Compression for the Husqvarna 350 Domed Piston?

[dsell]

Maybe my compression tester is going bad, but I just read 110 PSI on a 350 with the domed piston. After tear down, there isn't anything obviously wrong with the bore or piston like you would expect. So my question, what are you guys reading for compression on this engine?

 

[sefh3]

You might just need to replace the rings in it. Do you have another saw to compair it to?

 

[w8ye]

The 350 arrives from the factory with a dished piston though some people installed a flat topped piston from a 353XP in them.

A Domed piston would have to be a homemade field fabrication?

Some people take a cut around the edge of the piston in the squish area and then lower the cylinder which may create a raised center in what would normally have been a flat top piston?

 

[dsell]

The 350 arrives from the factory with a dished piston though some people installed a flat topped piston from a 353XP in them.

A Domed piston would have to be a homemade field fabrication?

Some people take a cut around the edge of the piston in the squish area and then lower the cylinder which may create a raised center in what would normally have been a flat top piston?

Sorry, I meant dished.

 

[dsell]

You might just need to replace the rings in it. Do you have another saw to compair it to?

I did, but I tore it down without thinking and I didn't test the compression. However, I'm putting that P/C on another case so I will test it this week.

 

[SawTroll]

The 350 arrives from the factory with a dished piston though some people installed a flat topped piston from a 353XP in them.

A Domed piston would have to be a homemade field fabrication?

Some people take a cut around the edge of the piston in the squish area and then lower the cylinder which may create a raised center in what would normally have been a flat top piston?

Delete that "XP" - but otherwise you are right.

 

[dsell]

View attachment 252147View attachment 252148View attachment 252149View attachment 252150View attachment 252151

This is the P/C blowing 110.

 

[3000 FPS]

Starting to accumulate some carbon on it. It is possible the ring was not sealing well because of some carbon. I would clean the piston well clean he ring groove well and put a new ring in and see what it does.

 

[TK]

A lot of the 350's I have tested compression on have come in between 110-120psi in almost new to quite used conditions. I'm not sure why the readings come in in this range but they do. Nothing wrong with the saw.

 

[dsell]

A lot of the 350's I have tested compression on have come in between 110-120psi in almost new to quite used conditions. I'm not sure why the readings come in in this range but they do. Nothing wrong with the saw.

Thanks. That's what I was wondering.

 

[3000 FPS]

A lot of the 350's I have tested compression on have come in between 110-120psi in almost new to quite used conditions. I'm not sure why the readings come in in this range but they do. Nothing wrong with the saw.

Wow if that is normal I do not know if I would want one those. It must be hurting for torque when put into wood or leaned on alittle. Even my little junk weed eaters and leaf blowers have 130 PSI.

 

[dsell]

It's strange because the pull rope seems higher than 110. That's why I questioned my gauge.

 

[UK Rich]

I have a UK spec 350. It doesn't have a dished piston, it's flat. It doesn't have removable transfer covers, they're part of the jug. It is an open port though. I think it has a different exhaust? Would I be wrong in thinking open ports generally knock out a slightly lower C/R than closed port?

My 350 however, is pushing out circa 160psi with no base gasket. Clearance is about 0.02something...

 

[TK]

Wow if that is normal I do not know if I would want one those. It must be hurting for torque when put into wood or leaned on alittle. Even my little junk weed eaters and leaf blowers have 130 PSI.

Look at the numbers on the new 550xps and the way they cut. No lack of torque there Compression is seemingly low on those as well (proper gauge or not) compared to others in its class. It's not always about compression, a lot has to do with the case, transfers, ports, carb, muffler, etc. That's why the 350's take so well to mods, especially compression increases. They cut really well when stock but take off when modded.

 

[TK]

I have a UK spec 350. It doesn't have a dished piston, it's flat. It doesn't have removable transfer covers, they're part of the jug. It is an open port though. I think it has a different exhaust? Would I be wrong in thinking open ports generally knock out a slightly lower C/R than closed port?

My 350 however, is pushing out circa 160psi with no base gasket. Clearance is about 0.02something...

You have an older model it sounds. No primer bulb, open port, smaller CC. They were flat tops. The newer ones with larger CC motors had dished pistons, closed port cylinders with removable covers, and a primer.

 

[3000 FPS]

Look at the numbers on the new 550xps and the way they cut. No lack of torque there Compression is seemingly low on those as well (proper gauge or not) compared to others in its class. It's not always about compression, a lot has to do with the case, transfers, ports, carb, muffler, etc. That's why the 350's take so well to mods, especially compression increases. They cut really well when stock but take off when modded.

I understand what your saying and do not disgree but, 110 PSI does not seem like much. I could understand 125 or 130 but 110 no thanks.

 

[SawTroll]

I have a UK spec 350. It doesn't have a dished piston, it's flat. It doesn't have removable transfer covers, they're part of the jug. It is an open port though. I think it has a different exhaust? Would I be wrong in thinking open ports generally knock out a slightly lower C/R than closed port?

My 350 however, is pushing out circa 160psi with no base gasket. Clearance is about 0.02something...

That's how the early ones, and likely all the Euro ones were + they had a 44mm bore and 49.4cc.

At some point, the EPA rules in the US made it nessesary to make them over 50cc, they used the 353 cylinder, but put a dished piston in there, to keep the performance (about) at the earlier level, and below the 353.
That easily explains a somewhat low compression - but 110psi... :msp_scared:

 

[TK]

I understand what your saying and do not disgree but, 110 PSI does not seem like much. I could understand 125 or 130 but 110 no thanks.

110 does seem low for sure. I would be looking for things like spitback from the carb and being a dog in the cut when pushing the saw before I start saying it needs a full rebuild I'd also be looking for another gauge to test it on just to be sure. I still can't believe how typically low the numbers seem when I test the ones that come into the shop.

 

[dsell]

Update, I had two 350's in the shop with dished pistons. I didn't test this one prior to tear down. It's back together now and runs like a champ. Cold pressure, 100 lbs., tested it 3 times. This piston and cylinder looked better than the one I posted pictures of that blew 110. I bet this one will increase after a few tanks. I've never had a saw that starts as easy. I'm surprised, most saws with 100 lbs you could pull on them all day long without a pop.

I just went out and confirmed my gauge. I recently bought a 55 and the owner showed a picture with a gauge connected at 135. I tested the 55 twice and it blew 135 each time.

 

[nmurph]

Are you pulling the rope until it stops climbing? Do you have other saws to test the gauge on?