feetupfun

I do have a M198 (a 238cc Sherpa T contemporary to the M212 Alpina) and it came with the original piston, so I will dig that out and take a photo

Only the M99 (325cc) Alpina model barrel is the same as the M92. After the M99 model Alpina, the stroke was made longer to make them 350cc, so the later Alpina "350" barrels are also longer, so are not the same as the (325cc) M92 barrel

Bultacos of that era used the same basic piston but the induction side skirt was shortened on the models that were designed for top end performance (Pursang, Astro) to increase inlet port duration. Not having a reed valve meant that shortening the skirt was a compromise and took away from the performance at low RPM. Alpinas and Sherpa Ts that I have worked on mostly have had the full length inlet skirt but some have had pistons with shortened inlet skirts (and other porting changes) that were previous owners work. People do fiddle around with engines. The important thing is that the inlet skirt provides the correct inlet timing. If you want to be certain of the inlet timing, you can confirm the inlet timing with a protractor or "degrees wheel" against standard timing. I rode a Bultaco with similar port timing to the M212 (M49) for a couple of years before I pulled it apart and discovered that it had a shortened inlet skirt (about 4mm). After the rebore and now with an original type MAHLE piston that had the full length inlet skirt, there was an improvement in low RPM power, but it would have also had improved ring sealing as well as the more conservative inlet timing.

US ebay usually has lots of those primary drive covers advertised. The original cover on a M92 is the most commonly available type of cover and sometimes called the boot heel shape. A good M92 cylinder will be much harder to find because it is a wearing part and unique to only a few models This is the first boot heel primary drive cover I saw when I searched on US eBay https://www.ebay.com.au/itm/BULTACO-RIGHT-SIDE-COVER-FROM-1971-ALPINA-125-DIRT-BIKE-TRIALS-BIKE-ENDURO/123068514902?hash=item1ca7748256:g:HNcAAOSwuIRamwb I'm sure there will be lots more listings

Replacement primary drive covers are readily available

https://www.ebay.com.au/itm/Ty175-Yamaha-Trials-bike-gearbox-gear-set/323173172248?hash=item4b3e9f4418:g:oMYAAOSwu4haukF4 TY175 gearbox in Australia. There was one in the US too just now when I looked

I see a lot of TY twinshock parts being advertised on eBay by wreckers in the US. There was a gearbox listed the other day, not sure if TY250 or TY175

Sorry, bikes are assembled

Maybe you accidentally did it as a preview

Yes your single seat looks to be in the normal position. The seat pad does shrink over time which makes that gap slightly bigger than the brochure photo. I assume you have tried buffing compound to get rid of the stain from the long seat touching the tank? My original TY250A model tank has some stains in that light colour area that I haven't been able to buff out, but I'm happy to just leave it alone. The world is full of repainted TY250A fuel tanks but there are not very many TY250As that have the original paint that still look as good overall as yours. I love the look of my original tank so much that when I ride the bike in trials, I fit a repainted tank, to avoid the risk of damaging the original tank. It's good that you have fitted suitable gearing. Riding at a steady 45 MPH should not cause problems with engine heat because 45 MPH is below the speed where air drag ramps up dramatically, but if you were wanting to go for a brief blat along a freeway (maybe 30-60 seconds at 60 MPH), a B8ES would be more suitable and if you were going to run it at constant high speed for more than a minute, a B9ES would be more suitable. The middle electrode on a spark plug has an ideal temperature. Too cold and it will collect deposits which conduct electricity and too hot and it will lose metal quickly. The length of the metal part of the centre electrode determines how fast heat is conducted away from the tip. If you look in there you will see that there are different lengths for different plug numbers. If a plug tip is getting too hot, it not only disappears quickly, but also radiates heat which can overheat the crown of the piston. It's always safer to run a colder plug than a hotter plug for this reason. Before you fit a B8ES, go for what is a normal ride for you with the B7ES and then when it cools off a bit, take the plug out and have a look at the middle electrode. Then fit the B8ES and go for a similar ride and then inspect the centre electrode and you will probably see that the deposit on it is a slightly different colour. Fuels are different throughout the world and other bikes have different jetting and are ridden differently which means there is not much point looking at photos of other people's sparkplugs but there are generalisations you can use to know of everything is fine on your bike. Because you have told us the oil type, mix ratio and plug number you are using and that you ride it mostly on the road, I can say that your plug tip and the ceramic insulation around it should look totally dry and with a colour in the range from mid brown to light grey. When you fit the B8ES and do the same test, the colour will probably be a bit darker. Bear in mind that the plug tip colour shows the recent history of what was happening inside the motor so if you are interested in plug colour from riding at 45 MPH, do the inspection somewhere very close to the riding and don't let it idle for long. For gentle road riding an air-cooled bike with correct air-fuel ratio, 50:1 synthetic oil is fine. You can re-use the head gasket by annealing it. Usually 14 PSI on a TY is enough to avoid having a tyre overheat or cause squirming on a road ride. The higher you go above that sort of pressure, the worse the ride on bumps. As for those paint chips, you can probably find some nail polish to match the colour. Nail polish is chemically compatible with the paint on the tank and it's also good fun taking a fuel tank to a cosmetics counter.

