Ossa Mar

[metisse]

Have been thinking about buying an Ossa around the 75/76 age to compete in the Pre 77/80 class in France and Spain.

Could any of the officionardos of the Marque point me in the direction of what to look out for and any sensible things/mods needed to bring it more up to date.

Not interested in making it something its not..... just want it to run and ride as well as it can.

Thanks in advance.

[b40rt]

Hi metisse, are you anywhere near Toulouse ?

Thanks Ross

[metisse]

Hi Ross,

About two hours away. I am north of Toulouse and towards Bordeaux in a little town called Sarlat.

[b40rt]

Hi metisse, I have sent you a pm.

Thanks Ross

[woody]

Hi Hamish - be a nice bike for that class.

There are 3 versions though.

MK1 250 up to early '74.

MK2 from mid '74 up to late '76 which included the 310 from late '75.

MK3 from late '76 up to mid '77 which was the MK2 with longer front forks and angled rear shocks,. At some point it also got the longer front pipe, but that could be classed as a '77 version.

Not much to look out for that differs from any other bike really. If looked after the motors are very reliable. Gear selection can sometimes be not as positive as others, say a Sherpa, but that can be caused by the gearbox not being shimmed correctly when reassembled. Having said that, shimming is a nightmare and trial and error and I've had them working perfectly, only to find no shims at all when the engine has been stripped for a crank rebuild

They're a nice handling bike, pretty neutral but with quicker steering than a Sherpa or Cota. The MK1 up to early '74 has a shorter swingarm so it is very nimble in tight stuff and changes direction quickly up rock streams. The MK2 had the swingarm lengthened by 1.25" to make it a bit more stable up climbs and grip better but you'd b hard pushed to tell the difference if you didn't know. The MK2 also has a bigger crank assembly, therefore the MK1 should pick up revs a bit quicker due to less weight to get moving. The MK3 felt too tall with the longer forks and angled shocks and most riders dropped the yokes and had about one to two inches sticking out from the top yoke. The shocks were maybe a bit too angled though. On the green bikes they raised the top shock mount a bit but they are '77 bikes.

The 250 engine has a lazy power delivery, being quite soft in comparison to say a 250 Sherpa. They rev like hell so 1st gear covers a lot of options in sections. The head gasket is actually an alloy spacer and comes in several thicknesses, so compression can be altered by that means. The thinnest is 0.5mm. Standard they generally came with a 3mm spacer, which is what most probably still have. The thinner versions were probably for the motocross bikes. The later green bikes had different porting I think and having tried a standard one for the first time ever a couple of months ago, it definitely picked up quicker than my MK1.

Front forks are on the softer side but work very well with a nice action, far better in my opinion than Montesa or Bultaco or anything else from the mid 70s. Back end works well with good shocks fitted. Even with good shocks, the older Sherpas can feel dead at the back but you get plenty of feel from the MAR.

Brakes are as good/bad as anything else from that era

Motoplat electronic ignition was standard on bikes up to the green versions when they also used points, going back to electronic on the Grippers. It can fail but Bradford Ignitions can repair the stator. The combined coil/CDI unit is still available new.

The clutch lever requires a pair of stilsons to operate and if you're lucky may finally disengage by the time you reach the next section.... I've fitted Barnett friction plates to mine which have a greater friction properties than 'cork' plates, therefore require less spring pressure. They also break immediately with no drag. With these fitted and the clutch arm lengthened, the clutch is quite useable. The springs can also be adjusted with the clutch cover still on as you can get at them through the inspection cover - unlike the bloody Sherpa...The nature of the engine though means that you rarely have to use the clutch in sections. The bike can come to a virtual standstill without stalling with the clutch still engaged.

I also have a '75 310 MAR and that is a better engine than the 250 (personal preference obviously) It pulls stronger from the bottom and can easily use 3rd in sections if I need. I prefer it to the 250.

