A forum for owners of Yamaha TTR250 trail and enduro bikes!

Susan Parker · Veteran Member

Continuing saga of PO55

mossproof · Super Guru

There is no o ring on the base of the 350 cylinder - not enough room to machine the necessary chamfer.

Susan Parker · Veteran Member

Thank you for that definite confirmation! I can proceed with the reassembly now...........

Susan Parker · Veteran Member

So, now the engine is all back together - can I ask for some advice regarding running in? Firstly does it actually need running in: I have been told that it doesn't require running in and to prevent the bore reglazing it is important to work it hard right from the start. And obviously some will say that, of course it needs to be run in again. What is the general opinion from those of you who know- it's all a Black Art to me...........

mossproof · Super Guru

Yes, you need to do a running in procedure to let the new rings bed-in to the newly honed bore. Wossner's official running in instructions are here:

cdn.shopify.com/s/files/1/2030/3551/files/WTB.00003-B_POWERSPORTS_BREAK_IN_INSTRUCTIONS_06-23-2021.pdf

For the first couple of steps, you can substitute stationary running in front of a fan with riding on road. What you are aiming for is short runs of multiple thermal cycles. Don't be too gentle, you need to put some force into the rings for them to bed-in, but you also mustn't use full throttle or heavy loads at part throttle (lugging) which can cause unnatural wear characteristics. Plenty of accelerating and decelerating (letting the engine do the braking on a down hill for eg)

Fortnine also has a good vid on running-in a new bike, some of which will be relevant to you.
I go with the "cheap mineral or semisynthetic oil for running in" system, and I also prefer to use paper element filters. Fresh, quality oil of your preferred type after about 100 miles should be fine, then ride as hard as you like. You are not having to take care with any other manufacturer-fresh components in this case.

www.youtube.com/watch

Have fun!

JOHNYBOY · Super Guru

yes do not put good oil in it for couple hundred miles make engine work hard do not over rev make them new rings bed in to bore and you will be fine and enjoy your ttr

Ttboof · Senior Member

I just rode mine but avoided riding it hard for the first couple of rides, years later its still going well

Susan Parker · Veteran Member

Thank you for running in advice. It would be a shame not to get it right after all this work - I do not want to have to do all that again if I can possibly avoid it!