old trials fanatic Posted December 12, 2007 Report Share Posted December 12, 2007 Well i have finally for my sins aquired an Ossa MAR Mk 2 Needs a bit of work, dont they all?, so i'm asking for a bit of help and info. Parts needed. Barrel and piston as mine has a couple of broken fins and i am a bit particular about things Chrome fork tubes. Mine are pitted. See above Silencer. Does anybody make an aftermarket one? Does anything else fit? Advice. It's fitted with a dished sprocket. Need a new one. Are these available anywhere? What gearing is the best compromise? Will only be used off road as not registered. My carb Amal Mk1 is showing signs of wear so will need a new one. Should i get a Mk1 ? or a Mk2 or what. If i stay with the Mk1 carb the jetting is currently Main 180, Needle jet 105 Needle U, Slide 2 1/2, Pilot jet 30. Is this right or can it be improved ? Bout it for now but any help and advice appreciated as always Quote Link to comment Share on other sites More sharing options...
woody Posted December 12, 2007 Report Share Posted December 12, 2007 Oh what have you done.... Getting a used barrell or barrell/piston as a pair is going to be a bit of a lottery to find one in good condition. If you buy one without seeing it get them to confirm that the exhaust threads are good. They can appear good and the ring can/will tighten up quite nicely on its own without the exhaust, giving the impression that the threads are ok. When it is on the bike with the exhaust fitted, the load on worn threads of trying to hold the exhaust in will prove too much if the threads aren't good and it will pull out, or just won't tighten when you try and fit it. Then there's the possibility that the piston may be worn and as far as I know there are no pistons in the UK at the moment. You need to buy from the States. If your barrell is ok apart from the fin I'd look to get the fin repaired with weld. Once you have to start forking out for thread repairs and pistons it's going to cost quite a bit. This isn't to say you won't find a good item but just watch out for the above. Keep an eye on ebay as they come up from time to time, Ellastone Offroad, A&B Autos, The Twinshock Shop are all possible sources. I've also been told that the later green bikes had different porting from the MAR. These are the barrells with the cut-outs in the fins (on the 250 that is - the 310 had cut-outs on all models, I'm assuming its a 250 you have) The MAR 250 had straight fins with no cut-outs, so again, something to watch if you want original look. Personally don't know about the porting being different. There is a WES rear silencer but it doesn't bolt straight on, I think you have to modify the outlet of the middlebox or something - whether this means an original silencer won't go back on I don't know. The original type bullet shape silencer is available as a repro from Spain and Dave Renham has had some in the past I think, or see the advert on th Mats Nyberg Ossa site. Forks appear on ebay but are being bought up for the Pre65 fiddle bikes as with anything else. They come up often in the States on ebay. You could buy a set from one of the trail bikes if it is only the stanchions you need as they will be the same - just depends if you can get them for less than a rechrome on your own Dished sprocket no longer available although there must be a few still lying around on dealers shelves. Bikes restored in Spain seem to be fitted with them but trying to find a retailer and then getting one will prove difficult. Steve Sell (think he trades as Marlimar on ebay) makes a new sprocket carrier which bolts to the hub and allows you to fit a modern GasGas type sprocket. He's also starting to manufacture other stuff too. Or you can just use the flat sprocket/spacer conversion that has been around for years from Sammy Miller. Gearing is personal choice, I run low gearing 10/42 but 11/42 is more common. Availability of a new Amal depends on which barrell you have and also which you replace it with. MK1 barrells had bolt on fitting, you can still buy bolt on MK1 Amal new. Some of these barrells also appeared on MK2 bikes, probably using up old stock. MK2 bikes used a push fit MK1 Amal. You can no longer buy these new. Mk2 Amal fits and was used on the later green bikes and Grippers. 350 green bikes used a Bing. Jets for MK1 or MK2 Amal are usually 25 pilot, 106 needle, 160 main, no. 3 slide, needle on middle clip. There is only one needle taper on the Amals (for 2-stroke) Anyway, a splendid choice of bike - you can look at the picture of the MAR on the Classic forum that Mr Greeves is about to buy for inspiration.... Quote Link to comment Share on other sites More sharing options...
02-apr Posted December 12, 2007 Report Share Posted December 12, 2007 Or you could do the period Miller mod and fit a Mikuni. Quote Link to comment Share on other sites More sharing options...
swooshdave Posted December 13, 2007 Report Share Posted December 13, 2007 Or get the Amal resleeved. Better than new. And costs less. Mikunis are for people who are lazy. Quote Link to comment Share on other sites More sharing options...
old trials fanatic Posted December 13, 2007 Author Report Share Posted December 13, 2007 Thanks for the advice guys. OOOOOOH i do like the look of that Ossa on the Classic forum. Incidentally a lot of the "mods" on that bike are the same as the ones i was thinking of doing so looking promising. Dont want to get too radical as i have always liked the look of the Ossa MAR especially the Mk1 but just want to make her useable and pretty to boot Will post some piccys when i get a bit more done. Keep the posts and advice coming guys Quote Link to comment Share on other sites More sharing options...
greeves Posted December 17, 2007 Report Share Posted December 17, 2007 OTF you can have a look here: http://ossacels.com The barrel you have to work it out slowly, not so easy, but maybe I can find one for you. Quote Link to comment Share on other sites More sharing options...
woody Posted December 17, 2007 Report Share Posted December 17, 2007 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 Quote Link to comment Share on other sites More sharing options...
daveh Posted January 14, 2008 Report Share Posted January 14, 2008 Forget the dished sprocket. Spindles are only 12mm dia and a tendency to bend. The SM conversion acually incorperates another bearing (4 in total for the rear wheel with this conversion). Bearing no 6210 RS(Rubber Seal) size 12mm-32mm-10mm. Same bearing for front wheel x2. Quote Link to comment Share on other sites More sharing options...
woody Posted January 14, 2008 Report Share Posted January 14, 2008 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. Quote Link to comment Share on other sites More sharing options...
mick annick Posted January 14, 2008 Report Share Posted January 14, 2008 Stick with the dished sprocket - I wish I had, and will be conveting back when I get an hour or two. I believe the ossacels website still lists a dished sprocket, though I can't find it at the mo. Mick Annick Quote Link to comment Share on other sites More sharing options...
swooshdave Posted January 15, 2008 Report Share Posted January 15, 2008 Did the Suzukis also have a dished sprocket? Quote Link to comment Share on other sites More sharing options...
woody Posted January 15, 2008 Report Share Posted January 15, 2008 Did the Suzukis also have a dished sprocket? 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. Quote Link to comment Share on other sites More sharing options...
mick annick Posted January 15, 2008 Report Share Posted January 15, 2008 Woody you want dished sprockets... http://ossacels.com/tenda/index.php?cPath=...764efeb7399a107 Mick Quote Link to comment Share on other sites More sharing options...
woody Posted January 15, 2008 Report Share Posted January 15, 2008 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 Quote Link to comment Share on other sites More sharing options...
mick annick Posted January 16, 2008 Report Share Posted January 16, 2008 Woody I've emailed to find out where they are / will they ship to the UK, but no answer yet. I know a couple of people in Spain if all else fails and will get one of them to get in touch. Did you see the mudguards? Look very good... Mick Quote Link to comment Share on other sites More sharing options...
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