Piston Burn/Wash Pattern -- What does my weird pattern indicate?

TheWizzerd

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This is a new 49mm steel sleeve build that I recently posted about the port timings etc. I got it to produce decent power finally, and its running OK.

However, after tearing it down to tweak/finalize the ports, I noticed an odd wash pattern that appears as if the fuel/air charge is simply screaming over the dome and right out the exhaust.

Does that appear to be the case to those who fully understand this?

What is generally the primary cause? My first hunch is the exhaust system not producing the appropriate reverse wave for proper scavenging, and allowing it to simply pump right through.

It appears that the transfers (only one is really visible here) are getting the flow toward the intake. (brown pattern on "left" (lower in pic) side of piston). It appears they may be uneven in their flow as no transfer pattern is visible on the right side, but that may be nothing at this point.


Any help is much appreciated. Thanks!
 

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weefek

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I don't have the answers you seek, I was only asking because it looks pretty fresh. Your original assumption sounds correct to me but I don't have nearly enough experience to be sure. Knowing how many miles are on a build helps with proper answers.
 

Chainlube

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This is a new 49mm steel sleeve build that I recently posted about the port timings etc. I got it to produce decent power finally, and its running OK.

However, after tearing it down to tweak/finalize the ports, I noticed an odd wash pattern that appears as if the fuel/air charge is simply screaming over the dome and right out the exhaust.

Does that appear to be the case to those who fully understand this?

What is generally the primary cause? My first hunch is the exhaust system not producing the appropriate reverse wave for proper scavenging, and allowing it to simply pump right through.

It appears that the transfers (only one is really visible here) are getting the flow toward the intake. (brown pattern on "left" (lower in pic) side of piston). It appears they may be uneven in their flow as no transfer pattern is visible on the right side, but that may be nothing at this point.


Any help is much appreciated. Thanks!
Is the piston at TDC? That wash pattern is correct, the transfers should force the fuel to the intake side.
 

TheWizzerd

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Is the piston at TDC? That wash pattern is correct, the transfers should force the fuel to the intake side.
No, not all the way at TDC in the pic. The piston is pretty much flush to the jug deck at TDC.

I understand the transfer wash is correct, and thats what you want.... toward the intake. What seems a bit odd is the streak straight from the intake to the exhaust with not much else in the way to the sides of that which I typically see. I understand there isnt a lot of time on it to let it really build up to tell also.

I am used to seeing a nice "mothman of point pleasant" pattern on the 2 stroke ultralight aircraft engines I am used to.

Was more curious if this is typical of the porting on these engines to create the "tongue" pattern, which I understand is not ideal.
 

weefek

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All I will say is these engines are not even remotely comparably to any type of engine used on an aircraft, regardless if it's an ultralight or not. They're not even as good as your proper chainsaw engine. Those engines are made my reputable companies with proper QC and engineering. These china girls are cheap knockoffs , at the best of times. I wish it weren't so, but at the same time paying $150 for an engine that's not quite up to snuff doesn't bother me all that much, if it works.

It works. Port timing, flow, etc are whatever they are, as long as it works. I mean hell just look at the matching of intake ports to intake mani and exhaust ports to your normal stock exhausts.... it's all terrible.

I have the OCD(ish) bug too which is why I bought a 2nd engine and completely rebuilt it, cleaned the whole thing, new bearings , seals, etc straight out of the box (still sitting on the shelf waiting for my original to detonate itself eventually). You gotta draw a line somewhere with these engines to be fair.

I have a feeling after running more the carbon / burn would show a different pattern.
 

TheWizzerd

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All I will say is these engines are not even remotely comparably to any type of engine used on an aircraft, regardless if it's an ultralight or not. They're not even as good as your proper chainsaw engine. Those engines are made my reputable companies with proper QC and engineering. These china girls are cheap knockoffs , at the best of times. I wish it weren't so, but at the same time paying $150 for an engine that's not quite up to snuff doesn't bother me all that much, if it works.

It works. Port timing, flow, etc are whatever they are, as long as it works. I mean hell just look at the matching of intake ports to intake mani and exhaust ports to your normal stock exhausts.... it's all terrible.

I have the OCD(ish) bug too which is why I bought a 2nd engine and completely rebuilt it, cleaned the whole thing, new bearings , seals, etc straight out of the box (still sitting on the shelf waiting for my original to detonate itself eventually). You gotta draw a line somewhere with these engines to be fair.

I have a feeling after running more the carbon / burn would show a different pattern.
Incorrect! They are more similar than you think. They are just 2 strokes. Of course some of the specifics differ, and "sometimes" more care is taken in the design and manufacture..... but none the less they are 2 strokes and all the operating principles are identical, and some of them can be every bit as craptastic as a china doll.

However, the typical ultralight 2 strokes are just scooter engines with an added re-drive. They are usually based pollini engines, and have little modification outside of the re-drive, and maybe some minor carb mods, mainly a priming circuit, and maybe additional low circuit orifice to prevent carb icing.

Ultralight engines are not actually aircraft engines. They are not deemed airworthy, or even called an aircraft engine by any "governing" body. They can be any engine you so choose to bolt on to the thing and are often simply ripped from scooters, snowmobiles, street bikes, lawn mowers, larger R/C airplane engines, or your single aunts 330cc personal massage device.

Actually, ultralight according to part 103 are not even aircraft. They are recreational vehicles. The FAA does not govern them, nor do they consider them aircraft. Nor are the people that fly them pilots, as they do not require a license.

There are some that are purpose built, mainly by Rotax, but for Part 103 ultralight use they are not aircraft engines, nor considered airworthy.

I have had many that are "purpose built", that are in just about every way just as crappy in the manufacturing domain as a china doll. Just as with the china dolls, that doesnt necessarily mean they are bad or unsuitable for the application. Despite rather crummy QC and manufacturing practices with china dolls, they are surprisingly decent and reliable. Thats the beauty of a 2 stroke. Simple enough to get away with crudeness.

Of course some are 4 strokes, but they are often too heavy to meet Part 103 and have adequate power. 2 strokes dominate the ultralight world.
 

weefek

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Wasn't disputing the operating principles. Like I said the quality control and port timing etc is sloppy from engine to engine. You'll never get a perfect engine. There have been guys on here and youtube chasing it for years. If that's what you're trying to do good luck to you sir.

From what I've seen, most scooters / snowmobiles / RC engines are actually much better quality than these china girls.

There's a big difference. Take a look at the Phantom 85 thread ALONE to see the major differences from jug to jug. I have experience with sled motors and there is absolutely no comparison in quality.

With these , you get what you get. Try and make it as best you can. But at the end of the day it all depends on what the s**tty mold made and what the 13 yr old chinese kid decided to make.

I work in the automotive industry and the tolerances / QC on these engines are basically make it and forget it. But most of them work. That's why you get so many random people here complaining about their engines failing or doing whatever.
 

weefek

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That being said I'd rather fly the wright brother's original airplane than ever trust one of these china girls on an ultralight.
 
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