Jim comstock breather

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Anyone got any info on the Jim Comstock breather for 71 Commandos.
 
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A pain to change sump oil so I don’t. Always a cup in the sump. I just hand pump the tank and in with the new oil and filter.
 

acadian

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If your 71 frame has the cross member the sump mounted breather may not fit, you can confirm with Jim himself
 
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Anyone got any info on the Jim Comstock breather for 71 Commandos.

What kind of info do you want? As mentioned first make sure it will fit your bike.

If the question is will it make a difference, yes it will. But it also depends on what you are trying to resolve.
 

Onder

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Send a note to Kenny, he is straight up and will sort you out.
 
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got mine since last year and i am very happy with it!
before i tried several types of reed - valves.....from BMW car supply reed valves to the ones from Mikes XS.
But the one from NYC Norton is a tailor made solution with very good quality that works great.
 
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NYC Norton is the exclusive supplier of the sump breather you mention, originally designed by Jim Comstock.

You can find them here: https://nycnorton.com/product/reed-valve-breather-kit/

If you have the frame crossmember up near your sump our breather won't fit, unfortunately.

HTH,

-Kenny
Hi, Kenny. I am working through my 850 and I noticed a breather in the "old magneto location" on the back side of the timing cavity. The bottom sump plug is compatible with the breather that I bought from you but I'm confused about that breather (these cases are prototype cases; I think they're either the first or second set from the foundry when the first 850 experimental cases were being made - I occasionally find things that are different from "production" cases).
Is the stub on the back of the timing side usually found on 850s? (There's no plate, it's a cast flat area where the plate used to be on the early 750 cases.) What do I do with the output from this breather with this setup and the NYC breather/drain plug?
Many thanks and best wishes, Bruce Henderson, NC USA
 

L.A.B.

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Is the stub on the back of the timing side usually found on 850s? There's no plate, it's a cast flat area where the plate used to be on the early 750 cases.
Item 38 (06-4200).


s-l500.jpg
 
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Interesting that the factory thought the timing chest with 2 enlarged holes in it above the crank and an exit pipe stub was a good enough for a breather.

Was this a Norton design that did not work well?

Just curious because I'm going to do something similar with an older 750 case.
 

lazyeye6

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I bought the Comstock sump breather directly from Jim a few years ago. Directions called for removing the timing side breather stub (it screws out) and replacing it with a supplied plug. This was for a ‘74 850. I believe cNw sells the Equivalent JC reed valve setup for models with the crossbar under the cases but which requires machining the back of the cases to install.
 
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Item 38 (06-4200).


s-l500.jpg
Thank you. OK, we have the stub on my cases, but it's different because the stub is fitted right at the corner between the back of that "timing case ear" and the actual case. Oh, the joys of working with non-standard parts. I assume that the stub is the same and, if there's a plug in my kit, the plug will fit OK (stub diameter appears the same).
 

L.A.B.

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OK, we have the stub on my cases, but it's different because the stub is fitted right at the corner between the back of that "timing case ear" and the actual case.

The only variation of the 850 breather stub I'm aware of is the 850 Mk3 timing case where the stub was repositioned to clear the starter motor and the unused Lucas starter motor lugs were also removed.


The blanking plate for the Lucas starter motor drive was deleted during mid-'72, reverting to a solid casting once again as it had been on the early 20M3S engine case, therefore, none of the 850 cases had the starter motor blanking plate.


I assume that the stub is the same

Without more detailed information then I have no way of knowing.


and, if there's a plug in my kit, the plug will fit OK (stub diameter appears the same).

Do you intend to fit a different breather as I can't see why you would want to plug the stub or breather hole if not?
 
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