371xp saw compression

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mtnwalker1

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I recently bought a used 371xp. The saw cuts fantastic and looks great. I tested the compression on it and it is only at 122 psi. I was thinking that it should be up around 140 psi. The jug and piston look great. Does anyone have any advice?
 
Maybe your testing method or gauge are off. If the piston and cylinder look good and it runs like you say, I wouldn't worry about it. IMO
 
Sure you didn't push the decomp button before you tested? I know it is a stupid question but it needs to be asked none the less. I would also suggest trying a different tester to double check your numbers.
 
Squish ?

Dunno about the 371, but 372's are not known for high compression in stock form.

Are you thinking the 372's need the base gasket dealt with to achieve adequate compression? My 372 only reads 129lbs.. Yet runs well and the the carb is an easy set.
 
I recently bought a used 371xp. The saw cuts fantastic and looks great. I tested the compression on it and it is only at 122 psi. I was thinking that it should be up around 140 psi. The jug and piston look great. Does anyone have any advice?

My advice is run it and love it... May I ask why you did a compression test? Just curious? Or having some problems...
 
Are you thinking the 372's need the base gasket dealt with to achieve adequate compression? My 372 only reads 129lbs.. Yet runs well and the the carb is an easy set.

That still is too low to be "normal", maybe you also need to take a closer look at your tester, and make sure it is equipped for the purpose? :msp_wink:
 
Pull the barrel and have a look.

The 371 runs only one ring so check and replace.

Leave out the base gasket.

It does sound like a comp gauge issue, but popping the lid on a recently purchased saw is not a bad idea and a chance to pick up a little performance.
 
That still is too low to be "normal", maybe you also need to take a closer look at your tester, and make sure it is equipped for the purpose? :msp_wink:

I know... And I know you, of all people, know the specs of these things. But I wouldn't be so sure of myself if I didn't come up with the same reading from both testers. Both had valves to keep pressure from bleeding off. What are you thinking the issue might be?
 
What really has me confused is that I bought a brand new Stihl 441 about a week before I bought this 371 and the 371 will out cut the 441 with this low of compression. Darned if I know.
 
Pull the barrel and have a look.

The 371 runs only one ring so check and replace.

Leave out the base gasket.

It does sound like a comp gauge issue, but popping the lid on a recently purchased saw is not a bad idea and a chance to pick up a little performance.

Do you use anything in it's place? Or are the machined surfaces precise enough to assure no leaks?
 
I recently bought a used 371xp. The saw cuts fantastic and looks great. I tested the compression on it and it is only at 122 psi. I was thinking that it should be up around 140 psi. The jug and piston look great. Does anyone have any advice?

I think a lot depend on you gauge and I would not pay too much attention to it. If the saw runs well, run it. If you have another saw, check its compression with the same gauge. My 371xp measures 130psi on my junk gauge. A 372xp checks in at 130psi as well. My pos ms361 choked out 140psi (who knew it actually had some lungs) and a schweet little dolmar 5100 can puff 145psi. Yup all stock.
 
Cent, you cheap buzzard (said in my best THALL dialect), you need to invest in a new gauge!!!!

walker,
does you gauge have the valve at the end of the hose that screws into the cylinder? you might also put an air compressor on the end to see if the readings are close. are you pulling the starter until the reading stops climbing? are you testing a cold engine?

130psi is low and you are losing performance. you can pull the rings and place them in the cylinder, above the exhaust port. use a square or something similar to get them in nice and square. then you can use a feeler gauge to check the ring-end gap. my experience with husky saws is that compression is usually around 150-160psi, though i don't have any time with a 371/372.

rings are cheap---about $6ea and relatively simple to change. i would verify that the gauge is accurate then replace the rings if it is.
 
Cent, you cheap buzzard (said in my best THALL dialect), you need to invest in a new gauge!!!!

walker,
does you gauge have the valve at the end of the hose that screws into the cylinder? you might also put an air compressor on the end to see if the readings are close. are you pulling the starter until the reading stops climbing? are you testing a cold engine?

130psi is low and you are losing performance. you can pull the rings and place them in the cylinder, above the exhaust port. use a square or something similar to get them in nice and square. then you can use a feeler gauge to check the ring-end gap. my experience with husky saws is that compression is usually around 150-160psi, though i don't have any time with a 371/372.

rings are cheap---about $6ea and relatively simple to change. i would verify that the gauge is accurate then replace the rings if it is.

What should the ring end gap measure on these particular saws?
 
I know... And I know you, of all people, know the specs of these things. But I wouldn't be so sure of myself if I didn't come up with the same reading from both testers. Both had valves to keep pressure from bleeding off. What are you thinking the issue might be?

This isn't about specs, but what compression they can be expected to have.

I don't remember what the correct type of adaptor/valve is called, but suspect the ones used here may not be the correct ones. That is a pretty common issue with comp testers, that is why I mentioned it.
 
they are probably ready for replacement with more than about 018-.020".

as mentioned bf, check that the decomp is closed and not leaking. you can check for leaks with a little soapy water.

As usual, your info is priceless... :rock:
 
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