In terms of mods, the chassis doesn't really need any, other than maybe lowering the footrests to compensate for modern bars which are lower than the bars fitted in the era. I've fitted my own silencer to replace the standard one which can get a bit noisy (it has no packing, just two baffle plates)

Carb was an Amal 27mm as standard but they were unique to the Ossa on the MK2 / 3 versions as they were a stub push fitting, not bolt on like the MK1. You can't buy them new but Mikunis were a period conversion anyway. Only mod for the engine is a reed valve which wasn't a factory option but was done by Ossa UK in 75/76. Certainly gives the 250 more torque and pull in higher gears. 310 doesn't need it.

If you want to get really clever, 310 reed valve engine with a 250 crank gives a 280cc motor. The reasoning behind this was that the 310 had better power but was a harsher engine, whereas the 250 revved higher and was smoother. The 310 with the 250 crank (shorter stroke) gave more power but retained the smoother 250 characteristics and higher revs. This needs a bit of work to the cylinder to get the port timing back though, spacer under the barrel and about 4mm taken off the top of the barrel. My own experience is that my 310 revs just as mentally as the 250 and isn't any less smooth, which is why I prefer it. That and the red / green stripes...

In my opinion, all you need for the Pre77 class is to get the bike working with decent brakes, suspension working well, engine to run as it should with clean carburation, Barnett clutch and lighter clutch action and that's it. 310 would be my preference but 250 is still perfectly capable - plus, the 310 is quite rare from that period. Footrests lowered is personal preference.

[metisse]

Cheers Woody,

Just the sort of info I was looking for.

Thanks for taking the time to jot it all down.

Merry christmas and look forward to seeing you again down in my neck of the woods

[trialsrfun]

Thank you Woody for an interesting & informative feature on the MAR.

I am currently restoring a TR77 Verde which I believe to be 1979 or 80, frame & engine no. begin with 700 which seems not to appear on any lists I have seen.

The sump guard is made from pressed steel, looks like a No. 10 shovel & weighs a ton. Luckily I was able to source an alloy shield which will be used on the finished bike.

Forks are Betor and longer than those on the earlier model, presumably the same as on the MK3. Rear shocks are moved rearward at the lower end & down to the upper side panel screw level at the top mount position when compared to a MAR, though not as far down as the MK3.

When I got the bike it was semi dismantled so I have yet to see it on its wheels, with the forks dropped through the yokes a little is the overall height then similar to the MAR?

I think there were some gearbox changes to the Verde model as well, do you or anyone here on TC know what the other differences were & how did the Verde bike ride when compared to the MK1 2 & 3 versions?

Edited December 24, 2013 by trialsrfun

[woody]

It's difficult to give an impression of the TR77 against the original MAR as my experience of the later bike is virtually nil. Just a brief go on a standard bike recently, as mentioned above and a go on Martin Beech's reed valve TR77 many years ago, but neither on proper sections.

Many years ago, I had two consecutive MARs, both '74 bikes. I really liked them and the second one was probably the bike I gelled best with out of all the bikes I've ever had. It had to go as I'd started work and needed another car. I bought another bike as soon as I could but it was a M159 Sherpa 325, not another Ossa. Not long after, my brother got a MK3 Mar. At one trial the Sherpa wouldn't run right so I took the MAR and used that, first and only time I've ever ridden one. My impression was that it was a tall bike compared to my earlier ones and that it didn't feel quite as stable. It was as standard, so the forks weren't pushed through the yokes, it was still like a chopper. I thought they'd spoiled the bike at the time.

On all the bikes, MK1 through to the Verde, the frame is exactly the same on each. The only difference is swingarm length, fork length and shock position. The MK3 on had more ground clearance than the previous bikes thanks to the longer forks (2" at least) and the repositioned shocks lift the back end slightly by pushing the swingarm downwards to the rear. But they seem too tall at the front with the ground clearance lessening towards the rear. If you an find a picture of one side on, you'll see what I mean.

