Horizontal Air Cooled Engine

[aostling]

It certainly does pump air, and the valves seem to hold it fairly well too.

The only attachment to the neck of the balloon is stated to be a one-way valve, perhaps from a tire or innertube. This must be what is doing the holding. The deflation might be caused by there being no rubber bands around the neck.

[Sid, you beat me to it.]

[Sparky_NY]

Sparky- Brian indicated that there was a check valve in left me with the balloon.
The valves are not holding the pressure.

You caught me on that one !

[Sparky_NY]

So, is the plug wet after cranking trying to start it? If it is that helps confirm the no spark theory.

[aostling]

It's none of those things. Here's the culprit:

https://www.youtube.com/watch?v=f389hIxZAOc

[Willy]

If the plug is wet it only means that the mixture is too rich to ignite, the plug may still fire but when there is way too much fuel vs air the plug will be wet since no combustion is taking place. Even a very rich running 4 stroke engine will leave a very wet plug and still run briefly.

This is what the R/C guys are running for compression testers. Very small volume to fill before a reading is obtained. Of course these guys will also very often use a motorized starting system but for those that hand flip the prop the small volume is helpful in obtaining a quick reading.
Brian with his drill powered starter would be able to quickly fill the volume of a short tube if need be between plug hole and tester.



A quick and dirty spark plug and ignition tester I built years ago based on an old Champion spark plug cleaner and tester, simply used a piece of plexiglass threaded on one end for an air fitting from a regulator and a spark plug thread on the other end. Much like the old Champion plug tester I could increase the pressure to the plug to see if it fired under pressure by adjusting the pressure from the regulator.

[J Tiers]

No picture, just the box.......

In any case, Brian already has the basis of the tester, just take off the balloon, and attach a gauge.

[aostling]

Has the plug been tested, as described here?


https://www.youtube.com/watch?v=N6Ng-yhCeNs

If so, what was the reading?

[brian Rupnow]

The engine just ran!!! God loves me after all. When all probable things have been tried, it is time to try the improbable. There was only one thing left to try that didn't involve machining something. I kept getting mixed signals about whether the sparkplug was really sealing against compression leakage or not.----So----Ten minutes ago I backed out the sparkplug, coated the threads with green 638 Loctite, then reinstalled the plug. Waited ten minutes and engine started up and ran like a trooper. I will get a video up tomorrow morning. I am so relieved.

[oxford]

Guess you proved a bunch of us wrong. A compression and leak down tester wouldn’t have done any good in this situation.

[Sparky_NY]

So it was a compression problem after all, not a lack of spark. Some soapy solution testing would have found that problem a long time ago and saved a lot of grief.

Any loctite would have sealed the threads but 638 is a horrible choice, that plug will never come out again. The blue low strength loctite would have been a much better choice. Then again it only has to run long enough to make the video and put it on the shelf, so unlikely there will ever be a need to remove the plug.

[J Tiers]

Guess you proved a bunch of us wrong. A compression and leak down tester wouldn’t have done any good in this situation.

Well it might have helped, since it would have exonerated every other part of the system as far as compression.

Ironically, it WAS the plug (a suggestion many made), AND it WAS a compression problem (a comment even more people made). Just goes to show ya.....

Interesting that it was "that big" a problem leaking through what appears to be quite a number of thread turns. It surely went away when the plug was sealed in the hole, but wow..... that's a lot of leakage.

I'd have suspected that big a leak would be audible. Apparently not.

[Jim Stewart]

Isn't that why spark plugs have sealing gaskets?

-js

[Willy]

I see that the plug has a brass sealing washer. One has to wonder why it did not seal. I can come up with a couple of reasons such as insufficient torque or a rough surface on the head to seal against but to bleed off that much air one would think it would have been audible when turning the engine over by hand, not so much when using the drill to start it though.

Either way congrats Brian, glad to see you found it and that the engine was designed and built to be a runner.

[Sparky_NY]

I'd have suspected that big a leak would be audible. Apparently not.

Probably not with the noise of the electric drill spinning the engine over BUT it should have been a hint when his hat kept blowing off anytime he got near the spark plug.

[brian Rupnow]

638 is my "go-to" choice for Loctite. It is an excellent sealant, but releases very easily with a bit of torque. Like I said, all of my engines run---eventually. Some run right away and surprise me. Some require much thought and fiddling with. Out of about 20 engines, I haven't seen this happen before. I keep thinking that if I build enough of these small engines, I will get to the point where I can diagnose whatever is wrong and fix it immediately. The most difficult thing is knowing that everything is adjusted and set properly, and still the engine won't run. Thank you all for your suggestions and your interest. To those who have gone out of their way to insult me, there isn't much I can do to change that. You are all grown men now, and whatever makes you like that is beyond anything I can do or say that will change you. ---Brian