feetupfun

It is possible that there is runout at the primary drive gear which causes a noise as the crank rotates (primary drive meshing having no clearance at one point). Easily diagnosed by trying it without the clutch fitted.

I found the MITAS was fine except where a Michelin would conform well to the shape of the edges of hard objects, the MITAs would not conform quite as well. I wondered why until I measured the depth of the MITAS carcass and found it had about 1/2" less depth overall than a Michelin/Dunlop (ie lower profile than Michelin/Dunlop). Less depth = shorter contact patch. Grip on dirt, smooth large rocks and large logs was fine with the MITAS. Test bikes were 2003 Rev 3 200 and 1976 Cota 348.

The WES exhaust on a Yamaha TY250 twinshock frame is intended to have a rubber joint between the front pipe and the main exhaust section. If you don't want that, why not weld a steel sleeve the right diameter onto the front pipe so they will slip together? A photo showing the WES exhaust on a TY250 and also a photo of the footpeg mod you are asking about can both be seen on the B&J racing website. http://www.bjracing.com/ Your bottom frame tube has no threaded end because it is an A model TY250 frame. B and later model frames have a thread in the end of that tube which is there to allow fitment of an alternate footpeg kit made by Yamaha for trail riding.

Hi Scott Yes I got your return message but I thought something had gone wrong as it only had what I had written. Mystery solved. Good to hear Hilary rides Trials. My daughter Zara is 7 and still on trainer wheels on her bicycle. She's not allowed to ride her motor bike till she can ride the bicycle properly. See if you can work out how to send "Private Messages" (PM)s via this forum. That way the messages don't get posted on the public forum. To do that just click on the PM button on a forum posting of the person you want it to go to. That will open a new screen and you can type the message and send it. I'll will send you a PM later tonight. David

Twinshock era trials forks usually have "topping" springs that compress just as the forks top out. It is possible to overwhelm these springs by using a lot of preload on the main springs in combination with light oil. Another possible cause may be insufficient oil ie the oil level goes below the damping holes on full extension. The plastic bushes you should find in your monty forks are "bottoming" cones which generate a greatly increased compression damping rate as the forks reach full compression.

If the backing plate can move after the axle is tightened, there is probably something amiss in the way the axle/forks/spacers/nut assembly is arranged. The backing plate should not be able to move around when you are riding or pulling on the brake. Check that the axle nut is not running out of thread (possibly caused by missing washer, wrong spacers or spacer in backwards or wrong axle or axle in the wrong way around) before it clamps the backing plate between the fork leg and the wheel bearing inner. If the backing plate can move, you will get very poor braking.

Thanks for the story on that bike JayLael. It's interesting about that Hodaka engined bike with the recently made frame being eligible for "classic" class in AHRMA. Are there any limitations on frame construction methods or materials for that AHRMA class?

Pinion puller photos sent by email to Roberto

Hi Scott Welcome to the Australian trials scene. What's this "46 years old!" bit. That is a pretty normal age for someone riding a Twinshock trials bike. Where in Australia are you? David Lahey "47 years old" Gladstone, Queensland

If you are talking about a 348 or 349 Cota, the primary pinion is on a taper and yes it takes quite a bit of force to get it off. Finger type universal pullers are not strong enough. I made a simple tubular puller which worked a treat. If you need help with how to make a puller, let me know.

Are you centring the drum on the shoes as you tighten the axle? Are the wheel bearing outers loose in their seats? Are the wheel bearings worn? Is the axle nut tight enough to hold the backing plate in position? Is the drum friction surface grooved or worn unevenly? Any of these things could give the symptoms you have mentioned (spongy feeling).

That certainly is a pretty unusual altitude to ride a trials bike. You will certainly benefit from reducing your jetting but I have no idea how far having only jetted for a two stroke riding up to 4000 feet ASL. For that I changed the main jet from a 240 to a 180 (Yamaha TY175). There was a fellow who used to post on this site from Indonesia who uses his TY250Z for mountain trail riding in Indonesia at very high altitudes. That being the same motor he may be able to give some guidance. I suggest you post in the Yamaha and maybe Techincal Help forums. It may also be helpful to someone who has jetted a bike for such low density air to know how cold it will be where you will be riding.

