Posts
10
Joined
10/4/2021
Location
GB
Hi all. I’d like to upgrade a 79 yz125 for vintage mx/scrambles. It’s been rebuilt a couple of years ago by a friend so I’m looking to upgrade the suspension, front and back, and then do meaningful upgrades that will improve engine performance and braking. What I would love to know first is what front forks and rear shock would be compatible with the 79. Later years, from 250’s, IT’s. Anything that will improve the old girl. Many thanks for your help.
I raced a 79 YZ400 a few years back. Forks are 38mm and were decent with RT emulators and the correct springs and 20wt oil. Ditch the long top out springs for something more normal. I bought a set of bent conventional KDX forks and swapped the springs/top out springs. The next step up would be 43mm forks off the 81+ YZs and some of the ITs had 43mm forks also. Depending on year you will need to get a new brake plate as Yamaha changed the clocking on the brake stay.
Out back you can rebuild the rear shock with a modern seal head, remove the travel limit spacer on the shaft and a RT gold valve does wonders. I've added a remote reservoir with compression adjustment in the past too. Spring for your weight and I'm not a fan of the dual spring setup as it really doesn't do much for the added cost but getting the right spring will help. The longer shock compliments the longer forks too if you go to 43mms or remove the top out spring on the 38s.
It was a fun bike once I got the suspension sorted.
Thank you 450. I’m thinking 38mm forks from a 250-400, regarding the rear, which shocks and which years were longer/higher? I know the shim gives an extra inch or so of travel but these 79’s seem to all sit very low at the rear. Also the swingarm, is that interchangeable with any other years, a longer arm may be of use!
Hannah did a lot to develop this bike. Since a lot of bikes were transitioning to more and more travel Hannah felt the handling suffered so he and Yamaha added the longer negative springs in the forks and put the spacer in the rear shock.
I'm not sure if the 79 250/400 swingarms are longer but the 80-81 arms definitely are but they are also wider so they won't fit with out some machine work. Their were aftermarket arms that were longer by 1 inch but I've only seen one come up on most of the forums/ebay I view. Once you remove the spacer and negative springs it'll be at least 1" taller and still handle well. The shock are all the same between the 3 bikes but the 125 has the longest spacer installed in the shock.
Work with the stock forks - to improve
new springs, emulators oil
send the shock to race tech, noleen J6
and have it set up for your weight.
leave the stock arm alone- run the chain adjusters at the max out.
the 79 is a light, short one year bike
adding heavy 38-43 forks will mess up what that bike is, and can do if set up properly.
The Shop
Thanks guys. I’ve a set of 43mm forks that I will try and see what I think. Sounds like they will be too heavy for the front, but believe it or not they actually appear the same weight! I’ll report back.
Brief update I’ve got some 81 forks and clamps to go on the 79. I’m measuring up a twin leading front brake plate too. The rear shock is being rebuilt with heavier spring, all balls seal head kit. 😉
Rear shock is back, a little hoppy due to 78 250 rear springs but way better than it was, also sits an inch higher due to spacer being removed, fitted 81 forks and they are long but again stiffer springs and way more travel.
Any ideas for a better front chain slider? Any other sliders fit to wrap around the front of the swingarm? I have chain rash already...
You may need to make your own.
Post a reply to: 1979 Yamaha YZ125 - race project