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QJ-2 shaft fit in bearings?


Old 10-23-2008, 08:26 AM
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Default QJ-2 shaft fit in bearings?

Hi Bob,

I own a fairly new QM-2 (about 25 runs) and I have noticed that the shaft is moving approx 1mm back and forth in the bearings when I removed the spinner backplate.

I am used to the Nelson bearings being a press fit on the shaft.

As I do not know the tolerances of the QM-2 I was wondering if this is normal?

I am not blowing plugs but getting 2 good runs from a HD plug then performance seem to drop off but this could be because the comp is not right or the engine is not fully run in yet.

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Old 10-24-2008, 08:29 AM
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Default RE: QJ-2 shaft fit in bearings?

The shaft is not a press fit in the bearings. In otherwords, the bearings do not serve to hold the shaft in position. But it should not be extremely loose either.

You should be able to remove the shaft from the bearings without any problem (during engine disassembly) with just a reasonable press. I can take the shaft out of my engines with just a tap of a wood mallet.

Chances are the cranshaft is not full-forward and the collet is slid forward a tiny bit.

Remove the backplate push the crankshaft full-foward up against the rear bearing ( from the inside). If need be, use a small block of wood and a mallet to give it a quick tap into position. That will ensure its up forward.

Then install the collet on the crankshaft up against the front bearing, mount the spinner backplate and a prop. Make sure there is no play when everything is installed.
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