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Old 10-13-2011, 05:58 PM   #1
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Engine overheat!

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I am new to ringed engines (used to abc), and i recently changed my ring in my os55hz. I ran half a tank today since changing it, and brought it down to find the temp on the engine is 295F. I noticed significantly less compression right away, and the piston ring is silver-ish, again. It didn't sound lean in the air, and it dropped down to idle fine as well, I was quite surprised to find the temp so high.

I was told (after) that there should be a mini brake-in process when changing a ring, I ran the helicopter pretty hard that flight.

The color of the plug to my surprise looked very new, and top of piston was still silver. Isn't a plug suppose to turn black in color when an engine overheats?

Anyway, my question is, am I safe to run this ring, or should i replace it? Should my piston and liner still be fine? It all lasted approximately half a tank.

I hope I was clear, and any help is appreciated!
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Old 10-13-2011, 06:34 PM   #2
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Re: Engine overheat!

Pull the ring from the piston and insert it into the bore. If it still has good tension then it should be fine. I would still go through a complete break in procedure regardless of the repairs. However, a new ring with a sleeve with some time on it may take even longer to seat as they usually work in together, (a used sleeve is considerably smoother and not as condusive to helping the ring face wear in). The reason for the richer than normal mixture till break in completion is to help lubricate everything adequately, help carry away the material and also remove the heat generated when things are new and tighter.

This is especially the case with ABC motors. Due to the sleeve taper they can be extremely tight until the break in is complete and can run a bit hotter as a result. Ringed engines are not so bad, but still require the procedure to ensure the bits all wear in together.

On that note my Fox motors have extremely hard liners, to the point you will wear out several rings before the sleeve is toast. They can take extremely long to break in, new or rebuilt.

Don't know about the 55, but the 50 heli engine was notorious for burning through the piston, especially near the exhaust port. In most cases this is the result of lean running, but other causes can be inadequate cooling airflow and/or too high a nitro and/or too high compression.

Some of the newer OS use plates sleeves and there have been lots of reports of the plating separating and coming off. Check the sleeve for extreme discoloration and if there are dimensional changes, (if the liner does not slide easily into the bore in any position till it hits the alignment pin then the bore may no longer be perfectly round.

One thing I might ask is if there were other signs of overheating or stress? If the exhaust is excessively black or the plug dies suddenly, (does not sound like the case here) then this can indicate excessive wear, to the point bits of metal can contaminate the exhaust or kill the plug. Having a plug fail on a new motor is not all that unusual due to the higher than normal wear rate till things seat.

As for the top of the piston and plug, the type of lube may play a part there. It sounds like you did not put a lot of time on the motor, perhaps not enough for excessive deposits, but synthetic is a lot cleaner than castor if the mixture is correct.
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Old 10-16-2011, 12:57 PM   #3
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Re: Engine overheat!

The only thing I can add to that is some of us add 141 ml of castor oil to the standard 4L fuel jug. This brings the oil quantity to 20%. Use Sig or oil from the hobby shop not the pharmacy. If you want to do the same with the synthetic lube fuels, you have to find a hobby shop that stocks the proper oil. I have not had any problems with the proper de-gummed castor oil. The main ingredient in our fuel is double distilled methanol not methyl-hydrate. Like he said the dedicated break in procedure is a lot longer than ABC engines. Head temps on my new or rebuilt engines run from 185 deg. F to 230 deg. F, if it goes over that I change the mixture and the throttle setting. With more running at various settings until it will not over heat at full throttle. I consider 240 deg. F too hot. I check the temperature of the glow plug and the head around it. You must keep your fuel jugs sealed so the moisture from the outside cannot get to it.

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