DA100 Right Cylinder runs hot

[dmcquinn]

My 18 month old DA100 is now running hotter on the right cylinder as compared to the left. Sometime as much as 90 degrees (F) hotter. This is measured in flight using EagleTree telemetry. Here are three sets of data. When new, you can see that the temperatures on the left and right cylinder generally were about the same. But now the right clinder is much hotter. I replaced the rings last week because they had stuck in the piston grooves. Even after replacement, the right cylinder gets significantly hotter. The cooling baffling is still the same as a year ago and is pretty good overall. I was hoping that replacing the rings would restore the engine to its original temperature range. But you can see that before and after the ring change is about the same.

The cylinders looked OK to me and I replaced the spark plugs. The chart labelled "routine flights May 2007" was when the engine was new. The other two charts were from the last couple of weeks just before changing the rings and just after changing the rings.

The engine starts fine and runs good, so maybe I should just not worry and fly...

[SmoothFlying]

What are you doing at the 12-13 minute mark to get it hot?

[dmcquinn]

I don't recall. Generally I fly a mix of conventional aerobatics and 3d. Never do more than a few minutes of either. I may hover around for a minute but then fly around a while. I'll go back and look at the flight logs. I should be able to tell when in a hover because the rpm should be up in the 4000 - 5000 rpm range and the airspeed should be near zero.

[Nogyro]

I've never recorded temps on my DA100 jugs, but I know my right cyclinder also runs hotter than my left. Everytime I've pulled the plugs since it was new, the right side plug is always cleaner than the left. I've got 75 gallons through it now, and it's never been a problem......

I fly a combination of 3D and IMAC.

[hawk21]

if you replace the rings you should do break in again
also check the spark plugs to verify that your mixture is right
one cylinder will always run hotter than the other

[jack strickland]

	Quote: Originally Posted by dmcquinn
	My 18 month old DA100 is now running hotter on the right cylinder as compared to the left. Sometime as much as 90 degrees (F) hotter. This is measured in flight using EagleTree telemetry. Here are three sets of data. When new, you can see that the temperatures on the left and right cylinder generally were about the same. But now the right clinder is much hotter. I replaced the rings last week because they had stuck in the piston grooves. Even after replacement, the right cylinder gets significantly hotter. The cooling baffling is still the same as a year ago and is pretty good overall. I was hoping that replacing the rings would restore the engine to its original temperature range. But you can see that before and after the ring change is about the same. The cylinders looked OK to me and I replaced the spark plugs. The chart labelled "routine flights May 2007" was when the engine was new. The other two charts were from the last couple of weeks just before changing the rings and just after changing the rings. The engine starts fine and runs good, so maybe I should just not worry and fly...

What is your reference when you refer to the right cylinder, is it sitting in the cockpit or are you in front of the engine?

[STLAV8R]

Have you called DA for their input?

[dmcquinn]

I use the term "right Cylinder" as viewed by the pilot. On the DA100, this is the rear cylinder.

When I called DA (Jeff?) to order the rings, I asked them about what would cause the carbon buildup and stuck ring. They suggested to use redline racing oil. At the time I had not noticed the heat differential. Because of the ring change, I am now more observant of the telemetry data and that's when I noticed the right cylinder running hotter. At first I thought this was caused by the ring change. But then I went back and looked at some data from before the ring was changed and noticed the cylinder was hot even before I did the ring change. So then I went back and looked at data from when the engine was relatively new and I saw that at that time, the cylinders ran a lot closer together.

I understand that they will vary in temperature from each other. But 60 or 80 degrees seems too much. OTOH, the engine is actually running quite nicely, so I don't intend to rush out and "fix" it. I've gotten about 2 gallons through it (organic oil) since the ring replacement. I intend to continue this process and see what happens.

