Vintage Dirt Bike Q & A

Hello all,
I'm new to the group. I just picked up an all original (except front tire) 1979 CR125R. The bike must have sat unused for years. Only the front tire has been changed. The 23" front DID rim is there along with all plastics and cables. The bike runs but I don't want to take it out for a spin until I get a chance to take it apart and make sure the head and bottem end are in good shape. I suspect it has broken rings - at least - because of the oil leak around the exhaust. Could also be a leaking oil seal - I'll find out soon!!!

I also own a 1978 XR75 (original owner), 1997 Z50R and a 2000 XR70. The CR is my first 2-stroke and I've been wanting one of these since I out grew my xr75 in 1980!!!!


later,
nola_fiddy

Its not unusual to have oil coming out of the exhaust flange on a two stroke I'd be very suprised if you have a broken ring. If the oil leak is excessive it will be the lefthand crankseal.The 79 CR125 runs a chrome bore with single ring piston though over time someone may of sleeved it with steel liner.
If it has good compression and makes no odd noises when running then I wouldn't worry to much.
As its a quick job to check its probably worth checking but the main thing is you run the motor with good quality pre mix oil with the fuel at the correct ratio,eg I find with modern oils 40 : 1 works well.

You were right spannerman, the ring was fine as well as the chrome plated cylinder. It is the crank seal that is old and cracked. I am in the process of changing the seals. Do you think I should split the case and change the gasket as well? The motor looks like it has never been serviced - it looks like it doesn't have much running time - it just sat for years.

thanks!

I can't see there being a problem with the gasket.
If the mains felt nice and smooth when you had the head and cylinder off and as you say its not done much work plus if your not doing a resto I would change the seals replace the transmission oil use quality 2 stroke oil and try it.
I suspect it will run fine.