feetupfun

The tool that is labelled as crap is perfect for setting the motor to TDC, and this is useful because a timing mark can be applied to the flywheel rim using a measured distance from the TDC mark. Once you have the timing mark in place, the points can be set on future occasions without needing any tools in the sparkplug hole. The circumferential distance between the TDC mark and the timing mark can be derived from the geometry of the motor components, or by using a dial indicator. The timing mark can be used to check the timing while the motor is running, using a timing light, which is the ideal way to test for correct timing.

I use 340mm Falcon Trial Classic shocks with standard damping and 50 pound springs on my TY250 twinshocks and have found them to have a fantastic action. 350mm shocks will fit OK, but if you want to fit 360mm shocks, you will need to do some work to prevent the swingarm hitting the brake pedal return stop. I haven't compared Falcons with NJB Experts for action because it seems that everyone that I ride with use either Falcon or Betor shocks. I find the steering is perfect with 340mm shocks so have not pursued using anything longer.

I couldn't understand the rule about eligibility of exhausts (or the need for a rule) so I think I am missing something in the translation. Same for the section on brakes - increased leverage on the brake camshaft maybe??

wow thanks greeves. Does appear to be quite strict. I'm going to do a machine translation into english and have a read

No thread. Its on a taper and they are typically hard to get off. Make a puller that spreads the load over the whole circumference of the gear and you can really go to town loading it up. Loading+heat+a sharp tap on the end of the puller got mine off

I didn't see anybody say this yet but on a 2 stroke, yes you should always kick with the throttle at least part open - except when it is cold and you have the enriching circuit on. If you open the throttle, the enriching circuit does not work.

Check the cap by squeezing a hose when the motor is up to temperature.

Here are the SWM shoes on the Bultaco backing plate illustrating the different spacing of the shoe pivots and camshafts of the two designs

Here are the SWM shoes in the front drum of my M198. This drum has just been resleeved and then machined to standard diameter. I took two photos - one as Brian asked for with the pivot ends touching and in that position the cam followers are not parallel and are 16mm apart at the narrowest part. The other photo is with the same SWM shoes held so the faces of the cam followers are parallel with each other In case anyone is wondering no they are not my hands in the photos

Will do

OK Mark brought over the SWM TL320 front shoes tonight. They are pretty close but some issues were visible comparing the shoes side by side. It looks like the PCD of the shoe pivot and camshaft centres on the backing plate are slightly different with the SWM centres being slightly closer to the axle. It also looks like the SWM cam is a different thickness to the bultaco cam. It would be pretty easy to get the pivot end of the shoes to fit, and get the pivot centre of the shoes in the right place at the same time. I might be able to get a bit more info by trying to fit them to the Bultaco but that will be a job for Later Ron - probably next weekend

The lengthened swingarm on my TY175 made it more relaxing to ride (due to the increased wheelbase) and the rear suspension worked better (due to increased wheel travel).

Yes there is an obvious trend - motors were developed over time to be shorter so the swingarm could be made longer

This is my hotrod TY175 showing the swingarm extension of 45mm behind the bottom shock mount

It might be different where you live, but where I live, bikes are fully depreciated age-wise within about 5 years, in other words they stop getting cheaper once they are about 5 years old and their value depends almost totally on their condition. This means you can buy something that is still a relatively modern design, but for similar money to a much older design bike (like that Scorpa). Bike design jumped ahead in the late 1990s and early 2000s when the Gas Gas was made a lot lighter, the Beta Rev 3 replaced the Beta Techno, 4 pot front brakes became standard fitment and Sherco came onto the market. Improvements in design since then have been incremental. Another change was in the mid 2000s when 4 strokes were released, but now this change which was seen as important at the time, can be seen as being just a ripple in the pond, providing something for people who prefer to ride a 4 stroke.

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.