1fireball

My Feedback: (1)

Thinking about my exhaust temps being low (if they are) I would say my exhaust sytem is not tuned for the rpm in wich I have the motor loaded.
If I am maximizing the exhaust heat at 950 degrees no matter if the needle is tweeked a little leaner and the motor is running ok and not getting hot I would assume I am not getting the supercharging of the cylinder that it should be.
I know this is a big can of worms but knowing what exhaust temps are for a known well tuned motor could help (I would think) fine tuning other combinations.
I know the exhaust gas temps increase as power is increased (more power makes more heat to a point) and there is a maximum you would want to see on any engine.
I also understand timing has a effect on the engines exhaust temps also... my question would be how much does varying the timing change the exhaust gas temps because of how the burn cycle is going out of the exhaust?

One more question for Pat. Have you ever ran an O2 sensor on a two stroke engine? If so is this a viable way to check mixture for us?

1fireball

My Feedback: (1)

I have a small chainsaw... and I will one day put the head temp sensors on there and see where they run. You are correct they take a beating and get any oil available and get filthy dirty and keep on going.

mmattockx

You guys aren't getting the key point with the equipment engines - they are carefully baffled and use forced air cooling. This is critical in their application because they are routinely beaten hard as you say. This is the major difference between the equipment engines and the R/C engines. If everyone baffled their R/C engines as carefully they could be used as hard with no issues. Overheating would be pretty much a non-issue, but that is not the case.

BTW, I am not against bench running an engine, so don't lump me with that group. I am just pointing out a very important detail that allows chain saw and whacker engines to survive their typical operating conditions.

When I get to it, I will bench run my G-62 with a DAQ system and post the results, but it is not going to be anytime soon. It would be nice if someone would post some results, but it doesn't seem like it's going to happen.

Mark

RTK

My Feedback: (1)

I've done that. My little Echo weedie runs well over 300 at WOT (tuned correctly), as do all my other lawn/garden two stoke equipment. If I remember correctly, the Rotax engines have a limit of just over 400. It's all in the design parameters.

mmattockx

RTK,

Where were you measuring the temp? That is good baseline info to have to avoid problems in our aircraft, thanks for posting.


Mark

RTK

My Feedback: (1)

I have been measuring a couple of fins down from the top trying to hit about the top of the chamber against the cylinder wall (not the fins). The in-flight testing I have done has shown this to be about the hottest part. (especially the back side of the cylinder not facing the wind so to speak) I used to use a sensor under the spark plug, but my friend took it back. If you can place a sensor on the cylinder wall where I did you will get an accurate enough number. Some engines can take the heat, others can not. I have one particular garden two stroke that has been running about 380 @ WOT for the last 15 years.
Venom used to make a wrap around sensor that was strapped to the cylinder wall and recorded High, Low, and current temps.
In the picture you can see what I am talking about, the actual sensor is on the back side of the cylinder.

Rcpilot

My Feedback: (78)

All gas engines should be strapped to the bumper of a 1971 VW Beetle and run WFO for 10hrs on bacon grease and coleman camp fuel mixed at 20:1.

You guys are all idiots. I'm the only one doing it right.

RTK

My Feedback: (1)

I bet that would work just fine

captinjohn

Check out some of the older, previous postings! http://www.rcuniverse.com/forum/m_57...tm.htm#5736391 Capt,n

the Wasp

My Feedback: (1)

Chainsaws & heat

I would think a Chainsaw engine would have a larger Piston to Liner "gap" than our plane engine,, I have seen 15yo saws that were so well taken care of yet had so much time on them that when we took them apart their rings have worn threw their Chrome Flashing in spots, and they still ran great,,

I stick to braking-in on the stand, brake-in a gasser plane engine on the stand is fine as long as you are "smarter than the engine"

Jim

Tired Old Man

My Feedback: (1)

The problem is that many are not.

The difference between aero r/c engines and saw engines with the clearances is nil. Other than the external appearance of aero specific engines and often a cheaper cylinder plating process in the aero intended cylinders nothing has changed between the types. The better aero specific manufacturer (singular, not plural) uses materials equal to the better saw engines. The vast majority of the r/c specific and clone manufacturers do not.

Lesson learned; Those engines originally designed and intended for "industrial" use applications and either converted or robbed for their internal and cylinder assemblies are much more durable than r/c specific engines. Leave MVVS and ZDZ out of this discussion because I haven't had an opportunity to dig into those yet.

Rcpilot

My Feedback: (78)

Typical ring gap is about .003 or .005 thousandths. I know that works on engines up to about 60cc. Larger engines may have more or less gap. I don't know.

