Fork Seals M159 ?

[sunny]

I have the Haynes parts diagram but it looks a bit different than what I found when i stripped the forks down. I found two seperate seals with metal rings in each fork leg (4 total). Should there be 2 per fork? It also had no retaining ring or circlip or a groove for one? The seals I have found locally at bearing shop have no metal ring. should it? Or just rubber?

The forks were very soft and I could compress easily and it did have some oil on the forks will new seals solve the softness? What weight oil should I use? I weight 250 lbs. I will be just riding trails and gravel roads etc..

Thanks for the help.

Sunny

[pedronicman]

You should have 2 seals in either side.

These could be 7mm or 10mm thick (each seal) depending on how deep they sit.

so you would use either 4 x 7mm seals or 4 x 10mm seals (2 each side)

Some sherpa forks had circlips but most didn't

if you dont have circlips - dont worry , the seals will not come out.

The seals wont make adrifference to the stiffness/hardness , this is done by

fork oil qty and grade and springs.

Standard fork oil should be 15wt and 180cc in each leg.

Use this as your starting point.

If still too soft either use 20w or a bigger qty ie- 190cc or 200cc

You can use 20w , but don't use lighter than 15w they will be to soft.

If this is still too soft then try new fork springs as 99% of sherpa forks were always

too soft and not plush at all.

Hope this helps.

[sunny]

Got the new seals and 20 w oil and rebuild the forks.... a bit of trouble getting the guts back together on one of them. They still seem soft and I can full depress and oil squirts out of the vent on the fork caps. What I am I doing wrong?

Sunny

[woody]

The chances are that the internals are probably a little worn by now which won't help damping and Bulto forks were always a bit soft on springing and damping anyway. Most of the damping is controlled by the holes in the damper rod, the large hole at the bottom does compression and returns the oil on rebound, the two smaller holes at the top do rebound but also allow excess oil through on compression. There is also a 'shuttle valve' piston assembly (usually circular with either holes or slots in it, but square and solid on 199B) that also controls some of the oil flow on compression and rebound. If this is worn (I have no idea how to measure tolerances on this) then more oil will flow and the damping will be softer than intended.

On my 199B I went up to 30W oil and gradually increased the quantity in an effort to stop the forks topping out repeatedly and also slow down compression damping. I got to the point where there was too much oil causing a hydraulic lock on compression but they still topped out on rebound (nothing to do with spring rate) I assumed that the shuttle valve was letting more oil through than intended due to wear. As there was nothing I could do about that I blocked off both rebound holes on one damper rod and one of the rebound holes on the other to reduce oil flow. The result is a much plusher fork using 7.5W oil - a bit lighter than normal due to the reduced flow rate. The bike has just had a good hammering in a 2 day National trial with plenty of big rocks, steps and waterfalls and the forks worked very well. Still a bit of experimentation to be done but as a starting point I was very pleased with the improvement.

I have one longer uprated spring with no spacer in one leg and a standard spring with a 1" spacer in the other and the spring rate of the forks is just about right too (for me obviously)

I have no idea how the valve in the fork caps is supposed to work but every Bulto I've ever had (and Ossa or Montesa) has successfully spewed air and oil out of these caps like a geyser. Whatever they are supposed to do they have never done it. Letting air out also makes the forks softer. I either block the hole or fit caps with no valve. The fact that the air doesn't come p***ing out also adds more resistance to the compression stroke. Never had a problem with blowing fork seals due to pressure build up in the forks.