KDXRIDER.NET

Clear up an argument between a buddy and I.....

My right side case is broken on my 98 rm250 I just bought..

So the argument is whether cases are matched pairs

I always thought yes but that got me in a 25 minute debate with a couple friends. I know you can buy them individually from ebay but that doesn't make it right...you cannot buy them individually from the factory.

Thanks in advance!

I don't know the actual answer, but I will tell you my gut says just replace the bad case half. Modern casting and machining processes by the Japanese manufacturers is so good that I bet it won't be a problem.

They would all come from the same casting, the only machined areas would be the flange where they join, and any bearing races. Also the top where the jug sits. I think you'd be fine replacing only one half, then if you needed anything machined flat that's easily done afterwards.

There was a thread here on that very subject not too long ago. The angles of the joint face between the 2 case halves where the cylinder mounts were slightly different. Poster was able to correct with a few minutes careful work with a file.

Even though the castings come from the same mold, machining tolerances could result in some mis-match, resulting is slightly different dimensions.

I had the same discussion with a number of different "guys who know" when I was looking into replacing a broken case half on an IT465. The consensus was that you would replace both halves in a perfect world but you would be unlikely to have any problems by changing just one half. I haven't actually put the motor back together yet so I can't say with authority if it will work.
If I were you I wouldn't worry about an unmatched half if that ends up being the most convenient repair.

Usually the case halves are matched at the factory after casting because there are slight variations from cast to cast. At the worst you would have to match the new half to the old one not being replaced. As Rad said, in a perfect world replace both, but in every other world just do one and make it fit!

Agreed. You can almost certainly make a one-off fit, but there is a pretty good chance there will be a small issue somewhere, so be careful. The mating surface for the jug being the most likely. If you can find a matched set, that would be best.

I agree Julien D about your statement on the chance of having a small issue somewhere. Because of minute differences in the casting/forging processes as a result of inconsistantcies of the materials, machinig equipment set ups at the factory, jigs that shift etc., I know you will not get the same EXACT reproduction of parts. Another factor is matching components (2 side case halves for example) made at the factory that "wear together" during operation. With that said probably the most important area that needs careful inspection would be the surface of where the base of the cylnder mates up to.

1998 RM250 case halves are (or were) sold as a set. I doubt us internet wizards are going to outsmart the factories that have assembled about one jillion engines.

Some Hondas halves are sold separately. I have never seen a KDX or KX crankcase half that is sold separately, only sets.

Right right. As I mentioned above, you have to consider the cylinder mating surface. That surely has to be finished after the case halves are bolted up together, so that both sides match perfectly and provide a flat even surface for the cylinder to mate to. That, IMO, is the biggest reason for matched sets.

You could easily "dry fit" the halves together and machine the cylinder mounting surface flat to avoid issues.

I'd try to buy one from the same year and even try to get the serial #s as close as possible. My thinking is you would be getting one that was cast at the same time as your other half, therefore maybe a better fit.

Slick_Nick wrote:You could easily "dry fit" the halves together and machine the cylinder mounting surface flat to avoid issues.

Ease is subjective. It would be bummer for me if I bolted them up and then had to sort that issue. I haven't got as much time as I would like to get this sort of stuff done. It wouldn't even be a concern with a matched set.


*And it might bolt up with no problem at all. If not, you can surely make it work. So I guess it depends on whether you can find a matched set. I see mostly halves being sold on fleabay. Matched set is probably gonna cost you! That being the case, I'd probably just go for it and make it work.

Ok so i called 3 bike shops and spoke to their techs they said if the factory sells them individually they can be replaced individually if they sell them as a pair they are matched and should be replaced with a matched set.

This is for someone that cant or doesnt want to or have time to do the machining that may be required to match old to knew. The shops replace them as a pair no big deal for me ill just find a used pair and go that route thanks guys!

It's not exactly the same thing, but I once sold the upper and lower cylinder head/rocker box of an XR200 to two separate people. The guy who bought the upper/rocker box from me said it didn't mate up properly to his lower cylinder head (the cam was binding in the cam bores). I think the answer is "you might get lucky, you might not."