What did I do wrong? Scored 490

[drf256]

Odd transfer. Hard to tell without the jug in my hand. Pics can be deceiving.

That is a rev limited saw. I built one. Very hard to tune because you’ll hit the limiter on a piss rev and think you are safe, and you won’t hear it being lean in the cut when the rpm drops below the limiter. I’m sure you eliminated the carb limiters as Echo’s tend to be very lean from the factory.

A bad port chamfer will cause vertical lines on the piston across the port width and generally nowhere else. Grooves a slug quickly. BTDT

You have transfer all over the place. I’d say debris in motor or lean condition and you need better chamfers either way. I use a builder case whenever possible for just this reason. No cylinder hits the saw until it’s fully done. If doing a saw with no possible builders case, the jug won’t touch the saw without a trip through the USC every single time.

Your port work looks very nice BTW.

 

[Duane(Pa)]

Don’t expect anything but more trouble if you don’t install a new ring. My son would say ”that’s garbage”

 

[Nutball]

BTDT? USC?

Maybe it was lean, I didn't hear much 4 stroking before each cut like I think I would. I'm certain I richened the carb before those cuts, and I did remove the limiters. It's just surprising that much damage happened after 2 minutes of use. At least I caught it early and it still got around 170psi after those cuts.

Yea, I decided on new rings too. I figured use the same rings since they might fit the scoring to get a better seal than new rings, but new should both wear down the scoring and wear into it better.

 

[redline4]

BTDT? USC?

Maybe it was lean, I didn't hear much 4 stroking before each cut like I think I would. I'm certain I richened the carb before those cuts, and I did remove the limiters. It's just surprising that much damage happened after 2 minutes of use. At least I caught it early and it still got around 170psi after those cuts.

Yea, I decided on new rings too. I figured use the same rings since they might fit the scoring to get a better seal than new rings, but new should both wear down the scoring and wear into it better.

BTDT=Been There Done That.
USC=Ultrasonic Cleaner

 

[Nutball]

Stock Echo transfer chamfer

 

[huskihl]

I figured use the same rings since they might fit the scoring to get a better seal than new rings, but new should both wear down the scoring and wear into it better.

There can't be anything on top of the plating that would wear into the new rings or help seal the old ones. It needs to be removed or it will just wear grooves into the piston.

Stock Echo transfer chamfer

View attachment 168032

Never seen them that sharp before. Although transfers aren't really wide enough for the ring to open into like an exhaust port

 

[Nutball]

I found a 3/32 flame tip diamond bit that makes chamfers a lot easier, it's still hard to polish small places. These transfers are super tiny in a 35mm bore. I couldn't hardly see my chamfers till I took pics. Not sure if I should go back and try Scotch bright?

 

[Nutball]

 

[dahmer]

From experience at work, many scotch brite are aluminum oxide, ANY of the pad that is left over can destroy an engine. By any part I mean even a single fiber. It got so bad at work because of idiots not thoroughly cleaning parts after using a scotch brite that management banned their use, called them “engine killers.”

 

[mettee]

Stock Echo transfer chamfer

View attachment 168032

Yeah way sharp.

On yours, if it were mine, I'd uniform the chamfers more. Still some areas that look like they would catch.

 

[mettee]

View attachment 168047 View attachment 168048

What is the weird mark on there

 

[Deets066]

So their trans are just like the outter plastics...

 

[Nutball]

So their trans are just like the outter plastics...

Gotta look sharp if they're gonna sell well

I used Scotch bright a lot on the 490 just experimenting with how smooth I could get the exhaust. I thought I cleaned it well though.

What about the 3000 grit woven pads? I saw them at lows next to the other fine grit papers. I almost thought it was cloth, but it looks like woven strips of 3000 grit paper strands.

 

[Deets066]

Gotta look sharp if they're gonna sell well

I used Scotch bright a lot on the 490 just experimenting with how smooth I could get the exhaust. I thought I cleaned it well though.

What about the 3000 grit woven pads? I saw them at lows next to the other fine grit papers. I almost thought it was cloth, but it looks like woven strips of 3000 grit paper strands.

Regardless of what you use it really needs cleaned well

 

[cus_deluxe]

I just use a little pink ball to chamfer ports when done, then lightly emory cloth in a split mandrel. Good to go.

 

[Terry Syd]

Take a look at a well worn cylinder and see how the rings have shaped the top of the port. You will notice that the wear is more pronounced in the MIDDLE of the port. That is because the ring tends to expand out into the middle of the port.

That shape is the shape you want for your chamfer/bevel.

I've notice some people will use a porting tool, like a stone ball to put on the chamfer. They move the ball across the port edge until they STOP at the edge and then go back the other way and STOP again. The resulting chamfer is deeper at the edges than in the center - exactly the opposite of what is desired.

I just use a bit of emery cloth on the end of my finger to put a chamfer in the center of the port that reduces in depth as it approaches the edge of the port.

That damage to the rings AND piston looks like it was from dirt/grit left in the building process.

 

[tickbitintn]

I'd say some grit in there from somewhere. I had a 350 look exactly like that after a muffler mod on one of my first project saws. Missed just a spec or two of debris when cleaning out the muffler.

 

[tickbitintn]

That being said; a good bottom end flush out, a good cleaning on said cyl (after a quick run through with a ball hone; to clean, hone and chamfer ports) and a new ring should make that as good as new. That is as long as the cyl is not gouged but just marked up a bit.

From the pictures the damage doesn't look bad. Scoring looks like its on the surface and probably wouldn't affect running condition or compression much. That is from the pics, if the cyl was in my hand my opinion may be different.

 

[Nutball]

I've got around 3 tanks through it now after polishing the cylinder and installing new rings. I'm just going to see what happens. It's been running great, and my friends like it a lot. It's doing 9-12 seconds in ~18" maple with an 8t .325 rim. The cylinder doesn't appear any worse, but it's hard to tell if it's better. Compression doesn't feel as strong as it did before scoring, but it sure runs strong. The pictures didn't show how bad the scoring was/still is. I'm concerned it went nearly deeper than the plating, but I'm not sure.

 

[Terry Syd]

In these kind of situations, I wonder what would be the most deposit forming oil to use would be. If the scoring grooves tended to fill with carbon, then after running a bit there would be less blow-by.

Then put in a fresh set of rings and probably most of the compression could come back.

EDIT: Probably run it on castor oil for a while.