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Main Bearing Play

Submitted by roger_allen on Sun, 26/04/2020
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Is there an acceptable limit on the vertical play in the drive-side main bearings on a '55 ES2? I am measuring about 2-3 thousandths. It wasn't noisy last time it was running, I decided to test/measure it just because I had the primary case off.

 

Thanks,

 

- Roger

Submitted by roger_allen on Mon, 27/04/2020

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The end-play is good.

Testing while hot won't be immediate. That requires at least partial reassembly, after which exact measurement will be less easy.

So I think it's going to stay the way it is for now. If I start to hear nasty noises, I will have a good clue what it is.

- Roger

Hi Roger,

Apologies for taking so long to reply, so hope you are still checking the thread. The maximum clearance of a C3 roller bearing with 30-40 mm bore is specified as 0.070 mm (0.0028") by SKF.

This clearance is a true radial clearance perpendicular to the axis of the bearing, which you cannot measure. If you are measuring the up-down clearance, the crankshaft will be rotating around the timing side bearing making an apparent increase in the measured clearance proportional to the bearing centres and the distance from the timing side bearing to the measuring point. This could be as much as 1.5 times giving a movement of 0.0042". Which is greater than your measured distance.

As the tension in the primary chain is always pulling the bearing contact to the rear any clearance will be at the front of the drive side bearing and to the rear of the timing side' with a slight rolling of the contact points caused by the upward and downward forces exerted by the suction and compression forces into the crank.

In any case there will be no 'hammering' in the bearing caused by the clearance.

As you have decided, I would also happily continue using the bike without concern and hope my explanation alleviates any remaining concerns you may have.

Regards

Dick 

 


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