Displacer Pushrod Gland Question

[jimlarsen]

One of the challenges I face with pop can engines is making a pushrod gland that moves freely while leaking very little. Has anyone here tried creating a stuffing box to hold some material around the gland and slow the leak?

[jesterthought]

For LTD's I've used a thin wire (guitar string) push rod in a close-fitting tube (or even just a hole in the end plate where the conrod is long, allowing for the small rock). There was very little friction or leakage.

[markombi]

In my engines I usually use teflon plumber's tape in a stuffing box, well oiled. the teflon melds together with oil and heat making a good sliding seal. I haven't tried it with a popcan engine but it works well with the usual engines.
Mark

[Ian S C]

I'v Used Carbon Impregnated Teflon for bushings, the swafe leftover from turning a bar of Teflon is put in a steel moldand heated until the steel turns blue, there was an artical about this in Model Engineer a good number of years ago in a series about Hot Air Engines, you may use plain Teflon. Don't use oil, it makes it swell. My second motor(modeled to a similar design to J.G. Rizzo's Dyna), after 2000hrs of running required a new crankshaft, and con rods. A few weeks later I started to rebuild it, and found that because of all the running it had done, and splashing the odd bit of oil about, the Teflon bush through the piston had swollen, and I had to rebore it so that the displacer shaft would go through. That was back in 1995, the motor runs as well now as it did then.
I'v used the same system on displacer shafts ranging from 1/8"dia to 1/2"dia. I have lately been using plain bushes, either brass or cast iron, all with stainles steel shafts. Ian S C