feetupfun

How do you avoid banging your shin on the lever while riding sections?

Looks like you're getting more of that wild weather potto

Have replied on Trials Australia

These carbies go very well too. I recently fitted this OKO to my A model when the original TK carby started to suffer from needle and needle jet wear

@zuma that's a fabulous looking airbox

Nice work. I'm also impressed that you did it all with the wheel assembled

The brakes on my M138 Alpina (with chrome plated drums) are amazing

Yes the one on the left seems to be the only one that cracks. One TY175 I bought has a triangular 6mm thick gusset there (goes right down to the junction of the frame tubes) and for what it is worth has no tube cracks at the upper ends of the gusset. The bike I'm referring to has cracks in the front uprights so it has probably been ridden very hard

If the existing carby mount attaches to the head with two studs, you might be able to use a (flange-mount) pit-bike carby. It would require a flat isolator and longer studs

Yamaha 506 is YB100 (two stroke)

That looks like a carby made specifically for a manufacturer for a particular model bike so will not be available new from Mikuni. It would be helpful to share what motor the carby came from.

My epoxy linings went dark brown after a few months exposure to petrol while the original polyester resin stays clear/light brown. Also a 40 year old unlined Spanish fibreglass tank will usually have exposed glass here and there.

Are you talking about the springs on the shoes or the springs on the camshafts? Which Sherpa T hubs are they for?

If it was on a TY250 and it ran, it should run on yours, but you didn't actually say what the barrel had been used on previously

Some alloy steels have a low coefficient of friction so be careful. Mild steel or cast iron are the go for brake drums

From the bikes I've seen, the second model 349 (the white tank model) was the first 51M to have the fork tubes close together.

Yes the earlier one has a narrower brake drum contact surface, the smaller spoke flange is part of the hub casting and the fins on the drum are machined not cast

DT175 gear ratios are better for trail riding and worse for trials

If you post your question in here http://www.trials.com.au/forum/viewforum.php?f=16 a bloke called Greg Harding will probably be able to answer any question about the conversion. Here is one of his Suzukis

Here is one type of M49 rear hub. I just measured the liner of this one as 144mm OD. Nominal ID is 140mm. I am planning plan to machine this one out to either no grooves or a maximum of 142mm ID with some grooves remaining. There is another type of M49 rear hub fitted to early build M49s that I will post up a photo of later if you think it is helpful. This earlier hub has a liner with the same nominal ID (140mm) but has a much bigger OD (147mm)

Piston manufacturers recommend a certain piston/cylinder clearance be achieved at workshop temperature during the rebore for their piston, so that when someone uses the bike to plough through deep sand in an Australian summer, there will still be enough piston/cylinder clearance to avoid seizure. For those of us who have mechanical sympathy for their motorbike engine and not get it extremely hot, we can get away with less piston/cylinder clearance (at room temperature), which means less piston rattle when we ride trials. What I was referring to about different pistons is that some pistons are made from an alloy that has a higher coefficient of expansion than others. This means that the difference in piston/cylinder clearance from cold to hot is greater in some pistons than others. In the case of those high coefficient pistons, there needs to be more clearance at workshop temperature and at trials temperature to be able to have enough clearance if the bike is ridden in a way that gets the motor very hot. Because of this requirement, the standard clearance recommended for high coefficient pistons is greater than for low coefficient pistons. If the person doing the rebore uses the standard clearance as recommended for the piston, a high coefficient piston will rattle more than a low coefficient piston at trials temperature. I was pleased to read the instructions that came with a piston I bought recently because it had three different recommended clearances for the piston, depending on the intended use of the bike it was going into.

They are a notoriously rattly motor and can function perfectly for many years despite obvious piston rattle. Because you have the motor apart, I would recommend that you decide if it needs new rings or a rebore by measuring the piston ring end gap using the standard method. Also be aware that some brands of pistons are more rattly than others.

Guy the 0.6mm is not the timing. It is the amount further advanced I set the timing compared with standard setting. As an example, if standard for the bike is 3 mm, I use 3mm + 0.6mm = 3.6mm I don't have a hyperlink to info about combustion chamber design. I spoke to the tuning expert on the phone.

Unless you are going to road register it, you can machine the drum out as far as you dare. The lining material is available up to 6mm thick so you have quite a lot of lattitude to play with. Bear in mind you don't have to machine out every last groove from the drum to get good brakes. Even something that is flat for 90% of the surface is way better than a drum with a surface that is uneven all the way across. The standard rear brake on them is quite strong by the way. Nothing like the little, lightweight Sherpa T rear hubs that came out in the mid 1970s

The rings you need to buy are determined by the diameter of the cylinder bore, the cross-sectional shape of the rings and the shape of the ends of the rings. A model TY250 came out in 1974 and has two rings of the same type with the top ring set down from the top edge. Later model TY250 twinshocks came with an L shaped top ring and a lower ring shaped like the TY250 A rings. Those numbers you posted are not the size of the piston or the rings. They look like something the manufacturer put there to keep a track of what type of blank the piston is and are not helpful for you. Sometimes but not always the oversize of a piston is stamped on the crown. Oversize numbers are nothing like 6-33. They are usually a number that represents the number of hundredths of a mm the piston is bigger in diameter than standard. They can also represent thousandths of an inch. Typical Japanese piston oversize stampings would be 25, 50, 75, 100. Imperial oversize stampings would be something like 010, 020, 030, 040 First work out what the piston is. A model, BCDE model or aftermarket supply, then measure the bore diameter. If it is a Yamaha or Wiseco piston you should be able to get rings. It is rare nowadays for people to replace just the rings on an old trials bike. A piston kit and re-bore is more commonly chosen due to the similar labour component for both jobs. A decent photo may speed up identification of the piston.