CRF150f Top End Questions

[JettaJayGLS]

So I come home to my dads yesterday to find a 2003 CRF150F sitting in the basement partially taken apart. At first I think..SWEET. But I then realize this isn't good.

My 16 year old brother's friend went out and bought it for $800. He has very very little knowledge about bikes/motors/maintenance. I guess the bike blew all sorts of black smoke. Inside of exhaust was full of oil/build-up all the way to the valve.

My brothers friend though to himself that it is just piston rings. I'm not so sure.

I eventually get suckered into helping them because that's what big brothers are for, and hey, I like this shit. I pull the motor, got the cylinder head off, then the cylinder (which fought me like you wouldn't believe) and finally the piston. Cylinder walls noticeably had oil on them. Also, the exhaust valve was absolutely filthy. I popped out the exhaust valve (against my better judgement because I know how much of a bitch it is to get it back in without the spring compressor) and the seats were surprisingly decent. They should lap out and be good, no major imperfections.

But now onto the cylinder and piston. There is scoring. It doesn't FEEL bad, but it LOOKs pretty bad. What do you think? Cyclinder and piston are junk?

Here are his options as I see them:
-Replace rings, put back together, hope for the best
-Send out cylinder, buy new piston/rings, have a solid bike
-Buy new cylinder (haven't looked up prices but for a 150 it may be cheaper than sending it out) and new piston/rings, have a solid bike

Remember. This is a 17 year old kid who just spent all his money on the bike itself...a few hundred dollars will kill him. This isn't my brothers bike, otherwise I'd help him buy the parts.

[JettaJayGLS]

Also worth noting that the scoring pictured is in 4 spots, seemingly at equal distances from each other around the piston/cylinder. At first I wanted to say at all 4 corners...it's a cylinder, not a rectangle. But I think that may help is describing it?

[Rambunctous]

Since you said that the cylinder doesn't feel bad buy a set of rings and install them in the cylinder without the piston and see what you got. Use the piston crown to push the rings up and down while checking out whats happening. I don't know much about those engines but do take a look at the PCV valve. May be clogged? Black smoke indicates a very rich condition. Stuck float maybe. Raw gas washing the lubricant away in the cylinder maybe? .....Just thinking this could be the cheapest option. Rings Piston and Gaskets. No Warranties. Just finger crossing. And some Rotella T6.

[csmutty]

Have him save up until he can afford to fix it right. New cylinder is probably cheaper. It was cheaper for my crf450 so I'm guessing it would be got the 150 too. If you need a good discount on parts hit me up. I get wholesale on factory honda.

I'd do new cylinder, piston, and rings at least. Hate to have him spend any money and then just have it crap out again after a couple hours of use.

[JettaJayGLS]

I actually found a full rebuild kit including cylinder, piston and all gaskets for 195. Looks to be oem Honda parts.

How would you check valve seals? Its possible the exhaust valve seal is no good and oil is dropping in that way.

[csmutty]

Don't know how to check it. But you could have been losing oil from all that blow by from the piston too.

[Kurlon]

4 corner seize is normally wringing it's neck without letting it get up to temp first IIRC.

Take the cylinder to a shop, have it measured to see how out of round it is, if salvagable hone and new piston and rings. If it needs to be bored https://www.procycle.us/bikepages/crf150-crf230.html 175cc kit for $160.

[JettaJayGLS]

Replaced cylinder and piston. Runs the balls. Granted, every other aspect of the bike sucks (front caliper, all wheel bearings, kick starter broke off, etc.) but runs great.