feetupfun

Excellent! Can you explain how this process works?

Dry blast then paint works very well

Yes, I've got one that I'd be happy to sell. It's too wide to fit the bike I bought it for. Location Gladstone, Queensland

A standard TY175 motor is 66 mm bore and 50 mm stroke which is 171cc swept volume. Your cylinder at 67 mm bore and 50 mm stroke has 177cc swept volume. After seeing your photo (showing 8 mm studs a lot longer than standard studs), I suspect that your crankcase cylinder mouth was earlier enlarged to match a bigger cylinder sleeve to allow the cylinder to have a bore somewhere in the range 70 mm to 72.5 mm and that "200cc" cylinder was later replaced with the standard cylinder that you are showing. If this is the case then it would be interesting to know if there has been something done to match the diameter of the standard cylinder sleeve with the enlarged crankcase cylinder mouth.

For a period of about two years a few years ago I had very severe reactive arthritis which is a normal and lingering after-effect of Ross River Virus. It mainly affected my fingers, wrists and elbows. It meant I couldn't hold on well. Through that period, I avoided any sort of heavy loading on the front end. To help with comfort in smaller stuff, I backed off the fork spring preload slightly and ran lighter fork oil and experimented with handlebar position all of which made the bikes easier to hold onto. All my trials bikes are twinshock era which I find are generally easier on the arms and hands than modern bikes. I also found that my heavier twinshocks were easier to hold onto and rode smoother than the lighter ones.

A DT175 barrel has different finning to a TY175 barrel. A DT175 head has different finning to a TY175 head and has two plug holes. A DT175 head and barrel is held on the same as a standard TY175 head and barrel is held on. Your next question is probably going to be where to get an oversize piston from for your big-bore motor. For that answer, you'll need to take some measurements. Bore diameter (accurately) or read the numbers on the piston crown. Piston pin centre to crown dimension. Was there a spacer under the barrel?

Here is a set of Gate Trials rules stolen from the Supp Regs for a Trials Club of Canberra Gate Trial. Their rules are slightly different to ours: This Trial will be a Gate Trial. These are the TCC Gate Trial Rules. • Highest score wins • Blue arrow / gate = 1 point • Yellow arrow / gate = 2 points • Red arrow / gate = 3 points • Maximum score per section is 7 points • If you put your foot down (dab) you score 0 points for that section • Only ride the arrows / gates you are comfortable with • It’s very easy to get greedy and end up with 0 points

Any trials bike. All over the world. The degree of difficulty is the same as what the riders would normally ride in conventional trials comps. There are three levels of difficulty and you choose your level of difficulty all the way through the section by choosing which gates you go through. In my local area, there are two clubs and a total of twelve trials per year, one of which is usually a gate trial. Gate trials are great for getting people thinking outside the box.

The first footing being a fail for the section is what I'm familiar with and seems to work well. Instead of the usual scenario of the best rider winning, it becomes a scenario of the rider who best knows their own ability who wins. Riding very conservatively won't win, but riding just conservatively enough to avoid footing gives the rider the best chance of winning. We run our gate trials with only one Observer and all riders completing the one section before moving to the next section. This makes it a very social event with lots of coaching and support for riders from the other riders. I love the mental challenge involved in deciding which gates to leave out. It can be quite a challenge for some riders to accept that rider skill is not the main factor in winning the trial. I don't know of any written rules, but with ours: Highest total points wins. Points are gained for riding gates. Either 1, 2 or 3 points per gate. Footing is a fail (zero points for the section). There are a total of eleven (I think) points available in each section. The most difficult gates tend to be worth only 1 point and the easiest gates tend to be worth 3 points.

A faulty thermostatic fan switch is one possible reason for a fan not running and very easy to test for by bridging the switch with the motor running.

As for John Cane's photo, yes he put it there because it's easy to get it wrong. It's no surprise that people get it wrong with the available parts diagrams being so incorrect. Did you compare the length of the spring+spacer that went in compared with what came out?

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Measure the sag on the fork tubes. The zero position for fork sag is with the front tyre off the ground. Your damper rods are early TY250A (welded-on bottom end). Later TY250 damper rods have the bottom end reduced diameter section made using a swaging process. Yamaha commonly change the design of something but retain the same part number if the two designs are interchangeable. Yamaha didn't make TY250 forks. They were made by Kayaba to Yamaha specs. Kayaba changed the design of TY250 twinshock forks in many ways between the first and the last version but they are functionally the same and the parts are inter-changable.

