When do you replace rings?

[Ray Bennett]

I have an older saw that is running strong but I noticed the compression dropping. On occasion I check compression by holding my saws up by the pull cord. My 044 slowly works its self to the ground. A compression test showed a little over 130. Even my old J-red's have around 150 compression. I looked at the piston and there is no scoring but I can hear a little pressure leak by until the second ring makes full contact when I am slowly turning the motor with the muffler cover off.

So my question is When should I change the rings? Is there a compression number you wait to drop to? Do you wait for performance do drop off. Or what is the deciding factor? This saw must have lost a little but it still out cuts all my other saws except my 660 so it surprised me that my numbers were so low.

 

[RiverRat2]

YES!!!!!!! Change them!!!!!

 

[RED-85-Z51]

What kind of tester did you use? Hose should be as short as possible, and have a Schrader valve on the tip.

Did you hold the throttle wide open, choke OFF, while pulling, and pull until it stopped climbing?


130 isnt totally worn out, but it isnt even close to new either. Id change em if your tester is the proper one.

 

[Lakeside53]

It doesn't matter how long the hose is if if the schrader is at the tip, and whether you hold the throttle open or not.

Less then 140 - time for something... bigger saws can get away with a little less. Most modern saws run around 150 mid life, 160-170 new.

130 is junk...

 

[Ray Bennett]

It doesn't matter how long the hose is if if the schrader is at the tip, and whether you hold the throttle open or not.

Less then 140 - time for something... bigger saws can get away with a little less. Most modern saws run around 150 mid life, 160-170 new.

130 is junk...

Ok, Would you recomend doing anyting else to the motor while im in there? This is the saw I was considering putting the big bore on anyway. Am I doing damage by using a saw that is low on compression? The saw is still ripping thru 20 inch oak without bogging down.

For what it is worth my tester is a craftsman with about a 10 or 12 inch hose, all my other saws test in the 150's with the same guage. The release valve is near the guage.

 

[RED-85-Z51]

Ok, Would you recomend doing anyting else to the motor while im in there? This is the saw I was considering putting the big bore on anyway. Am I doing damage by using a saw that is low on compression? The saw is still ripping thru 20 inch oak without bogging down.

For what it is worth my tester is a craftsman with about a 10 or 12 inch hose, all my other saws test in the 150's with the same guage. The release valve is near the guage.

Ive got one of those, it always gives me low readings when used on 2 strokes and very small 4 strokes. On bigger engines, and electric start things, it seems to be fine.

Lakeside, yall dont hold the throttle open, and use a short hose tester at your shop? That's odd, it's SOP where I work.

 

[Lakeside53]

It doesns't matter where the release is - it just need a valve at the tip.

Other stuff? na.. just a very light hone. Check your piston though - most need to be replaced when the rings are shot -too much taper. If your piston is polished on the skirt, replace it.

 

[Lakeside53]

Lakeside, yall dont hold the throttle open, and use a short hose tester at your shop? That's odd, it's SOP where I work.

What does the length of the hose have to do with it other than the number of times you need to pull to pump it up?

 

[RED-85-Z51]

What does the length of the hose have to do with it other than the number of times you need to pull to pump it up?

We feel like the air in the long hose creates a slight cushioning effect, and with a small displacement, the results are skewed.

Also, As per an Echo survice Bulletin "Compression testers should have no hose, or as short a hose as possible to attain accurate readings"

Like I said though, I was using my personal long hose tester at work, and I was finding that alot of stuff was coming up at the low end of the spectrum. My boss gave me a new Tester with a 1" hose, and immediatly the readings on everything came up to a more realistic level. MY tester was working perfectly, as I tested it by using it on a mower engine, then using the short tester, and the readings were the same.

 

[Ray Bennett]

Ive got one of those, it always gives me low readings when used on 2 strokes and very small 4 strokes. On bigger engines, and electric start things, it seems to be fine.

Lakeside, yall dont hold the throttle open, and use a short hose tester at your shop? That's odd, it's SOP where I work.

Funny you should say that cause I have never had a saw test over 155 with my craftsman guage no matter how new. When I got the low test on my guage I borowed a different guage and got around 140 which may expalin why the saw is still running really good.

Also Am I doing more damage by running a saw as the compression drops?

 

[RED-85-Z51]

Funny you should say that cause I have never had a saw test over 155 with my craftsman guage no matter how new. When I got the low test on my guage I borowed a different guage and got around 140 which may expalin why the saw is still running really good.

