New piston rings?

[t_andersen]

I have a Stihl 064 with a compression measured to be 125 psi. From what I have been reading here, that's on the low side. Does that mean that I should change piston rings as a sort of preventive maintenance?
Thanks
Tom

 

[DanManofStihl]

rings

if you change the rings you will also need a new jug to go with it or you will just fry those rings.

 

[Lawn Masters]

Thats assuming the jug has scoring on the walls of it, if the rings are just worn, but the jug is fine, I think there should be no problem.

 

[fishhuntcutwood]

I agree with oldsaw. Rings wear through normal use. When they wear, replace them. Now if they're damaged, then yeah, that's a different story. But with 125 lbs, it sounds like normal wear to me.

Jeff

 

[ron in sc]

Does that mean that I should change piston rings as a sort of preventive maintenance?

Is the saw real hard to start?

Does it lose power during use when it gets hot?

Does it practically die when it gets hot with use?


I had the three symptoms above and new rings made my saw run like it was new.

 

[sedanman]

"if you change the rings you will also need a new jug to go with it or you will just fry those rings."

How so? Do you have replace the engine block every time you re-ring an automobile? Re-ring it and let it fly.

 

[t_andersen]

Is the saw real hard to start?

-Yes, it takes about 10 pulls!

Does it lose power during use when it gets hot?

-Not at all!

Does it practically die when it gets hot with use?

-Not at all!

Rgds Tom

 

[stihltech]

rings

Your problem is not rings.

 

[DanManofStihl]

rings

When I had talked to my auto tech teacher awhil ago he said if you did not hone it out or replace the jug that it would just fry them. My local dealer said the same thing but I believe my tech teacher more because I know they just wanted to sell me a new jug.

 

[Al Smith]

I've replaced several sets of rings,without new cylinders and never have had any complaints about them.Now that 125 lb compression test,if it cuts good and starts good,don't worry about it.The old saying"if it aint broke,don't fix it"

 

[Lawn Masters]

As I said earlier, if the cylinder walls are not scored, or damaged in any way, then just stick new rings in it. anyone that tells you to replace a jug that is not damaged when doing rings IMO shouldnt be speaking.

 

[whatsnext]

What's the ring gap when you fit them into the cylinder? I'd leave 125 psi alone though if it were me.
John......

 

[ron in sc]

if the cylinder walls are not scored, or damaged in any way, then just stick new rings in it.

That's all I did. And it cured the 3 problems I mentioned above.

 

[njforestfire]

ron - just out of curiousity, did you re-check the compression? Would be interesting to see how much of a change it made. Do you have numbers before and after?

 

[Chris11]

Hello,

as a matter of fact, rings wear out. They loose a bit tension. For this reason in race engines rings get replaced regularly. It gives only 1%+ performance there but this may make the difference. If the jug looks good there is no reason not to change the rings and break them newly in.
Very little risk and little money involved. Since the Jug has to come off anyway there is the perfect time to inspect it.

Christian

 

[ErrolC]

A good source to end the debate..go to your local motor cycle shop and ask to speak to someone up with the play on MX 2 strokes..don't be surprized to hear the top riders replace their rings (only) each meeting or so to keep the cylinder "fresh". You can't hone the "jugs" unless they are from an old saw with iron or steel cylinder inserts. modern saws from about the early 70s on have been using either chrome or Nikasil electro plated coating direct on the ali block casting for 2 reasons..being hard material, it lasts longer within defined tollerances..more importantly there is netter heat transfer from the piston - through the rings - to the cooling cylinder block. When the cylinder bore starts to score/scratch the contact between the cylinder and the rings diminishes and the rings (& piston) run hotter, leading to further wear and scoring..2 strokes unlike 4 strokes, have their rings pinned so they can't rotate around the piston (because thre ring end could pop into a port and jam/seize), by replacing the rings while the bore is still clean (score free)..because the rings are pinned, they tend to wear differently adjacent to respective ports and go out of round..new rings (for all 2 strokes these days) are finely ground (round)..by keeping you saws rings fresh..they will tend to wear your bore "round" and help it last a whole lot longer. Go speak to the local hot motorX 2 stroke mechanic and make up your own mind...
To check if the rings are sagging and losing tention, add a squirt of oil down the plug hole after test the compression, and compare the 2 readings (there shouldn't be more than 10psi difference with good rings)..
If you do, do a ring replacement..get someone to tickle up the porting a little..don't change the port shapes or size (especially at the cylinder wall, just smooth out the casting and match the cylinder port passage, to the crank case passage unless you really know what you are doing...you'll be amazed at the difference

 

[Gypo Logger]

I've replaced rings as a matter of course on my 385. Wether it needed it or not I don't know cause I didn't have a compression tester. Anyway, I kept the old ring in the bottom and put a new ring in the top. The saw really got up and talked though. I learned this trick off Ken Dunn who is now reinstated after I got him and Rotax Robert and Dennis Harvey banned. Even though I made them overnight sensations. LOL
John

 

[ron in sc]

did you re-check the compression?

John,
I did not check the compression, prior or after. But when I say it was real hard to start before I meant nearly impossible.

I did measure the new and old rings and the difference was very slight.

 

[ozflea]

I'm sure the 064 would have a chrome bore and as these bores cannot be honed or rebored it will leave you little option as regards re-ringing the saw.
If it had a Nikasil bore you could hone it same as a steel bore.
Just fit a new set of rings and be done with it as thats all the bore on a 064 will allow.

Mc Bob.

 

[TimberPig]

When I had talked to my auto tech teacher awhil ago he said if you did not hone it out or replace the jug that it would just fry them.

The problem is that the rings will often not seat properly if you don't break the glaze from the old rings. Normally a little oven cleaner and a Scothcbrite pad will clean the bore up enough to allow new rings to seat properly. The new rings won't actually fry, but they won't seat in properly, which I assume is what he is meaning with the term "fry".