John Cane has a reference photo on his website showing TY250 fork internals which might help you. https://www.tytrials.com/trailandtrialsuk/cat_88541-Front-Forks.html

Your photo shows TY250A forks apart from the fork spring which is single rate and longer than standard. The standard spring is dual rate, thinner wire, shorter and the ends are tapered on the OD. The spring in your photo looks like what I bought from B&J Racing about 15 years ago to try in a TY250. The B&J set I bought were exactly the right length to use without any preload spacers. In my opinion, the Magical springs provide a superior action for most riders compared to both standard springs and the B&J Racing springs. The parts diagram you said is from "Majesty" is not showing TY250A forks. It is from the TY250 Owners Manual but sadly is not what TY250 forks look like. The TY250 fork diagram from the TY250 parts book also has a few mistakes which can cause confusion. Your forks in your photo look standard except for the fork spring.

If you are using Magical springs with original damper rods, for your weight, 10 weight fork oil should be OK. You didn't mention buying the aluminium damper rods so I'm assuming you are going to use the originals. To start with, set the total Magical spring+spacer length the same as the original spring + spacer length. That will be a few less mm preload than original because your original springs will have sagged a bit over time. For reference, standard A model fork spring free length is 400mm. When you have done that, measure the sag with you aboard and adjust the preload until you get about 60mm sag with you with all your weight on the pegs. Once you have set the preload, go for test rides to see if you want to change to 15 weight oil. Standard TY250 forks have very light damping so I wouldn't go below 10 weight fork oil. If your forks have the drain holes on the sides (early A model) then the standard oil quantity is 175 ml per leg. If your forks have the drain screws at the back (everything after early A model) then the standard oil quantity is 162 ml per leg. The two types of forks have different design (different volume) damper rods.

The cam face can be refinished by welding and machining. The cam end of the pushrod may need to be refinished too. It's meant to be hemispherical. I've seen NOS cams advertised on eBay. Yamaha and EBC and Goodridge are good. Haven't tried Vesrah. Yes milling the grooves is a warping risk but some people do it. I would think you can buy new steel plates from Yamaha if you think there's a problem. I use wet-and-dry paper on mine. I'm still using the original steel plates after four rebores and two new conrod kits.

A lever arm extension reduces how far the plates move apart so can make disengagement worse. Old friction plates can make disengagement worse. If they are more than few years old I would replace them. It usually takes quite a few hours of serious clutch punishment to polish the roughness out of the steel plates. Yes bead blasting is a good thing for the steel plates, as is 120 grit wet-and-dry paper lubricated with kero. Some people mill grooves in them with a milling machine. Anything that helps the air to get in between the plates without bending the plates is a good thing. Is the pressure plate staying parallel with the basket as it moves out? Is the cam face pitted?

The LT ignition wiring from the magneto to the HT coil is usually black coloured. The other wires from the magneto are for lighting and should be insulated from each other and the frame. It doesn't matter how you make the connection for the LT ignition wiring as long as it is secure and electrically insulated from the frame. Bultacos usually have a wiring connector strip near the front downtube but using it is optional. One wire from the kill switch connects to the LT ignition wire. The other kill switch wire connects to the bike earth (frame/motor/stator plate)

One way to help know what year a Rev 3 is, is to count the spokes. The wheels changed from 36 spoke to 32 spoke in about 2005. If it was me buying it, I wouldn't care what year model Rev 3 it is. They are all good to ride. Condition would be the important thing. From the photos it is impossible to know if it is a 200, 250 or 270. The 125 had a different exhaust to the one in the photos.

An excellent outcome

The "American" stator coil and the "European" stator coil are probably the same item and the difference in resistance values you are seeing in the reference material is probably a typographic/transcription/translation error. I have looked at my reference sources for that resistance value and found the same error as you found. If it was me I would just rewind it with the same number of turns, using the closest wire diameter I could find to the original. The resistance value of the stator winding is not a critical value. It is provided in workshop manuals for fault-finding purposes.

There should be a circlip on the shifter shaft on the left side of the motor. The circlip bears against the shifter shaft oil seal and prevents the shifter shaft from moving towards the right. It may not be immediately visible because it may be concealed inside a plastic roller/wheel that protects the shifter shaft from the chain rubbing.

Maybe one of the gudgeon pin clips came loose and put a big groove in the bore and it needed a 2.0 mm oversize re-bore to clean up the bore so they could keep riding it?

0.015" is good. 0.15" is way too much.