Pat is right though. Ring gap on an industrial engine is the same as an aero engine of same displacement. Bearing clearances are the same too.

Bacon grease!!

1fireball

My Feedback: (1)

No replies to my questions... I would think this means its to big of a can of worms.

captinjohn

I talked with a well know piston ring maker. He said most small engines the cylinder/sleeve will expand more than the ring. Thus you can use .001 for end gap for the piston ring. He has set up many and never seen a problem. Just a obsevation I wanted t pass on. Capt,n

Tired Old Man

My Feedback: (1)

"I have installed a eagle tree system on my ZDZ 210. I have data but I am no expert in this field yet. The things I have learned is you can through out the lazer temp gun to check temps after you land. My experiance tells me (maybe just my airplane setup) that in the air at WOT my head temps (2nd fin down from the top of the cyl) are 95-110 deg. When you land the plane the temps climb to 160-180 before you can get to it with a temp gun (my lo end is a little lean). My exhaust temps (I have egts about 2 inches from the piston) are Idle 450-550, wot one cyl. will be around 950 max the other about 910 (that is extended upline wot runs). Vertical rpms around 5400 with a 31X12 three blade Mej.
It will turn about 6400 flat out and starts to rip slightly. I have leaned the motor twice on the top end (about 1/32) and saw about 20 degree jump in exhaust temp the first time and no change the second time. I run mtw tuned pipes on the motor and have not tuned the length yet.
I have started by extending the headers 2 1/2 inches. I am very interested in comments on what I am seeing.
Pat are these exhaust temp. close to optimum or not? I have a friend who runs a car dyno and he said temps around 1200 are common and 1300-1400 for brief seconds are ok. Those are 4 stroke car engines. I would like to know approximate exhaust temps to look for with a 2 stroke.
Very interesting thread and I am not trying to step on toes just want to get others opinions (and thats what they are). "
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800 to 1,000 for egt's is pretty common, and imo is near the peak as it stands. Much over that and things start to melt. Changing the header lengths most certainly effect the egt's since you will be changing the fuel charge that entes and exits the engine. Nice to hear your monitoring using egt instead of cht. Cht is slow to react to changes while egt is immediate and notes the true state of the fuel charge used. Unfortunately manufactuers don't provide max egt ranges for their engines so you're in a trial and error game where the errors require replacing the piston and ring assembly.

If anyone has egt info that could help you prevent cylinder melt downs it would be nice to post it for reference. Note that due to large differences in metalurgical composition there will be a large spread between what is acceptable and what will be over the top with different engines.

1fireball

My Feedback: (1)

Thank you Pat,
I am a ex drag racer that has run all combination of power adders for cars N2O ,alky,screw blowers. mechanical and electronic fuel injection, turbos etc. I built race car engines for 15 years and owned my own cylinder head shop. Engines and power excites me. I know I have alot to learn about two strokes but its the challenge of something new I like.
I bought this today to start down the learning path for 2 strokes. I put my competition version 3-W 275 on there for size comparison.
I want to start with some custom tuned pipes for this and my ZDZ 210. I would like to eventually work on a EFI for my 275 and maybe even alcohol. I have alot to learn but its what I love about life.
Pat...have you had any experience on this particular machine?

RC Extreme power

My Feedback: (24)

Had lost track of this thread and just did a lot of reading from different posters about there pro and cons to using a test stand for breakin.
I think one of the big difference in some engines not over haeting on a stand is how and what they are made from, I think the more powerfull engine ( for a lack of a better word) that have smaller cooling fins to save weight and are putting out a little more power tend to heat up more than others, with three inlet ports, I don't know it that makes a difference or not.

The engine that was sent back to me had no oil in the piston, muffler or in the outlet port, The lower end had some and not hurt so that tells me it had some kind of oil while running, It got so hot that the muffler was black and rings were egg shaped, I have the same engine on two different planes , One with about 25 flights and the other with about 10 flights, Both mufflers in these planes are lightly colored right around the outlet port. So that tells me the engine I repaired got really hot at one time.

So I guess it all boils down to each persons way of wanting to treat there engine.

Milton

Tired Old Man

My Feedback: (1)

I don't have any direct experience with either the 275 or the 210. As for the 3w, their metalurgy is unchanged pretty much across the board with their products so keep that in mind when playing with the EGT's. The ZDZ probably won't be much different. Get the basic mixture sets done before working the header lengths, then adjust as needed. That will include some rather pricey prop experimentation as well.... Wood props might be the better bet since you can buy over size and cut down to find the winning combo