Autocockers bored to 11/16?

[2cBillB]

I was warned that having this done to my many would take away from the threading in the frame. I did read a little bit that back this up. I was wondering if anyone had theirs done and could chime in?

It's a pre 2K mini, so I was hoping to get the banjo 2K modded and have it board for 11/16 to run the tornado valve. Truly loved the look of the old slabs. Is it overkill to do the 11/16 bore? More importantly would it take away too much of the frame?

[DocsMachine]

The front grip screw is just ahead of the typical 'Cocker valve chamber. On the older guns, like this circa '95 body, you can see the front screw is ahead of the valve chamber, but doesn't break through to the front-block-bolt passage.



On a later model, like this post-2000 vertical feed 'cocker, you can see the valve chamber was deepened, and the "front block bolt" area- an inner valve chamber extension- was made slightly shallower so that the screw hole fits "in between" them.



To fit an 11/16" valve, you really only need to bore out the valve seat itself- the spot where the brass part is in the first image.

As for the rest, that's an easy mod to bore the pre-2K internal passages tp post-2K specs. Whoever you have do it just need to pay attention to that grip screw area and not drill through it.

That said, I did save a body someone bored out- all the way through- to take an 11/16" valve. I fitted a plug in place of the grip frame hole and redrilled and tapped it for a non-through tapped hole.

Just keep in mind that if you go that route, you'll have to dig up- or have made- a Merlin spec front block bolt.

Doc.

[2cBillB]

Thanks Doc,

I appreciate the explanation and illustrations. I will have them bore to the valve seat 11/16 and hopefully the 2K banjo mod will give me a little more airflow.