[jack strickland]

	Quote: Originally Posted by dmcquinn
	I use the term "right Cylinder" as viewed by the pilot. On the DA100, this is the rear cylinder. When I called DA (Jeff?) to order the rings, I asked them about what would cause the carbon buildup and stuck ring. They suggested to use redline racing oil. At the time I had not noticed the heat differential. Because of the ring change, I am now more observant of the telemetry data and that's when I noticed the right cylinder running hotter. At first I thought this was caused by the ring change. But then I went back and looked at some data from before the ring was changed and noticed the cylinder was hot even before I did the ring change. So then I went back and looked at data from when the engine was relatively new and I saw that at that time, the cylinders ran a lot closer together. I understand that they will vary in temperature from each other. But 60 or 80 degrees seems too much. OTOH, the engine is actually running quite nicely, so I don't intend to rush out and "fix" it. I've gotten about 2 gallons through it (organic oil) since the ring replacement. I intend to continue this process and see what happens.

I have had a lot of success balancing the temps in many twins, that I have built, and for other modelers. If you want to try this, you can add, say 2 for a start, extra cylinder base gaskets to the right cylinder, this opens the intake ports to the fuel charge a little sooner, so as to make the fuel charge more even thereby reducing the different temps, if you get them within 20 degrees+- of each other, that will be ok. May I refer you to a thread about this subject? It was started on 7-22-07, titled twin equal head temps. Hope this helps.
Jack

[dmcquinn]

Thanks, Jack. I read every word of that thread. Very good onfo.

This same engine, when new, had near-equal temperatures measured using the same system in the same plane with the same cowl-baffling and the same mufflers. Now a year later, the difference shows up. I don't know what changed. But I like the idea of adding another gasket as it is easy, low-cost, and low-risk. I can't imagine that it could hurt anything to try this.

[jack strickland]

	Quote: Originally Posted by dmcquinn
	Thanks, Jack. I read every word of that thread. Very good onfo. This same engine, when new, had near-equal temperatures measured using the same system in the same plane with the same cowl-baffling and the same mufflers. Now a year later, the difference shows up. I don't know what changed. But I like the idea of adding another gasket as it is easy, low-cost, and low-risk. I can't imagine that it could hurt anything to try this.

Just one other thing that could cause trouble, there may be a problem in the reed system, just remembered, I had one do this, and the reed system was the problem, you might try changing the reeds, or there might be a leak in the right cylinder at the base gasket. Just more thoughts. Regards
Jack

[dmcquinn]

The reeds looked fine, no curl or splits or cracks. In your experience, can the reeds look visibly OK and still be a problem?

What is your opinion of permatex ultracopper gasket sealer on the base gasket? Apparently the DA factory applies no sealer at all. Both gaskets appear to have been installed dry at the factory. When I re-assembled the cylinders, I applied a very thin layer of this on both sides of one gasket (the right cylinder) and only on one side of the left gasket (because it was stuck pretty good to the crankcase).

I reused both gaskets. Note however, that my temperature issue started before I ever touched the engine.

[JimC-MD]

Have you tried something simple like switching the temp probes from side to side to see if the data stays consistent? In the graph you showed from early on you showed temps pushing up at times (equally). Then later on, after break in, when we typically stop flying as conservatively, you show the large variance. I wonder if the description should read that the left cylinder is running colder than the right instead of the converse. My first step, with an engine that "runs fine" would be to verify my instrumentation.

[dmcquinn]

Thanks for the idea, Jim. After landing, I checked the left and right with an independent instrument (InfrRed temperature meter). The right was about 160 and the left was 130 after landing and taxiiing back. So I think the data are fairly accurate. I also glued a balsa strip onto the right side baffle to tighten up the tolerance between the baffling and the cylinder. In other words I closed up a small gap in my baffling on the right side just to make sure that it was not a baffling issue.

Maybe the right ring has properly "seated" and the left ring has not? I have only about 2 gallons through the engine since replacing the rings.

[rcflyer]

Hi dmcquinn, I am seeing the same behaviour with my new DA100 i.e. right cylinder much hotter than the left and the right plug cleaner than the left. Mine is still on 1:32 lawnboy mix. There are a few things I would like to confirm with you. Are you seeing a higher exhaust emission and black oil from the left muffler, and hardly any from the right? What is your peak rpm now, and what oil mixture are you using? Thx