yz c fork question

[gurt]

Hey everybody, I'm in the process of doing the fork seals on my '76 yz 125c. My problem is that I don't know what weight of fork oil, or how much I should even put back in. I measured just under 9 oz per leg (roughly 265 ml) when I took them apart, but that seems kind of low to me. I was also wondering whats a good starting number for air in the forks as well, since there was no pressure at all in mine. Any help on this would be great. :nod:

 

[chicoman]

My shop manual states 6.1oz of 10 weight oil, and says it's a non air fork.

 

[gurt]

Hmm... maybe the air caps on mine are aftermarket. I'll try the 10 weight and see what happens. Thanks for the help.

 

[digifox]

sure its a YZ? lol J/K
For the Air
Yamaha Suggests 0 PSI but you can run UP TO 16 PSI

And the level...IDK about the `77 YZ but my 80 IT holds 317cc of 10wt
IDK if they use the same forks or not...

 

[dirt bike dave]

The '77 YZ-D forks are not the same as the '76 C forks.

I had a '76 YZ-125X with the dual air chamber forks (no springs at all). Those things were also on the '76 YZ250 and 400. The 1976 YZ 125 'C' had conventional spring forks.

For your 'C' forks, I would worry less about the specific cc volume required and more about the oil level. Basically, take the springs out and compress the forks. Fill to about 4" from the top (however much it takes). Put the springs back in and ride. If they are too soft at the end of the travel, add more oil. If they are too stiff and don't use the full travel, take some oil out.

If the oil has been drained and you are replacing with fresh oil, stroke the forks a few times before you measure, so that the oil circulates to where it needs to go.

Oil level has a big impact on stiffness at the end of the travel. Oil weight mainly effects rebound damping. Altering the oil level is an essential tuning technique no matter what the manual says the cc volume should be. I've had some bikes be way off (for example, my '84 KDX200 needed about 2" more oil added over the volume specified in the shop manual)

As mentioned before, I would start with 10w oil. Air caps were common back then, but adding air is discouraged. Use the caps to let air out. Use of air pressure in those forks is a bandaid if you are too heavy for the springs. Instead of air pressure, use spring stiffness, pre-load and oil level and weight to tune the forks.

 

[gurt]

Ok, mine are definately the C type forks with the springs. The oil level is a very helpful way to do it! thanks to everyone for the advice. I knew somebody around here had to know!