Connecting rod issues 92 KX 250

[duncanstives]

Hey guys my discount KX250 top end is now apart... Shows no catostrophic damage... Looks perfectly fine (will get replaced anyway... Just glad to see the jug is not messed up or something) but the lower connecting rod bearing has issues (I think)... It does not have excessive up/down play... In fact it has no play... At all and its hard to move the connecting rod on the bearing... This seems it should spin freely and that what it did on my KDX when I rebuilt it.


I assume the case must be split to change this? Anyone done it? For what its worth the crank itself turns fine (which is to say smoothly), the surfaces all look lubricated though the lower connecting rod looks less so... I am hoping there is an easy(ish) way out of spliting the case as I don't have a huge collection of specialty tools...

Thanks.

 

[dirt bike dave]

Sounds like the big end bearing is shot. It happens, but repair is costly and may not make economic sense.

If you don't repair and it lets go, it will probably take out your cases, and the shrapnel can easily destroy your cylinder, too.

Splitting the cases and re-assembly can be a pain, but is doable. Some bikes do require specialized tools, but you may be able to improvise.

In case you don't know, the connecting rod is one peice. There is no cap like there is on a car connecting rod. You cannot replace the big end bearing without pressing the crankshaft itself apart and sliding the rod off. The new rod and bearing gets slid on, and the crank re-assembled and pressed together. That's a job for a specialist. If you don't have one in your town, you may be driving, or shipping your crankshaft to a specialist.

An alternative is to get a replacment crank/rod assembly. All new crank, rod and bearing. Might be hard to find and expensive, but may be worth considering, because you could reassemble it all yourself.

When I blew up a '99 CR250, it was not much if any more expensive to buy a crank assembly, because Honda had pretty fair prices on them.

If you are going that deep into your motor, you should replace the crankshaft bearings (the ones on the ends of the crank, that fit into the cases). And you'll need a complete gasket set. You are going to rack up a big parts bill, unfortunately, even if you do your own labor.

 

[duncanstives]

Found a used crank assembly for $138 on fleabay... Claims no up and down bearing play and LOOKS to be in good shape. Worth it?
Also: further research (and measuring) shows the bike has been bored to 265 and sleeved... I am not against the sleeving on principle because, while it may not dissipate heat quite as well it should (in theory) have a bit better chance of surviving and encounter with some grit or stuff should I be less than 100% on maintenance or dunk it in some water (two things I would NEVER do... Noo... NEVER!)... Piston is a wesco and I guess that's what will be going back in because that's the only manufacturer making 68.5mm pistons that I can find.

Anything else I should know? Incidentally the piston checks out as a 93-00 model though the bike vin decodes to 92... I am just assuming the engine or parts of the engine have been swapped at so.e point.