MAR models (I'm including the green models in this) are all the same. On the 310/350 (whatever you want to call it) MAR they are spaced wider apart (sideways only) than the 250 so a 250 cylinder won't go onto a 350 crankcase and vice-versa (unless you elongate the holes - messy). I think that all the Grippers have the studs spaced the same as the 310 MAR, so to fit a MAR head to 350 Gripper you'd need the 310 MAR head - which you'd need anyway to match the 350 Gripper bore size of 77mm. You may need to check the compression ratio too as the 250 MAR heads differ, some have a deeper recess than others where they join to the top of the barrell, so you can get a higher compression ratio with some than others. Not sure whether there are differences with the 350 MAR heads but you'd need to check it is the same as the Gripper. You can achieve a lower ratio if needed with thicker head spacers but if you need a higher ratio and the MAR head has a deeper recess than the Gripper you may need to skim away some of the head casting around the combustion chamber, otherwise if you fit the thinner spacer the casting hits the barrell before the mating surface of the head touches the top of the liner and it won't seal. A conventional exhaust should work ok as I was forgetting that one of the other mods that was one at the time was to fit a Phantom motocross barrell to the MAR with a reed valve fitted. This worked ok with a MAR exhaust so there is no reason the Gripper engine shouldn't. MAR side cases will fit the Gripper engine no problem - do you want to sell the Gripper cases? (if they are the ones with the cloverleaf on them) Gripper engine in a MAR is a mod I've seen done a few times by the Spanish - seen them on photos and videos from their classic trials. Maybe Mr Greeves knows one or two tips for the conversion.

Where's over here? Surely fitting a Gripper engine and laying down the rear shocks puts it out of the Pre76 class? Pre76 Ossa is MK1 or MK2 250 MAR or the first 310 MAR. Gripper engine was 1980 and laid down shocks were MK3 MAR from '76 on. (I'm not bothered what you do as it's none of my business but modding a Pre76 Ossa with Post 76 parts to ride in a Pre76 class seems a bit of a contradiction - you may as well enter on a Gripper...) If you fit a Gripper engine what will you do for an exhaust, Gripper exhaust is expansion chamber which won't fit a MAR frame, will it work properly with MAR type exhaust? I have a '75 310 MAR and apart from lowered footrests, a skimmed head and Mikuni carb it is standard. Being perfectly honest, if I was to use it in a Pre76 class there is nothing else I would do to it. In standard form any MAR is as good as anything else Pre76. It's a nice handling bike, quick steering (in its era) good suspension at the front and with a good set of shocks plenty of feel at the back. Weight isn't an issue, or at least doesn't bother me anyway. If you want the engine to pick up a little quicker, 250 or 310, you could skim the flywheel. These weigh about 7.5 - 8 pounds. I've tried an enduro flywheel on a bike some time ago, these weigh about 6 pounds. I found it a bit light and although the engine would pick up quicker it would also stall a lot easier than with the standard flywheel. Skimming the original flywheel to somewhere inbetween the two should improve engine pick-up without sacrificing the low speed plonk which the Ossa is so good at. If your carb and ignition are good they are almost impossible to stall. A reed valve also improves torque and engine pick-up on the 250 (never tried one on the 310) and I think they should be ok for Pre76 as Ossa UK were using Harpower reed valves on their bikes then (Roger Holden could confirm this as he has just started posting on here) A TY250 reed block could also be used as this was another conversion done at the time by Romat.

Friend of mine has had TLR swingarms chromed, they are easy as all the surfaces are accessible. No idea on cost as it was a 'back door' job. Looks good with the red finish on the rest of the bike.

I don't think you've any chance of getting a frame chromed for

My 320 has a slotted backplate and welded up crank pin - Shirty mods ?? A mate who looked at the barrell said that it had been ported but I wouldn't know/can't tell. Maybe an ex-team bike

Oh dear OTF - I think that Greeves has just ensured that you and I may well be relieved of some serious amounts of cash. You'll pee yourself when you look at that site It's a bit of a random guess navigating your way around it but there is some nice stuff on there