feetupfun

Being a mid 1990s design, that Scorpa is not a modern design (brakes, suspension, weight) so if you want something that is amongst the best to ride, it would not be the one to choose. Another thing is that the modern bikes all feel quite different to ride to each other, so when you say that Gas Gas and Beta seem to be the best makes, you seem to be saying that you haven't tried them yourself. It is definitely worth test riding a few different bikes to see which you prefer. You haven't said how old or fit you are or if you want to ride in a competitive manner. Ideal bike depends a lot on these factors.

First off test the damping with the chrome rod at the bottom. If the damping works nicely that way, you have enough oil in them already. If damping is lost completely when the chrome rod is at the bottom, then you need to add more oil and run them chrome rod up position. The air gap is needed to allow for the volume of the rod going inside as they compress. 12mm shaft x 100mm travel = 11.3 ml. I would leave about 10 shaft volumes of air space = 113 ml of air space. If your shaft is only 10mm diameter, then about 80ml of air space should be OK.

OK so I measured some bikes and here are the wheelbases and footpeg loaction ratios expressed as percentages (100xfootpeg to rear axle/wheelbase) Cota 348 50.75" 28% TY250A 50.5" 28.7% Godden Majesty 250 52" 27.4% M49 Sherpa T 53" 29.7% OSSA MAR 51.5" 26.2% KT250 51.5" 28.2% TY80 41" 30.7% GasGas50 (2011) 39.25" 33.1%

sounds like a stupid question, but are you testing them the right way up?

My theory is that its the ratio that is important rather than the actual distance ie a longer wheelbase needs the footpegs further forwards in absolute terms than a bike with a shorter wheelbase, but the ideal ratio (for trials) of those distances will be independent of wheelbase. The ratio I'm on about is footpegs to rear axle/front axle to rear axle. I plan to do some measuring on the weekend to see what my various bikes have as that ratio. I just measured some bike wheelbases that were easy to get to tonight: Standard TY250 twinshock 50.25 inches Standard Cota 348 50.75 inches Standard Godden Majesty 250 52.5 inches Standard M49 Sherpa T 53 inches sorry my only standard TY175 is in pieces - my memory is saying 48.5 inches for that one

The TY250 swingarm is shorter than the TLR swingarm mainly because the TY motor is longer. The most important dimensions for handling are the distance from the rear axle to the footpegs and from the rear axle to the front axle. Yes a longer swingarm will improve the action of the suspension, but the practical upper limit for swingarm length is that the swingarm pivot needs to be behind the motor (for ease of manufacture). The TY250 wheelbase is a bit shorter than most other trials bikes (TLR included) so some people add a bit of wheelbase to get them to be more like other bikes to ride. If you do extend the swingarm, I recommend moving the pegs rearwards to correct the resulting fore-aft weight distribution change, and to add any extra length to the rear of the lower shock mount. You can safely add 25mm to the standard TY250 swingarm and it will still be one of the best turning twinshocks around.

fit the bearings to the crankshaft first by heating the bearings. When the crank is cool (some people put it in the freezer to get it nice and cold) heat the casings to fit each side, one at a time. That will minimise the side loading on the crankshaft. If there is too much resistance when the bearing outers are being fitted into the cases, pull them into place with a puller rather than pushing on the other end of the crank. Work out the positions for where you want the bearings to go before you start, so the bearings end up at the right spot in the casings. Once you have worked out the position, you can use the seal carrier as the stop for how far to insert the bearing. One way to do this is to use the old gasket and the chosen shims.

Brian I will be getting a hold of the SWM brake shoes next week. Mark has avoided yet again servicing the brakes because he has some shoes from his other SWM to lend me

Moving the motor will upset the left-right balance of the bike, which for most people is more important than gaining additional chain/wheel clearance

yes the bearing inners rest against the crankwheels on both sides. The shims are to hold the crankshaft in the right spot so the conrod runs in the middle of the crank pin. Be careful you don't bend the crankshaft during assembly of the bottom end. This is a common mistake whe rebuilding motors that have a crank that can be adjusted side to side and it causes the primary drive gear teeth to bind at the tight spot. I suggest that once you get the crank in the middle, you make sure it is straight before deciding what shims to fit for final assembly. The motor was made to use 0.5mm thickness gasket material for the crank seal carriers and the centre gasket.

