Parsell & Weed intake valve spring

Home Model Engine Machinist Forum

Help Support Home Model Engine Machinist Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.


Jun 4, 2021
Reaction score
Corning, NY
I have a full size P&W, and am in the process of doing a rebuild on it, since it has been 40+ years since it was originally machined. In the
process, I have discovered the wire gauge the original spring is made from is too large.
A search of spring companies hasn't yielded too many results. Any suggestions for a good supplier?
The spring needs to be 3/4" -1" unsprung height, wire size .012" - .015", and inside diameter just over .187

I have been documenting this rebuild, and will start a thread soon. It is getting a governor rebuild, updated ignition, raising the compression (more on that topic later),
new skid and fuel system. It really needs a whole new governor next winter, since the machine tools I had access to in the late 70's were less than great,
and so were my skills at that time. No time for that this year, but it is first in line for next winter after the shop gets relocated.
I've made springs in that size range from music wire and various cobbled up attachments to the lathe toolpost to control and tension the wire. A google search on spring making, maybe with home shop added to the search terms, will turn up a wealth of options and methods.

Like many other things, it seems like a big deal until you do it once or twice, then you wonder what the fuss was about :)

I usually order my springs from They have thousands of different ones, and some that are close to what you're calling for. By going with a little larger in diameter, you can handle a slightly heavier wire and still maintain a light spring rate. The page below has three springs with free lengths of 3/4, 7/8 and 1 inch, 0.020" wire diameter and a 0.240" OD, leaving 0.200 ID. Spring rates are 3.73, 3.16, and 2.74 lb/inch. By using one of the three, you can vary the pre-load on the valve and hence the amount of force needed to open it. Here's the catalog page:

I've also wound my own behive shaped springs for our 1/3-scale Parsell & Weed kits from 0.16 music wire, but have found that I don't always have the time to make them, so have gone with a standard spring that can be cut to length. (MSC # 06981195) I really like the look and "action" of the shop made springs; however, you can see from the 2nd photo, sometimes it takes multiple tries.

Hoping this helps.


  • 2015-03-18 PWV- 001.JPG
    2015-03-18 PWV- 001.JPG
    4.1 MB · Views: 1
  • 2015-03-18 PWV- 003.JPG
    2015-03-18 PWV- 003.JPG
    3 MB · Views: 1
  • 2015-03-18 PWV- 004.JPG
    2015-03-18 PWV- 004.JPG
    3.6 MB · Views: 2
As Stan says, it turns out to be a relatively simple process. The key component was a simple jig to allow me to tension the wire. I'll try to describe it, but honestly it is harder to describe than it is to make. I started with two pieces of 1/8" (3mm) thick steel, roughly .375" (10mm) wide by 2.5" (63mm) long. I set these at a slight angle in my mill vise and milled down the center using a v-cutter, giving me an angled groove across the length.

I put the two pieces of steel together, with the grooves facing each other ...

... and tacked the sides just at the end where the groove is largest.

Here's a view of how it looks at the other end:


This gives me a jig that can feed the music wire through, entering easily on the "big" end, but springing the jig apart a bit as it gets to the small end. I can hold this jig firmly in the lathe tool holder (tightening down fully on the welded end), but vary the tension on the wire by how much I tighten down the tool holder at the small end.

To use this, I turned a mandrel to the appropriate diameter (a bit smaller than the desired ID to allow for spring back) and drilled a hole through to start the end of the music wire. I turned the chuck a few times to get a close wrap at one end of the spring, then applied the half nuts to start spacing out the coils of the spring (of course, set the gears to achieve the desired pitch). When the spring is as long as desired, open the half nuts to allow a couple of turns of close spacing at the end. Stop everything and snip the wire. My lathe can go down to 30 rpm, so I did this under power, but if that slow a speed were not available, it would be easy to turn the chuck by hand.

Here are a few pictures of the process:




For those who have never fooled around with making springs, and can't get why I so like simple solutions, have a peek at:
A lovely tool, for those who enjoy tool making or who have lathes similar to a Taig that does not do single point screw cutting or a lathe that is a change gear machine and you hate fiddling with gears it might be just your thing. It is a great example of how much more involved a tool can be brought to the party!

I really like the gizmo you have created. Compared to all the belleville washer or spring and UHMW discs toolholder style solutions, or complex clamping mechanisms that require lots of fiddling, your design is elegant in that it is straightforward and simple. As soon as I can get back to the shop I'm going to make a few. One fairly small for Sherline and Taig scale machines, one for my SB10. Thanks for such a creative and simple solution to managing wire tension.

I immediately liked the simplicity of Todd's wire holder in the post before yours, but it can be a bit tricky to get just the right tension with a cap screw, at least for me. This is particularly the case with very fine wire.

In the past I've always just cobbled up some bit of oak, delrin, brass, or maple and some sort of clamping, including all the foolishness of managing wire, hardware, and toolpost. AKA "Using your third and fourth arm adjust the tension while maintaining control of the wire with your left foot and third right arm".

Only a wee bit of exaggeration there, but not too much.
Thanks! I honestly had no idea how other people do the tensioning until I just now saw the video in Todd's post. Blessed by ignorance, this is the first thing that occurred to me, and fortunately it worked just fine.
Last edited:

Latest posts