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Drawings for Nelson and Turbo Head buttons? Cox_ba12




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Drawings for Nelson and Turbo Head buttons? Empty

Drawings for Nelson and Turbo Head buttons?

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Drawings for Nelson and Turbo Head buttons? Empty Drawings for Nelson and Turbo Head buttons?

Post  uliner Mon Oct 25, 2021 3:40 pm

I find myself with a manual lathe (small sherline), some 6061 some time on my hands.

I have made some glow head conversions with normal plugs, but that is easy for cox heads.

Looking for dimensions for turbo plugs and Nelson, thread, seat angle, and all that.

Not looking to make them for money, just for my own use.

I'll draw it up in solid works and share it back if I can.


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Drawings for Nelson and Turbo Head buttons? Empty Re: Drawings for Nelson and Turbo Head buttons?

Post  Scotland421 Thu Nov 04, 2021 9:48 am

Trumpet shaped or ae bubble wi ae 10mm squish band at ae 5 degree angle tae the glow plug. Nelson plug or similar.
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Drawings for Nelson and Turbo Head buttons? Empty Re: Drawings for Nelson and Turbo Head buttons?

Post  aspeed Thu Nov 04, 2021 9:38 pm

Turbo plugs are a 60 degree angle and the hole is 3/16". The tap drill size is 7.25 mm, and the tap is 8mm x 0.75 pitch. I found a good combustion chamber shape for .049s to be a 90 degree countersink. Maybe an 82 or 100 degree countersink may be better. I looked at a Merlin plug and that is what they looked like. I am sure Al Kelley played with a lot of designs before production. When I compared them to some old TD heads they were overall quite similar with the shape. Of course that is just a starting point and experimentation is due. The Nelson plug is a 118? degree or so angle. It is just whatever the standard drill angle is. The tap drill size is 1/32" less than the OD of 13/32" ? I believe. The depth of the plug to the bottom of the squish band is around .062" for an .049 and maybe .100" to .120" on a .15 IIRC. The hole size on a Nelson plug is about 1mm larger than the turbo plugs. That is why I prefer the turbo plugs for the smaller motors. I made a bunch of slugs that fit the plugs and left the combustion chamber and liner face blank for each motor. I made a .500" diameter step .100" deep to hold in a collet. 7/16" dia. would work maybe on a smaller motor. Have fun making them. I did. I have an old Hardinge chucker turret lathe, very high tech for 1952. Some heads were 7,000 rpm better than one I had been using. Most were 1,000 or 2,000 RPM better than a standard plug head. You may have trouble cutting a thread to fit a Cox. A Merlin or Norvel collar may be used, or use a burned out Cox or whatever head.
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