woody

Don't forget that those bikes had the pivot point moved forward so if anyone does come up with the length of the swingarm, you need to also know how far forward the pivot was moved. The same length swingarm on the standard pivot would probably be too long. Commerfords only did this conversion to the 340 models, but there was a 198b that was also done at the time by Reg. It was a special order by the customer that purchased the bike from them and was the only genuine conversion to a 250 model

But I imagine he at least wants to enjoy riding up the sections, not get bounced from rock to rock like a flea on speed if he uses genuine pre65 forks

Any 35mm forks can be used and turned down to slip inside the 3TA bottoms - Marzocchi, Ossa, Butaco etc. 35mm is max diameter allowed. For yokes, there are essentially two choices. Either period BSA yokes or the aftermarket billet yokes made by Alan Whitton and others. REH, Ceriani, Ossa, Bultaco etc aren't allowed. By 2015 though, the criteria may have changed again.

Good enough for the selector mechanism yes

You only need take the clutch cover off to check the selector mechanism and spring so start there, as it does sound like a broken or weakened spring. - assuming you haven't smacked the gear lever on something solid, which could present other problems

ok, I see, my knowledge of materials etc is pretty limited so not sure what the one I have is made from. Didn't realise they made them from two different materials, so I'm guessing mine isn't aluminium. They never mentioned materials when I tried to buy mine. Three times I've tried to buy a carburettor direct from Amal and three times they've told me I'd have to wait about 5 to 6 weeks as they didn't have any built up and the next production run wasn't due for another few weeks. I bought it from Surrey Cycles in the end, delivered next day.

ok, didn't realise they were different. New concentric - do you mean the Premier with side fixing pilot jet? I've got one on the BSA and the low down response is much better than the standard concentric I had before. It no longer has an erratic or unpredictable pick up off idle. Now pulls cleanly and smoothly from idle every time.

Thanks Mick, I did wonder initially if it was referring to monoblocs but as we were talking concentrics I assumed concentrics in the end. Can this trick be used on concentrics? I don't know what those bleed holes actually do. Someone did explain once but I've forgotten. As usual...

ok, understand that thanks. You could just try a 2 stroke jet then as they are the same but without the holes, saves the soldering.

Can't advise on the best option of 22 or 26mm for an Ariel, but if you're buying a new carb I'd consider the new Premier version with the pilot jet in the side. I've fitted a 22mm Premier to my BSA which is a long stroke C15 (337cc) and it's an improvement over the normal concentric. Much much smoother and predictable off tickover and seems stronger through mid range to top end. Main jet is 130 and needle is either 105 or 106, can't remember which. Pilot is a 17 (new numbering convention for these as they are completely different from the normal pilot jets)

I'm lost with this one ?? What hole, where? Needle or needle jet? The needle doesn't have a hole in it. The 4 stroke needle jet has two holes at the top, the 2 stroke needle jet doesn't have any.

They're gone as I machine them down to them. Never had a nut come undone so it's never been an issue, although it should be possible to drill new holes in what's left of the nuts, just in a different position

One thing to be careful of if backing off the spring tension is that the nuts will foul the inside of the clutch case and it's not pretty if you start the bike and that happens - trust me... They can't actually be backed off that far before they do foul as they are quite deep. What I've done is machine them to half their depth which allows them to be backed off as far as you want without them catching the case. With Barnett plates fitted, they require less tension, so a light pull can be achieved on the lever without the clutch slipping. The only pain with the Bultaco is that adjustment can only be done with the cover off, so if you back them off too much and then find it slips, the cover has to come off again. I generally set mine by riding it around the garden with the cover off before fitting it all together.

