Acceptable compression ?

[Jjd56]

Recently resurrected my Sachs-Dolmar 120 Super with help from this forum and wondering what these had for compression when new and what would be the threshold for a top end refresh/replacement. I got 134 psi when I measured with some light oil in the cylinder (since it had been sitting for a few years). It runs well as is and I have no reason to suspect there is a problem, but I am curious.

 

[Marshy]

I think you answered your own question... if it runs well then I wouldn't worry about it. About 135 is plenty for a healthy running saw.

 

[jltrent]

Those gauges are not alwasy 100% right...Usually if they have 135 a new set of good quality rings will boost it upwards tp 150+ if the piston skirt is not worn to bad.

 

[Jjd56]

I think you answered your own question...

Good to know. I won’t be making any heavy demands of the saw so it it ain’t broke I ain’t gonna fix it.

 

[Brent Nowell]

Length and type of hose can affect the numbers, I learned that just recently. Point being your numbers compared to others doesn’t mean much. If you think your too low, maybe you actually are not.

 

[Jjd56]

[QUOTE="jltrent, post: Usually if they have 135 a new set of good quality rings will boost it upwards tp 150+ if the piston skirt is not worn to bad.[/QUOTE]

thanks for that.
So there is potential for more power if needed.
Still would like to know the numbers when this saw was new....

 

[Jjd56]

Length and type of hose can affect the numbers, I learned that just recently. Point being your numbers compared to others doesn’t mean much. If you think your too low, maybe you actually are not.

Did not consider the hose as a factor! Mine is rubber, about a foot long and fairly stiff, no braiding on the outside. My guess would be that I’m over 135 at this point.
Based on a prior reply, I’m not going to touch it.
Thanks.

 

[Brent Nowell]

The way I understand it is that they are such small displacements every little factor affects the number. I mean look at the volume of a rubber hose with an ID of 1/4” and 12” long that comes out to almost 10ccs right there. That’s a fifth of most saw engine sizes

 

[old guy]

If your tester does not have a schrader valve in the end of the hose that screws into the cyl., your reading is low.

 

[dmb2613]

people are hung upon compression, if you can pick the saw up by the rope and it does not drop fast it should be ok

 

[lostone]

I just went through this with a saw build. I have an OTC that was reading 122, ring gap is tight, schrader valve at end of hose. I changed the schrader valve and still the same reading then bought another tester (cheap one) with a shorter hose and schrader at end of hose, same reading. The only thing I believe that is affecting my readings is altitude, taking 4% for every 1K puts me at about 140 at sea level. I know this build wont have a lot of compression since it's .038 on squish but if I gain another 10-15lbs as the rings seat it wont be bad. Saw starts easily and runs fine, seems to have plenty of power so far for a new build.

 

[old guy]

people are hung upon compression, if you can pick the saw up by the rope and it does not drop fast it should be ok

Just ok is not good enough.

 

[Brent Nowell]

Just ok is not good enough.

Well if it starts, and runs and doesn’t miss then I’d say you’d have to agree with that?

 

[old guy]

Well if it starts, and runs and doesn’t miss then I’d say you’d have to agree with that?

That's ok for my cars, but my saws gotta be all they can be.
I think nothing of tearing a saw down 3 times in a week just to change something.

 

[Jjd56]

So there's no doubt a saw, or car, low on compression will still run but it's the numbers that matter when evaluating its condition compared to new.
AND the equipment used to test needs to be good.
Does anyone with Sachs-Dolmar saw maintenance experience know what the compression on a new 1985-6ish 120 Super would have been?
I would like to know but it may be a spec lost to history where this saw is concerned.

 

[joe25DA]

So there's no doubt a saw, or car, low on compression will still run but it's the numbers that matter when evaluating its condition compared to new.
AND the equipment used to test needs to be good.
Does anyone with Sachs-Dolmar saw maintenance experience know what the compression on a new 1985-6ish 120 Super would have been?
I would like to know but it may be a spec lost to history where this saw is concerned.

160-175 psi
My Makita DCS 6800i (same saw in green) tested right around 170, saw was well used but internals were excellent. If it runs good I wouldn’t sweat it.
Fact
DCS stands for Dolmar Chain Saw

 

[pioneerguy600]

So there's no doubt a saw, or car, low on compression will still run but it's the numbers that matter when evaluating its condition compared to new.
AND the equipment used to test needs to be good.
Does anyone with Sachs-Dolmar saw maintenance experience know what the compression on a new 1985-6ish 120 Super would have been?
I would like to know but it may be a spec lost to history where this saw is concerned.

My brand new 120S bought in August of 1985 would register 170 on my Snap On gauge and 173 on my Tuffy brand gauge. My dads 116SI would reach 175 when cold, it had some hours on it by the time I tried his.

 

[Deleted member 117362]

My 372 is at 210. 262 was 190, rebuilt a 55 no run time 180. Most stock Husqvarna are around 150. Results may vary.

 

[anlrolfe]

How many hours do you have on the new rings? I suspect they will settle in and compression will go up once it gets broken in a bit. Feed it quality fuel and oil, tune it a little thick and run it. Check it again once you get a good stretch of run time under its belt and I'd suspect it will test better. Don't get hung up on a number if it's running good. That's the real test.

 

[blsnelling]

The way I understand it is that they are such small displacements every little factor affects the number. I mean look at the volume of a rubber hose with an ID of 1/4” and 12” long that comes out to almost 10ccs right there. That’s a fifth of most saw engine sizes

Not really. That's only a factor of there isn't a Schrader valve at the tip. A long hose only means you have to pull more times.