Aluminum piston in cast iron cyinder

[Brian Rupnow]

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

 

[canadianhorsepower]

hey Brian

how thick is your piston crown. If the piston crown is to thin and gets to hot you wont have any combustion and your motor will slowly decrease in RPM til it stops. Choking it to resart is a good indication of that
when your choking it your also cooling down your piston crown

If I can make a sugestion Start your motor stone cold and time how long it will work. Let it cool down for 3hrs and do it again if under same circonstance the time is almost the same chances are that this is the problem

good luck

 

[Brian Rupnow]

The piston crown is .140" thick. Thats not a lot, but then its only a 1" dia. piston. A hundred other people have built this engine with the same piston specs, and theirs seem to run okay.

 

[t.l.a.r. eng]

Do you have a check valve between the carb and tank to keep the fuel at the carb?

 

[canadianhorsepower]

The piston crown is .140" thick. Thats not a lot, but then its only a 1" dia. piston. A hundred other people have built this engine with the same piston specs, and theirs seem to run okay.

Yes maybe but remember you pyton seal is probably more effective
there for making more power and hotter piston.
are they all using aluminium or cast for piston

 

[Brian Rupnow]

Do you have a check valve between the carb and tank to keep the fuel at the carb?

Yes, I tried that---it works very effectively to prevent "run back" of the fuel to the tank, but it didn't help keep the engine running any longer.

 

[canadianhorsepower]

Hey Brian your an expert with these piston
1/2 hour would give you one with 250 thou thick

 

[Brian Rupnow]

Luc--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.

 

[mu38&Bg#]

Have you eliminated vapor lock? Does choking it as it's stalling keep it going?

I seriously doubt the piston expansion is a problem.

 

[aonemarine]

Scratching head....perplexed look on face with one eyebrow raised.....
Think we can get a video of it dying out to get a better Idea of things?? Its really difficult to say without seeing it. Your battery isnt going dead is it?

 

[Brian Rupnow]

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.

 

[aonemarine]

Guess you found your gremlin

 

[Brian Rupnow]

Guess you found your gremlin

I honestly don't know. Every i.c. engine has its own quirks. My other i.c. engines were all real monsters to get running.---but----Once they ran, they ran good. This engine actually ran without too much pain, but it has never been "quite right". I get frustrated, because sometimes whan an engine doesn't run right, the reason for it is so elusive. And I don't have any "go to guy" that I can go to for help. When it comes to techy stuff, everybody I know comes to ME for help. All I can do is play detective and listen to what others have to say on the forum. I hate to solve problems by process of elimination, instead of logic, but sometimes it comes to that.---Brian

 

[t.l.a.r. eng]

Almost sounds like the tank is not vented, or maybe a fuel quality issue?

I wouldn't think an electric starter would be needed for a hit-n-miss.

 

[Brian Rupnow]

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.

 

[neseng]

VITON 'O' rings and high temperatures are a BIG NO-NO! When viton is exposed to high temperatures, it degrades and one of the nasties produced is 'HYDROFLOURIC ACID' which is a deadly poison.

Aqueous hydrofluoric acid is a contact-poison with the potential for deep, initially painless burns and ensuing tissue death. By interfering with body calcium metabolism, the concentrated acid may also cause systemic toxicity and eventual cardiac arrest and fatality. (...and it only takes very small quantities to do the damage!)

I would NEVER even entertain the idea of using 'O' rings, especially Viton, in the applications you have suggested or in any application exposed to high temperatures on any engine.

If the Viton 'O' ring shows any signs of having a sticky, brown coating after use, DO NOT HANDLE IT with bare hands, remove it with a tool and dispose of it safely and then thoroughly wash the component that it was removed from.

By the way, you may find the the slowing and stopping of your engine after heating up, is in fact the 'O' ring binding on the cylinder walls and trying to roll within its own groove. 'O' rings are not designed for rapid reciprocating operations under high temperatures and with minimal lubrication, That is why all 'real' IC engines use cast iron rings, even the cheapie Oriental imports!

Stay safe and live long! Cheers, Norman.

 

[Brian Rupnow]

Guess I shouldn't have licked my fingers after I changed those pistons!!!

 

[neseng]

.........Yes, very funny! ....but far less amusing after you have had your tongue and your fingers amputated as the surgeons try to halt the insidious spread of the poison through your system! ....By the way, hydroflouric acid even dissolves glass, so human tissue and bone is no obstacle!

 

[aonemarine]

Guess I shouldn't have licked my fingers after I changed those pistons!!!

Well maybe it will save you a buck or two on that tongue piercing

 

[canadianhorsepower]

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

Hi Brian, before you do anything i would run both matting part
on a granite block just to check how flat they are.

I would agree with your opinion of assymetrical design if the gasket would have split at the other end "see picture" but having such a big dark area
leeds me to think that something is not straight.
oh yes one more thing the blu silicone doesn't resist to heat well it could be that when both bolts are secured that the stuff get squeeze away then would melt and causing your problem I personaly would not use any but you shoud try the red one for high temp