feetupfun

I had a test ride many years ago on either an 88 or 89 at Bennoble (Robert Marsden's bike) and absolutely loved it. After riding it, I couldn't believe that people still bought Yamaha monos after that TR34 had come out

The monoshock DT frame is made from larger section tubing and has a longer (heavier) steering head and heavier hubs and brakes than TY175. On all the DT175 twinshock and monoshock models, the swingarm is about 75mm too long for trials use and the extra length is in the gusset at the front end of it. The monoshock DT175 front end with leading axle forks has very limited turning angle due to the lack of offset in the yokes and the width of the frame at the steering head. The frame is much deeper between bottom frame rails and seat rails than than a normal trials bike so body english is limited. Even with all that wrong as far as trials competition is concerned, all you need to do to make them great fun to ride in extreme terrain is to move the footpegs back a few inches so you can more easily ride standing up.

Where I live, the only time my trials tyres see daylight is when I'm out riding and it takes about 5 years from new for Michelin X11 to go hard enough to noticeably lose performance and about 15 years to when they start falling apart

Looks like a very neat job. There's something similar over here made from a 1980s monoshock DT175 converted to twinshock rear end and the big frame tube where the shock normally goes has been used as the fuel tank on it. How does your TS185 go?

Firestone trials tyre with a distinctive vee or chevron pattern to the blocks. You can see them in photos from the period. I've kept a front one for reference.

I've got an early M49 which shares frame design with the M27 and I have found 360 mm shocks work the best for me

What is it about the bike being road registered in 1983 that convinces you that it is a 1980 model?

As a matter of interest in the vibration stakes, did you know that when Yamaha produced the second and later models TY250, they used a lighter conrod design, compared with the A model. This had a noticeable effect. I have a few bikes with TY250 engines and the one with an untouched, original A model engine in it has enough vibration at one particular RPM that the vibration transferred to my body causes loss of vision. This doesn't happen when trials riding because the RPM never stays constant long enough and I'm standing up, but when I'm trail riding in 4th or 5th gear and find that particular RPM and am sitting down, the vision thing happens. When I do the same sort of riding on my other TY250 powered bikes, I don't get the vision effect. The other motors are TY250D model with original conrod and TY250B model with original conrod.

There is usually a price premium for competition eligibility. From what I see advertised in the US, that TY at $US1500 is fairly expensive even accounting for it being eligible for "old bike" class in trials competition. The best value trials and dirt bikes are the ones that have depreciated in value due to age but not old enough to be eligible for bike age class competition. If you aren't a nostalgic type rider there is no good reason to buy a 1970s bike.

Wrong DT by the looks. I bought mine from John Cane. I just now looked up the Yamaha part number shown on the packet on John's page and did a cross-reference using that part number and it says it is made for DT100A, DT100B and TY175. 437-22151 00

The proper sealant stays soft so it's no big deal splitting the cases again. It's fairly common to weld the pin to the crankwheels but the person splitting the crank will be able to tell if that is necessary when they push it apart by how much force it takes.

Turning any trials bike tightly requires training and practice. Your Techno looks completely normal. Yes later bikes have less rake. Later bikes are also lighter, have better brakes and better suspension.

those engine and frame numbers are for a Model 80 (250) Sherpa T which means it would have been made in 1971/72

PM reply about using a flat tool sent and yes you can easily make the tubular tool that Yamaha shows if you have a lathe. Yes the LH end of the A model crank is the same as the LH end of the later models. The RH ends differ slightly because the A has a spline drive and the later models have a key drive

I made a tiny boring bar to machine the ID of the bushes with the sleeve gear in the lathe chuck, because I wasn't confident of getting the diameter right with a drill

I've seen an M49 with a red Clarke plastic tank and it looked pretty good

Here is a photo that shows how the seat/tank unit rests on those lugs

Here is what the lugs would have looked like originally. My photo shows an M85 frame. My other M85 frame (the pretty one in the photo) has nothing there at all and a M80 frame on the other side has no lugs either. The lugs do line up with the side mounts on the airbox like in vintagenut's airbox photo but what purpose they are intended to serve I don't know. As far as I know both my M85s were sold new in Australia and came with fibreglass tanks.

The oil you see is probably condensed vapour/smoke from the combustion process. Modern two-stroke oils can be so good at resisting burning that they can cause what you are seeing. Once the sound absorbtion material in the exhaust is fully wet with this oil and it can't hold any more, it will start coming out wherever it can. It really doesn't do anything except make a mess so if you can manage the mess then you don't have to do anything. If you rode the bike hard enough the exhaust may get hot enough to stop the oil condensing inside the exhaust. Also if you ride it hard enough with oil already in there, it may clean it out to some degree. If you decide to clean out the exhaust by taking it off (it can be cleaned out a few ways when off the bike) but still continue to ride in the same manner, it will continue to fill up with oil. I've seen bikes with a drain line at the low point and when the bike is parked, they put a container under the drain line to catch what comes out.

The part John Cane sells for the TY250 is actually a DT swingarm protector and as he says on his web page, you will need to trim it to make it fit the TY250 swingarm. I just trimmed one for a TY250 swingarm a few weeks ago.

Yamaha TX500 also and many other 34mm tube diameter Japanese forks made by Kayaba in the mid 1970s

Wear grooves in the basket fingers can cause sudden engagement. You didn't mention removing the grooves. Where the lever is when the clutch engages is adjustable via the cam and cable. First set the cam to give 90 degrees angle between cable and cam arm at the point when the clutch starts to disengage. If you can't get 90 degrees then there is something wrong. Set the cable adjustments to put the release point where you want it. If there is not enough cable adjustment then there is something wrong.

A Reflex is probably similar in power output to a standard TY175, maybe even a bit more powerful, so if that was a reason you got rid of the Reflex then a standard TY175 will probably disappoint you. A standard TY175 will also be a fair bit less powerful than your GasGas 200 was. A standard TY175 handles far better than a standard RL250. All the RL250s I've ridden go like a train so if power and a seat are the most important criteria to YOU, then the RL would be the pick. If you like to modify things, the TY175 can be made more powerful and the handling of the RL250 can be improved. They are both good to ride sitting down unless you are over about 5'10" in which case the TY175 will feel camped and the RL250 will be great.

It sure looks like a 348 frame to me. It was a very distinctive series of frames with the removable pieces that go from the swingarm pivot to the cylinder head. All the 348s and the first two 349s had those struts like that. Yours has had extra plates fitted for the footpeg relocation but otherwise looks standard for a Cota 348. As for the engine number, do you know where to look but it has been erased or you just haven't found it? The tank graphics are 1978 model 348

Paul just a thought. I've seen a couple of M199B that have the taper top fork tubes, like a pre-74 Bultaco fork tube. I don't know enough about 198B to know if it's the same with some of them too. If yours is like that it might be a different thread to the tubes with the parallel top tubes. I'll check a taper top tube soon and post up the thread size