The cost of living must be different here. All the talk about how expensive modern trials bikes had me get out the calculator and do some figuring. Based on what a first year apprentice machinist is paid here now ($AU18000 PA) and what I was paid in 1977 for the same job ($AU2900 PA), a new trials bike ($AU1400 Sherpa in 1977 and $AU8500 Beta Rev3 in 2006) both cost 6 months pay. Depreciation rates on trials bikes here are generally $1500 for the first year and then $1000 per year until the bike is about 5 years old by which time bike condition is far more important than the age of the bike.

That frame in the Dirt Bike magazine test may well be a Sammy Miller frame made for a Sherpa and then modified in the US by <mention of this company is not permitted on Trials Central> Specialties to fit the TL250 motor.

The sections for twinshock bikes where I live provide a lower risk of injury with sufficient technical challenge. The twinshock sections are also less tiring which means I can enjoy riding all day.

There is always the option of having a replica frame made but the cost factor is considerable and there are very few people willing to pay. There is lots of labour required to copy a frame and if the production run is only a few dozen frames as it would probably be for people who want to build a TL250 motor Seely replica, you could expect to pay $1500 US to $2000 US for each replica frame.

Craig Mawlam was advertising twinshock Jialing powered trials bikes last year. His majesty moto website doesn't load any more. If you want to make contact with Craig, I think he is eBay seller "c1crm"

I'm glad you are coming to your senses on this. Did you really think you could build a replica of a Honda works trials bike for less $$ than the cost of a modern production bike? What you seemed to be seeking was a high spec bike with many custom built parts. For that you should expect to pay many times the price of a new current model trials bike (unless you provide the labour). Twinshock can be an economical class to compete in but not if you want to ride a works replica special based on something as unlikely as a TL250.

My 10 cents worth for what to include in any proposed UK national rules for twinshock trials bikes: Put an era limit on the bike ie major components of bike must have been manufactured before (say) 1986 Specify which major components are controlled (frame, engine external appearance, forks external appearance) Specify mechanically operated drum brakes and cable operated clutch Specify air cooling Specify twin shocks (not sure about the works OSSA but the idea is to exclude 1985 TY250N Yamaha) Non controlled mods are things which people fiddled with at the time like tanks, seats, mudguards, shockie mounting location, shockie type, exhaust systems, frame chops (steering angle, wheelbase, tubes removed under engines), fork travel Bikes should be able to be bitzas as long as the major components were made within the era or are exact replicas.

I wonder why they spared the engine and tyres from a similar silvery fate?

Sounds pretty likely you have found the problem. While you have it apart, see if you can work out why the washer was like that. Is it possible an impact on the shifter caused the problem?

Mr Clean the XT500/TY hybrid photo posting tells me you've definitely got a pretty wicked sense of humour. I'm beginning to wonder if this whole thing about lightening your TL250 isn't just leading us all on. It hasn't emerged yet why you have chosen the heaviest trials bike sold in that era to lighten as much as possible. Do you enjoy a challenge or is it just a Honda 4 stroke thing? To answer your NEW QUESTION, yes they are completely different bikes. The TLR250 is based on a completely different engine, has a completely different frame and running gear.

I'll assume that you either don't know or that it shifted fine before the big rest. It is possible that the indexing plunger is not holding the shift drum exactly in the right spot. Common causes for this are old gummy gearbox oil on the shift drum and in the plunger cylinder and a drum indexing plunger spring that has relaxed.

What Billy says does make sense but why do you need a battery for the fan? It gets very hot here in OZ and we just leave the motor idling when inspecting sections so the fan runs when needed. Sometimes the motor runs for hours without stopping or problems during summertime (well over 100F) events.

More info needed Neutrals between which gears? Upshifting or downshifting? Does it happen when you shift with the motor stopped? Is the shifter moving back freely after you shift? Is the shifter moving all the way back to the mid position each time? Did it have the problem before the several years rest? Why do you think something is loose in the cases? I suggest you post questions about your 172 in the twinshock or mechanical help forums