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DT 250B crankshaft bearings clearance

09 Dec 2019 05:00
Wessi
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DT 250B crankshaft bearings clearance #1
Close to re-assemble the crankshaft I noticed the bearings I purchased aftermarket have C3 clearance. Today I saw in the parts list, C4 is original. Stupid question, maybe, but better don´t install? Does somebody have experience with C3 installed?
Don't want to open the cases next time again...
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09 Dec 2019 09:48 09 Dec 2019 09:52 by Pillsbury.
Pillsbury
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DT 250B crankshaft bearings clearance #2
C4 has more internal radial clearance than a C3. Both have more internal clearance than a standard bearing. I would go with what Yamaha used. I have not used anything less than stock ratings, but I have used other make bearings.

1970 DT1-C Grand Prix race bike
1970 DT1-C Street tracker
1968 Honda CL90
1973 Honda CR250
1974 Honda MR-50
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1947 Mustang
1974 Suzuki TC185

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09 Dec 2019 15:41
RT325
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DT 250B crankshaft bearings clearance #3
Left side is super tight on the shaft & in the case & not sure what mine are but can see why they recommend C4 on the left. C3 on the right would be good as only tight in the case & shaft slides in. If you got the left bearing off the shaft easily or the bearing wasn't tight in the case then C3 will be ok on that side too. [in my opinion]. Also yamaha have steel inserts in the case for the bearing in those early days so the bearing 'should' be tight in that no matter what. One more thing & unlikely on a big shaft like that but have seen numerous small motors where the bearing on the left has been spinning on the shaft so its a loose fit but move it out 5mm or more then its tight to get off [as it should be but] but of course should be tight all the way home to the crank wheel or ya getting nowhere.

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11 Dec 2019 04:45
Wessi
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DT 250B crankshaft bearings clearance #4
Tank you for your reply. Maybe I was wrong, the parts list writes for the DT 250 just Bearing 6206, the DT 400 has B6306 C4 ( 72mm outwr diameter instead 62mm and 19mm width instead 16mm) so different pair of shoes. A pitty, there is nothing written on my old bearings. So I will install my 6206 C3 Koyo bearings.
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