Vintage Dirt Bike Q & A

Hello all;

I am a newbie to this forum, glad to find it. I recently was given a '75 CR125M, looks pretty good, plastics are OK except for the rear fender with a crack in it. The engine was rebuilt with stock size piston - I am good friends with the guy who owned it since new - and the bike seems to run pretty well. The expansion chamber has been pretty beat up. He put new seals in the forks, but no oil. I have been told to put 135-140 CC in each by Dan at RE-MX while buying some parts, but don't know which weight to use. Can anyone advise me? How about the crankcase oil viscosity? What about finding a replacement Chamber and rear fender without selling my Kid?

I am just fixing this up to be a rip around bike - I have been away from MX for about 24 years and am pretty excited to have somthing to ride again. Last bike was a new '80 CR125, and this should be pretty fun, I think. Just waiting for the front spocket, throttle tube, clutch cable and seat cover to come in to take it for a rip!

Fork oil, in the day was ATF, which has a viscosity of about 34cSt@40C, not that I really understand what that means. You can either use type F ATF or modern fork oil. Generally, that is about 10 weight fork oil, but it greatly depends on the brand. Look at the very bottom chart on this page and go down the column until you are in the 34 range on the second column and you'll see what I mean.

http://www.peterverdonedesigns.com/lowspeed.htm

I don't know the 125s well, but Honda recommended 10w40 or 30 wt transmission oil above 59 degrees F for the 250 back then. And you can often find a decent rear fender and occassionally a decent exhaust on "F-bay." But sometimes you can have the exhausts repaired. And you can always use a vintage universal rear fender, do a google search. They sometimes don't protect the back of the airbox as well as the factory fender, but they work and look OK.

Mitchie;

Thank you very much for your reply and info. I appreciate it.

MN