Dropping the forks through the yokes on later bikes, to give the same length from spindle to top yoke as the earlier bikes, should in reality give the same feel as the MK2 as the difference in height at the rear is minimal and could be lost with spring preload, It is that minimal however, it's probably not worth it. I think, with the MK3 / Verde set up this way, if you rode one alongside a MK1 and MK2 and didn't know which you were on, I think you'd be hard pushed to tell which one you were actually riding.

The gearbox changes were needle rollers on the layshaft instead of bronze bushes from the TR77, and at some point, maybe the TR77 again, the addition of two pins to the underside of the selector shaft fork. The only reason I can think of for the addition of the two pins was to keep the gap between the fork tips and the selector drum within the recommended measurement

[trialsrfun]

Thanks Woody for the TR77 info.

Good luck Metisse with your MAR, I think it very satisfying to rebuild a bike to ride, much more so than just buying the latest model you can afford.

Steve Sell @ Marlimar OSSA besides being the place to go for your OSSA bits sells a replacement ignition system if the Motoplat is up the creek. No point whatsoever in restoring a bike if the carb & ignition are past their best.

[heavydabber]

Woody's absolutely spot on with his verdict on the TR77, I've got one myself, and Ossa seemed to think that the holy grail of trials was to increase ground clearance as much as possible and the best way to do it was whack longer shocks and forks on the standard geometry - which gives the centre of gravity of a giraffe. One way to bring it back to MAR geometry (but not for the purists) is fit shorter shocks (13.2"?) and shorten the front fork damper rods by an inch at the bottom, but this requires engineering. From memory if you try to drop the forks too far up through the TR77-type yokes (different to MAR), they foul on the handlebar?

A lot of TR77's also ran Motoplat points type ignition rather than the usual Motoplat electronic. Allegedly due to supply difficulties during the throes of the Spanish industry, but the points are the same as Bultaco/Montesa and are available though genuine originals are better than the pattern stuff if you can get them

[trialsrfun]

Was the TR77 originally fitted with longer shocks than the MAR? Do the inclined shocks lift the ride height of the rear of the bike or because the lower mounting point is at the end of the s/arm does it remain the same.

[heavydabber]

That's a good question and I think the answer's yes, they were around 14" (I think). Certainly the whole bike is "jacked up" compared to a MAR. I've got a Trials and MX News from 1980 with a test of the TR77 and they're enthusing about the nearly 14" of ground clearance - and then describing how the UK contracted riders of the time (Tony Calvert etc) were cutting and shutting the steering head angles to try and get them to steer......I think they were being touted as Ossa's second coming.....

As Woody says, shock angles moved down and up between the MAR, Mk3 and TR77, a good way to tell is to compare the top shock mounts relative to the side panel mounting tabs; the Mk3 has them adjacent to the lower tabs; on the TR77 they've moved back up to the upper tabs.

There's a very useful American website called "Ossa Engineering" with promo pics and quantities by engine and frame number of everything Ossa ever built, TR77 numbers were about 600 in total, I think.

Edited December 25, 2013 by heavydabber

[feetupfun]

I suspect that this might be a Barnett clutch kit

http://www.inmotiontrials.com/product/clutch-plate-set-all-models/

[woody]

No, that's not Barnett. Just look on the Barnett website for part numbers

http://www.barnettclutches.com/ossa.html

If you search the Ossa forum for Barnett, one of the latest topics had the name of a dealer in the US that suppies them, can't remember it offhand. I got mine from Doug Elke ebay shop but that was a while back and he doesn't seem to be around anymore

[scot taco]

In the US try Ossa Planet,Ossa World or Speed and Sport Vintage.I get all of my parts from Alex Snoop in NY,but I,m not sure if he ships overseas.He is a great guy to deal with,but does not have a website,just an email asnoop13@optonline.net

Edited October 23, 2014 by scot taco