Also Am I doing more damage by running a saw as the compression drops?

If they are really bad, the searing hot burning gasses can escape past the rings, and burn down the side of the piston. Usually you see a darkened skirt when this is the case. Sometimes the 2nd ring catches the blow by, and the top of the piston, and the gap between the 2 rings wil lbe brown, but not below the 2nd ring. Until the 2nd ring goes, at which point it can cut into the piston like a torch, and actually burn out the piston BEHIND THE RING, and into the case, or just burn the ring, and burn down the skirt, eventually through it, and into the case.

This is an extreme though, takes a very long time, and really bad rings.

 

[Lakeside53]

Also Am I doing more damage by running a saw as the compression drops?

Lower compression is lower Hp... Blow-by can put a lot of junk in your crankcase. At some point around 125 will get hard to start... .

 

[Ray Bennett]

thanks for the info guys

 

[gonecountry]

Not to hijack the thread, but about the schrader valves.

what do you mean by "schrader valve at tip" ? you dont mean at the tip that screws into the sparkplug hole do you? Because the compression testers I use at work dont have them, or is this something to use for 2 stroke?


Educate me please

 

[RED-85-Z51]

Not to hijack the thread, but about the schrader valves.

what do you mean by "schrader valve at tip" ? you dont mean at the tip that screws into the sparkplug hole do you? Because the compression testers I use at work dont have them, or is this something to use for 2 stroke?


Educate me please

Yes, the proper testers have a schrader valve built into the tip tht goes into the plug hole. It lets air in, but not out.

 

[Trigger-Time]

Not to hijack the thread, but about the schrader valves.

what do you mean by "schrader valve at tip" ? you dont mean at the tip that screws into the sparkplug hole do you? Because the compression testers I use at work dont have them, or is this something to use for 2 stroke?


Educate me please

Think of it as a big valve stem, like on you car tire, Schrader valve on mine
has a valve core just like one on a tire, same as on a tire the valve is one
way valve......air in but not out.

 

[gonecountry]

Think of it as a big valve stem, like on you car tire, Schrader valve on mine
has a valve core just like one a tire, same as on a tire the valve is one
way valve......air in but not out.

Thanks, but I understand what they mean by at the tip now. I wasn't sure from the first explanation thats why I asked. Because the release is sort of a schrader "type" valve. The set in the shop is an old SnapOn set so they were proabably supposed to have cores in them. But 20 years of techs ahead of me no doubt lost them. Shop tools are always mistreated.

 

[RED-85-Z51]

Thanks, but I understand what they mean by at the tip now. I wasn't sure from the first explanation thats why I asked. Because the release is sort of a schrader "type" valve. The set in the shop is an old SnapOn set so they were proabably supposed to have cores in them. But 20 years of techs ahead of me no doubt lost them. Shop tools are always mistreated.

We replace our Gauges with new ones quite often, at least a couple times a year. It's good practice, and it's always good to know you are getting an honest reading.

I dont have to sit there and say.."100psi, thats close to the cutoff, I wonder if it's the gauge"...ya know?

 

[gonecountry]

Yes, I'm sure replacing them often is good practice but now days in a auto dealership we almost never use them, they seem to be most commonly used is small gas. The one in the shop might get brought out 3-4 times a year now in a shop with 13 techs. But only rarely do we get problems that require a check. I used a compression gauge more when I was taking automotive in trade school than I have in the last 7 years. Infact now that I'm thinking about it i better check to see if it is there, I may have just not noticed it.

 

[RED-85-Z51]

Yes, I'm sure replacing them often is good practice but now days in a auto dealership we almost never use them, they seem to be most commonly used is small gas. The one in the shop might get brought out 3-4 times a year now in a shop with 13 techs. But only rarely do we get problems that require a check. I used a compression gauge more when I was taking automotive in trade school than I have in the last 7 years. Infact now that I'm thinking about it i better check to see if it is there, I may have just not noticed it.

On a busy day, Ill use mine 7+ times, easily.

On a slow day, 2-3 times.

If a 2 stroke anything comes in with any type of running problem, pull the plug, and do a compression test. If it fails miserably, it's toast.

If it is marginal, peer down the plug hole, if it looks bad, toast. If you dont see obvious damage, pull the muffler.

If a Briggs OHV engine starts hard, or slowly, compression test will tell you if the valves need adjusting to make the compression release work again.