Dirt Rider Magazine

Ok, a 139 is faster than a 144 for reasons i won't explain right now. As for break-in procedure, what one are you using now? I took this off another forum:

Note: BIP= Break-in procedure
If the rings are replaced, a new piston installed, the cylinder replaced, the crankshaft rebuilt or replaced, or new engine bearings installed, perform the following engine break-in procedure.
Before breaking-in the engine, note the following:

a. Perform the BIP on the flat ground. To prevent engine overheating, avoid riding in sand, mud or up hills.
b. DO NOT run the engine with the throttle in the same position for more than a few seconds.
c. Check the spark plug frequently during the BIP. The electrode should be dry and clean and the color of the insulation should be light to medium tan.
1. Begin BIP by riding the bike for 10 minutes using no more than 1/2 throttle. During this time, shift the transmission frequently to avoid luging the engine while avoiding high engine rmp.
2. After the first 10 minutes, turn the engine off and allow it to cool down.
3. Ride the bike again for 10 more minutes, following the suggestions in step one.
4. After the 2nd 10 minute ride, turn the engine off and allow it to cool down.
5. Next ride the bike for 10 minutes, using no more than 3/4 throttle. Again, shift the transmission frequently to avoid lugging the engine or running it at a high rpm.
6. After the third 10 minute ride, turn the engine off and allow it to cool down.
7. Repeat steps 5 and 6 three more times.


Most important thing is to make sure you don't lug it!

http://www.mxnewsfeed.com/phpbb2/viewtopic.php?t=189

I had a 92 CR500 that I re-did the top end on, and now it's insane!

1. started it up and warmed to operating temp.
2. shut it down to cool.
3. started it to op-temp and rode it not going over half throttle and keeping a normal load on the engine. accelerate through all the gears, then go back down through the gears. Doing this for 10 mintues. shut off and cool down, check head bolts and nuts, look for leaks.
4. repeat step 2 & 3.
5. repeat step 2 & 3 but ride for 30 minutes, shut off & let cool down.
6. Ride it !
Ya gotta gove those rings a chance to seat against the walls of the cylinder. If you lightly putter around, your rings won't seat right. When you go for real power, they won't perform right because they seated at a low power setting.
Now, that being said, that doesn't mean to go out and tach it out in every gear. You have to have that load on the rings so they expand and break in to the cylinder right. That's what the cross hatch bore marks are for (after they hone your cylinder) They're for seating the rings. You only get one chance to do it, so do it right.

when you have an open door you should always walk in BIG BORE