clearances for split cases?

tx246

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#1
here is the deal. i had my rod bearings go south on me and they got caught up between the crankweights and the case(bottom). being steel, they chewed and deformed the case ever so slightly. i took the dowl pins off and mated the halves. the tranny end there is no daylight but as you work your way to the front, there is some clearance. i can slip a .010 guage in there and run it from the front to where the crank lives.

i marked the case halves with marker and placed them face down on a sheet of glass with some 400 wet dry. the markings came off fairly even but i still have the .010 clearance.

i looked in the factory manual and there is no clearance given for the cases. i know it has to maintain a seal but at what pressure? this bike uses a paper gasket. should i use a bit of yamabond too or do i need to have it machined?

the bike is a 2000 cr250.

thanks in advance for the replies.
 

BSWIFT

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#2
Gene, if there is no binding on the crank, I would think some yamabond should work but I'm no expert.
 

tx246

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#3
i know what you mean there Swifty. im scared to have it machined true in case i close down end play on all of the tranny shafts, crank ect.
 

evenslower

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#4
Can you get a center gasket in a slightly higher thickness to make up for what little you would lose in machining?

Or you could just buy a new KTM. I'm just saying.............
 

tx246

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#5
man, it must be slow at work to find you in this forum. i would love a 200exc but im glad i didnt sell the honda and have this happen to someone else. i would of felt bad. im gonna give this thread a day or two before i haul it up to the machine shop and see what they say.
 

BSWIFT

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#6
It actually seems to me that your crank width is not correct. If you changed the rod and bearings they should be the same as when removed. If the gap is 1-2mm, adding a gasket between the cases wouldn't be to bad, however, if it is much more, your end play on the tranny parts becomes pretty big and could cause shifting issues or worse.
 

tx246

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#7
Brian,
The cases are bare so that eliminates problems with bearing/crank fit causing the problem. The tranny end of the cases mate perfectly. Im questioning the clearance in the crank area and whether or not it will seal. That clearance of .010 is with no gasket and the cases not bolted together. Im sure the bolts will pull some of that clearance out too.
 
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#8
I agree with BSwift. I'd at least bolt it together with 3bond or Yamabond and gasket and see what you think. Gasket will give you some wiggle room and you might seriously think about the torque pattern you are going to use when tightening together. As you already know, Yamabond isn't going to fill a 0.010 gap, but center of gasket can compress some at apex and cases will distort some near front. Maybe it will work with no crank binding. It will only cost you a gasket to see (unless you think it's OK and it's really not and it destroys your crank and cases).
Do your gear clusters have shim washers on the ends?? If so, maybe you can machine cases straight and magically find thinner washers.
 
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#9
I would put it together with the sealer and pressure test it. Keep an eye on it. I do not believe it may be as big a deal as you think. If it was a pair of cases without a gasket I would be worried!
 

tx246

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#10
i think im going to bolt the cases without tranny, crank and gasket o see what happens to that clearance. if it tightens up to smaller than what the gasket thickness is, ill put er together. what psi should the bottom end hold? im guessing that it shouldnt be much as most of the pressure is on top of the piston.
 

DWreck

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#11
Gene,

If I was you I would try and recoup some of the cost of repair from that Oklahoma speedster you bought it from. He clearly went way to fast for what that motor was designed for.

Just kidding. Sorry I don't have anything useful to add to this thread but hope you find an easy/ inexpensive fix for it.
 

evenslower

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#12
tx246 said:
man, it must be slow at work to find you in this forum.
Not lately bud. Actually the opposite. I came in here to get my mind off work for a change and I see my buddy is having issues. I'm pretty much useless when you get to the point of having case halves in your hands so I'll just sit back and learn.
 

tx246

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#14
actually, this time I took my time taking it apart and labeling everything. normally I use the bucket approach and it usually ends up taking a lot longer figuring out where that last bolt goes than it should.

Im gonna get serious about getting this thing together this weekend. Ill post results.

John- sorry to hear about the workload but you are the bigdog now so delegate like you have never delegated before.

As for you Dereck go make up some premix so us smokers can get a lap.

I really cant complain about the rodbearing failure. This is the first time the cases have been split. Surprisingly, the crankbearings where still flawless.
 
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#15
Do you have the parts yet? Motorsports is advertising hotrod engine kits for 320,gives you everything! The dealer gets them through parts unlimited,for a more better price!