Engine Siezing Then Freeing

Iceberg Sat Jan 30, 2021 8:09 pm

I have one .049. Runs pretty nice. About 15k and runs sweet. Maybe run 40-50 flights to date.

It occasionally will be running well in flight them slow and stop. When I recover the plane the motor is siezed but with very little effort will free and be ok. Then will run again ok. But periodically will do the sieze thing. What could be the reason? I think that must be the piston ball getting tight on partial rotation?

What do you think?

Granted I am running during winter times with about-3 but until sieze motor running sweet.

What does the know think?
Thanks Iceberg

dckrsn Sat Jan 30, 2021 8:19 pm

Hi Ice. Are you citing Celsius or Fahrenheit?
If -3c, air temp shouldn't be an issue, but -3f might.
Bob

**Cribbs74** Sat Jan 30, 2021 8:23 pm

Usually sagging and then seizing is caused by a really lean run. In fact what you described is a textbook lean run.

However this may not be the case, it just sure sounds like it. Do you launch with the engine screaming or it is it more like a wet 2 with occasional high speed bursts?

Ron

Edit: depending on what oil content/type it can come out of suspension in cold weather and then you might be only pulling in raw methanol/nitro.

Ken Cook Sat Jan 30, 2021 8:30 pm

When was the last time you had the crankshaft out of this engine? Many times the castor goo becomes embedded onto the shaft and inside the case. Disassemble, polish the crank if possible and rid the case of the goo. I've had it heat up and act like a brake on the shaft causing this seizing like attitude and then it becomes free.

Iceberg Sat Jan 30, 2021 8:50 pm

It has been a few months since removing the crank. It is celcius. I am running Traxxas 33% with 10% castor added.

Last week had multiple great runs. Today one good flight them the sieze thing in flight.
Thanks
Ice

Ken Cook Sat Jan 30, 2021 9:37 pm

What is 33%? Are you saying your oil content is 33% and you added another 10% or that 33% is your nitro?

Iceberg Sat Jan 30, 2021 10:19 pm

33% nitro

balogh Sun Jan 31, 2021 1:15 am

Cold air has high relative humidity that may accelerate varnish build on cylinder wall. Check cylinder wall, if brownish near the TDC then that might be varnish seizure.

Ken Cook Sun Jan 31, 2021 7:27 am

You make no mention of the cylinder type be it thin wall, stepped wall or thick. With the piston/cylinder off of the engine does it bind at all as it nears the exhaust cut outs? Do all this testing with a clean washed cylinder and piston. A thin wall that possibly has a slight twist within the bore can offer undesirable results such as your experiencing if it did twist. Also a air leak within can cause the engine to go very lean sounding as though it's seizing due to the way the engine shuts off. Is it a product engine or a integral tanked Bee?

I have to question the high humidity in cold air. I do most of my spraying in the colder temps due to lack of high humidity. However, high humidity does constitute higher varnish levels but Ice has been running higher levels of synthetics due to his location. I wouldn't think that cylinder varnishing is the issue at hand.

Iceberg Sun Jan 31, 2021 8:05 am

Hi Ken Balogh Cribbs.
Thanks for the comments

I launch at full rpm This motor does this even occasionally in warm weather.

I couldn't tolerate it any longer. I tore it apart last night. Crank was good. Cylinder (thin wall) was good but the piston did have pretty loose socket. I am guessing that when hot the expansion was allowing the ball to slightly bind with the socket???

I put a much better tighter piston into the motor and put back on the plane. I hope this will fix it. I'll try next weekend. Thanks guys very much for the appreciated comments.

Talk soon. RC Plane

Iceberg

balogh Sun Jan 31, 2021 8:38 am

A loose socket may also change timing and quantity of fresh charge into the cylinder, leading to erratic run. You are lucky the ball end has not punched a hole into the piston crown.

**Cribbs74** Sun Jan 31, 2021 10:17 am

You have been doing this for a while and have gained a lot of experience so all I can suggest is to not launch at peak. Come off of peak a little and let the engine unload in the air. In this way you will never have to be concerned with going too lean during your flight. Your reset will help.

gkamysz Sun Jan 31, 2021 10:33 am

About humidity. 100% relative humidity air at 30°C contains ~30g of water, while at 0°C it contains ~5g. It's odd that humidity would play a part in varnish when a product of combustion is water, but it's what is said about castor varnish.

I would think the fuel Ice starts with has a fair amount of synthetic so should help prevent varnish. You can determine a lot of the condition of a cylinder with a light and loupe.

A loose socket can't bind and I just don't think a tight socket would stop an engine. In terms of expansion we can assume the socket would expand at the same rate as the rod as the material and temperature is similar if not the same.

I've never heard of castor dropping out of methanol with low temperature, but this is easily tested.

Iceberg Sun Jan 31, 2021 11:07 am

Thanks Cribbs
So you're saying that when leaning fuel with NV and peak rpm hits. Richen the needle a little bit to slightly slow or richen mixture then launch plane and allow loading change in the air? That way avoiding too lean.

I'll try that. Even with cold air temperature the leaning risk is still present Cribbs?

Thanks
Ice

**Cribbs74** Sun Jan 31, 2021 12:10 pm

That’s what I am saying. And yes it doesn’t overly matter what temp it is outside, although I suppose RH and temp could have an affect when really hot or really cold. Kind of like how we choke our cars on cold days to deliver more fuel and less air.

No matter the temps I am always going to launch a little richer to compensate for the prop unloading.’

I wouldn’t dismiss what Ken said about an air leak. This is also a likely scenario

Surfer_kris Sun Jan 31, 2021 12:12 pm

I've found that it is a little different to fly when it is below freezing. I'm running all castor fuel in the small engines and the castor fuel gets thicker with the cold so you have to open up the needle a little extra in the cold. It also tends to change during the day, as the fuel in the fuel bottle is a little warmer when it is fresh out of the car.

Sound's like the engine might simply lean out in the air, a slowly decreasing rpm is an indication of that. So just try to set it a little richer and fly again.

**Cribbs74** Sun Jan 31, 2021 12:28 pm

This ^

Castor can become like glue when cold.

gkamysz Sun Jan 31, 2021 3:00 pm

I agree that fuel viscosity may be coming into play. However, that assumes the fuel is warm initially and cools in the tank after the engine is started/launched.

**Cribbs74** Sun Jan 31, 2021 4:41 pm

gkamysz wrote:I agree that fuel viscosity may be coming into play. However, that assumes the fuel is warm initially and cools in the tank after the engine is started/launched.

He is flying in 26 degree F weather. Wouldn’t take long to get that small amount cold Even warmed up in the car or his jacket the 26 degree tank will cool it down fast. Of course it probably burns off pretty fast in flight!

gkamysz Sun Jan 31, 2021 8:17 pm

What I'm saying is that if viscosity due to temperature is the reason for what's happening fuel and tank have to be warm when the needle is set, then cool off to change the fuel flow. If set while the fuel and tank is cold it wouldn't change. If it's happening randomly, it's hard to say.

**Cribbs74** Sun Jan 31, 2021 9:01 pm

Got it. Makes sense.

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