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The rubber torsion bush method is quite common on motorbike swingarms and it works fine. It can be tricky to remove them if you ever need to. They do last a long time and require zero maintenance. The original bushes in my 1975 KT250 are still working perfectly. The bushes are also called Silentbloc bushes in industrial catalogues. I recently replaced that sort of bush in my Whitehawk Yamaha swingarm and the replacement bushes were available from a local engineering supplies

Maybe it is because we both live so far from the UK, but this is my take on the problem too. I find that there are lots of times that aftermarket parts I buy need a few tweaks to fit properly, not just ignitions

To answer another one of your questions, lowering the front of the bike by sliding the fork tubes upwards improves the steering geometry for trials, but does nothing to the fore-aft mass distribution of the bike and rider, so it will not make the front heavier. It will lower the handlebar grips If you want to lighten the front, move the footpegs rearwards relative the rear axle. This can be done by moving the peg mounts rearwards, or moving the rear axle forwards. On your bike the wheelbase would not benefit from being shorter, so don't move the axle forwards By the way I'm not suggesting you need to lighten the front, that was your suggestion. If it was my bike, I would fit aluminium rims (to reduce steering inertia), aluminium trials handlebars (to reduce steering inertia) and slide the fork tubes up about 20mm

You can reduce the trail and make the steering rake steeper by sliding the fork tubes upwards in the clamps, yes, as shown in your photo. The fork caps currently on the forks will limit how far you can slide the tubes upwards. Options are to get fork caps that don't have the air valve cap sticking up so far, and fitting handlebar risers If you do slide the tubes up, test for mudguard clearance against the frame and exhaust with the forks fully compressed before you ride it

that photo does not illustrate the trail. If it was to show the trail, the tilted line should be drawn through the steering axis. That photo has the tilted line on the centre line of the fork tubes.

I helped fit an Electrex ignition to a friend's Ty175 about 3 years ago and did not come across that problem you are illustrating. Maybe the kit you were sent is for a different bike. I know that the Ty175 and Ty250 backing plates are similar but different so it could be that

the google translation of the text from the Tarticle is: The Montesa-Honda announced through a press of Honda Motor Europe, which in 2015 will continue the production of the Cota 260 4rt. We still know little or nothing about how will be the new montesa, what is certain is that it will continue to be available, the two versions that will be marketed from the beginning of September. Honda has announced changes at both the chassis section that bike but still has not leaked any more precise information about it. As far as the engine will continue on the road to 4 times PMG-FI electronic fuel injection, already tested last year by the two riders HRC Fujinamy and Bou. Since last April, the Montesa's racing department was taken over directly by the HRC under the name of the Repsol Honda Team, it will not be moved by the establishments Montesa-Honda neither the staff nor even the headquarters of the company. The Honda is at pains to specify that these changes have no consequence in the commercial sector and that the model will continue to be marketed under the brand Montesa. Good news for fans of Cota 4rt but a big disappointment for those who believed that the Montesa could finally go back to maybe 2 times with an innovative system with electronic fuel injection.

gearbox 300 ml primary drive 200 ml

the pattern of the holes in this IT250/YZ250 crankshaft advertised on eBay UK looks a lot like the pattern of holes in the works crankshaft shown above

When stripped for competition a standard TLR200 is pretty much the same weight as the other popular full-size twinshock trials bikes from the early 1980s. Many people make their TLR200s lighter using different exhaust systems and fuel tank/seat arrangements. As good as the TLR200 is, they are not the lightest-feeling bike of the twinshock era. The small Montesas, the TY175 and some TL125 specials I have ridden all feel lighter than even a lightened TLR200 They are a full-sized bike and are very similar in height and length to the other full-sized trials bikes of the early 1980s.

If you are using the standard ignition then 0.4mm to 0.5mm plug gap

There is no oil level in a two-stroke crankcase The gearbox and the primary drive cases have separate oil systems, and there are no dipsticks, tell-tale screw holes or level glasses in either. To make sure there is the right amount of oil, drain them, and then refill with the recommended quantities. If the motor is working properly, the oils should stay where you put them. If not, oil can transfer from one to the other, or get sucked into the crankcase, or leak out or do any combination of these things. Measuring what comes out when you change the oils is a valuable technique for monitoring what is happening inside.

look up the catalogues/reference material of current piston manufacturers and see if you can find a piston that has the same dimensions or can be modified to suit your cylinder. You will need to know nominal diameter, height from centre of pin to crown, centre of pin to base of rear skirt, gudgeon pin diameter and piston ring locating pin locations. There are very few of those bikes in use so you may well be the first person wanting a piston for many years, so you might have to do some legwork If you post up those dimensions, someone might be able to help you with the search. If it is just the L ring you want, then you can measure yours up and search for one of them. I know there are still lots of new L rings out there for old Yamahas and Bultacos, and probably others had L rings too If you are desperate you could have a new groove machined to allow fitting of an available ring, or have the old groove machined to suit an available ring, of the right diameter

