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Enduro Engine - 2 stroke Cylinder, Piston, Tranny, Bearings, Clutch, Pipes & Silencers, etc.


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Old 02-13-2011, 07:49 PM
CDBiker220 CDBiker220 is offline
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Default Crank bearing spinning in case...

So i posted before about crank end play on and 07 EC300. Turns out the right side ball bearing was loose in the case, and the crank. Causing the crank seal to leak. It slides right on and off the crank, and their is ridge on the bottom side of the case bore so it needed popped out with a hammer, but when in the bore it would spin. Would actually move in the bore up and down alittle and in and out. Clearance on the crank was zero and not loose. but slid on by hand. Should be an interference fit on both crank and case correct? Might just send the crank and case to RB Designs...from his website looks like he can handle this. The rod and piston bearings seamed like new, so I dont plan to rebuild the whole crank if i dont have too. All other bottom end bearings were perfect other than the sprocket output shaft bearing felt a bit tight, might replace it. Any advice other then talking to RB?


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Old 02-13-2011, 09:18 PM
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Thats the best plan. Sounds like a mfg tolerance problem on that case. Sorry to hear about that, not common. Good thing you checked, surprised it did not vibrate.
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Old 02-13-2011, 09:28 PM
CDBiker220 CDBiker220 is offline
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It did vibrate a good bit more then my dads 2000 GG 250. But only a tad more then my yz250. So i figured it was just cuz it was a 300. Hopefully its ever smoother now. It will be nice to know that everything will be good in the bottom end when im done, plus now I know how to tear it down and how everything works. It didnt look like it spun much or anything, crank looks fine. It was raced in the 6 days....so it had a hard life...not surprised to find some problems.
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Old 02-15-2011, 11:55 AM
CDBiker220 CDBiker220 is offline
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Well looks like RB will not be able to help me, apparently he does not have the material to fix a the bore for a bearing that size. Anyone know anyone else that does this kind of work I could talk too?
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Old 02-15-2011, 12:05 PM
hannesd hannesd is offline
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does axial crank play always mean that the bearing is loose in the cases?
i do have some axial play, about 1mm orso...
mine does not really vibrate that much.
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Old 02-15-2011, 12:23 PM
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Axial means "in/out" on the line of the crank axis. Radial means "up/down" or "side to side" to the radius.

There is (or was) another place that can do that. I found it at one time but don't remember offhand. Time for some web footwork.

I suspect how Ron does it is machine a sleeve with the proper fit for the bearing as the ID, and bores the case for this to fit tightly on the OD. I also suspect he does it this way to avoid welding, but I'm not saying it can't be welded and rebored.
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Old 02-15-2011, 06:59 PM
CDBiker220 CDBiker220 is offline
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The problem is that he did not have material to do a bearing as large as mine, and the smallest amount of material he could aquire was $150. plus labor. So just wasnt economical. I found a local machine shop called dutchman racing that builds race sportbike engines and does other various high performance engine repair. They are going to take a crack at it. So I'll see what they have to say, dropped it off today
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Old 02-15-2011, 08:48 PM
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"Take a crack at it" does not give me confidence. Ask me how I know. Ron's work on the other hand is impeccable. I would ask what he needs and try to source it for him cheaper if $150 is too much. Hell, we are moving to another building at work and loosing our shop, going to outsource mode. We have a lot of stock and machines that will be sold. My neighbor also owns a shop. If not I'd just pony up and know its done right.
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Old 02-16-2011, 11:53 AM
Neil E. Neil E. is offline
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I did this repair on a 68 Bultaco. This was before I had any large shop equipment. I had a supplier bore the engine case out about 3mm larger first. Then I machined up a steel sleeve that was a slight press into the case. The bore was sized so the bearing fit was correct after installation. It was tricky getting the tolerance perfect, but it turned out well. I rode that bike for years, sold it to my brother, he later sold it to one of his friends.

The material used for the sleeve is not important. It can be steel, stainless, brass or aluminum. The usual method is to: bore the case out; warm the case and press in the insert; let it cool then finish bore the insert to size. This is all done in the same setup, but you need a lathe and mill available at the same time.

If the bearing "just" spins (meaning the slightest of free fits), you could loctite the OD to hold it in the cases. It really depends on the amount of play. While not recommended, I've seen bores carefully centerpunched in even rows to raise the metal enough so the bearing is located. The "space" is filled with red loctite.

Most engine cases temperatures are around 200-225*F, so the locitite will hold. It usually takes about 300-325*F to break the bond.
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