Center web bearing bore size

Information relating to the Matchless G12 or AJS Model 31 650cc twin
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Center web bearing bore size

Postby Yves.Astein » Fri Jan 04, 2019 9:01 pm

Hello all,

I am reworking my 59 G12 standard Engine. The krank is receiving a regrind. Does anyone know the messurement of the outside diameter of the center bearing bore in the center web.

I have searched all of my books and Workshop Manuals and forums, with no luck. All I have found was the connection rod big end bearing bore diameter Does anyone know the right value for the center bearing ?

Thanks !

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Re: Center web bearing bore size

Postby alanengineer » Fri Jan 04, 2019 9:24 pm

I think you might find it in the 'owners handbook'

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Re: Center web bearing bore size

Postby Duncan » Fri Jan 04, 2019 9:33 pm

Hi Yves

I may have misunderstood but the regrinding dimensions are given in the workshop manual, the centre web is like the conrods and has a pair of shells within it with split thrust washers on the sides.
Page 28 re-grinding.PNG

Page 83 Technical Data.PNG
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Re: Center web bearing bore size

Postby Yves.Astein » Sat Jan 05, 2019 6:56 pm

Hi Duncan,

Thanks, but I have all the information you have posted. I think we are having a misunderstanding. Sorry for not knowing the right term.

I mean the diameter of the bore in the center web. Where the bearing shells go into.

To say it in other words, I am not looking for the crankshaft diammeters (the inside of the shells) but for the center web diameter (the outside of the shells).

I have the bore size for the diameter of the conrod bore for the conrod bearings, but I dont have this mesuremnt for the center web. And the guy that is grinding the crank for me, said he needs to make sure that the bore in the center web has the right measurement, so that the center bearing shells have the right tightness when it’s tightened.








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Re: Center web bearing bore size

Postby Duncan » Sat Jan 05, 2019 7:07 pm

Hi Yves

I did think that was what you were asking for but its not something I have ever been asked for before when having a crank ground, I would be unsure where to find this information unless the shell manufactures have it, my only suggestion would be to torque up the two halves of the centre web and measure them, then compare with someone else?

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Re: Center web bearing bore size

Postby Mick D » Sat Jan 05, 2019 7:14 pm

Hi Yves

Unless you are using non standard shells why would you need this dimension? - Is your centre web damaged?

Just curious.

Regards Mick

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Re: Center web bearing bore size

Postby Yves.Astein » Sat Jan 05, 2019 10:59 pm

Duncan wrote:Hi Yves

I did think that was what you were asking for but its not something I have ever been asked for before when having a crank ground, I would be unsure where to find this information unless the shell manufactures have it, my only suggestion would be to torque up the two halves of the centre web and measure them, then compare with someone else?


Hi Duncan,
guess Ill just hope that all is good with the center web. After searching for some while I already told my engineer that I don’t have much hope of getting those values, but I wanted to have a try anyway.

Guess if those values are not common, then troubles with worn center web‘s won‘t be either..

Thanks for trying to help !!!!

For anyone else comming across this thread who might want to know the bore diameter for the conrod. I have found:

min. 44,983mm (1,7710 inch)
max. 44,996mm (1,7715 inch)

Yves

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Re: Center web bearing bore size

Postby Yves.Astein » Sat Jan 05, 2019 11:07 pm

Mick D wrote:Hi Yves

Unless you are using non standard shells why would you need this dimension? - Is your centre web damaged?

Just curious.

Regards Mick


Hi Mick,

the engineer that takes care of my crank grind is concerned of checking everything.

He has a lot of experience with BSA and triumph but not so much with Matchless / AJS.

He might be a little bit to much on the safe side there. German over engineering, maybe ;-)

But I believe its quite usual to check the con rods, so doing the same for the center web isn’t generally a wrong thought I guess.

Greetings Yves



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