Can you see why it is leaking? Is the vent hole clear? Has the blanking plug come loose/been knocked out of position? An option to JB weld is to fit a new blanking plug or refit that one using sealant

I would think you could pick up one of those brake plates from a wrecker fairly easily. If you are stuck post up the important dimensions and I'll have a look to see if I've got one spare (axle diameter, drum diameter and a photo showing the outside)

Plenty of montesacotaphiles in Australia Daniel

I don't think that a carby like the standard TY175 carby is available new from Mikuni. I think they do a 22mm carby but it is flange mount so you would need to machine off the flange and fit an inlet spigot.

You can buy that clip from bearing shops

Mk1 and Mk2 AMAL concentric are notorious for wearing the slide needle and needle jet, causing the motor to run rich. The standard jetting works fine when nothing is worn. Yes there are lots of alternate carbies that will fit and work well and not suffer rapid wear. Keihin, Mikuni, Dellorto and OKO are all popular and are reliable and long-lasting. I don't want to recommend a particular brand, just that you should buy one that has been pre-jetted for your bike by someone who knows what they are doing.

I want to try these fork legs in the Godden Majesty (and the emulator forks in the TY175) so I can directly compare the fancy damper rods with the emulators but haven't done it yet. The two bikes are quite different in weight and weight distribution so it wouldn't be a direct comparison unless I swap the forks over

25mm in top tube. Front downtubes cut part-way through, bent then rewelded near front engine mountings. The only change near the headstock is relocating the front tank mounts.

Steering head angle is a personal thing and my favourite head angle for use with a Yamaha twinshock front end is that of a standard TY250 twinshock, which is slightly steeper than a standard TY175. When I extended the frame and the swingarm of that TY175, I made the head angle on the TY175 the same angle as a standard TY250 twinshock. The steering head was moved forwards 25mm and the swingarm was extended 45mm. It ended up with the same wheelbase as a TY250 twinshock. I remember giving a template for the axle plate extensions to someone in the UK soon after I put photos up on the forums at the time, but I don't remember who it was. An Aussie friend was modifying his TY175 at about the same time as I was doing mine and he didn't want to go to the trouble of modifying the main frame cradle, but did want to steepen the steering head angle slightly and lengthen the swingarm. He made his new axle plates with the axle slot lower (his axle slots were 35mm further back and 5mm lower than standard). His bike also handles very nicely.

I've recently fitted those damper rods to some TY250 34mm forks. The forks have the standard springs and are fitted to a lengthened TY175. So far I have only tried Dexron ATF with a 125mm dip. I have ridden dry and wet rocks and banks in practice and at one trial. The compression damping and rebound damping are both stronger and I found the overall effect to be very agreeable. The front end seems less busy overall and is much plusher on big landings. The previous setup on this bike was standard TY250 34mm forks with 10WT fork oil and 125mm dip.

Castrol MTX or anybrand Dexron ATF. Both available from Supercheap The usual Aussie joke oil is Goanna oil, because if you use it, the bike will be able to climb anything

The only weather limitations I have is that sometimes in summer it can be too humid to spray paint. Summer is workshop season here because it is usually too hot to ride except for a brief period in the evening before it gets too dark

Whatever floats your boat - basic rider, museum piece, dunger, tricked-up competition special, time capsule. One person's dream bike can be another person's nightmare For me the whole thing is a passion and cost/return in dollar terms is totally irrelevant. I just do whatever I feel like doing and get huge enjoyment from the process

Hi Bevelferal I'm another Queenslander and if your Techno still has standard springs it should be perfect for your weight.

photos please