Echo CS-590 wont idle, scoring on new piston. Air Leak?

[freebilly]

I recently purchased a "lightly" used Echo CS-590 from an older couple (still had the security tag stuck to the bottom). I took it home and put fresh 50:1 in the tank and fired it up. It popped right away but would only stay running past half throttle. Anything less than half and it would stall hard. When it died, I would have to reapply choke to fire it up again. Assuming the low jet was plugged, I cleaned the carb. It was spotless inside and diaphragms were soft, but I noticed the low speed needle had a very slight bend in it but didn't seem to affect the way it seated. Saw still only ran at WOT. Ended up pulling cylinder to reveal a piston that had deep scoring on the exhaust side and nearly melted rings, I assumed from running straight gas as these saws come with valve stops that don't allow them to be tuned lean. I was able to save the cylinder and after sanding with green scoth brite it only had very minor scoring below the exhaust port, all aluminum transfer was removed. The new OEM piston and rings slid into the cylinder smoothly with no snags. Saw was reassembled and fired up second pull. It was running much better now but still not idling and would only stay running in you held throttle past 50%. At WOT the saw 4-stroked appropriately. Backing the low needle out 3-4 turns seemed to allow the saw to idle. After running the saw in this condition for 1-2 minutes there is already scoring on the new piston. I'm thinking next step is pressure test? Assuming the saw was lean from an air leak for this small amount could that have scored the piston already? I'm hesitant to check for leaks with brake cleaner as it doesn't want to idle and I'm trying to avoid further piston damage. Attached is a photo of the new piston.

 

[RiverLogger]

Compression?

 

[irhunter]

IMO, there are really two kinds of saw repair people.

1. Someone who thinks they will replace fewer than two pistons in their entire lives.
2. Everyone else.

Type 1: you need to pay someone to P&V test your saw after every single new piston.

Type 2: right now, you need to buy/make/cobble together a P&V tester.

As to the OP: Welcome to AS! Yes, you need to P&V test the saw.

https://www.arboristsite.com/threads/show-us-your-pressure-vac-tester-and-block-off-plates.368677/

 

[James.Morris609]

Compression?

What about bottom end ? Did you check crank bearings see I'd there was any play when you had it apart. Also the market is flooded with these Echo 590s. They have been bought off liquidators on pallets of other things that have been returned to home depot. I mean if you rebuilt the top end and the same thing is going on. I don't think it's an air leak problem. I believe it's bottom end. That's just my opinion. This past season alone I've worked on over t0 590s that came off liquidation pallets. If you look on marketplace you tell me how many t90s and 4910s you see? I guarantee they were returned to home depot then a place like triangle liquidators buys all that stuff and the have auctions online you bid on these pallets full of anything that they had returned at that particular time. This is why you see so many 590s and smaller echos you do t see the commercial line of Echo unless it's a private owner. Because Home depot doesn't sell commercial Echo products.

 

[James.Morris609]

What about bottom end ? Did you check crank bearings see I'd there was any play when you had it apart. Also the market is flooded with these Echo 590s. They have been bought off liquidators on pallets of other things that have been returned to home depot. I mean if you rebuilt the top end and the same thing is going on. I don't think it's an air leak problem. I believe it's bottom end. That's just my opinion. This past season alone I've worked on over t0 590s that came off liquidation pallets. If you look on marketplace you tell me how many t90s and 4910s you see? I guarantee they were returned to home depot then a place like triangle liquidators buys all that stuff and the have auctions online you bid on these pallets full of anything that they had returned at that particular time. This is why you see so many 590s and smaller echos you do t see the commercial line of Echo unless it's a private owner. Because Home depot doesn't sell commercial Echo products.

Sorry for the misspelled words and numbers was typing fast

 

[huskihl]

Limiter caps are put in place by the EPA so that you cannot tune your saw excessively rich. Nothing to do with the manufacturer preventing you from tuning too lean. Chainsaws were around for 50 years before the EPA got involved and the manufacturer didn’t limit jet travel.

Most 590s are known to be tuned too lean from the factory and won’t allow the jets to open far enough. If a saw like that is run when it’s cold outside, it ends up with scoring on the piston like in your pictures

 

[freebilly]

What about bottom end ? Did you check crank bearings see I'd there was any play when you had it apart. Also the market is flooded with these Echo 590s. They have been bought off liquidators on pallets of other things that have been returned to home depot. I mean if you rebuilt the top end and the same thing is going on. I don't think it's an air leak problem. I believe it's bottom end. That's just my opinion. This past season alone I've worked on over t0 590s that came off liquidation pallets. If you look on marketplace you tell me how many t90s and 4910s you see? I guarantee they were returned to home depot then a place like triangle liquidators buys all that stuff and the have auctions online you bid on these pallets full of anything that they had returned at that particular time. This is why you see so many 590s and smaller echos you do t see the commercial line of Echo unless it's a private owner. Because Home depot doesn't sell commercial Echo products.

This saw was purchased from an Echo dealer near the person I bought it from. She still had the slip from original purchase. The bottom end bearings were in good condition and had no excess play. I’m thinking air leak into the bottom end via crank seals? I’ve had many saws that still idle with bad crank bearings. This saw acts like it’s not getting any fuel below half throttle.

 

[freebilly]

Limiter caps are put in place by the EPA so that you cannot tune your saw excessively rich. Nothing to do with the manufacturer preventing you from tuning too lean. Chainsaws were around for 50 years before the EPA got involved and the manufacturer didn’t limit jet travel.

