Vintage Dirt Bike Q & A

the motor has been sitting for about 4 years. i drained the oil and it looked like pepto bismol coming out. so i pulled the side cover. Ive never seen oil so bad. totally black and gummed up on everything. so i took out the clutch and cleaned everything up. Clutch plates and friction plates were froze together until i took them out. my question is, do you guys think i could get away with a motor flush to clean the tranny, or should i do a total motor disassemble? the motor turns over real nice, but i am going to pull the head to double check it anyway. looked down the spark plug hole and just saw a little carbon on the piston, nothing out of the ordinary. i have the capacity for a dis-assembly, but not sure i have the patience. but i want to do it right so my motor will last. only has about 4k original miles. its a 74 Honda mt125. there is no rust inside the side cover. only a little on the kick starter shaft where its on the outside of the motor. when i cleaned up the gears behind the side cover, they looked to be in great condition

I'd suggest changing the oil (10W-40 non-synthetic motorcycle oil, like Bel-Ray EXL or Spectro) and running the bike about 50 miles, changing it again and running it about 100 miles, etc. This worked well on my MR175 - after 4 or 5 oil changes the old oil came out clear/yellow like it went in. Now I use 400 mile change intervals.

I recently pulled the clutch cover off my spare MR motor for the first time, and the oil was milky-white with water contamination. I cleaned it all off and now everything in the clutch compartment looks perfect. After pulling the kickstarter shaft (broken return spring), I looked in the gearbox and it looked great there as well; a clean oil film on everything, and no rust at all.

I think that rain water has a hard time getting into the gearbox, but can get into the clutch area via the clutch actuator arm seal, fill cap, etc.

The pink color looks strange - I wonder if it's automatic transmission fluid?

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

thanks for the advice. i bought some motor flush today. im going to fill the crank case with it and jack up the rear end. then put it in gear and cycle the kick starter to run it through the gears. drain it, strain it, and repeat until minimal amounts come out. then add a little to some oil and actually run it a little to warm it up and get the last little bits out. hopefully well see some difference and i wont have too many difficulties. ill be sure to post my results. i have a 73 thats been sitting a couple of years too. i checked the dipstick and it looks way better. the oils still actually looks good. so that gives me a little inspiration. and in reguards to your thought of it being ATF. i had a couple other people say the same thing. so it sounds like that may be a possibility. at least nothing is seized and after cleaning a few parts manually, they look really good.

put it all back together and got it running. am in the process of my many oil changes. ran rough at first, but i adjusted the points and it purred like a kitten. starts first or second kick now every time and doesnt even need choke. just chasing electrical ghosts right now, fixed half of them and only have one more problem with rear running lights. so far so good, its registered (only 72 dollars to switch title and pay registration) and only 2$ a month to insure! looking promising so far.