piston/cylinder ?

[Ray Bennett]

I have a 290 with a scored piston that I am about to rebuild for my dad. Recently I read on this site that the Piston and cylinder have to be machined together. I thought I could just replace the piston. I would like to do that in this case because the cylinder has very little damage. Am I correct? Can I just put in a new piston? Or is the other post correct that I have to use a P/C . That were made for each other. I wish I could find the other post re read it. Maybe I misunderstood something or maybe some one was wrong. I also need to know where can I get muric acid. I have one little line on the cylinder that needs cleaned up.

 

[Bowtie]

Any hardware supply should have muriatic acid. you can replace the piston, rings, wrist pin and circlips without replacing the cylinder if the cylinder is useable. Be careful not to get the acid directly on the aluminum ports!

 

[Ray Bennett]

Any hardware supply should have muriatic acid. you can replace the piston, rings, wrist pin and circlips without replacing the cylinder if the cylinder is useable. Be careful not to get the acid directly on the aluminum ports!

Great, thanks, Much, That helps a lot. I will keep the acid off the aluminum.

 

[Jacob J.]

The muriatic acid most likely won't get rid of all of the residue, but most of it. The last remaining little bit can be gotten with emery cloth and WD-40 or liquid wrench. Sand it out with your fingers. Be careful of the open transfer port divider, it's thin and there's not much chrome on it.

 

[bcorradi]

You may be thinking of crankcase halves being machined together instead of the piston and cylinder. There is no problem putting a new piston in a used cylinder.

 

[Ray Bennett]

You may be thinking of crankcase halves being machined together instead of the piston and cylinder. There is no problem putting a new piston in a used cylinder.

I was wondering that as I was posting, Maybe im loosing my mind from so much time on AS. And so many oil threads.

 

[RiverRat2]

I was wondering that as I was posting, Maybe im loosing my mind from so much time on AS. And so many oil threads.

I hope You are not loosing your mind,,, cause I may be too,,,, It seems I remember I read that somewhere on this place too!!!!! that the P/C sets were matched as close as they can get them.....

And I think that transplanted Kiwi up in Washington state that said it!!!!!!

so it must be so,,,, LOL,,,


You have been given good advice by the gang,,, I have a couple of saws that I did just what you were told,,, One is and old 044 and that thing runs better than it did when it was new,,,,, but thats to be expected,,,,, with a dualport muffler and a carb adjust!!!! :greenchainsaw:

 

[andrethegiant70]

Hi, Ray, jut one word of caution on replacing the piston on this saw. Since it is a clamshell design, there is a significant "taper" to the crankase where it cones down in diamer beneath the bore....I drove myself absolutely buggy trying to hold the rings close enough to the piston to get them to slide in. On a flat-bottomed cylinder, its easy, but I found this one to require a LOT of patience. I got on AS and expressed my frustration to find that there were some guys who'd had a similar experience and a few that seemed get the piston in without too much trouble. Whatever your experience, don't use force, as rings are too expensive.

They DO make a ring retaining system for this very purpose.. I ended up making my own, it was crude but it worked. Andy (I think) told me about the Stihl version... my dealer was unaware of it.

Good luck, great little project!

 

[Lakeside53]

And I think that transplanted Kiwi up in Washington state that said it!!!!!!

so it must be so,,,, LOL,,,

Transplants? I have no stink'in transplants. I'm all OEM.

 

[Bowtie]

Hi, Ray, jut one word of caution on replacing the piston on this saw. Since it is a clamshell design, there is a significant "taper" to the crankase where it cones down in diamer beneath the bore....I drove myself absolutely buggy trying to hold the rings close enough to the piston to get them to slide in. On a flat-bottomed cylinder, its easy, but I found this one to require a LOT of patience. I got on AS and expressed my frustration to find that there were some guys who'd had a similar experience and a few that seemed get the piston in without too much trouble. Whatever your experience, don't use force, as rings are too expensive.

They DO make a ring retaining system for this very purpose.. I ended up making my own, it was crude but it worked. Andy (I think) told me about the Stihl version... my dealer was unaware of it.

Good luck, great little project!

