Pressure test help.

[Mgage09]

I have never had an issue pressure or vac testing a saw with a decompression valve until now. I have never plugged a decompression valve hole to pressure test a chainsaw…. Well currently I’m working on a 3120 xp. I have been through two Oem decompression valves. Neither would hold pressure. I get a slight leak out of the holes in the valve. Just looking to hear from some more experienced builders on what the general practice is…. Plug them for the test? Put them in knowing you’re leaking? Any help is greatly appreciated. I put a call in with my parts supplier. They’re going to contact Husqvarna directly.

 

[ballisticdoughnut]

Plug the decomp and do pressure/vac test again. If you know it’s leaking eliminate the leak. Don’t really need a decomp valve on the 3120 anyway.

 

[Mgage09]

Thank you very much for getting back to me. I just watched some you tube videos. I see Matt Olsen and Jon from custom saws both plug their decompression valve holes for the test. It’s almost as if they’re saying they always have a slight leak. They seem to put the decomposition back into the saw? Seems strange. As far as deleting it goes…. I would much rather keep it.

 

[Mgage09]

Thank you very much for getting back to me. I just watched some you tube videos. I see Matt Olsen and Jon from custom saws both plug their decompression valve holes for the test. It’s almost as if they’re saying they always have a slight leak. They seem to put the decomposition back into the saw? Seems strange. As far as deleting it goes…. I would much rather keep it.

Also my Stihl manuals all say plug the decompression valve hole for the test.

 

[ballisticdoughnut]

Also my Stihl manuals all say plug the decompression valve hole for the test.

Decomp valves leak even when closed. May not be much but they do leak. And yes, proper procedure is to plug the decomp for a pressure/vac test.

 

[J D]

Under normal working conditions the compression of the motor helps the decomp to seal.
In the past I have fixed valves that leaked badly with lapping compound & a few rotations.
I have also put a smear of grease in a valve to get it to seal for a compression test.
Sometimes all you need to do is twist them or pull on them lightly & they will seal

 

[muddy42]

It depends whether the leak is with the thread or the seal plunger itself. Often the plunger area gets carboned up and can be revived with a wire brush and some oil. The threads can benefit from some grease. You can clean out the hole with a pipe cleaner and solvent.

If all else fails plug it for the test also with some PTFE tape!

 

[Okie]

The Old vintage Homelite EZ chainsaws have a decompression valve that ALWAYS LEAKS little bit but not enough to upset the saws idle and performance and is not made to be removed from the power head.
I can manually push in on the compression release pintle's plunger and get enough of a seal to pressure test. so I just ignore the slight valve leak except when pressure testing the EZ's block by having a soap/water mix handy when applying pressure.

 

[stihltech]

I rarely remove the decompression valve when testing. I want to know if it leaks.
I clean them by spinning it with my fingers when closed to help it seal. You can go further and use light valve grinding compound ( or a scouring powder) to get a seal.
If bent or never seals, replace it.