feetupfun

TM125 springs will fit in TY175 forks but were too stiff for me on initial compression. They are straight rate springs. TY175 springs have a soft initial spring rate which suits trials riding.

Other than TM125 springs I didn't try any others in TY175 tubes.

If you have an extra inch of preload over standard you have probably reduced the available fork travel by allowing the springs to coil bind before all the fork travel is achieved.

TY250 springs are too big in diameter to fit TY175 tubes.

If bottoming out is your issue, I hope you have tried using heavier oil.

190 pounds rider is not that heavy for using TY175 springs. I suggest you see how sacked out your springs are and if they are sacked out, get some good standard TY175 springs and set the preload to around 25mm and use heavy grade fork oil.

What is your actual preload dimension? What fork oil are you using? What is the free length of your springs? Are you sure you actually have TY175 springs in there?

OK good. I wonder why they did that. The KT250 is similar with 14mm at the top and 12mm at the bottom

No I haven't looked for blank nipples yet

Theres a sheet of mesh or perforated steel plate about 1.5mm thick with a hole for the steel tube. The mesh rests on the flats in the casing, then a flat piece of filter foam, then another piece of mesh to contain the foam, then a washer, a light coil spring and washer that all fits over the steel tube.

The airbox cover/lid also has a hole and there is a large headed screw that screws into the steel tube. It holds the cover on and compresses the spring. The length of the tube limits how far the screw can compress the spring.

As for the bearing ventilation, the crank seal holders rest against the bearing outers and the seals themselves are very close to the bearing

Yes that's what I'm saying

Excellent news. Now I know you know about working on motors, I can tell you that the Bultaco design has a few things going on that are relevant to the main bearings.

The relative expansion of the crankshaft to the casings is not managed well and even with C3 ball bearings, the shaft will either move inside the LH main bearing or one of the main bearings will move within the casing with each heat cycle of the engine. Because of this, lots of Bultaco motors suffer from either worn seats in the casings or worn crankshaft on the LH end or both. Some people mod the bottom end to take a roller bearing as the main bearing on the drive end which helps with the differential expansion issue. I've managed it with the Bultaco motors I've rebuilt by fitting steel sleeves into the casings of motors with worn casings and replacing the LH crank halves on cranks with worn bearing seat. The RH main bearing seat on the crankshaft doesn't get wear because the bearing is clamped between the seal sleeve and the crankwheel.

Next thing is that the main bearings are not ventilated so they don't last that long. Jap bikes have ventilation passages that let the air-fuel mix flow through the main bearings. I don't know if the lack of ventilation causes failure by overheating, lack of lubrication or from carbon contamination, but on modern trials engines without ventilation of the mains, they use shielded main bearings to get them to last longer. I haven't tried this on a Bultaco.

Not a weakness but beware that some Bultacos have two separate ball bearings on the RH end and there is a snap ring between them.

Regards

David

Hi Lee. I'm not certain what you are asking but I'll tell you what I know.

If you are asking about changing crankshaft seals from outside the inner casings then yes you can but you do have to remove the seal carriers from the casings because the seals can only be fitted from the inside of the carriers. Make sure to use gaskets the same thickness as what came out because the inner ends of the seal carriers are used to prevent outward movement of the main bearings without squeezing the crankshaft.

As for removing the seals from their carriers I haven't tried using a blind hole bearing puller. I usually warm the seal carrier to loosen things up and pull/push them out either with my fingers or with a seal removing tool.

If you are asking about changing main bearings from the outside of the casings I have heard of people doing it without separating the cases by welding a tube to the inner race, warming the casing and pulling on the tube. I've never done this myself because there is less risk of damage to the bearing seats if you separate the casings first, and Bultacos tend to suffer from bearing seat wear.both on the shaft and in the casing holes.

I hope this helps

Regards

David

The standard carby is notorious for running rich due to rapid wear of the needle jet and needle. When the carby is in tip top shape they run great with the standard carby.

I run 50:1 with an Aussie semi synth Penrite

I suggest again to measure the height of the new and the old plate packs. I suspect that it will be shorter than what came out.

It does sound like the clutch is slipping. Why was the clutch replaced? When was the clutch replaced? Is the plunger pressing a bit even when the cable is loose? Does the new clutch plate pack measure up the same height as the old pack? If it is shorter then that will reduce the clutch spring force.

Yes I remember the posting about the 348 that had a slipping clutch when kicked but don't remember how it ended up.