I installed a silicone deflector today on my O.S .46 AX. I noticed that the engine was somewhat hotter than it used to be when it didn't use the deflector. Is this normal? Should I expect this to hamper the engine's performance or lifespan?

The engine should not run noticeably different with the exhaust deflector. Are you sure the engine is not running too lean? Were the temperature/humidity levels considerably different on the two days?

This can happen if the ID of the restrictor is to small, use a larger diameter deflector.

Using a deflector like this
http://www2.towerhobbies.com/cgi-bin...?&I=LXL378&P=7
should NOT cause any problem if properly installed. Don't let it pinch off any due to the install and don't install a homemade one that is too small in diameter.

I use the same ones that Bruce does and have never had a problem.
You may need to readjust your high end needle a bit because of slightly more backpressure.

Needle was readjusted and just to be certain I opened it about 1/4 of a turn when I noticed this, but it didnt change significantly. The engine used to com back from a flight really hot but it didn't boil water as it didn't fizz when I touched it with a wet finger, now t does.

It sounds like you were already running too lean and still are. Just shouldn't be THAT hot.

yep you have been running lean, the weather conditions changed and you're even leaner now. remember what ever you have set on the ground you will lean out a tad bit more in the air....you want to see a bit of exhaust in the air

I always get a smoke trail, so it suggests that im not leaned out. Why would you suppose that I was already running lean?

you can be running lean and still get smoke out the pipe, that little pipe extension shouldn't make that much difference unless it's smaller than the muffler exit tube,the exit should be larger so as not to restrict exhaust flow.

Use the pinch test to set the mixture. Go to full throttle, and once it settles out, qiuckly pinch the fuel feed to the carb. If the engine note changes to slightly increase in RPM, then the fuel mixture is right. If it dies out, it is to lean, so adjust it out more (more fuel, richer mixture). Once you hear that slight increase in the rpm sound, then it should be alright.

I use a 90 size exhaust deflector on my three OS 1.20 AX's with no noticeable increase in engine temp at all. And, I use deflectors on my .46 as well as my .50 with no noticeable change in temp. So, it must be to lean.

Yeah this engine is set with the pinch test. Im positive its not running too rich, I just want to rule out the possibility that the heating is due to the darn deflector.

Then take the deflector off for a flight and do the test again.

Back to back testing is one way to improve the odds you're doing good testing. BTW, my 49AXs all come back too hot to touch, and I'm absolutely positive they're not running too lean. And all have lengths of silicone tubing on the mufflers, even on the Pitts mufflers. But no lengths are over 3".

Two cycle engines usually do not overheat when a 2" or 3" flexible hose is added to the muffler's outlet. The commercial ones have rougly the same inner diameter as the mufflers they fit. And the silicone tubing that fits the mufflers has almost exactly the same I.D.

Any two cycle can overheat with too long an extension, but the overheating comes from back pressures that're greater than the design expects. And that backpressure would create a loss of power, because it would be stopping the hot exhaust gasses from exiting the cylinder. And those backed up gasses would be inhibiting the incoming fresh charge. So you would see a reduction of the engine's power. It would show up clearly on a tachometer. And any experienced modeler would detect the loss of rpm without a tach.

If you're not detecting an obvious loss of rpm, the conditions for overheating aren't coming from an increase in backpressure, which is the only thing the extension could do to cause overheating.

As I recall you are using 0% Nitro fuel. I think that also tends to run hotter.

A lean engine can sometimes make more smoke than a rich engine simply because the rich engine is not hot enough to turn the oil into smoke. Don't judge fuel mixture by a smoke trail.

Are you using a stock muffler ???? ENJOY !!! RED

Yeah I'm using the powerbox muffler that comes with the engine.

and how long is your deflector?

and have you noticed a drop in max rpm from the engine with that deflector?

Take it off for one flight.
If the overheating goes away, it was caused by the darn deflector.
If it doesn't, you got some other problem.

deflectors cause too much backpressure and make the engine overheat.you will have to richen it up too much to overcome this,take it off

"too much backpressure"

When backpressure becomes "too much" the engine will not be able to reach peak rpm. It will lose power. It's very simple to judge when the backpressure is too much.

Deflector's don't always produce too much. Short ones usually don't show any effects at all, other than keeping your model clean.

It takes two flights to test. It takes weeks to argue and where are you after all the time reading. Our hobby is kewl that we can find our own answers in about 10 minutes flying.