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brian Rupnow
04-26-2013, 02:14 PM
Perhaps someone with more experience than myself can help me out. My Odds and Ends hit and miss engine has a strange problem which I can not get to the bottom of. I am running a grey cast iron cylinder and an aluminum piston. I couldn't get the metal rings to seal on the original cast iron piston, so I made a new piston of aluminum and put a viton o-ring on it. The engine immediately started and ran. However---it only runs for 5 to 10 minutes and then seems to be labouring, and quits. However, if I immediately turn the flywheel by hand, it seems to be turning freely, not seizing. If I choke it a bit and spin it with my electric drill, it starts easily again. I have tried both my home made carburetor as per Philip Duclos' plans, and a purchased Traxxas 4033 carburetor---same thing happens. I have tried a different coil---same thing happens. I have tried it in both hit and miss mode and with the governors tied down, and it still does the same thing. I am going to give it a try with a different spark plug and see what happens. My first thoughts were that the aluminum piston would expand at a greater rate than the cast iron bore and perhaps start to seize the piston in the bore, but if that were so, then surely I would feel it when I turn the flywheels by hand immediately after the engine quits. I have tried to pull the sparkplug to diagnose the problem, but I really can't tell from doing that.--The fact that I need to choke it a bit to restart it even when its hot seems to indicate that it is running out of gas.--But--I see no air bubbles in my clear fuel line. I may resort to putting the cast iron piston back into the engine with a Viton ring on it and see if that helps. I really have ran out of ideas here.---Brian

Peter.
04-26-2013, 02:38 PM
Could be the aluminium is expanding and binding on the walls of the cylinder. Machine the top third or so of the piston sides at a shallow taper to allow the crown to expand but not bind. The running time might be the time it takes the cast iron cylinder to warm through, reducing the amount of heat drawn from the piston.

ahidley
04-26-2013, 02:41 PM
I would think that the rubber is squeeging off the cylinder wall oil and thus getting stuck. A cast ring wont wipe it off, it will squeeze it down very thin. The purpose of honeing the cylinder is not to make it smooth but to make tiny scratches/grooves for the oil to adhere to. The angle of the hone job is ment to also hold the oil on the cylinder wall. You said that you have to make it reall rich to get it started again so I would think this would "lube" the cylinder again until the process starts again.

brian Rupnow
04-26-2013, 02:51 PM
I have 3 other i.c. engines running the viton o-ring, and they will run all day. One has an aluminum piston and a mild steel cylinder, one has an aluminum piston and a cast iron cylinder, and one has an aluminum piston and a 316 stainless cylinder.---and like I said in the first post, if it was starting to seize from differential expansion, wouldn't I be able to feel the drag when I turned the flywheel by hand immediately after the engine stops?

brian Rupnow
04-26-2013, 03:03 PM
Whatever is going on, it has something to do with heat. The engine runs much longer when I start it cold than any of the times I start it after it has warmed up and quit. I'm going over to the place I buy 0-rings and buy a couple more Viton rings and put the old cast iron piston back in. I can't believe that my problem is differential expansion, but I can't think of anything else right now.

Jess13
04-26-2013, 05:40 PM
Is there a condenser in the ignition system? It sound like it is breaking down.

If it was seizing up you would feel the drag. But, bad compression could be a different problem that could also cause a lose of vacuum to draw in the fuel.

A hair line crack in either the cylinder or a intake manifold would also be something to look for.

Vacuum building in the fuel tank?


Just thinking out loud here.


Jess

brian Rupnow
04-26-2013, 06:11 PM
I swapped out the pistons and put a new Viton ring plus one of the cast iron rings on the old cast iron piston. Started it cold, and had one good long run, then it started to slow down and quit. The way the intake manifold is designed on this engine, I find its very difficult to seal everything adequately to prevent vacuum leaks. I just pulled the intake/carburetor/exhaust manifold off and there is definite signs of exhaust "tracking" and vacuum leaks on the gaskets. I am entertaining the thought of doing a bit more machining and o-ringing the mating surfaces.

danlb
04-26-2013, 06:25 PM
It sounds like it could be vapor lock. Is the carb mounted directly to the engine, or do you have some spacer or gasket?

