Hey Guys,

I've been doing RC all my life. I've had a ton of nitro engines but I have never had a "Ringed Piston" i.e. the OS .32 SX-H. I was flying my helo this weekend and my engine was acting funny. It was almost like an electric motor on dying batteries. I would be hovering and the engine would start dropping rpm's no matter how much throttle I gave it. Even Idle Up wasn't responding. I almost crashed because the head speed started dropping with the more collective it was getting trying to get the engine rpm back up. I would land and the engine would pick up power again. I know my piston and sleeve are trashed because the temp of the engine at shutdown was 305, which I thought was weird because I had good smoke the entire flight. I try not to go over 210 when I fly and I didn't mess with any settings since the last time I flew, which the engine ran fine. Also, the piston goes all the way through the sleeve without getting tight. So I got new ones on order through my LHS. My question is this, what does the ring do for your compression? I know rings in a real engine keeps the oil out of the combustion chamber. But our lubricant is in the fuel. So what is the advantages of a ringed piston? I'm thinking it has to be for compression reasons. Any knowledge is greatly appreciated.

Chad

US Navy Chiefs...Since 1893
118 Years of Dedicated Service.

http://www.carcraft.com/techarticles/77899/ Read down rings are about halfway. Very hard to tell by smoke alone as has been said many times on here. If more questions fire away somebody will answer. Chris

Chris

I know my piston and sleeve are trashed because the temp of the engine at shutdown was 305

Maybe not. Ringed engines are a lot more forgiving to a lean run or two than ABC/ABN engines are. If the sleeve and piston are not scarred, scored, or galled, they are probably just fine.

Also, the piston goes all the way through the sleeve without getting tight.

The piston in a ringed engine is SUPPOSED to go all the way through the cylinder without getting tight at the top. You're used to ABC/ABN motors that don't have a conventional ring. Those motors have a slightly tapered sleeve with a very tight fit of the piston at the very top. ABC/ABN motors depend on that tight seal for their compression. If you have an ABC/ABN motor with a loose fit of the piston at the top, you'll have a engine that won't run well.

The ringed motor does NOT depend on the fit of the piston in the cylinder for its compression. That is the job of the RING. The piston should just drop through the entire sleeve unimpeded in a ringed motor. The sleeves in a ringed motor are usually NOT tapered, and the ring seals with a tiny gap at its ends. If the gap is too small, the ring will become tight in the motor as it heats up and you'll have a badly running motor. If the ring gap gets too large, you'll have a small compression leak, and a loss of some performance.

The rings in your "real" engine work the same way. The piston is not a tight fit in the cylinder, it does NOT provide the compression seal. Your car's piston may generally have three rings per cylinder. The top two are there for compression, the third one is there as an "oil ring" and it's job is to keep excess oil out of the cylinder by scraping it off the cylinder walls, back into the crankcase.

Back to your 32. I've got a SuperTiger Blue Head 60 that I bought in the late 1970s. It has seen many many gallons of fuel through it in planks. It still runs just fine. A ringed engine, if taken care of, can give you long years of service.

If your cylinder and piston aren't scored, galled, or scarred, and if your ring is simply worn from too many gallons of fuel, you can simply buy a new ring for about $20, and CAREFULLY install it in place of the old ring. Carefully because it's made of cast-iron, and is brittle. They break very easily if you aren't careful putting them on. You can also stretch them out of round if you aren't careful at putting them on.

Once you have the new ring on the piston, take the cylinder and if you have access to a brake hone from an auto shop, put it in your drill and lightly hone the inside of the cylinder, moving it back and forth to form a cross-hatch pattern on the cylinder wall. Your aim is to break the glaze on the cylinder wall. If you can't find a brake hone, you can carefully use some fine-grit wet-or-dry sandpaper (wet) to break the glaze. Clean the cylinder well, reassemble the motor using liberal amounts of oil, then fire it up, and go through a new-motor break-in procedure.

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The symptoms you describe -- slowly losing power while hovering -- are a bit spooky for me. I had that happen in the early 1990s when I switched fuel from Red Max 15% (what I had been using when I lived in Missouri), to Cool Power 15% (the only stuff I could buy locally in Albuquerque, where I had moved to). My Schluter speed 61 in my Champion was running fine. My last flight of the day was a nice, calm hover as the sun was setting. Only, I had to keep increasing the throttle a notch at a time to maintain about a six-foot altitude in hover. Finally, at nearly full-throttle, the heli just wouldn't stay up.

Later that evening, I took the motor apart and found that the bronze bushing in the bottom end of the connecting rod was gone, and that the bottom end of the con rod was about to break into a million pieces, and the end of the con rod journal on the crank was scored.

A few days later, I had a SuperTiger X-40 motor stop dead cold on a takeoff with my Dirty Birdy. I took that motor apart, the bottom end of the con rod and its bushing were toast.

I was using the same fuel in each motor. Each motor died due to having too little lube in the fuel. I fixed both motors, and switched fuel. I haven't had THAT problem since.

I'd check both ends of the connecting rod, the wrist pin, and the end of the con rod journal for signs of abnormal wear, if I were you.

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Provided that your ring, sleeve, piston, and con-rod are healthy, look to gunk in your carb's needle valve body for some kind of obstruction. Over the years I've found little balls of fuzz, bits of grass, and even a well-pickled aphid in the needle valve body. And I use a filter on my fuel pump pickup line, as well as an in-line filter on the helis.

