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Gearbox layshaft bush wear
#11
If you are only going to shim behind the flange you might get away with splitting the shim and wriggling it into the gap, in which case you'd only have to drive the bush a mm or so forward.
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#12
Lots of things to try tonight after work. Thanks for the drawing Terry, that was what I had in mind for the puller idea. The flat piece would have a threaded hole in it. I will make it and try the drift idea first. I did think about just trying to whack it out then taking off any damage to the end too. The shaft has a flat on it on the part that goes inside the bush. The flat stops 3/8ths or so before the end of the bush. I imagine a little off the end isn't going to hurt.

When you fit the altered ratio gears what do you actually change. As this box is all apart is it work waiting till I can get those since it will only all have to come apart again. Does the lay shaft need to come apart anyway?

Simon
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#13
Hi Simon,
I am sure we can find you a better gearbox here in Wellington. .
Another way to correct the wear on the thrust face is to machine the bush back and fit a needle roller thrust in it place- (They have a hardened washer each side)- not too difficult to do.
The pressure on this face due to the tooth angles is quite high. Combined with the grinding paste produced by the gears wear is accelerated.
One of the reasons straight cut gears give more power at the back wheels. the herringbone gears in a 4 speed crash box eliminates these forces to a large extent.
Give me a call if you want some help-027 779 7031.
Cheers Steve
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#14
Simon fitting different ratios you change the first motion shaft (input gear) and the front layshaft section so you need to remove the bush to remove the circlip behind
          it to dismantle the layshaft assy. Gear ratio chart attached.


Attached Files Thumbnail(s)
   
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#15
Very handy chart, thanks for that. I find it cool that with the box apart I can see exactly how it works and how changing one gear set affects all the ratios.

And thanks Steve, I need to give you a call sometime anyway. I still have your front wing here and some paper for you. I want to try to make this gearbox serviceable if I can. Mainly for the experience. With everything I have done on the car so far just finding a better one seems a bit of a cop out as I have touched everything else. I'd like to have a go at making it work. If it goes wrong I get a better one. And eventually there won't be any better ones so learning how to fix one now might be wise. When I restored my MGB the only thing I didn't touch was the gearbox and it's the thing that went wrong! 

I am making progress. I got the bush out without damage. I made this little puller by cutting a piece of steel strap into a rectangle, drilling and tapping an 8mm hole in it then turning it down on the lathe. I had to file a chamfer on one corner so it would tip over but it worked. I used it as a puller with some threaded rod and got the bush out.

[Image: main.php?g2_view=core.DownloadItem&g2_it...74eebb2b85]

The ring was to be used as a spacer. I then had to add a socket to give me more depth to get the bush all the way out.

[Image: main.php?g2_view=core.DownloadItem&g2_it...dacf3ef55f]

That worked well and no damage to the bush. Just out of interest what does the Q.88 on the lay shaft mean?

Once I find out if I can get a close ratio set I will decide what to do next but will leave it all apart for now.
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#16
Hi Simon
Well done!  You are shaping into a good engineer-  Arent lathes useful !
 The Q 88 number is the pairing number for your gearbox clusters. you will likely find the same number in a similar position on the input and output clusters (1st and 3rd motion  shafts ) Four speed crash boxes were full of these numbers.
  The gears were  lapped as pairs  in a fixture to ensure silent operation and the numbering was to prevent them  being mismatched  when the pile got knocked over by the apprentice!
I look forward to hearing from you.- Did you buy some running in oil ?-worth the expense  as this can influence the life of the engine from the start.
Cheers Steve
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