Update on making the piston. It's done except for one cut. Possibly two, but I'll explain in a minute. The engine plans call out a Vyton plastic piston ring, but when I look at sources online, I need to specify which blend of Vyton I want and that isn't called out in the drawings. I emailed the designer two weeks ago and never heard back. Since the last postings I saw from him was that he was taking a break, it's possible he's on a summer vacation trip somewhere.
So I did the next best thing and went to
Otto Gas Engine Works
who makes many sizes of cast iron piston rings and ordered three of the
recommended size, last weekend. He shipped immediately, Tuesday after
Memorial Day by USPS. They said delivery by Friday but the rings now appear to
either be lost, or somehow, somewhere they're still in the postal system, just
not being picked up by any scanners. Meanwhile the guy at Otto said to
wait to cut the ring slot until I had them for best sizing results.
Every feature is cut except for that. I'm not 100% sure if I'm going to use two cast iron rings instead of the one Vyton, so that's the only real question. The Webster I did last year had two cast iron rings with a smaller bore and stroke. Sounds to me like two might be better.
Nothing to brag about, just to show the oval counterbore made by moving a 7/16" (0.4375") end mill back and forth 0.282" is cut, the circular counterbore is cut, the through hole for the wrist pin is visible as well as the threaded hole (#5-40) for a screw to grab the pin. All of these things were done by moving the blank to the mill, finding where X and Y zero were and using the CNC (manual entry) to go to specific spots to cut.
Before that, when I went to check the piston and cylinder for a sliding fit, I found that the cylinder had a narrow spot in it, closer to the top than the bottom, about .001" too narrow. Hard to call being small by 1/1000 a wasp waist, but removing that gave the piston an easy sliding fit.
In this view, you can see a groove near the wider stock in the vise
jaws. That's where the piston gets cut off the rough stock. If I
make one ring slot positioned where the print says, it's 0.170 from the end of
the piston to the closest edge of the ring slot. If I cut slots for two rings, I don't
know where they need to go just yet.
The last time my package of piston rings was scanned was Thursday, June 2nd at 11:23 PM in Linthicum Heights, Maryland. Since it's two days later and it hasn't shown up anywhere else, I suspect it fell off a bench, a truck, or something. A year or two ago, I had package shipped here from South Florida that instead of coming here from post office facility near Orlando, went to Pittsburgh, PA. That one never stopped being in updates; it was clearly still in the system. This one isn't inspiring confidence.
Potential tropical cyclone one update.
Longtime readers will know my standard line about tropical storms, "it's a poopy day with a press agent." This one never even became a tropical storm. I think every forecast since they started calling it "Potential Tropical Cyclone One" has predicted it would become a tropical storm by the next forecast. So every three hours from Thursday until now, when the forecast was issued, they essentially were saying, "this time we're sure! It will be a tropical storm in the next update!"
We had rain all day - actually from mid-afternoon yesterday until mid-afternoon today. Much of the time it was small droplets, kind of extra chunky humidity. The wind wasn't noisy, didn't seem strong, and I'd be surprised if we saw a 25mph gust here. It was simply a poopy day with a loud, trumpet-sounding, press agent
Him, question for you, SiG. I myself have never built any such engine.
ReplyDeleteWould there be any significant difference in sliding friction between the single Viton ring and the two iron ones? Could such a difference have any effect (+/-) on engine performance?
Excellent questions. In order: I don't know and I don't know.
DeleteI've seen guys make engines like this and swap between cast iron and Vyton and it ran either way. I don't know if that's the usual case or not.
It seems that plastic on cast iron would have a different coefficient of friction than cast iron on cast iron. It also seems that Vyton hasn't been adopted widely for commercial engines. Maybe it just doesn't last as long as cast iron rings do or doesn't perform as well (or at all) in engines made for higher performance than these little model engines.
I ordered a few feet of fuel hose awhile back, left Atlanta, went to Louisiana, back to Atlanta then to Mobile back to Louisiana then delivered to Mobile. 3 weeks. It was a test, USPS failed.
ReplyDeleteIs it Vyton or Viton? The piston looks really nice!
ReplyDelete"Extra Chunky Humidity"....I'm gonna remember that one!