Dave

Ok, So more than likely I ordered the wrong thing and should have ordered a new ring instead. Would bad fuel do that also? On this flight I finished off a gallon of fuel that I have had for awhile. I would say at least 8 months, because I had it before I went on deployment back in June of 2005. With all the temp changes recently down here and the fuel sitting in the garage. I have a fuel pump mounted on the gallon. Is it possible that I might have gotten some condensation or moisture in the fuel that would cause it to loose it's potency? Thanks for the advice as always.

Chad

US Navy Chiefs...Since 1893
118 Years of Dedicated Service.

Bad fuel will do strange things. An open jug that's sitting, not properly sealed can slurp up moisture, and the volatile stuff like methanol can disappear.

Fuel with water in it acts odd. The motor may run fine, but just stop for no apparent reason, or it may run well, but not idle or transition well. It may run for the entire tank, but just run like crap.

I always keep my fuel jugs stored with the original caps on them. My pump is a hand pump. The pickup line has a filter on the jug-end. I open the jug, drop in the pickup, fuel the heli or plane, then immediately re-cap the jug. In the past thirty years or so, I think I've only had one open and partially used jug go bad over time.

It's not uncommon for me to end up with a half- or third of a gallon of fuel at the end of the flying season here, have the remainder sit capped in my garage all winter, then start using it in the spring. The stuff just works fine.

I'd try a new batch of fuel, and look for something in the carb. As long as the guts of the motor look fine, if you have reasonable compression, and you don't have slop in either end of the connecting rod bushings, the motor should be quite happy.

Any chance you could post some good clear pics of the innards?

Dave

I took a real close look at the piston and sleeve, and I do have some scratches on the piston. It also looks burnt on the top. My conrod and bushings are tight as hell. No play at all. Actually had a hard time getting the rod off the crankshaft. As far as pics, I don't have a good digital camera for close ups. I will have to borrow a buddies this weekend and I will get them posted up. My new piston and sleeve came in today but I didn't get a chance to go get it. Will pick it up tomorrow and put the motor back together and put some new unopened fuel I just got in it and see how it goes. Oh, The ring looks fine but like I said, I've never had a ringed engine so I'm not sure what is good and what is bad. I sqeezed it with it still on the piston and it looked like the gap closed all the way, that, and its kind of hard to get it back into the sleeve. I hope that's telling me that it's still tight against the sleeve. Will find out when I get the new P/S.

Will let you know how it goes. I'm half tempted to put it all back together now and try it with new fuel just to see if it was the fuel causing this issue.

Chad

US Navy Chiefs...Since 1893
118 Years of Dedicated Service.

I believe the OS piston has a small pin in it to locate the ring gap, and to keep the ring from rotating once it's in the sleeve. Make sure you line up the gap and the ring before assembly. Gently squeeze the ring and the piston should easily go into the cylinder.

The burnt stuff on top won't hurt anything. Here's a pic of a piston from one of my OS32 ABNs that ran a bit lean a couple of summers ago:

That's a badly scored piston, and the cylinder looked just as bad. Small scratches on the skirt of a ringed piston are usually not bad.

Dave

Ok, Got the new piston and sleeve in on Friday. I got the engine back together and I am now leaning towards my old piston and sleeve being shot, and probably bad fuel to add to the problem. I got mad compression compared to what it was. I did get a pic of the old piston, just need to get it off my buddies camera and I will get it posted Monday. It's pretty scratched up. I haven't had a chance to fire it up yet due to other projects I am currently working on. That's the bad part about having more than one hobby. I will try and get it in the air tomorrow after work and let you all know what happens.

Chad

US Navy Chiefs...Since 1893
118 Years of Dedicated Service.

Ok, here is a pic of the piston from my engine.

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The scratches you can actually feel how bad they are. The are not just surface abrasions. They are more like gouges than anything. I did a real good inspection on the engine when I had it apart and didn't see anything that might have caused this. My compression was null and void.

I fired up the new piston and sleeve tonight and it ran fine. I ran approx 1/2 tank of "new" fuel through it and had no problems. Temp was around 160F. I think that is the highest my tamp gauge read. I will keep it down around that level for a couple of tanks and do a run in cycle on it.

Thanks for all the help on this as always.

Chad

US Navy Chiefs...Since 1893
118 Years of Dedicated Service.

A picture is worth a thousand words.

That's one fried piston. Those aren't simple score marks from an occasional bit of dirt, that's a full-blown run too-lean-too-long piston. I'll venture a guess that the scoring is adjacent to the exhaust port.

You done good by replacing the piston, sleeve, and ring, Vern!

Now let's see, how many more words till I get to a thousand....

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by the way, does the fuel you're using have castor oil in it? That brown gunk on the skirt looks like varnish from a castor-based fuel.

Dave

by the way, does the fuel you're using have castor oil in it? That brown gunk on the skirt looks like varnish from a castor-based fuel.

I use Morgan CP 30% for fuel. Not sure if it is castor based or not. It doesn't say on the label. I don't think it is. I think it is just a major burn mark from 305F. LOL.

Chad

US Navy Chiefs...Since 1893
118 Years of Dedicated Service.

It's not completely obvious from the Morgan Fuel website, but it appears that castor is part of their "lubricant package" for Cool Power.

Dave

No , Coolpower has synthetic oil only . If you have have been running a fuel with a little castor , it would have almost certainly survived 305 degrees .

At the end of the day , it gets dark .