Model Engine Maker

Help! => Specific Engine Help => Topic started by: AOG on March 29, 2018, 03:35:48 PM

Title: Stuart twin oscillator problems
Post by: AOG on March 29, 2018, 03:35:48 PM: I need some help getting my Stuart twin oscillator running. I am having issues with the rotary valve. To be blunt it’s leaking like a sieve. I have used my standard procedures for preparing oscillator cylinders on the valve. I’ve gone up to 800 grit sandpaper on the valve and standard useing my old surface plate to keep them flat but I just can’t get a good seal. Any suggestions?

Thanks

Tony
Title: Re: Stuart twin oscillator problems
Post by: Jo on March 29, 2018, 03:37:09 PM: Have you tried some heavy oil on the two surfaces?

Is something not square? i.e. is it leaking only on one side?

Jo
Title: Re: Stuart twin oscillator problems
Post by: Gas_mantle on March 29, 2018, 03:51:55 PM: Hi Tony, sorry to hear you can't get it running :(

Can you take a pic of the parts at the affected area so we can see how it goes together etc.
Title: Re: Stuart twin oscillator problems
Post by: AOG on March 29, 2018, 04:00:41 PM: Quote from: Gas_mantle on March 29, 2018, 03:51:55 PM
Hi Tony, sorry to hear you can't get it running :(

Can you take a pic of the parts at the affected area so we can see how it goes together etc.

I’ll try to get some pictures after work.

Tony
Title: Re: Stuart twin oscillator problems
Post by: bent on March 29, 2018, 05:34:20 PM: Do you suspect the casting may be porous? You can seal the surfaces with a coating of cyanoacrylate (super glue) then sand it smooth, this sometimes works for us (I'm the engineer for a valve mfg. company).
Title: Re: Stuart twin oscillator problems
Post by: Jasonb on March 29, 2018, 06:55:46 PM: Is the hole for the valves pivot tapped square to the face and what strength spring are you using, it can be quite a bit tighter than the cylinders as you only want it to move when the lever is pulled/pushed
Title: Re: Stuart twin oscillator problems
Post by: AOG on March 29, 2018, 11:26:26 PM: Jason called it. The pivot isn’t tapped square to the standard. As a result the valve is slightly cocked. I straightened as best I could and now it’s running on about 40 psi. Unfortunately the valve is still leaking pretty badly. Any suggestions short of plugging and retapping the standard?

(https://uploads.tapatalk-cdn.com/20180329/a99b3a71a35c01cfd92ba8e11aa735da.jpg)

Tony
Title: Re: Stuart twin oscillator problems
Post by: 10KPete on March 30, 2018, 12:42:52 AM: When I built my single I hit the same problem. Even if the hole in the cylinder is perfectly straight the thread pulls the shaft off square when the thread bottoms, at either end.

I put a piece of 360 Wet or Dry between the standard and the cylinder (a little hole for the shaft, and I had finish milled the standard and drilled the hole in the same set-up) and turning the cylinder by hand seated the cylinder. Some 660 paper finished it up.

Chuck up the cylinder by holding the shaft and turn the lathe by hand. You'll know soon how square the shaft is!

Hope this helps,

Pete
Title: Re: Stuart twin oscillator problems
Post by: Jasonb on March 30, 2018, 07:23:58 AM: It would not matter if the valve was a bit loose on the pivot pin so you could just open up the hole a little.