I cut out my own ring compressor for that saw out of the plastic from a windshield wiper bottle. Trimmed it to where it fit right and they went in perfect on the second try.

 

[Ray Bennett]

Hi, Ray, jut one word of caution on replacing the piston on this saw. Since it is a clamshell design, there is a significant "taper" to the crankase where it cones down in diamer beneath the bore....I drove myself absolutely buggy trying to hold the rings close enough to the piston to get them to slide in. On a flat-bottomed cylinder, its easy, but I found this one to require a LOT of patience. I got on AS and expressed my frustration to find that there were some guys who'd had a similar experience and a few that seemed get the piston in without too much trouble. Whatever your experience, don't use force, as rings are too expensive.

They DO make a ring retaining system for this very purpose.. I ended up making my own, it was crude but it worked. Andy (I think) told me about the Stihl version... my dealer was unaware of it.

Good luck, great little project!

Great info , thanks much I will take my time and if my ring compressor does not work I will try Bowtie's method

 

[bcorradi]

Transplants? I have no stink'in transplants. I'm all OEM.

OEM = Old Expired Man? j/k

 

[Lakeside53]

or...

Older
Experienced
Maniac

 

[bcorradi]

Hey that works too....lol

 

[Airecon]

I have a question about P&C's, I hope you don't mind me asking here. I use to read in dirt bike mags that to properly determine wear on a P&C you mic them. I don't read about you guys doing that with saws. Then I think some of the MX racers ( with chrome bores) may have just replaced the rings and then piston after so many races. So how do you guys tell if a piston or cylinder is worn past limits? Can you pretty well tell by just looking? On average how many re-rings, piston changes can you do before the chrome cyl is shot? On my dirt bike I took it apart and carried the P&C ( steel bore) to the shop and they mic-ed it. The piston was shot, but cylinder was ok.

What about ring end gap do you guys check that too? When I replaced my dirt bike piston I just put the rings on and put it back together- so far so good.

 

[Lakeside53]

Good questions...

Unlike a dirt bike, a decent pro saw cylinder has a life measured in low thousands of hours... So generally if it's not scored, it's o.k. A second re-ring/piston to end of life means you have been cutting for 4000-5000+ hours... so the rest of the saw is pretty much dead by then.

You can try measuring the bore, but you'll generally only see 10ths (inch) of wear and it's not worth doing. If it looks o.k., new rings and maybe piston.

OEM Rings come pregapped. I see 3 -6 thou per inch of bore.

Piston skirt wear.. Subjective, and you generally hear it first (slap). I like to see less then 0.08mm taper on a 50mm pistion..., but that's me. If the pisiton machining marks are worn off, that's a good indicator it's getting there.

 

[SawTroll]

I hope You are not loosing your mind,,, cause I may be too,,,, It seems I remember I read that somewhere on this place too!!!!! that the P/C sets were matched as close as they can get them.....

And I think that transplanted Kiwi up in Washington state that said it!!!!!!

so it must be so,,,, LOL,,, .....

I hardly believe that he has posted that......

 

[Lakeside53]

RR2's o.k... mostly... He just gets some bad influence from Mow.:greenchainsaw:

 

[Ray Bennett]

Good questions...

Unlike a dirt bike, a decent pro saw cylinder has a life measured in low thousands of hours... So generally if it's not scored, it's o.k. A second re-ring/piston to end of life means you have been cutting for 4000-5000+ hours... so the rest of the saw is pretty much dead by then.

You can try measuring the bore, but you'll generally only see 10ths (inch) of wear and it's not worth doing. If it looks o.k., new rings and maybe piston.

OEM Rings come pregapped. I see 3 -6 thou per inch of bore.

Piston skirt wear.. Subjective, and you generally hear it first (slap). I like to see less then 0.08mm taper on a 50mm pistion..., but that's me. If the pisiton machining marks are worn off, that's a good indicator it's getting there.

What does piston slap sound like and when do you hear it? All the time? Wide open throttle. Idle?

 

[Lakeside53]

Usually at idle and when you are pulling it over. You can also hear it by just turning the flywheel back and forth by hand around TDC/BDC.

Increased spitback though the carb is an indicator of a worn piston.