Guys.
Has anyone ever checked temps on the 106? Right after landing without taxing in right on the cylinders with engine off, useing a lazer temp gun. Can anyone give me some idea on temperatures? I'm running a 28x12 MSC prop. with engine baffled I get readings about 215F on one cylinder & 225 on the other. I would assume it would be hotter on the ground than in the air because of no air flow, would that be correct?

Thanks.

Temps are only good if you take them when running and under the plug with a couple. Different surfaces will also reflect differently, causing abnormal temp readings too.

If you have your engine baffled and not lean you should not have a problem. Listen to it when it runs and that will tell you more than any temp gun made.

If you really want to get fancy run exhaust temps when you are flying and adjust the needles accordingly.

I have a 3W 100 (about 4 years old). On the test stand last weekend, no baffles, with 27x12 prop, both cylinders were around 200 degrees F. it varies somewhat depending upon where you point the temp sensor. I was pointing from the rear with the engine running, and pointed at the cylinder near the spark plug. also about halfway down the fins. After shutting off the engine, I also shot it from the front. Outside air was about 60 degrees. I have had the temp sensor for about a year and play around with it from time to time. Sometimes after landing, and idling back down the runway, the temps are about 180. If I get it too lean, it will go over 220. sometimes one cylinder is 20 degrees cooler than the other. never more than 20 degrees. I have read of other engines that varied by a lot more. hope this helps.

Quote:
"I'm running a 28x12 MSC prop."

That's some big lumber.I've never heard of anybody running a 28x12 on a 100-106 twin. It's possible your over loading it resuting in those temps.I'd try a 28x10 or a 27x10.

The prop 28x12 is ok for Bolly or mesjlik but for MSC is it a lot of load.
The temperature is accptable is you take it inmidiatly when the engine is shut off.

(centigrade in brackets) For an aircooled engine, 240 F (115) would be quite OK. 200(98) is low, 280 (140) is high.
Infrared guns are nice toys to compare things, but by no means precision instruments for laboratory use. You need thermocouples instead.
Having said that, that heat gun is very nice to check the cylinders of your twin. They very seldom will match, due to unequal mixture strength to both cylinders. It needs special care to have both cylinders within their margins. So if one cylinder approaches 280 degrees, it is time to richen the top end a bit more, or check ignition timing, compression ratio, spark plug, or whatever else influences that cylinder temperature.
Two points should be measured:
the junction between plug and cylinder head, and the first cooling rib on the cylinder. Take a mean of the two.
The plug measurement may be used to define whether you need a cooler or hotter plug type. The measurement is just the other way 'round as in glow plug engines. High temperatures require a colder spark plug. (in glow engines, high temps require a hotter plug)

All in all, it is purely relative, and largely dependent on engine type, amount of fin area, fin finish, engine shrouding , etc ad infinitum, so it is of very little use to state one single temperature as "best", as can be seen from the range provided at the beginning of this post.
Set your needles by ear first, then by reading the plug. Having done that, define temperatures for future reference and quick checkups.

As a good rule of thumb, an r/c engine should run between 175-215 for best longevity. The IR temp sensors are so-so for readings as have been pointed out.

Here is an old-fashioned method that works well - if the head is hot enough to sizzle water, spit etc on - ITS TOO HOT (i.e. above 220)


It is not uncommon for the engine to go above 220 on break in, but it should fall off with a richer mixture an/or more oil.


My DA100 runs consistently at 184, my 3W-75 runs at 194 and the ZDZ80 ran at 205 - all measured with an RCATS telemetry unit on the plane and in flight - thermocouples installed under the plug, and on the cylinder base bolt (case temp and head temp)

DP

I HAVE TO ASK..........why are you running that size of prop?..............you must only be getting 5500rpm or close to it?

Think of it this way............the bigger the prop the more the load on the engine.........the more the load on the engine the less the rpm.........the less the rpm the slower the big fan on the front turns.........the lslower the big fan turns the ess the cooling on the AIR COOLED motor.

If you have a noise problem put on a 3 blader

I HAVE TO TELL YOU.... I'ts the same temperature with a 28x10. The 28x12 is running at 5710 RPM. Lower RPM is better for the engine.

This thread might be of interest when looking at temp #'s

http://www.rcuniverse.com/forum/m_96.../tm.htm#964307

Lower rpm is not better for the engine!!

Hi loads produce heat not high rpm................high rpm produces cooling