125 rebuild failure

[chaz24367]

I just put a new top end on my buddies 1994 cr125.
This was a new cylinder, piston and ring.

It started and seemed to run fine yesterday for a break in. He ran around a few minutes and warmed it up. We then let it cool down before running again. He then made a couple of moderate laps and stopped the bike on the track and it would not restart. There seems to be NO compression! I have not pulled the top end off yet to see what it lloks like.

I am just wondering what others may have to say about this.

Thanks

[ctroger24]

Did you do your break-in properly? And you say it "seems" like there is no compression or you actually checked it?

[mrcribbs]

When you tear it back apart I bet you find that the rod bearing is junk.

[chaz24367]

Originally Posted by mrcribbs

When you tear it back apart I bet you find that the rod bearing is junk.

Pulled the top end off and there is a little play in the lower rod bearing.
I'll be splitting the case in the next couple of days.

[dklassen]

Sorry to hear about the grief you're having. I'm curious if you were aware of what caused the initial problem with the top end. If there was some sort of failure then you need to know what caused it in order to ensure it won't happpen again. A 15 year old 125 should not be run with the factory crank bearings unless it was in storage for most of those years. Even so the seals would need replacement a few times by now. I have seen a number of 20+ year old Honda CR's that still run, some on the stock parts they left the factory with! However, replacing the crankshaft assembly, bottom end bearings + seals should get everything in order down there. Now you need to diagnose the top end issues. Good Luck.

[chaz24367]

I was able to split the case last night. It looks like there is a few bearings or something missing from the lower rod bearing.

With missing bearings I would have thought that there should be more play in the rod bearing than there is.

This explains the original top end failure as well as this one. Should have just pulled it all apart to begin with.

(there was a piece of metal in the original top end when I pulled it apart.)
Thought that it was maybe a spark plug tip. The guy riding it removed the plug that was in it and threw it in the dirt after it broke the first time.

It appears that the bearing gave up some of its goodies inside and sucked them right up into the cylinder.

Gotta go find a new crank now.

[chaz24367]

Originally Posted by ctroger24

Did you do your break-in properly? And you say it "seems" like there is no compression or you actually checked it?

No compression check there was no need to check it. It was THAT bad.

Beak-in, lol. I am a complete noob with bikes. I searched the 'ol net and found about 1,000,000,000 different break-in procedures. I gathered up the most common "theme" for break-in.

You method do you use or follow?

Thanks

[dklassen]

Did the new top end get damaged this go round? When looking for replacement parts you'll never go wrong with stock Honda parts however if money is an issue, I have had good luck with Wiseco bottom end kits that have the crank, bearings and all the seals and gaskets. We put one in my sons KX65 last season and it has worked very well. As far as break in goes it wasn't your procedure that went bad and yes there are a lot of break in theory's out there. My best suggestion for a two stroke is not to lug the engine but to warm it up and ride it at medium revs on a MX track which provides on/off throttle situations for about 15 mins the first time. Let the motor cool down and then you can run it hard. This has worked for me with no failures in the last 20 years. I know others will have their own opinions and I'm not saying this is the only way, it has just worked for me in about 15 bikes. Keep us posted on your progress.
DK

[chaz24367]

Luckily there was no damage to the cylinder itself. The head and piston both got chewed up pretty good.

I am in the process of ordering the wisco crank, pro x piston, and cosmetic gasket kit. Might even have it tomorrow.

Your break in is basically what we were going for.

I'll certainly update when I get the new parts.

[Mainjet2001]

Originally Posted by dklassen

Did the new top end get damaged this go round? When looking for replacement parts you'll never go wrong with stock Honda parts however if money is an issue, I have had good luck with Wiseco bottom end kits that have the crank, bearings and all the seals and gaskets. We put one in my sons KX65 last season and it has worked very well. As far as break in goes it wasn't your procedure that went bad and yes there are a lot of break in theory's out there. My best suggestion for a two stroke is not to lug the engine but to warm it up and ride it at medium revs on a MX track which provides on/off throttle situations for about 15 mins the first time. Let the motor cool down and then you can run it hard. This has worked for me with no failures in the last 20 years. I know others will have their own opinions and I'm not saying this is the only way, it has just worked for me in about 15 bikes. Keep us posted on your progress.
DK

Good advice. I run my bikes through 2 to 3 heat cycles in the same process. Never had a failure.
Might add to coat the bearings (crank, lower and upper rod) with oil during assembly.