Gentlemen,

My DA-50 quit shortly after take off last week on a hot day. Landed - no problem. Suspected the engine went lean and overheated.
I richened the needles and it ran fine.
Inspected the carb, tank, and fuel lines and they appeared OK.
Upon examining the outside of the cylinder and fins, they appeared to have a pinkish cast in color.

What - if any - are signs that a 2 cycle engine (DA 50) has overheated? How can I determine if the engine has been run too hot and my need servicing?

Thanks - Jaketab

I'd make sure the high needle is 2 turns out and only tune the low needle. The high basically needs to be all the way out since it's not cable of being too rich. You tune the low needle for a good transition and the high end follows along. It runs fine when tuning like this. It won't overheat, I have flown in high 90's and same humidity level, never a dead stick. I'd guess your engine is fine if it runs well and has good compression. The tick sound is in every DA 50, not a biggy.

Pinkish means it was hottish, but as Joe mentioned, if compression is good and it runs as usually, don't worry.

Carb tuning is one thing, engine cooling is quite a different bunch of bananas. Rich carb settings cannot make up for lack of cooling. These larger engines need to get rid of about 4 kiloWatts of heat by cooling alone! (think 4 paint stripper heatguns) That cannot be done with a rich mixture. You need ample cooling flow through the fins, good air guidance and good air extracting suction.

Engine overheating can only be checked by dismantling the engine, and subsequent cylider liner, piston dome and piston skirt + ring land inspection. Loss of compression is a sign of piston and/or cylinder damage, and should be cause for immediate attention (read engine repair)

To tune your DA50R lean the high speed needle for peak rpm, then richen it to loose 200 rpm.
lean the low speed needle til the motor balks when you flip the throttle from idle to wide open then richen it till you get a good transition.
When breaking in a new motor it should be a little rich but not to rich or it will get all carboned up the rings will stick your plug will get all carboned up, not good.
I would not run it with the high needle all the way out, asking for trouble.
the manual says high speed needle 1 & 7/8 turn out. low speed needle 1 & 5/8 turn out.

If in doubt call DA they will tell you what to do, They are very help ful

I have a lot of experience tuning this engine (mine anyway). The high end on mine could not get rich enough to drop the RPM's 200. I could never get that to happen. It's common knowledge that the carbs can't supply enough fuel to get rich and drop 200 RPM's on the high needle. You'll see threads discussing this very issue. I'd scratch my words "all the way out" and use the words "2 turns out". You won't get into trouble setting it there. What's trouble is setting it too lean hence the reason for this thread (unless airflow was the problem). Setting the low end to what DA recommends is actually trouble. It will bog and possibly crash your plane from fuel build up at idle. It actually happened to Chris at Extreme flight. He had his low needle set too rich and almost cost him the plane. DA will not actually tell you the proper way to tune an engine. They just tell you some factory settings which are usually too rich on the low end. My friend and I can both attest to that on three of these engines now.

Edit: Well what do you know. The thread was in the the first page of this gas engine forum:

http://www.rcuniverse.com/forum/m_28..._1/key_/tm.htm

Well I am sorry that youall have so much trouble with you DA50's
I tune mine as described above and have no problems. I must have the only two DA50's that run good

Thanks all for replies. It was definatley my fault for leaning the needles too much. I was trying to correct previous adjustments because I had been fowling the plug from what appeared to be running too rich. In my orginial question, I was looking for infomation on how to detemine if I had caused any damage to the cylinder or piston from overheating.

I plan to fly this afternoon and will post some tach numbers for reference.

Thanks - Jaketab

Jake - use a prop no larger than a 21-22x8 till you get familiar with the engine .
A pink DA is an overheated DA--
proper air exit setup and correct nedle settings are easy on these if you simply avoid too much prop load and spend time learning how to set the needles - there is NO magic setting -except -once you go past two turns -the HS needle is effectively wide open.

I'm in agreement with Mr. Reivers. There seems to be a bit of confusion here between poor tuning and engine heating. You cannot use the mixture as the primary means of carrying away waste heat. It cannot be done in our applications without tremendous volumns of fuel passing through the engine, and fule of a different type at that.

Make sure you have positive airflow through the engine and ample exit area for the heated air to escape. A baffled engine stays cooler than one without, and an engine tuned on the lean side will over heat faster than one properly tuned..

ok...so anyone have an opinion on whether baffling would be required on the H9 27% Extra 260 to keep the Da 50 from overheating?

Ok - if anybody is still here - flew today and the only deadstick I had was from running out of gas because my high end is much richer then before. Used 24 oz gas in 17 minutes of hard flying. Here are the numbers just for reference.

DA-50 well run in on WH 300LX. Bolly 23-8 wood. Altitude 600 feet. Temp 83F. Medium humidity.
Final adjustments after several flights. High needle 1-7/8. Low needle 1-1/4 but did not adjust to sag on throttle yet.
Static RPM range 6300 to 6330. RPM's were read after each landing.
The number of landings matched the number of take-offs.

Is this OK or should I expect a little more rpm?

Jaketab

Well that explains it then: your prop was too big. You should be running more near the 7000 RPM mark. Try a 22x8. Your needle settings are right where they should be. I have tuned a few of these now and can get them running nicely (except inverted at idle, that's another story).

I am glad you had some good flights and are enjoying you plane, that is what its all about.

Joe AP

I have a 22-8 Bolly but I like the 23-8 much better. Slows better and hoovers better.
My engine is also a DA-50 that will not run inverted at idle. I am familiar with that lengthly post.
One other DA-50 at my field does not have that problem. The difference in set ups is his runs the stock DA side muffler and I have the Slimline Pitts. The stock DA muffler seems to turn about 300 more rpm then the Pitts.

Jaketab

I guess it's all about what prop works best for you. I'm glad you got to run well now.