Upshur's opposed twin engine

pileskis · Oct 21, 2024

Brian Rupnow said:
And as the sun goes down---both cylinder heads have been pressure tested. The first cylinder head had no leaks around the valves at all. The second cylinder had very little leakage around the valves. Very small leaks will seal themselves after the engine has been ran for a while..

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Brian Rupnow · Oct 21, 2024

And your point is?? I've done this before. It works.

pileskis · Oct 21, 2024

Brian Rupnow said:
And your point is?? I've done this before. It works.

Maybe you wouldn’t have to if you didn’t take shortcuts?
What’s going to happen every time you have to take a plug out as part of the debugging process??

Brian Rupnow · Oct 21, 2024

No problems removing the plugs, as long as the plug has a good hex on it and you own a set of sockets.

minh-thanh · Oct 21, 2024

pileskis said:
Maybe you wouldn’t have to if you didn’t take shortcuts?
What’s going to happen every time you have to take a plug out as part of the debugging process??

Brian Rupnow said:
No problems removing the plugs, as long as the plug has a good hex on it and you own a set of sockets.

Maybe because they are not completely clean, a little oil... so the loctile glue does not work much.
Personally I would not use that glue for that position, O-rings or make a copper ring (machined from sheet or cut a copper ), it only takes a little time instead of having to fix the spark plug thread or rebuild the whole cylinder head

TonyM · Oct 22, 2024

Brian Rupnow said:
Today I pulled off both cylinder heads and blew an amazing amount of crap out of the holes which lead to the ends of the sparkplugs. I checked my spark timing with both heads off, and of course I was way off where it should be, so I reset the timing to give sparks at top dead center of the piston strokes. I didn't really like that spring device I had bolted in place to hold the throttle lever from moving, so I took Jason's advice and made up a very thin brass washer to fit between the carburetor body and the rubber o ring which holds everything in place. From what I see right now, my carburetor doesn't seem to be sucking up gas from the tank when the engine is being turned over by my starting table. I'm running Viton o-rings on my pistons and both cylinders have good compression. I'll have a closer look at my cam timing tomorrow.

Hi Brian
When it is all cleaned and reassembled, check that the inlets are not drawing air around the small Jubilee clips. Those very small ones do not close round and can distort plastic tube. That's why spring clips, even home made ones are better for sealing small bore plastic tube. Assuming the tube is a reasonable fit on the spigots, then jubilee clips look a bit overkill. You shouldn't need clamps as those tubes are fairly captive and won't easily come off.

Jasonb · Oct 22, 2024

I doubt Brian's Loctite is working as it should hence his ability to easily remove the plugs where most of us would need to use heat to weaken the Loctite and then be faced with cleaning out it's remains.

Dirty oily surfaces are one. Excessive gap due to things like using the wrong tapping drill as previously mentioned and probably already damaged thread due to trying to seal it without a soft washer washer. Thread repair to one of the already stripped threads. Excessive Loctite applied and sitting ouside the joint which also attracts dirt.

I'd actually be wanting to test at a lot lower than 60psi as that is only likely to be reached as the piston gets towards the top of it's stroke. Far better to test the 15 to 30 psi range where the piston goes from BDC to about half way up, with less pressure on the valve that is where you can loose a lot of your gasses. Small leaks may well seal when the engine has run but they can also stop it starting in the first place, why not sort them now while the head is off instead of having to strip it down later.

Hockeypuck58 · Oct 22, 2024

This is awesome information, I’m glad I joined this group. Crazy amount of knowledge in this place. I wish I could sit down with some of you. Anyone live near Chicago?

Brian Rupnow · Oct 23, 2024

The engine is completely finished mechanically and electrically. The valves all seal, and the head gaskets don't leak. The distributor seems to be doing it's thing and the plugs spark alternately. The motor doesn't seem to want to suck gas up from the carburetor, and yes, there is a breather hole in the gas tank. Today I'm going to have another look at the cam and spark timing, because there is very little else that can be wrong.

dsage · Oct 23, 2024

Do you feel suction if you put your finger over the carb air inlet?
With your finger over the inlet will it suck gas? (assuming clear gas line tubing you should see it move)
Is the tank fuel level at or very close to the carb level.
Is the needle valve open a bit?
All stuff you know but....

Brian Rupnow · Oct 23, 2024

Right now the spark timing is 180 degrees out of phase. That's a simple fix, just rotate the rotor 180 degrees and then lock it down. I'll do that first, then try a little quick start sprayed into the carburetor.

Jasonb · Oct 23, 2024

You don't say what compression you have now that the engine is all back together. If it won't compress then it also won't be making a vacuum either to suck anything in.

Brian Rupnow · Oct 23, 2024

As I turn the engine over with the starter and hold my thumb over the carb air intake, I can see lots of bubbles blowing out around the cross drilled hole for the rotating throttle shaft. May have to try a store bought carb and see what that does.

Sparky_SC · Oct 23, 2024

Brian Rupnow said:
As I turn the engine over with the starter and hold my thumb over the carb air intake, I can see lots of bubbles blowing out around the cross drilled hole for the rotating throttle shaft. May have to try a store bought carb and see what that does.

That sure sounds opposite of what you should expect. Bubbles blowing out means pressure where the carb should be at vacuum.

Don't even need a carb in place to develop vacuum at the intake ! Valve timing highly suspect.

Jasonb · Oct 23, 2024

I'll second that

What compression have you got as that could also be low if timing out

minh-thanh · Oct 23, 2024

Just cover your finger on the suction port if you feel the suction "pulse" when the engine is running you will know the lobe timing is ok
If there is none or just blowing out then check the lobe timing again
*** That only ensures if your engine is airtight.

Sparky_SC · Oct 23, 2024

minh-thanh said:
Just cover your finger on the suction port if you feel the suction "pulse" when the engine is running you will know the lobe timing is ok
If there is none or just blowing out then check the lobe timing again
*** That only ensures if your engine is airtight.

Yes !

That plus visually check that the intake valve opens as the piston starts descending in its bore and closing near the bottom. Anything radically wrong with the timing can easily be seen visually.

Just a visual check on the "suck, squeeze, bang, blow" theory goes a long ways in initial troubleshooting.

pileskis · Oct 23, 2024

Sparky_SC said:
Yes !

That plus visually check that the intake valve opens as the piston starts descending in its bore and closing near the bottom. Anything radically wrong with the timing can easily be seen visually.

Just a visual check on the "suck, squeeze, bang, blow" theory goes a long ways in initial troubleshooting.

rklopp · Oct 23, 2024

I hate to ask, but are you turning the engine the right direction? It's like a Briggs--while the output shaft turns the usual counterclockwise when facing it, the flywheel, being opposite the output, turns clockwise. I had to switch the polarity of my airplane starter when starting the Upshurs via the flywheel end.

Jasonb · Oct 23, 2024

Brian is "runing" it the opposite way as his starter box only goes in one direction.

Upshur's opposed twin engine

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