Friday, May 7, 2010

Old Style Benjamin Stems from New Sheridans

Precision Airgun owner, Chuck Trepes, asked me to modify some new style Benjamin/Sheridan valve stems to work with vintage Benjamin pump guns. Seems the new Sheridans and Benjamins use a fairly normal coil spring inside the check valve, while the older Benjamins used a conical shaped volute spring. The new stems have a post that the spring fits over, but it's too large in diameter for the old conical spring.

What is the #99-079 number on the envelope? I'm going to guess that these are actually Crosman part #397-038. The one on the left has the smaller diameter post that Chuck needs.

As long as I roughly match the diameter, the spring will stay in location.

Really a perfect job for a small lathe like this. The model Chuck provided didn't have any semblance of a truly round post. It varied by several hundredths in diameter. I settled on turning these down to the average diameter.

As long as the volute spring fits over the end, it's a go. This was such a non-precision job, I just used a comparison caliper rather than measure each piece. I was still within about two or three thousandths of an inch over the batch.

I can't find my notes as I write this. Believe I took the diameter to 0.248". I'll find it and edit if necessary. The important part is the spring fit, not the actual number.

In about 20 minutes, I had six done.

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