KX100: replacing connecting rod bearing

[Danappger]

Ugh... my engine locked up; turns out it was the connecting rod bearing on the crankshaft; it's frozen tight. I have it apart as far as I can at this point (don't have the flywheel puller). Once I get the flywheel off I don't have a problem splitting and reassembling the case (done it before), but what's involved in separating the crankshaft and replacing the bearing? Is it likely the crank and/or conrod are shot too?

Is this a common problem? I got the engine (not on a bike; it's on the KX100 paramotor discussed in this thread) used; dunno the history but it looked pretty good though I only have about an hour of running time on it.

-Dana

 

[bikepilot]

I'v split the cases on a KX100 before, but have never taken the crank apart, I do know that it requires a special jig and must be trued. Typically, most people would put in a new crank assembly at this point, either stock or wisco. Also, you could have an engine shop re-build your crank, though it typically ends up costing about the same amount, the only benifit of having it done by a shop, is that they often can ballance the crank better than the factory does and you will end up with a little smoother motor. One thing to be aware of is that it is common for the rod to be bent if the bering seized suddenly. They rod is normally replaced every time the main bearing is replaced for this reason and due to the fact that the bearing actually rides on the inner bore of the rod.

Its not a common problem on KX100's to seize the crank, though it does happen on high hour motors or in situtations of poor lubrication.

I don't know what kind of pre-mix you are useing, but it needs to be specifically for a liqued coold MX bike as pre-mix for air cooled motors will not work well because of the temp differnce - dito for jet ski oil. I have tried several different brands of 2 st oil and have found that my motors (including two KX100s) last longer and stay cleaner with Yamalube 2r. I mix it at 32:1 for normal riding and 40:1 for tight/slow/beginer riding. For your application I would recomend trying around 24 - 28:1 due to the continous high rpm useage.

Definately work on the jetting, standard dirt bike jetting is probably too lean for continous high rpm useage. I would start by going one or two sizes larger on the main jet - keep going richer untill you notice a power loss, then go back one leaner (or if its a very small power loss leave it rich). A richer mixture will provide better cooling and lubrication for the crank.

I am facinated by paramotoring (used to fly gliders in the UK) and would love to see some pics of your setup if you have any online:)


I'd probably do the top end as well while you have it appart. Mic the cylinder and order a piston to fit, pro-x as well as most others offer pistons in minuete size differences to accomodate production tollorances of the factory cylider as well as cylinder wear.

good luck:)

 

[WillyM]

You should take the crank to a dealer and have them press it apart.
Yes the connecting rod is junk.
I would also price a new crank assy.might be cheaper.