Sorry Brian I haven't got that far on the M198 yet. I might be able to try the Fantic type shoes more easily now though because my riding buddy Mark bought Steve Harvey's SWM which I think might have the same shoes as a Fantic.

Pommy says "don't you know the Queen's English?" Aussie says "yes I'm sure she is"

I think Brian is asking about the front brake

I suspect that having the offset pivot ends on the Bultaco is not helpful because it twists the shoe. They make it tricky to adjust the shoes outwards too! I moved the pivot holes inwards on my M49 to move the shoes out, by making bigger holes on a new centre and fitting bushes in those holes. Lots of work compared with the more common rocking pivot design. Also I think the material that the linings are made from is important. There is a big range of friction material in the market. One of the best I have found is whatever my local brake shop used to reline my KT250 shoes with. It works brilliantly. Another thing is that not all Hondas have brakes that work. I rode an otherwise beautifully set-up TL125 and it had a nice solid feel to the brake lever, but absolutely no retardation. We had swapped bikes and when the other rider came back with my bike he commented on the way my brakes had worked. I don't know how he even rode that Honda in sections. Just thought of another thing. My OSSA MAR now has great brakes after lots of attention, and there was one thing quite unusual I had to do to get them so good. The axle hole in the backing plate was not concentric with the shoe OD, and there was not enough clearance between the axle and the backing plate hole to get them concentric in service. A bit of filing to enlarge the axle hole in the backing plate was just what the Doctor ordered. Maybe some Bultaco backing plates are also not perfectly concentric? ps your Mother is looking very good tonight

TY175 frames distort and the footpegs bend down and the swingarm may crack too if an adult-sized person does repeated pancake or rear wheel landings from even only 3 feet high to flat ground. As for poor old Handel, he'll be Bach in a minuet Jumping up 3 foot ledges is a doddle but if you deliberately overjump the ledge and land on the rear wheel repeatedly, you will crack the swingarm

yes that is where they go, and they are to locate the crankshaft in the right place. You will need to understand shimming to put that motor together without damaging it

for what it is worth, the motor in the Majesty video is a 320

For second hand parts ebay is good New parts: In Motion Trials in the UK and South West Montesa in the US For more detail you might have to say what parts are you needing and where are you located

Another thing to consider is the (lack of) corrosion protection provided by running weak premix ratios and synthetic premix oil. Semi synthetic premix oil is better for protection from corrosion.

and all I can tell from that photo is that it is probably a post-1972 model 247. The tank/seat is pre-76 but that really doesn't say much because it is common for 247s to have the wrong year seat tank fitted. A photo showing the clutch cover and knowing the engine and frame numbers would help with the dating process What is the silvery looking lump on the front downtube?

Those rims are for tubed tyres The second plug hole can be used for a decompressor. Some people used them back in the day It is also possible to use the second hole for a sparkplug suitable for riding on the road. Quick change over of the cap when you go to ride trials again without any tools needed.

yes swapping yokes is probably easier than making changes to the frame, but it can't achieve the desired result. Apart from the theoretical reasons I have already posted, evidence for this is that if it worked, fitting different yokes to twinshocks would be a popular modification. What is popular, is fitting the forks and yokes from a later model bike, which improves the action of the front suspension. Making the steering more like a modern bike requires a steeper steering head angle.

All you do by altering the yoke offset is to change the trail and the wheelbase, does nothing to the steering rake angle. Steering rake is the angle of the steering head, not the angle of the fork tubes. If you increase the trail by using different yokes, you will need to move the axle forwards (ie use leading axle forks) to regain a decent trail dimension. Eccentric sleeves in the steering head or on the steering stem are used on other bikes to adjust the steering rake, but I suspect the Ty175 steering head is too small a diameter to fit eccentric sleeves. Another issue to consider is that if you just make the rake angle steeper without also moving the steering axis forwards, there will be clearance issues with the front mudguard on the frame and exhaust. Another issue with just steepening the rake angle is that you will shorten the already-short wheelbase

ACM has been going for two years now in Australia and the experience has been very much as old trials fanatic has already described, including the lack of Fantics. We run them on the same line as the Twinshocks. I would like to add that I would not count on too many new people coming to ride "old-bike" trials because of ACM class, rather it is riders who previously would have ridden Twinshock or Pre 65 who are riding the Air Cooled monos. I suggest you have a later cut-off than 1990 so that Yamaha Pinkys can ride.

does it really lock up the gearbox, or is it just dropping into gear?