Most 590s are known to be tuned too lean from the factory and won’t allow the jets to open far enough. If a saw like that is run when it’s cold outside, it ends up with scoring on the piston like in your pictures

These saws have a hole in the high nozzle that allows fuel even when fully seated. The limiting caps were removed and the saw was tuned rich for break in. It was run for about 60 seconds and was 4 stroking appropriately at WOT at 12,250 rpm. This scoring occurred with both screws set at least 1.5 turns out

 

[freebilly]

Compression?

134 after the top end rebuild granted rings aren’t seated yet

 

[freebilly]

IMO, there are really two kinds of saw repair people.

1. Someone who thinks they will replace fewer than two pistons in their entire lives.
2. Everyone else.

Type 1: you need to pay someone to P&V test your saw after every single new piston.

Type 2: right now, you need to buy/make/cobble together a P&V tester.

As to the OP: Welcome to AS! Yes, you need to P&V test the saw.

https://www.arboristsite.com/threads/show-us-your-pressure-vac-tester-and-block-off-plates.368677

IMO, there are really two kinds of saw repair people.

1. Someone who thinks they will replace fewer than two pistons in their entire lives.
2. Everyone else.

Type 1: you need to pay someone to P&V test your saw after every single new piston.

Type 2: right now, you need to buy/make/cobble together a P&V tester.

As to the OP: Welcome to AS! Yes, you need to P&V test the saw.

https://www.arboristsite.com/threads/show-us-your-pressure-vac-tester-and-block-off-plates.368677/

IMO, there are really two kinds of saw repair people.

1. Someone who thinks they will replace fewer than two pistons in their entire lives.
2. Everyone else.

Type 1: you need to pay someone to P&V test your saw after every single new piston.

Type 2: right now, you need to buy/make/cobble together a P&V tester.

As to the OP: Welcome to AS! Yes, you need to P&V test the saw.

https://www.arboristsite.com/threads/show-us-your-pressure-vac-tester-and-block-off-plates.368677/

Thank you for a straight up answer. P/V test through the impulse line at 7psi resulted in approximately 5psi lost in 2 minutes. I will be digging further into the saw with soapy water tonight. Appreciate it

 

[huskihl]

These saws have a hole in the high nozzle that allows fuel even when fully seated. The limiting caps were removed and the saw was tuned rich for break in. It was run for about 60 seconds and was 4 stroking appropriately at WOT at 12,250 rpm. This scoring occurred with both screws set at least 1.5 turns out

If it was 4 stroking at 12,250, it wasn’t scored from an air leak.

 

[david newbie]

I had that happen to a new piston when the cylinder wall wasn't perfectly smooth after sanding. I think I did not and it enough. Seems to me ( a newbie!) that it shouldn't score that quickly from a minor air leak?

 

[ZeroJunk]

You can buy a new saw. Or, you can buy a used saw.
I'm thinking most members on this forum can take whatever and make it work.
And, there is the cost.
I'm thinking you got stuck from from an "older Couple"
Is what it it is.
Buy a new saw or learn. Like , what is the difference between what I am saving and a new saw.

 

[ZeroJunk]

BTW, people don't sell you a like new saw because it is like new. Hillbillian 101.

 

[freebilly]

If it was 4 stroking at 12,250, it wasn’t scored from an air leak.

I had that happen to a new piston when the cylinder wall wasn't perfectly smooth after sanding. I think I did not and it enough. Seems to me ( a newbie!) that it shouldn't score that quickly from a minor air leak?

That was my same thought. I sanded for almost 2 hours with green scotch brite until I couldn’t any high spots with a microscope or feel anything with my finger nail. But I agree it doesn’t seem likely running lean caused this damage this quickly. Going to flush the bottom end to remove debris and try again once i check seals and replace the carb low needle

 

[freebilly]

BTW, people don't sell you a like new saw because it is like new. Hillbillian 101.

they do when they’re almost 90 years old and their kids bought them a saw they can’t handle. Some people just need to downsize. I paid 30$ knowing there could be potential issues. I’m not upset about the deal, simply giving background information and looking for a solution.

 

[freebilly]

You can buy a new saw. Or, you can buy a used saw.
I'm thinking most members on this forum can take whatever and make it work.
And, there is the cost.
I'm thinking you got stuck from from an "older Couple"
Is what it it is.
Buy a new saw or learn. Like , what is the difference between what I am saving and a new saw.

I posted to try and learn? Isn’t that the point of this entire site? I have 25+ running saws. I’m posting to diagnose an issue that I haven’t encountered before.

 

[ZeroJunk]

I posted to try and learn? Isn’t that the point of this entire site? I have 25+ running saws. I’m posting to diagnose an issue that I haven’t encountered before.

Four stroking at 12,250 like huskihl said doesn't indicate an air leak. If it was turning that RPM because that was all the fuel it was getting it would die in the wood instantly.

The low idle fuel is always there and added to the overall WOT fuel level. So if the carb has no fuel running at idle that could have been enough to put it over the edge if the limiters had it lean to begin with.

 

[freebilly]

Four stroking at 12,250 like huskihl said doesn't indicate an air leak. If it was turning that RPM because that was all the fuel it was getting it would die in the wood instantly.

The low idle fuel is always there and added to the overall WOT fuel level. So if the carb has no fuel running at idle that could have been enough to put it over the edge if the limiters had it lean to begin with.

Running out of ideas. She’s air tight now and still won’t idle. Dies hard anywhere below half throttle. Carb kit, new piston, new seals. Only thing left is the low needle with the ever so slight bend in it. Maybe enough that the saw isn’t getting fuel on the low end?

 

[ihookem]

Freebilly, if you only paid 30 bucks for the saw , you are in good shape, except for the time and some other money you put in it. I would buy a new saw .. Keep the bar cause that will wear out someday so you already have a spare. The loop is worth 20 bucks.. You also have new spare parts .. I see it this way cause I hate working on tools though.