Motorcycle Repair: 75 mt125, piston cylinder, penetrating oils

Question
Hi Bill,

I see from your profile that you have extensive experience with 60s Hondas.  Could you help with my 75 MT125 Elsinore.  

The engine is frozen  and is probably not usable.  Is it possible to replace this with a 75 MR175 engine?  I have access to a used 175 engine that is in good shape.  Any suggestions that you may have would be appreciated.

Also, my daily rider is a 1990 CBR600.  This bike has over 200,000 miles on it.  It does run well, but I was wondering if you knew how long these engines would last.  Should I be looking at replacing it?

Thanks for your help.

Oscar

Answer
Oscar, I believe that the MR175 is a stretched version of the CR125 motor, rather than a de-contented CR250 motor. Check online microfiche illustrations with part numbers to see if there is a thread of either 125 or 250 series parts being used in the MR175 engine.

Unless the engine has filled up with water or other contaminants, usually "seized" engines just have stuck pistons in them. Liberal use of penetrating oils and/or some heat often will break the piston/cylinder bond loose and perhaps a rebore can freshen it up again. If it is worse than that, then the motor should just be swapped out.

Wow, that is amazing that you have put 200k miles on a CBR600. It wouldn't hurt to track down another good used motor to keep in the garage for a spare, but there are other considerations to keep in mind on a high-miles bike...  suspension components including bushings and bearings, steering head bearings and brake components, mostly. I don't know of anyone else who has put that many miles on a CBR600, so you are a pioneer in longevity for that model, I think.

Keep riding safely...

Bill Silver