Nice model Alpina. They have a great look "round barrel" 250 Bultaco motors like yours are prone to getting quite hot if ridden slowly in hot conditions, mainly due to the close fin spacing. 260 degrees F near the sparkplug is nothing unusual, and also quite meaningless unless it is measured while the bike is being ridden. For what you are trying to achieve (checking the jetting), observation of the behaviour of the motor (how it runs at different RPM and throttle position) is the more usual way to check the jetting. If you are going to ride it through long sand washes or at sustained high speed, then I would suggest also doing plug chops using s "safe" heat-range plug (NGK BP7ES or BP8ES). A more sophisticated method for setting the jetting for road riding is to use a cylinder head thermocouple that fits between the head and the body of the sparkplug. I see that the carby looks like the original AMAL concentric. They are prone to rapid wear of the needle jet, needle and slide, so generally run too rich everywhere except full throttle and idle unless they have just been rebuilt. Why do you want to fit a tacho to an Alpina? Does the fork brace hit the front guard on full compression of the forks? It would hit if it was on my Alpina

Yes it must have had plugs in the balancing holes at some stage Something odd: I've not seen crank balancing holes on the opposite side of the crank wheels to the big end pin on a trials bike before. I'm thinking aloud about what might be the reason: We know this motor is currently 250cc. Maybe when the crank was made, it only had balancing holes in the pin side of the crank wheels, and it was balanced to suit a bigger diameter(heavier) piston than what is in it now. Then for some reason the motor was then converted to a smaller piston (the 250cc it is now), and to get the crank balance right, balancing holes had to be put in the non-pin side of the crank wheels

yes you have to take the clutch cover off to get the drive gear off the inner end of the pump shaft

RAD Hard Chroming in Sherwood, Brisbane, Australia are highly regarded for rechroming fork tubes. Last set I had done there were AU$150 per tube plus freight

Michael I looked at your blog, but was not able to comment on there about the rebore on the TY175. Pistons are made smaller at the top (at room temperature) because the top of the piston expands more in diameter than the bottom of the piston when the motor is running. It is usual to use the diameter of the piston at skirt height for setting the clearance and yes it is very unusual for a cylinder rebore specialist to suggest that the customer should achieve the desired clearance by shaping the piston. The machinist should either bore to the right size, or bore undersize and then hone to size

As you found with the motor when you pulled it apart, they usually have only one metal shield on that bearing and it is located on the outside of the bearing. That bearing has a shield to better manage where the oil goes inside the gearbox and primary drive case while you are riding and falling off. The reason the shield goes on the outside is that there is a better oil supply to the bearing via the gearbox side, compared with the primary drive side. It is common for bearings to be supplied with two shields, or two seals, to reduce inventory in the supply chain. Yamaha have been rationalising many parts in their supply chain for many years, so nowadays you might buy a genuine Yamaha magneto case breather for example, or a genuine nut or bolt for a TY175, and find it is a different colour or finish than the original item, but it still fits and works as intended. The unwanted shield can be easily removed

You are pretty lucky to not have a leak at the head joint, with that bolt missing/broken. Yes fixing it is likely to be do-able. What is needed to fix it will not be known until you know what the female thread in the barrel is like

We use 50:1 in our 2010 GasGas Boy 50 and it runs fine (no smoke) but does drool a lot of black gunge from the exhaust pipe drains

white smoke can also be from gearbox oil getting sucked into the crankcase. It will disappear from that tiny gearbox pretty fast if you are seeing lots of smoke

My memory of the reason for the bearing seals in Sherco motors is that when that motor design went into public use in the late 1990s, they had open (seal-less) main bearings, and also suffered premature main bearing failures. It was found that running sealed bearings extended the life of the bearings, so now they come new with sealed main bearings and recommend that sealed main bearings be used when the main bearings are replaced. I don't want to go into the theory for why the seals help with bearing life because it is a subject like "how much oil should I use in my premix" or "what brand premix oil is best"

correct, it will make it run lean (even hotter) before stopping. That's why I said it doesn't always stop the motor in time to prevent it seizing - but if you do nothing it will definitely seize

if you can manage it, turning the bike upside down stops the motor instantly. I have saved two motors this way Also I suggest you try out the exhaust blocking technique with a runaway engine, rather that testing it out by seeing if your motor can start from cold with a bung in. It actually works very well in real life. I have also saved motors this way and you don't actually need a glove or a rag. If you can seal off the exhaust fully with your bare hand it is not unbearably hot to perform, unless the bike has been ridden at high speed just prior to the incident. If nothing else is possible/safe, turn the fuel off (this is not very quick acting, but it may stop before seizing) Something that did not work for me in one incident was using the use the rear brake (it just overheated the brake disc) I've had so many of those episodes (stopping peoples runaway trials engines), that I have become an advocate for using lanyard switches