On thing to check is that the pins that the nuts screw onto aren't bent slightly. They're pretty weak and bend easily. If just one is off centre, the cup that the spring sits in can foul on the pin and stop the pressure plate coming off 'square' on that pin, the result being, the plate doesn't come off as squarely as you think it is. Take all the springs and cups out and eye up the pins in the holes of the pressure plate. They should be dead centre. If not, they're easily bent into the correct position with a screwdriver. From what you've said, your adjustment of the freeplay on the pushrod has been done correctly, so that brings you back to spring tension. Once you're satisfied the pins are true, reset the tension. They don't all necessarily need the same tension to get the pressure plate to come off square. I've had them where one is a full turn more / less that the one next to it. Is the clutch arm positioned correctly on the timing cover. If the angle is too far forward you may not be getting full travel on the rod. Correct number of plates fitted?

Glad you enjoyed it, thanks for the support. Not a bad entry for a boxing day trial. A bit wet... the weather over the last few days had rearranged some sections, blown markers out and the stream had risen and removed tape as well as markers. A bit of re-plotting needed this morning because of that, plus marking out 9 and 10 but the sections seemed to ride well enough on the whole, from speaking to a few riders during and after Results will go on front page when done, but probably not until tomorrow eve earliest at a guess

Yes, Speed and Sport was the dealer someone recommended previously

Yes, OTF, I had one on a Majesty 320. Reasons I did it were several The Majesty had been modified with a steeper head angle (and I wouldn't do that again either) and was fitted with mono forks. The result was a shorter wheelbase, even with the leading axle forks, so the swingarm needed to be lengthened. I had several choices, lengthen the standard swingarm, get another to lengthen or, I had a mono swingarm which I could modify to fit. I didn't want to ruin thae standard one, couldn't be bothered to wait for another t/s arm to come along to lengthen so I decided to use the mono item. Plus, the Majesty rear hub was broken all around the flange, so I could use the mono wheel with the swingarm (as I had a complete mono in the shed, fit for only breaking) And finally, it was an easier job for me, with limited welding / fabricating skills to make the mono fit. The mono arm is way too long in its standard length. I cut the front pivot mounts off, far benough back to give the length I wanted. Welded on a tube, same ID and OD as the original to utilise standard bushes / tube, spindle etc. Made up mounts for the shock mounts and in it went. Would I do it just for the sake of it? No. Basically, a swingarm is two sticks of metal attached to the frame one end and carrying a wheel and shock mounts at the other. There is no advantage at all in replacing the standard arm with one from the mono. I did it for a reason, as above, but it didn't work any better than a standard swingarm lengthened. It was still just two sticks of metal etc. Unless you've a specific reason for doing it, it really isn't worth the bother and will offer no advantage at all.

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

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

There's nothing in the rules as far as I'm aware that prevents this but the practicalities of sharing make it difficult. By the time one has ridden the section, gone back and handed the bike over, there is a fair delay before the second rider completes the section. Especially if it is difficult to get the bike back to the start of the section, depending on section location etc. Multiply this 40 times for a 10 section 4 lap trial and you could still be on your second lap when all other riders are finishing. Then you have to consider observers, who aren't going to hang about for a prolonged period for two riders as they'll think you've retired when you don't appear on consecutive laps like everyone else. You could put your faith in the goodwill of other riders, queue together which means that when rider 1 rides the section, rider 2 stays at the head of the queue and rides immediately the bike is returned. If other riders are willing to let you get straight on it and ride, it would at least get you through the sections quicker. I guess some will be accommodating, some will whinge.

Just the trials, there's no practise at the venue

Yes, given the conditions, that's the best option. Been up today to set sections. Very very wet. The weather forecast for the venue, on the BBC website which I checked before I set off this morning, said fine weather from tomorrow through to 27th, so sections will dry out to some extent and have been set with that in mind. Then I get home and see an all new forecast with torrential rain forecast nationwide tomorrow and carrying over onto Tuesday... Great, the weather shafts us every time we have a trial. Never mind, it'll be ok on the day, I'll be up there at first light on boxing day to make any adjustments

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.

I've used Shell V-power (optimax before that) for years and have had no issues with fibreglass or rubber being eaten away. I don't drain the tanks, the fuel is left in.

Yes, I've used them as well as others I know They do a very good job, therefore get a lot of work so they're always busy. Turnaround is usually a few weeks, plus you're right in the xmas period as well.