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Atlas Barrel - rebore to +0.060, hone or ditch?

Norton Models (not Commando or P11)

Re: Atlas Barrel - rebore to +0.060, hone or ditch?

Postby lcrken » Thu Apr 13, 2017 8:48 am

Bernhard,

If you had an Atlas barrel with liners that you could remove, it's because someone had previously bored it for liners. The Atlas barrels did not come from the factory with liners.

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Re: Atlas Barrel - rebore to +0.060, hone or ditch?

Postby lcrken » Thu Apr 13, 2017 12:55 pm

Picture of an Atlas cylinder with broken section showing grain of cast iron. Very clearly no liners here. Also no liners visible in the original post pictures.

Image

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Re: Atlas Barrel - rebore to +0.060, hone or ditch?

Postby texasSlick » Thu Apr 13, 2017 2:01 pm

I happen to have my Atlas cylinders sitting on my credenza. As I am the original owner, I can attest to the fact these are as originally fitted.

Examination with a 5X loupe reveals:

1) There is a uniform sand casting texture where the outer diameters of the cylinders join the base between the tappet bores (the non machined area inside the gasket flange). There is a smaller non machined area at the rear, dead center between the cylinders, that has the same texture characteristics.

2) There is also a generous radius where the outer diameter of the cylinder joins the non machined base area.

3) There is no visible joint in the machined surface where the lower cylinder spigots merge into the tappet bores.

These factors rule out a pressed in liner. Let's put this issue aside and return to helping the OP with his original question.

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Re: Atlas Barrel - rebore to +0.060, hone or ditch?

Postby lcrken » Thu Apr 13, 2017 7:54 pm

texasSlick wrote:These factors rule out a pressed in liner. Let's put this issue aside and return to helping the OP with his original question.

Slick


Good idea. I've posted too much already, and none of it about his original question.

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Re: Atlas Barrel - rebore to +0.060, hone or ditch?

Postby Rohan » Fri Apr 14, 2017 2:45 pm

But you've / we've clarified a number of things the OP may need to have been concerned about,
after some of the posts here !

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Re: Atlas Barrel - rebore to +0.060, hone or ditch?

Postby Mike T » Sat Apr 22, 2017 2:03 pm

Thank you everyone. I'm still following this thread with great interest and I appreciate all your guidance.

I haven't visited the machine shop yet, but only yesterday I came across a possible alternative..

I may have the opportunity to purchase 1 or 2 barrels locally. One is a barrel by itself and in nice condition. It looks like it might be usable or may just require a hone. However, the second barrel and head are in beautiful condition.

The stamping numbers on the barrel are the same as the Atlas project, but it looks like they are for a Commando, not Atlas?

Neither barrel seems to be "spigoted", which I understand is where there is a lip on the head of the barrel bores that fit into the grooves of the Atlas cylinder valve cavities in the cylinder head. The second barrel/head looks like it has been newly re-bored or honed and is in very nice looking condition. I'm not sure if those valves look right, but I will get the chance to see it again soon. 2 of the valves look to have seats and the other 2 don't.

My question is, would these barrels and the head fit the Atlas crankcases or would there be a lot of other things I would need to consider?

Thanks again for all your help. I'm very grateful.

Here's a video containing a few clips and photos of the two barrels & head.
phpBB [video]
1974 Norton 850 Commando MK2A
1964 Norton Atlas 750 ("Shep" project bike)
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Re: Atlas Barrel - rebore to +0.060, hone or ditch?

Postby Hortons Norton » Sat Apr 22, 2017 4:14 pm

I think the barrels would fit but the head would need some other way to attach the Atlas style head fixing bracket?? You may be able to drill the center hole and tap to size?? Nice looking stuff there. Also the head bolts may be different too.
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Re: Atlas Barrel - rebore to +0.060, hone or ditch?

Postby Rohan » Sat Apr 22, 2017 4:24 pm

And also the Commando head has the head oiling fitting to the side, not on top.
So would stand out as different, and would require different oil line fittings.

Whether performance would be any different is a question, not seen any discussion of this ?
Probably not...

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