woody

Yes, they are 20 x 1mm. I bought this for a Marzocchi yoke which should do the job as it fits the Ossa thread also http://www.ebay.co.uk/itm/131705365599?_trksid=p2060353.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

Check that the crankcase screws are fully tightened, you never know. If the are, lie the bike on its side, clean off the affected area with brake cleaner and apply plastic padding petrol patch or such like - something that is oil / petrol resistant. I stopped one leaking like this once until I had time to strip it and find the actual cause (crack in the casing in my case due to the bashplate being hammered out of shape from hard use over many years and therefore touching the cases) I've used araldite to fix a split in my Commerfords slab tank and this has lasted a few years now, but you'd have to put the bike upside down to use araldite, as if it's only on its side, the araldate will just run downwards away from the required area when applied

You can send me a PM if you want with any questions but to be honest you're better off just putting them on the forum as there are several on here that are knowledgeable on Ossas, so you're more likely to get the answer you need than just asking one person Putting the forks in the other way around was done by some to improve the front brake action, I believe the idea behind this was that when you roll a bike backwards the brake always seems to work better than when it's going forwards, therefore if you reverse the front end so that the wheel in forward motion is now going in the same direction as it was when it went backwards in the conventional position, the brake will work better Never been convinced of this myself as the brake will seem to work better backwards as there is no weight on the front wheel therefore less resistance / force for the brake to overcome, plus the wheel is barely moving when going backwards, in comparison to the speed it will be rotating, or the forces imposed on it, when going forwards. It won't actually cause a problem fitted that way around as the axle is in-line therefore steering and handling aren't affected. The fork drain plugs though, are now at the front instead of the rear of the legs. Re: the bashplate - I'm referring to the fact that it is still what looks to be a perfect fit on the clutch side which means it hasn't been bent up in the middle, which forces the back down and away from the frame due to repeated impacts from hard use. None of the bashplates I have can be bolted up to the frame at the rear on the clutch side as the two don't meet

The cylinder is the definitive ID for 250 as only the 250 up to the MK3 inclusive had solid fins. All 350 had split fins. On a MAR it isn't possible to fit a 250 barrell to a 350 engine and vice versa due to different stud spacing. But that aside, your engine / frame number is also in the MK3 250 sequence range. Your bike is identical to the one my brother had. Only the MK1 and very first MK2 MARs had split outer fins on the head, the 350 and later MK2 and MK3 all have solid outer fins. The green models had a different style head with mounts for a head steady The chassis ID charts must have come from Ossa records originally but no idea who obtained them, but not all are as comprehensive as others with some missing number sequences that others have, and some sequences missing from all of them. There are still the odd few bikes out there that have had little use, even some that have never been sold or used from new if stories are to be believed, but yours definitely looks as though it's had little serious use, if any.

Frame number lends itself to the 76 250 - the series that begins 56**** so they could have run into the 57 too with the MK3. The Ossa frame numbers aren't as well documented as the Bultaco for example and some number runs don't appear on any listings. I had an all green bike which began 700 with matching frame / engine but there is no mention of a 700 number run on any of the lists available. Your also has the correct features for the MK3 with damper position, swingarm and forks. The early MK3 had the short front pipe and torpedo silencer but later MK3 had the longer front pipe (or maybe only on the 350 version?) with much longer back box, as seen on the green models. Not sure about your front pipe from the picture as it isn't clear whether it's original Ossa or not, so it could have originally had the longer type? My brother had a MK3 250 back in the era, it was the same as yours. All 350 trials motors had the barrell with split fins, only the 250 up to the MK3 had solid fins like yours has, the green model 250 changed to split fins Your bike looks as though it's done little competition use as the bashplate still fits both sides...

It's a '76 250 Looks to be in original spec apart from the rear silencer which should be the 'torpedo' shape

It could well be a Keith Horsman conversion as he was a Montesa dealer in the 70s, rode a 247 and developed a reed valve for them (Harpower) although I don't know which carb he would have uised on the Mont. He subsequently fitted them to Ossas and Bultacos. He did an Ossa for me many years ago and it gave an increase in torque and let them rev a bit more, so yes they're a worthwhile improvement. A clever man was Keith, self taught engineer who sadly died a few years ago now. I enjoyed a few trips to his home when he was doing work on my Ossas for me - always had a tale to tell

If your bashplate has taken a beating and pushed up in the middle it can touch the engine which means impact shocks transfer to the crankcase and can cause cracks - it's not always the sump plug that causes the problem. When the bashplates were new there was enough clearance that the sump plug was well recessed and nowhere near protruding. Bashplates can be pressed back into their correct shape.

I've just put an OKO 28mm on mine (non power jet) as the original carb was no longer any good. Initial jetting is 48 pilot, standard 112 main, needle, needle tube and slide all standard (by standard I mean what they come with) Needle raised one clip from standard First impression is good, It has loads of torque, picks up very well of idle and pulls really well in first to third up climbs. I've a spare flywheel fitted with about 10oz shaved off it which helps pick up but I doubt it needs it. It's a strong motor. I haven't yet given it any real stick as it's a new engine build but at most I may try the next size up on the main as there is the faintest trace of pinking when hot.

