feetupfun

The ideal fit of the pin in the piston is such that it has no play when the motor is running. Aluminium expands more with increasing temperature than steel, so piston pins need to have a slight interference fit when at room temperature. For this reason, it's fairly common (in any motorbike engine) that a piston pin may need more than a push with a finger to get them to move at room temperature. Common methods for dealing with this are to either warm up the piston or use a piston pin puller.

That is true if completing the reassembly of the motor with the motor separate to the rest of the bike

I use a socket with the OD machined down to fit onto that nut. Yes a clutch holding tool is required the way you are doing the work, but if you are going to pull a Bultaco motor apart again, consider loosening the shaft nuts with the motor still in the frame and a chain and back wheel in place.

Yes brake was originally on the right but it is very common and easy to convert the late model Sherpa Ts to brake on left to get a better feel. Brake on right used a bowden cable to cross over which dulls the feel. The change to brake on right was around 1975 not 1985. The shocks look like gas Girlings which were a popular aftermarket choice back at the time when this was a new bike. Yes the fork tubes can be rechromed. Also new tubes are available at a comparable cost. If this is a 198B/199B which is what it looks like, it is a very rare bike, and the last Sherpa T model made by Bultaco. As for the year they don't really have a single year because they were produced over a period of a couple of years in the early 1980s when Bultaco was in the final stages of closing down. For parts supply, the best thing to use to identify the bike for the parts supplier are the engine and frame numbers

Not a production bike. I can see Yamaha and Honda parts and a lot of custom work. Frame started as a pressed steel backbone type Honda frame.

I'm quite interested in the development in the design of Bultaco frames, especially Alpinas and Sherpa Ts.

In Australia Yamaha fitted minimalist road rego equipment and gained approval for road registration. I rode my 1996 model until 2002 and absolutely loved it. It was a very capable bike for racing and exploring and was totally reliable. The power curve was amazing (no steps and plenty of go at all revs). With the standard exhaust it was so quiet I had many close up encounters with emus and kangaroos who had not heard me approaching.

I have marked the frame elements red in this photo

I just noticed that the frame in your photo is different to a 115 frame and a 116 frame I have here. Yours is missing some frame elements that connect the rear uprights to the central rear down-tube. Your model 115 frame looks like my model 138 frame in that section of the frame. Your headstock gusseting looks the same as these 115/116 frames which is different to the 137/138 frame. The 137/138 models followed the 115/116 models so I'm wondering if your frame may be near the end of the production of of the model 115. Here are photos of the model 115 and model 116 frames I am referring to

I've got both and they sure do look the same

Sometimes oil doesn't drain out because there is thick sludge in the bottom of the gearbox. Try poking something through the drain hole to see if that is why no oil came out. Another thing to consider is that your bike has two gearbox compartments that are separate. You should also change the oil in the second compartment.

Everything is possible, but if there is only one hole in the head, then the head will need to be removed and some finning machined away and a hole bored and threaded to create a second hole for the decompressor. They can't both go in the same hole.

Yes that's a helpful book. The OKO D slide is a copy of the Keihin and getting the jetting right on an OKO on a trials bike is very different to jetting a Mikuni VM

One interesting thing I've noticed is that some 199Bs had fork tubes and top triple clamps with the tapered top attachment that was phased out on Sherpa Ts in about 1972

Larry can you measure up the important dimensions of your Cota 200 piston to help with finding something suitable. Pin centre to edge of crown Pin diameter Width between pin bosses Length of rear skirt Nominal diameter Ring location pin locations

Will do. Thanks

It did take 48 years to do all that 😄 so I reckon I've actually done pretty well

I'm 62 going on 18 too and have been riding trials all my life. Here are the trials riding injuries I can remember: ACL torn due to jumping backwards off a bike at the top of a bank and landing on my feet awkwardly because of a stick that prevented my knee bending. Broken ribs from falling down a bank tangled up with the bike. Torn rotator cuff from falling onto shoulder. Torn calf muscle from landing from a jump without being warmed up. Bent nose and cut forehead from face-plant after brake cable hooked over fork top clamp. Leg burn after handlebars broke and landed on the exhaust header. Leg burn after crashing with leg trapped against exhaust header. Broken pinky finger from crash with my chest against on a rock with my hand between my ribs and the rock. Fingers squashed between levers and grips multiple times hitting trees and logs. Lots of lower leg injuries from impacts with kickstarts (when kicking), footpegs (when crashing) and sticks flung up. Ankle injury from a vine loop pulling the front of my foot down and under the peg. Knocked out from an upper cut to the jaw from the handlebar end when crashing. Head impact that knocked me off the bike when front of helmet hit an unseen tree branch (going up a bank looking into the sun). There is a longer list for enduro injuries but that was not the question

Has the motor been lifted? It may be a header pipe made for a different model. It may just be poorly fitted. What ID prefixes are your frame and motor? I think I see your motor prefix is 92 but what is the frame? The original finish on a model 92 header pipe is chrome plated. The tank looks right for a model 92.

How well did the multi-drill deal with the hardened bolt shank? I've got a similar problem but with a handlebar clamp bolt and am trying do decide how to deal with it

The visor came with my trials helmet and it is still there and I've never used it. If I'm going trail riding on a trials bike, I use a motocross helmet

The standard fuel tap thread in an Alpina tank is a metric thread M12 x 1.5

Viton rubber is the go for petrol o rings

Looks like it's been through hell. Has it been chewed up by an animal?