Ball bearing replacing Timing side bush

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Ball bearing replacing Timing side bush

Postby sheddweller » 21 May 2020 11:13

On pulling my K 350 Sport down, I found that the Timing side bush had been replaced with a Ball Bearing measuring 40x62x12. Searching the Forum hasn't bought up any mention of this approach. Sadly the narrow race left most of the oil hole in the crank exposed, which I believe may have led to premature Big end wear. Can anyone tell me the dimensions, or bearing number of the Roller bearing usually substituted for the original bush.
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Re: Ball bearing replacing Timing side bush

Postby EVguru » 23 May 2020 19:17

Do your crankcases have the three screw holes used to pull in and remove the plain bearing carrier?

Early engines used the ball race on the timing side and the roller bearing conversion is in essence converting the crank back to that style. The roller has the same dimensions as the ball race.

Remove the sludge trap plugs and see if the main bearing oil feed has been capped off internally.
Paul Compton
http://www.morini-mania.co.uk
http://www.youtube.com/user/EVguru
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Re: Ball bearing replacing Timing side bush

Postby sheddweller » 23 May 2020 23:45

Paul,
Yes it does have the 3 holes. As I said it is a K model, and the plain bearing has been replaced with a 12mm wide 6908 Ball bearing. I was asking if anyone could provide the dimensions of the Roller bearing that is commonly used in this conversion.
Garry
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Re: Ball bearing replacing Timing side bush

Postby sheddweller » 24 May 2020 00:12

I have found listings for a replacement Cylindrical Roller Bearing on the Danish Morini site. NJ206=30x62x14 and NU1007=35x62x16. Is the original oil feed to the Plain bearing usually blanked off via the sludge trap when the Plain bearing is replaced by a Ball or roller bearing?
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Re: Ball bearing replacing Timing side bush

Postby EVguru » 24 May 2020 07:29

I didn't pick up on those bearing dimensions!

Someone has obviously tried to limit the material that has to be ground off the plain bearing journal to fit a ball race, but they've ended up with a very lightweight bearing!

The original timing side ball race was a 6206 - 30x62x16. A roller bearing of the same dimensions with a flangeless inner race is the usual replacement, that's an NU206 series. My preference would be for a non polyamide cage, we had one melt on the ex NLM race bike (because the inner race had been fitted too tight).

Don't forget, C3 internal clearance on all the engine bearings.

The oil feed has to be capped off by plugging the internal drilling somewhere.
Paul Compton
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http://www.youtube.com/user/EVguru
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Re: Ball bearing replacing Timing side bush

Postby harrymuffin » 24 May 2020 09:56

Simplest way to blank the feed to the original plain bearing when converting to a roller bearing, is to tap a brass plug into the hole on the crankshaft journal rather than go to the palaver of blanking the feed from the big end.
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Re: Ball bearing replacing Timing side bush

Postby 3potjohn » 24 May 2020 10:49

This prompted me to look at my pile of old bearings. I have a K on which a roller conversion was done a good dozen years ago. This one says 206E on the outer race and NU206E TVP2.C3. Looking at again there seems to be some faint witness marks around the periphery as if it has spun. As said only faint. ( not a patch on a BMW gearbox bearing ). I wonder if I used a smear of green loctite on the new one. Should have made a note.
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