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Technical Section / Re: Initial start up turns into total rebuild !
« Last post by repete on Today at 12:56:29 PM »
Hi fellas

At some point I need to make decisions based on guidance gathered.

When originally looking for info on the layshaft measurements I saw nothing about tolerances.  That doesn't mean it's not there and I have time to re-check.  I don't need to catch a ferry like John did.  LOL
But given the experience of Ray, John, etc. I'd be very surprised if anything were to be found that's contradictory.

Regarding the blind layshaft bushing, I had 4.5 thous clearance between shaft and bushing.  Allowing for a wanted 1 - 1.5 thous design clearance for the oil would leave 3 - 3.5 thous of wear space.  I'd be surprised if that were acceptable in any piece of machinery.  And even if "usable" it certainly puts it closer to the end of it's useful life than it does a fresh start.  Ditto the other "end of a shaft" bushings I replaced.

On the 7/16-20 UNF nut, I didn't say it was impossible to get - just inconvenient after two trips to two different hardware stores.  I only even mentioned it because I found it surprising.  Eventually I know I'd find them at a hardware store, tractor supply, etc. but the running around is time and money better spent.  For $5 shipping I can place an internet order with a distributor and get additional product for the same amount of $$$ the hardware store would charge, will not be driving place to place and can stay home and do something else with my time.  If I lived in a rural area where I would enjoy the drives I'd be happily running all over the place.  I generally like drives/rides.  But unfortunately for me I live in a suburban hell (urban sprawl) where driving 4 miles involves 15 traffic lights and takes 20 minutes. 

The fact that two of the most knowledgeable fellas say 1.5 thous that is what it will be!  I like a consensus... removes doubt and second guessing.   So, I've got a plan now regarding the new bushing which is 1.5 thous between the layshaft (after dressing it up) and the bushing.

John - that running in of a rebuilt gearbox with an electric motor was genius and is a great story!!!!

ALL of this input is valued & appreciated and I thank each of you!!!!!!

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Technical Section / Re: Initial start up turns into total rebuild !
« Last post by Owen on Today at 11:46:58 AM »
What do the BSA service sheets say?
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Technical Section / Re: Initial start up turns into total rebuild !
« Last post by timsdad on Today at 07:05:52 AM »
I agree with John - I'd give it at least a thou' and a half for safety's sake. Which means I'd probably have left it running with the original bush still in there. I feel it would have been a waste of time mentioning this at the outset because folk mostly do what they want to do and not what I think may be best.

Also, I'm very surprised you can't obtain 7/16" UNF plain nuts - they were introduced to us by the USA decades ago and are still easily available here despite being replaced by Metric a long time ago. Have you tried at a tractor or truck spares supplier? Do you have trade motor factors on your industrial estates?

Ray
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Technical Section / Re: Initial start up turns into total rebuild !
« Last post by chaterlea25 on Today at 02:01:51 AM »
Hi Pete,
0.5 thou is too tight, space is needed for the oil and to take into account tolerances of the time the bike was made
1.5 thou is ideal for the BSA
I seized a BSA A10 gearbox when I did not five the sleeve gear bushes enough clearance, It seemed OK when on the bench. This was on the morning of catching the afternoon ferry to France with the bike :o
An ultra quick strip down and hone the bush some more and we made the ferry with 30 min to spare
The next A10 gearbox I built also seemed a little tight as it was built from bits, I made up a jig with an electric motor to drive the gearbox, I started off running the box in top gear then changed down to third and so on each time for about an hour, I connected a speedo for fun and by the time 150 miles clocked up it was fine and running cool

John
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Technical Section / Re: Initial start up turns into total rebuild !
« Last post by repete on Yesterday at 04:49:13 PM »
The oil has to be somewhere so will fill half a thou' gap between shaft and bush and leave nil clearance. If you start off with less than half a thou', it's likely to nip up.

You can feel this running clearance when it's dry but, after a squirt of clean oil, the clearance disappears.

Ray

Room for the oil makes perfect sense.  Just so that I'm perfectly clear on this.... no less than 1/2 thous?  Meaning 1/2 thous is acceptable?  Or not even as tight as 1//2 thous.... keep it closer to a full one thous.?
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Technical Section / Re: Initial start up turns into total rebuild !
« Last post by timsdad on Yesterday at 04:28:53 PM »
The oil has to be somewhere so will fill half a thou' gap between shaft and bush and leave nil clearance. If you start off with less than half a thou', it's likely to nip up.

You can feel this running clearance when it's dry but, after a squirt of clean oil, the clearance disappears.

Ray

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Technical Section / Re: Initial start up turns into total rebuild !
« Last post by repete on Yesterday at 04:16:29 PM »
I've had other bushings with 1.5 thous clearance and I was able to feel & see side to side movement.  My opinion is nearly valueless compared to the collective experience of those here guiding me but wouldn't I want something closer to .5 thous ?  Keep it nice and snug but still able to slide in and out and rotate without binding ?
The guys in the shop are fully capable of holding a tight tolerance.
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Technical Section / Re: Help To ID More Compoments Required
« Last post by timsdad on Yesterday at 04:15:17 PM »
It was a styling thing. Most of the Brit manufacturers started putting instruments into the tank around that time so they had to either get one jump ahead or keep up with the opposition. Fortunately, the practice didn't last too long.

Ray
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Technical Section / Re: Initial start up turns into total rebuild !
« Last post by camman3 on Yesterday at 03:56:37 PM »
The OD 0.685 of layshaft is 2.5 thou down on 11/16 inch which I would guess as being the original diameter :-\
Even 2.5 thou is probably the maximum clearance you would want on a new bush, so as you are doing, a purpose made bush is in order with 1 to 1.5 thou interference on OD... imo
Graham
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Technical Section / Re: Last Few C11 Parts To ID
« Last post by Tim K on Yesterday at 02:49:27 PM »
There is also a compete bottom end and an OHV head. The bottom end is marked ZC11 so I’ve taken that to be a post war C11 engine.
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