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 Gearbox confusion

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Number of posts : 156
Registration date : 2011-07-25

PostSubject: Gearbox confusion   Tue Sep 27, 2011 1:06 am

Perhaps with the season having just finished, this isn't the best time to ask you weary racers for advice, however....
My son and I are attempting to rebuild a bantam racer with D5 based
racing engine which we acquired dismantled together with some spares. We are
doing a dry build to sort out what is and isn’t there. It is obvious that
someone has put a lot of time and effort into tuning the unit which we would like
to complete without too much grief! The bike, when completed, will initially be used for parade laps on the Northern Ireland road circuits while son aspires to building a more competetive one.

Our first problem is when the gear cluster
is fitted into the right hand case, (both layshaft bushes have been converted
to needle rollers) the left hand case will not close up due to the layshaft top
gear fouling the mainshaft roller bearing on the l/side as if it is not pressed far
enough along the shaft.

Can anyone with experience be kind enough
to give some guidance on the following points?

1/ What distance should this pinion be
pressed down the shaft?

2/ As the original bush was of the top hat
type with a blind end which held the shaft in location, how do we now prevent
the shaft from floating sidewards with the inevitable self-destruction that would be caused.

Although we have looked at the ‘BTW’ and
noticed needle bearings in use, the ‘Gearbox problems and Diagrams’ page show
thrust bearings, so we are little the wiser.'
Son has added some photos on picasa;
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Number of posts : 256
Localisation : New Zealand
Registration date : 2006-12-01

PostSubject: Re: Gearbox confusion   Wed Sep 28, 2011 11:45 am

Nice looking bike.
The mainshaft bearing is in too far, it needs pressing out til flush with cases on both inner and outer surfaces. Then layshaft will fit.
I have similar needle roller conversion in my short stoke engine, the layshaft is located between bronze thrust washers at either end to replace the top hat flange. You may need to press the layshft bearings out til they are also flush and counter bore an outer cover plate.
Or, do the UK type ball bearing conversion on the clutch side and locate the layshaft from the RHS
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Number of posts : 156
Registration date : 2011-07-25

PostSubject: Re: Gearbox confusion   Thu Sep 29, 2011 7:31 am

Hi John

Many thanks for your quick reply and great information- very much appreciated.

Could you possibly give any more details on the ball bearing conversion on the clutch side set up?

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