When you restart it, does the run time remain the same? That would point to fuel delivery.

Dan

J. R. Williams
04-26-2013, 07:19 PM
One way to seat the rings is to have the engine ingest a quantity of the old "Bon Ami" cleaning powder while the engine is running. That was a standard procedure for the old Cat single cylinder lube test engines. Another thing to consider is the compression ratio, as there may be to large a volume above the piston at top dead center.

brian Rupnow
04-26-2013, 07:23 PM
This is probably the worst case of "exhaust tracking" that I have ever seen!!! I put new gaskets on the carb and the intake/exhaust manifold two weeks ago. Of course, they were not a heat resistant material, and I didn't really think they would need to be. This gasket sets between the intake/exhaust manifold and the cylinder port, so it not only lets the exhaust exit the cylinder in the wrong place (which is a relatively minor evil) but it also has to hold compression in the cylinder during the compression stroke. I am going to see about getting a smaller Viton o-ring and machining a recess in the cylinder body to locate it. This problem was caused, in my opinion by the assymetrical design of the manifold body. You can see on the gasket that instead of having the bolts on the same centerline as the port, they are both offset to one side.
http://i307.photobucket.com/albums/nn294/BrianRupnow/CONTINUATION%20OF%20MAIN%20ALBUM1/ALBUM%20THREE/exhausttracking001_zpsd17d11c4.jpg (http://s307.photobucket.com/user/BrianRupnow/media/CONTINUATION%20OF%20MAIN%20ALBUM1/ALBUM%20THREE/exhausttracking001_zpsd17d11c4.jpg.html)

lane
04-26-2013, 07:38 PM
I have built all of Phils engines and the all work good.Only difference is I built all of mine larger they can be seen on my web site . First off get more oil to the cylinder . They will heat up and start to stall . Especially when new after things get broke in the will run as long as gas is supplied.
For the problem of manifold leaks I found that if you will make a very small thin sleeve and bore the body out a little to insert it to a shoulder and do the same on the head are block with the sleeve in place and a good gasket made of that dark gray gasket material you buy at a auto parts store all will work well no more leak.

brian Rupnow
04-26-2013, 08:04 PM
Thanks Lane---I had thought of that also.

Peter.
04-27-2013, 03:44 AM
Just want to add Brian, that the way I test for suspected intake leaks on a bike is wave my plumbing torch around the intake rubbers (un-lit) and listen for a change in the engine note. You have to be careful not to use too much gas that it gets drawn in the carb.

Arcane
04-27-2013, 08:06 PM
This is probably the worst case of "exhaust tracking" that I have ever seen!!! I put new gaskets on the carb and the intake/exhaust manifold two weeks ago. Of course, they were not a heat resistant material, and I didn't really think they would need to be. This gasket sets between the intake/exhaust manifold and the cylinder port, so it not only lets the exhaust exit the cylinder in the wrong place (which is a relatively minor evil) but it also has to hold compression in the cylinder during the compression stroke. I am going to see about getting a smaller Viton o-ring and machining a recess in the cylinder body to locate it. This problem was caused, in my opinion by the assymetrical design of the manifold body. You can see on the gasket that instead of having the bolts on the same centerline as the port, they are both offset to one side.
http://i307.photobucket.com/albums/nn294/BrianRupnow/CONTINUATION%20OF%20MAIN%20ALBUM1/ALBUM%20THREE/exhausttracking001_zpsd17d11c4.jpg (http://s307.photobucket.com/user/BrianRupnow/media/CONTINUATION%20OF%20MAIN%20ALBUM1/ALBUM%20THREE/exhausttracking001_zpsd17d11c4.jpg.html)
What's that on the edges of that gasket? It looks like melted gasket material to me (hard to see on my monitor) or is it just an RTV "gasket sealer"? If it is a melted gasket, I'd say that would be a problem. Once it gets that soft it probably allows loss of compression and might even allow a vacuum leak that would lean out the air/fuel ratio.

brian Rupnow
04-27-2013, 08:23 PM
Nah, thats just Permatex blue gasket maker. The gasket is a peice of cardboard cereal box.

sasquatch
04-27-2013, 08:45 PM
Agreed , the way those bolts holes line up is strange, why wouldn't they be in line with the port?