Author Topic: Keyway width puzzle  (Read 504 times)

Jordan

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Keyway width puzzle
« on: April 16, 2019, 08:20:24 AM »
I removed a pulley from my CS1, to put on the other (exhaust) side for driving an alternator.
The key was a loose fit, so I made a new one on my mill/drill.
I was surprised to find the keyway on the crankshaft measures 14mm wide, not the expected 9/16" which is slightly wider.
At first I thought it just wanted some dressing with a file, to remove burrs that made it seem narrower.
But, it really does seem to be 14mm, with no discernible lip after cleaning it up.
It even measures 14mm at the bottom of the keyway, at the extreme end of the crankshaft, so it's not just because of deformation.
I reduced the width of my new key for the part that engages the crankshaft groove, the only way it would fit - OK now.
Is this really a metric sized keyway?

38ac

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Re: Keyway width puzzle
« Reply #1 on: April 16, 2019, 12:23:54 PM »
It is what it is 14mm ;)  The original erectors knew well the importance of close tolorances and good fit of the gibb keys, you may be assured that it didnt leave Dursley in that condition. Field bodge? India crankshaft.?   How it got that way is anyones guess. More could be told if I was actually looking at it.
My best guesses are that a loose flywheel damaged the keyway and it was  machined wider or  an Indian crankshaft.
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ajaffa1

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Re: Keyway width puzzle
« Reply #2 on: April 16, 2019, 12:33:28 PM »
I`m with 38ac, anything made before the 1970`s in the UK would have been imperial, after that your guess is as good as mine. If it has had replacement parts made in India they might well be metric.

In Australia I can buy imperial thread nuts and bolts that are made out of metric hexagonal bar. Thus a 3/8" bolt might require a 14mm spanner, go figure.

Bob

listard-jp2

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Re: Keyway width puzzle
« Reply #3 on: April 16, 2019, 01:42:21 PM »
If it is Indian crankshaft, it is highly likely that it will have recessed centres in the ends of the crankshaft. One of the rare occurances where the Indians improved on the original design.

Jordan

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Re: Keyway width puzzle
« Reply #4 on: April 17, 2019, 03:23:26 AM »
The crankshaft has centres drilled at the ends, but they aren't recessed.
It looks as old as the rest of the engine, made in 1953.
14mm is less than 9/16", so the keyway hasn't been widened.

Mine engine was originally part of a Start-o-matic.
Could it be how these were made,  to prevent easy fitment of the heavier flywheels to standard engines?

38ac

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Re: Keyway width puzzle
« Reply #5 on: April 17, 2019, 07:48:57 PM »
Well once more I learn to never assume. I admit to have never measured a Gibb key on a CS, just removed and reinstalled them. I only have one CS around at the moment and it is a very early 10/2 that has the OEM crankshaft in it and the keyways measure 14MM , who woulda thunk it? I have plenty indian cranks around and all of them measure 9/16" or just the opposite of what one would assume.
No, the heavy flywhweels did not use a different key width as I have swapped things back and forth. How your flywheel s got to be 9/16 is once more anyone's guess but as I said earlier you can be assured it didn't leave Dursley that way.
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ajaffa1

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Re: Keyway width puzzle
« Reply #6 on: April 18, 2019, 10:12:29 AM »
I am as confused by this as the rest of you, I thought that Lister made everything in house, perhaps at times of high demand they out sourced to other manufacturers. Hence the discrepancy.

Bob

broncodriver99

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Re: Keyway width puzzle
« Reply #7 on: April 18, 2019, 10:56:20 PM »
I have 3 original cranks and one Indian crank I can check this weekend. That is quite strange for one part to be metric. Who would have thought?