Time for a new Horizontal Hit and Miss engine

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I am a fan of Blondie Hacks and she is not afraid to show us her mistakes etc. Plus no long winded explanations as a rule.
Hi Brian, rather than buy a die to make a compression tester adapter to do just the same job as you, but on my motorcycle engines, I simply took the threaded end of a used spark plug and silver soldered it onto the adapter, which had a schrader valve stem (from an old inner tube) brazed onto the other end for air supply and gauge from my tyre pump.
Keep on keeping on.
It seems like a useful thing to make up one of these adapters for any sparkplug size we're likely to be using. Before trying to turn the engine over for the first time, stick the pressure tester into the cylinder and test how well it seals. I can almost talk myself into saying every cylinder could have a test port for a pressure tester in addition to the spark plug. A shrader valve is - what? - 1/4" OD? Bicyclists use a skinnier valve, a Presta valve that's closer to 1/8", but they require a different size fitting on the pump side. Adapters are like $1.35-ish each on eBay. (Not my listing)

Either make an adapter for every engine, or if we end up building engines always using the same sized plug, it's only one adapter.
Bob--You're right, and since we only use a couple of sparkplug sizes with these small engines, a proper test set up could have interchangeable ends to suit either size of sparkplug threads. I think it would be extra unnecessary work to build an engine with a second port for this testing, but the sparkplug hole is always there. I mentioned a Shraeder valve because that is what I always thought that all tire tubes had. I don't think that the size of valve matters too much, because it doesn't have to flow a high volume. The beauty of a test rig made like this is that it actually measures the leak-down time after outside pressure is removed, and a "finite" measure of seconds is a very good indication of whether the valves are sealing properly. I have always just blew into the end of a tube connected to one of these sparkplug adapters with my mouth, and you can hear which port the air is leaking from.---Brian
I would like to find a sparkplug which reaches deeper into my combustion chamber. The plug I am currently using in an NGK CM-6. it has a M10 x 1 pitch thread on it, and the threaded portion is 8.6MM (that is 0.338" imperial) long. I would like to find a plug available in Canada with a longer threaded portion about 16mm [5/8"] long but with the same M10 x 1 pitch thread. I have used up my google-foo and can't find what I am looking for. It doesn't have to be NGK. Can anyone help me out here please.---Brian
Okay---Got it sorted. The boys down at Partsource helped me out. The plug is an NGK-R and has an M10 x 1 thread and is 0.730" long in the threaded portion. I actually made a 0.125" thick bronze washer to go between the sparkplug and the cylinder head to give me the correct amount of sparkplug protruding into the combustion chamber. Thank you Jason for your help.---Brian
The longer sparkplug did the trick. The engine is firing regularly on every other revolution of the crankshaft. It hasn't taken off with a roar and made me grin like a Chessy cat yet, but I'm a lot closer.
The longer sparkplug did the trick. The engine is firing regularly on every other revolution of the crankshaft. It hasn't taken off with a roar and made me grin like a Chessy cat yet, but I'm a lot closer.
Great job, Brian. Always a pleasure watching your builds and troubleshooting techniques.
No joy today. Ignition is working fine, big fat spark at the correct time. I have a second home built carburetor that I know works because I have used it on many of my engines while setting them up, so I put it on the engine today. Still, not running. More testing shows that the intake valve is still leaking, enough that the engine won't "bounce back" when spun by flywheel. (It will "bounce back" if I put my finger over the carburetor intake). Tomorrow I will see what is going on with that leaking intake valve. I needed something to cheer me up, so I went to Youtube and typed in "brian rupnow engine"---many videos of my past engines are on there, so I watched them for half an hour. I'm happy now. Going to shut things down and go read a book.
So, what are we looking at here? This morning I came down to the bat cave, dismantled the cylinder head, reseated the valve cage with my George Britnel tool, and reground the valve with 600 grit paste, then reassembled the cylinder head. The cavity inside the cylinder head is filled with Naptha gas, and I'm waiting to see if remains in there, (which means the valve and seat are air tight) or runs out around the valve.
I would not think that the fact that it holds liquid would necessarily mean that it holds under pressure.

What do you use for valve material? In the past I have used steel, 1018 or 12L14. Recently I have been using 303 stainless. I have also found that the problem can be the stem not sliding freely in the guide. It seats but too late.
Gordon--I find it to be a fairly good method of checking for how good a seal the valve has with the seat. This time it did anyways. My engine has good compression now, and has a very obvious "bounce back" when you try to spin it with the flywheels. It has been a frustrating day. Good spark, good compression, good fuel---but no protracted runs. Many "almosts", but nothing longer than about 20 seconds. Although the engine fires and tries to run on it's own, it is running very slowly and I don't know why. Adjusting the spark timing doesn't seem to have any great effect. Most of these hit and miss engines will take off and rev so high they scare you half to death if the miss mechanism is disabled. I spent the afternoon with a different gas tank, trying it at different heights in relation to the carb, but didn't get anywhere with that. Tomorrow I will try it with a purchased carburetor, because I'm running out of things to try.---I always use cold rolled steel for my valves, and have never had a problem with it.
Brian, what do you think about larger, heavier flywheels? I'm thinking maybe more inertia would help.
How well does it run on starting fluid? That will eliminate (reduce) the suspicions of your carb being the issue (and all the work to try another one). If everything else if fine then it should take off on starting fluid.
Time for an admission of stupidity. Taking a fresh look at this thing this morning, I see that the discharge side of the carburetor was up tight against the back wall of the adapter. There was no possible way for the air-fuel mixture from the carburetor to make its way thru to the cylinder. I take full blame for that one. Now I know why playing with the spark timing and the fuel mixer needle didn't seem to be having any effect. big HEAD SLAP for me. I am currently making a new adapter.---Brian

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