I Need Help with my CR125

[DirtBiker125CR1313]

So I was riding my 07 Honda Cr125r at my local track today and it was riding normally for about 20 mins or so. Then when i was going around I had a sudden loss of power. So I stopped to try to figure out what was wrong and I noticed that there was no compression when I pushed down on the kick start with my hand.
I think that it needs a new top end but I am not sure because I am very new to dirt bikes. Also the top end only has 15 hours on it. I don't push the bike hard either. Could you guys help me figure out the problem? Do I need a new top end? Or is it something completely different?

-Thanks

 

[BJames]

Unfortunately you won't really know until you have a look. The first thing to do, take off the pipe, and look into the exhaust port. If you see bad scoring and scratches on the piston, you know that you need a top end. If it looks ok, then remove the head. If you put the piston to the bottom of the stroke, you can inspect the bore. Again, any scratches or scoring, you need to do a top end. If it still looks ok, Pull the whole cylinder to inspect further.

Doesn't matter if your top end has 1 hour or 100 hours on it. If you sucked sand or dirt, it could be ruined. If it was run lean it could be ruined.

The good news is that if you just need a top end kit, and you do the work yourself, you're only going to be out $150 or so.

 

[Uchytil]

Ask yourself if you are going to repair the problem, or have a friend help, or take it to the shop. Chances are yes it needs a top end at 15 hours. There are so many variables associated with engines like; how hard to you ride, level of routine maintenance, etc. If you have the manual Honda supplied use that as a guideline. In all of my years around this sport I've found that making good friends goes a long ways to learning how to maintain, and repair, a bike. If you paln do do some of these repairs yourself, and you want to learn, you should invest in a compression tester to get an accurate read. Compression is a guideline BTW, in other words not all combustion chambers are exactly the same. Knowing what a fresh, broken in, topend reading is helps later when you diagnos a worn on. Percentage of loss is what most people go by. I could go on but there may be some threads to search for in here or you could get the a great book by Eric Gorr about maintenace and repair of dirtbikes.

 

[DirtBiker125CR1313]

Alright I will take a look at the piston and cylinder. I hope it just needs a new top end. I can do that myself. Thanks for the help guys.

 

[DirtBiker125CR1313]

Ok so I took the expansion chamber off the bike and looked into the exhaust port at the piston. It had a big groove on it. I am going to take the head off for inspection of the cylinder. I just hope it doesn't have any grooves on it.