Author Topic: Initial start up turns into total rebuild !  (Read 18893 times)

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Offline timsdad

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Re: Initial start up turns into total rebuild !
« Reply #450 on: January 26, 2022, 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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Online repete

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Re: Initial start up turns into total rebuild !
« Reply #451 on: January 26, 2022, 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.?
pete ("repete")

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Online chaterlea25

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Re: Initial start up turns into total rebuild !
« Reply #452 on: January 27, 2022, 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

Offline timsdad

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Re: Initial start up turns into total rebuild !
« Reply #453 on: January 27, 2022, 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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Online Owen

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Re: Initial start up turns into total rebuild !
« Reply #454 on: January 27, 2022, 11:46:58 AM »
What do the BSA service sheets say?
1940 C12 (350cc)
1945 C11
1953 C10 & C11

Online repete

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Re: Initial start up turns into total rebuild !
« Reply #455 on: January 27, 2022, 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!!!!!!

« Last Edit: January 27, 2022, 01:09:06 PM by repete »
pete ("repete")

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Offline ROB KEMP

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Re: Initial start up turns into total rebuild !
« Reply #456 on: January 27, 2022, 05:44:53 PM »
I am not trying to find fault as everyone does things their way but i reckon about 80% of bsa  and triumph  gearbox bushes do not need replacing ,a bit of wear will not affect the gearbox in any way .  As long as the bearings are replaced and new seals and gaskets these gearboxes will out last most of us . An original factory bush with a bit of wear is far better than the replacement crap that seems to be supplied as replacements ,

Online Tman

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Re: Initial start up turns into total rebuild !
« Reply #457 on: January 27, 2022, 07:28:34 PM »
I fully agree, and have said so in the past. These bushes have an easy life and will likely never wear out no matter how many years the bike lasts.
It's rather like Triumph twin cam bushes that "restorers" always felt they had to replace years back, and they removed perfectly good bushes to replace them with after-market Taiwan parts, and then proceeded to amateurishly hand ream them (usually without the benefit of the Triumph piloted reamer) leaving the bushes in a worse state than when they'd started the job.

Online repete

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Re: Initial start up turns into total rebuild !
« Reply #458 on: January 27, 2022, 08:09:41 PM »
For those of you that are opposed to replacing bushings, what is an acceptable amount of free play between shaft and bushing before you'd consider it worn to the point of needing replacing or getting close to the end of it's useful life?

2.5 thous ?  3 thous ?  4?  5?  6?

And if a shaft's smooth metal surface is compromised and has been running inside of a bushing, what is the acceptable amount of shaft degradation to be tolerated?  And what of the bushing then?
pete ("repete")

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Online camman3

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Re: Initial start up turns into total rebuild !
« Reply #459 on: January 27, 2022, 09:26:07 PM »
As a blind internal bush on a 11/16 shaft, running in constant oil supply, I'd think up to 5 or 6 thou clearance would be perfectly ok....but like you Pete i am interested in others opinions.
Graham
1957 C12
In sunny (sometimes) Christchurch, Dorset, UK

Online repete

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Re: Initial start up turns into total rebuild !
« Reply #460 on: January 27, 2022, 10:55:25 PM »
Measurements aside, this is what I'm seeing.

Note: subsequent to initial post I added a photo of a new unused busing for comparison.
« Last Edit: January 27, 2022, 11:08:20 PM by repete »
pete ("repete")

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Online chaterlea25

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Re: Initial start up turns into total rebuild !
« Reply #461 on: January 27, 2022, 11:03:43 PM »
Hi All
I have found that the inner layshaft bush wears the most in the gearbox , The same bush is fitted to the heavyweight C series 4 speed as used on the A and B series with 350, 500 and 650
So my experience tells me that the least wear will happen on the lowest power bike and the most on the 650's
For some reason these bushes do not seem to wear evenly and expect to see scoring and ridges on the shafts especially on the bigger bikes. Its the roughness that needs addressing before worrying about a couple of thou wear.

This bush takes the highest load in the gearbox as the final reduction gears next to it are under load in first, second and third gears

John

Online repete

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Re: Initial start up turns into total rebuild !
« Reply #462 on: January 27, 2022, 11:37:11 PM »
John - the layshaft bushing on the inner case (replaced) was actually oblong by about a 6-7 thous difference measuring at 90 degs across.
I am totally comfortable in my decision to replace these based on both measurements and physical condition.
Every moving part has an an ideal mating tolerance, an acceptable operating range of wear and a point where the operating range of wear has been exceeded.
I have talked with enough folks who's opinions I respect and have established what is both the ideal (in this case) interference for bushing installation into the case as well as the allowable clearance for the shaft and room for the oil.
However, the point has been brought forth that these bushings (paraphrasing) last forever, don't wear, etc.
I understand that these have a long life expectancy and replacements of today are apparently not as good.
But with that said, and as someone that is a lead production inspector for a defense contractor there has got to be point where something crosses the line from acceptable to not acceptable.  Good enough isn't good enough... it doesn't fly.  Pun somewhat intended but it's reality.  Where is that line?
So, summing up my point...
Yes, these bushings last a very long time.
NOTHING that moves and/or contacts something else lasts forever.  There's wear.
So being that I and all that have been reading this are being told that the original bushings rarely need replacement it begs the question... what is the criteria?  When is the right time?
Thus my earlier question.
How will others who may be faced with this in the future make that determination?
I think these are all valid points/questions.

My path has been chosen, but someday someone else is going to be facing this as well.
pete ("repete")

"We are mere custodians of mechanical things. Our job is to care for them, improve them and pass them on to others.” - Peter Egan

Online Owen

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Re: Initial start up turns into total rebuild !
« Reply #463 on: January 28, 2022, 06:30:35 AM »
Have a look at BSA service sheet 702 as it gives bush and shaft tolerances. I had a heavyweight gear box with the same type of wear as you have which was caused by low oil level. That gearbox kept giving me issues changing between 1st and 2nd gear.
1940 C12 (350cc)
1945 C11
1953 C10 & C11

Offline timsdad

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Re: Initial start up turns into total rebuild !
« Reply #464 on: January 28, 2022, 08:27:13 AM »
I think most of the roughness and wear occurs in a bike's early life when most of the mileage is clocking up and oil changes are getting neglected. When they get dragged back into daylight these days, they get clean oil at regular, short intervals and the wear just about stops. Very few owners will do the miles to put enough wear on bushes that may be anywhere near their wear limits, whatever that may be.

In my experience, it's end-float in a lay shaft that causes gear change problems, not slightly worn bushes, Several years ago, I had a Laverda start to make a real racket and vibration coming home one night. With much cocking of head and listening at different speeds, I thought it was a lay shaft roller bearing and the next day I discovered that it was. The cage had broken right up, so the shaft end could lift up and down at least 1/8", but the gear changing had still been fine. On a Triumph Twin, if new lay shaft needle bearings are not positioned accurately in the crank cases, to keep the end float at the correct tolerance, smooth gear changing will suffer.

We all have bikes for different reasons and many folk just want a project or to simply do them up. And I think you're wrong there, Rob, - I'd say it's nearer 99%.

Ray
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