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MG MG Y Type - YT crank dog nut shims

Hi, can anyone tell me the purpose of the shims between the crank dog nut and the front end of the crankshaft. How do I determine what shim thickness might be required? The three shims there now, a bit distorted, seem to be about .1 mm each for two, and .5 mm for the third. Are they just flat shim brass initially? The manuals in CD Parts List (p29 Section F), lists three thicknesses, .125 mm .25mm and .5mm. Number needed = "As rqd"
thanks
K G Mills

KG

I am not an engineer by any means and I dont have much of an idea but it could be as simple as the fact that you probably would not want a direct face to face fit of the back of the nut to the crank because as you crank the engine the nut would tighten up against the crank shaft. Putting 2 or 3 shim spacer washers in between would prevent the tightening becoming so much that the nut would be difficult to undo even if the engine was locked in position.

I will be interested to hear if there is a more scientific reason though.

Paul
Paul Barrow

Hi again,
Paul, your thinking about brass being good for locking but being undoable is good. Nevertheless, the real reason for the shims, is , and why didn't we know this, to orient the dogs to put the starting handle in a good place for manual cranking. Presumably, that means with the handle just a little past its lowest position. It would be trial and error to get the right thickness. (Found this from a web search.)
cheers Kevin m
K G Mills

Kevin

Now that you say that actually it does ring a bell with me. Yes totally correct in terms of the positioning of the stroke and yes it would be a total PITA to get it correct!

Good luck with that one and if anyone has a magic solution lets hear it please!

Paul
Paul Barrow

Hi Kevin & Paul,
The shims are for adjusting the position of the crank handle - get it right and you can easily start the car with the handle, get it wrong and it just won't work.

So how do you set it up ?.

If you use TDC on No.1 as a reference, you want the crank handle to be at around 10:30 o'clock at TDC. This means than when you pull the handle up, it fires past the vertical part of the swing, providing maximum leverage and allowing the handle to swing away from your hand.

Do up the lock nut with no shims at TDC no.1 and check the handle position. The pitch of the dog nut is 1.5mm, which is about 0.060", or 0.005" per hour on the clock hand - fit the appropriate shims to correct the bolt position.

Never try to start a car by pushing down, always pull up and never put your thumb over the handle - open hand with fingers under the handle.

A good old fashioned motor engineer should find it easy to set it up.

BTW - all crank handles have the driving pin orientated the same relative to the handle.

Tony Slattery
The Classic Workshop
A L SLATTERY

Thanks Tony for the explicit info on positioning. Re thumbs etc, I was "brought up proper" with regard to that.
Sorry this is a day or two in coming, been to sunny Qld. Rained every day.
cheers Kevin M
K G Mills

This thread was discussed between 06/06/2015 and 15/06/2015

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