Steve's Ossa business is part time, not his day job, but he will reply to phone calls when able as long as you don't block your number. He doesn't, as don't many of us, answer if a number is blocked.

ok thanks Andy, will do next time

Glad you and your son enjoyed it Roger. It was very slippery in places but nothing overly demanding - a good learning exercise for riding that type of condition.... I remember he had 3 good cleans on my section and rode it well. The results go straight onto the club facebook page when done as most of the riders are on there looking for them before I've got home..... Then I normally put them on the front page here but hadn't got around to it immediately and ended up fairly busy last week so overlooked it. A soon as I get Admin to the club website sorted they'll be on there as well but not sure how long that will take. I used to e-mail them out but lost the group email I had and it's a lot of effort to create that again, plus not everyone puts their email address on the entry form. Hope to see you at future events and hopefully the next one will be a little drier. 28th May (Saturday pm) 28th August 30th October 26th December

I've uploaded them onto the news page but no idea how long it will take for them to appear as TC administrators have to authorise it. The Stafford Auto website is not up to date. I've just taken over running the club and don't have admin access to it so I can't put the results on there, or do anything with it until I do, and at the moment I don't know who previously maintained it. The results are on the facebook page which is public, so any facebook user should see them. If your not on facebook then no you won't see them. Facebook is real time and a lot quicker and easier to use which is why a lot of clubs use it now. I can send you a copy if you PM me your email address

There is no club that I know of that doesn't accept it

The two clubs with the 'fussiest' rules accept it, so which don't?

Premier has a redesigned pilot circuit which uses a new type external pilot jet that is located on the opposite side from the airscrew

It's a standard size bearing so easy to source a new one. Once you have it removed, you'll find the number stamped on it (as with the clutch side roller) I can't remember what they are as it's a while since I did mine The crankcase has a hole in it as the bearing outer case is closed at one end, so it seals the hole when in situ. To remove just warm the casing and tap it out with a drift from the outside inwards

I had a C15 trials using an early (1959) motor. It had standard road gears when I had it and I used it like that for some time. I didn't feel it created any gearing issues. I then had the opportunity to acquire a trials box for it. In all honesty I don't feel it gave any advantage at all. With either box I could use 1st or 2nd gear when needed. If I remember rightly, it was slower on the road with the trials box. I don't know how the two boxes in that earlier engine compare to the two in your engine, but In retrospect I'd be happy to have left it on the standard box.

There are supposedly ways of doing it but don't forget it's used as an octane booster so if it's removed the octane rating is reduced

But we never saw the effect on tanks back then as people have experienced now. I've seen an Ariel fibreglass tank that was turned to jelly inside. We never saw that happen to any of the fibreglass tanks back then, the worst we got was crazing and maybe leaks due to some of them being poorly made, but I never saw or heard of any melting as the Ariel tank did. And trials bikes had fibreglass tanks in the 60s with no issues and ethanol seems to have been present throughout that period too. Similarly we didn't see problems with petrol pipe, rubber seals or other components that people are reporting as being affected now. I use Shell V Power and fortuitously or otherwise haven't experienced any of these types of issues, and it reputedly has up to 5% ethanol in it. I've also started a bike that has had the petrol left in the tank for nearly two years and it took a few kicks to run and ran with no issues afterwards, so not sure where the idea fuel goes off after 15 days comes from. The period between it being refined and finally getting into the fuel tanks of our cars could be longer than that... If they could run cars on pure ethanol 100 years ago without it attacking rubber components, gaskets, seals, etc, there should be no reason why in this age of superior technology and understanding it should present today's industry with the types of problems being reported - you'd think. Which is why it makes me think there is more to it than ethanol. But I'm not a chemist so I don't know, just what I think based upon the history of using ethanol more than a century ago and as an additive all through the last one

Ethanol has actually been mixed into fuel for a lot longer than we imagine - for decades. It was what engines were originally run on before petrol in the 1800s. Following the discovery of petrol, fuel switched between petrol and ethanol for some time, the one in favour at any given time being dictated by tax levy or politics. In the very early 1900s they were looking to ethanol as the fuel of the future due to its cleaner burning and higher octane properties. Race cars used ethanol rather than petrol for better performance. It was regularly used as an octane booster for anti-knock in petrol right through the 1900s. Supermarket fuel uses it is an octane booster now. It makes you wonder if ethanol really is the culprit of problems seen now, but if so, makes you wonder even more why it has only recently become one, given the technology available now as opposed to decades ago with no apparent or reported problems. I use V Power and so far, no issues with anything

It will be on ebay in completed listings, the last time it was on was a couple of weeks before the show

I've used them in Ossa and Bultaco, Colin from TY Offroad has used them in TLR Honda - only positives, no negatives

No it didn't, neither did the equally over priced Beamish and Sprite

They've tried to sell this on ebay about four times recently with a £4k starting price, not surprisingly no-one has bid. It's a scruffy looking thing with the wrong exhaust, seat, sidepanels and the tank needs a big repair. I think £4k is ambitious for a restored M10, this one is way over priced, but so is everything they sell. They want £2k for the ropey Beamish next to it