Pressure testing how long and how much psi?

[Okie294life]

I have a mini mite pressure tester have got the saw case sealed up and holding pressure. How long should it hold positive pressure, and how many psi? How long should it hold negative pressure and how many psi?

 

[Yukon Stihl]

It depends on who you ask or book you look in
The last ones I rebuilt held vacuum overnight
For pressure max 5 psi, I would be happy if it holds for an hour

 

[L34]

I use 5psi for 2 minutes.(POS)
And 10inch/Hg for 2 minutes (NEG)

 

[huskihl]

+/- 7 psi. I watch long enough to see that the needle isn’t moving.

 

[lone wolf]

10 plus and minus ,1 minute no movement at all with reading glasses on, and spray all area's with soapy water to double check. Always works fine. If a small tiny hard to pinpoint leak occurs the best way to find it is dunk in water.

 

[Gord404]

7P&7N, - 15 min.

 

[PV Hiker]

+/- 8 psi on both. I start with vacuum and then pressure. Pressure first can pop a seal out and make a better seal missing a vacuum leak.

While testing, rotate the crank around. The gauge will go up and down in value but should not loose value overall.

Time, a few minutes or so per test checking for no drop. Drops then more time and searching for why.

Edit to add...
If I can't get the hand pump to build up any pressure. I hook a hose to my air compressor tank turned down to 10 psi and spay it down for finding the leak. Good continuous air source. Even put it in a bucket of water at times.
.

 

[Ronie]

I use 9 or 10 psi but I've read 8 psi in one Husqvarna manual and if you loose more than a pound in 30 seconds it fails.

 

[Vintage Engine Repairs]

So long as the needle doesn’t move after 10-20 seconds it’s fine. Waiting minutes or hours is a waste of time.

Pressure and vac 7-10 psi and turn crank on vacuum a few rotations too.

 

[lone wolf]

So long as the needle doesn’t move after 10-20 seconds it’s fine. Waiting minutes or hours is a waste of time.

Pressure and vac 7-10 psi and turn crank on vacuum a few rotations too.

Agreed. But I feel better if i wait a minute.

 

[irhunter]

Before tearing into a saw, I always get the service manual...and, I just test to the standard in the manual.

 

[Vintage Engine Repairs]

Agreed. But I feel better if i wait a minute.

Certainly doesn’t hurt, I’ve just never found it necessary.

 

[mbret2004]

+/- 8 psi on both. I start with vacuum and then pressure. Pressure first can pop a seal out and make a better seal missing a vacuum leak.

While testing, rotate the crank around. The gauge will go up and down in value but should not loose value overall.

Time, a few minutes or so per test checking for no drop. Drops then more time and searching for why.

Edit to add...
If I can't get the hand pump to build up any pressure. I hook a hose to my air compressor tank turned down to 10 psi and spay it down for finding the leak. Good continuous air source. Even put it in a bucket of water at times.
.

 

[Patrick62]

I agree with the 10 to 20 second time frame. WIth me, it is usually really good, or really bad.
I have one saw that I will chase down it leaks, somewhere... someday... no hurry on that one.
It seems that I use about 5psi for pressure, not sure what I shoot for with the negative.

 

[mbret2004]

+/- 8 psi on both. I start with vacuum and then pressure. Pressure first can pop a seal out and make a better seal missing a vacuum leak.

While testing, rotate the crank around. The gauge will go up and down in value but should not loose value overall.

Time, a few minutes or so per test checking for no drop. Drops then more time and searching for why.

Edit to add...
If I can't get the hand pump to build up any pressure. I hook a hose to my air compressor tank turned down to 10 psi and spay it down for finding the leak. Good continuous air source. Even put it in a bucket of water at times.
.

Agreed! One has to remember that when pulling vacuum, in/hg, you need to double the psi value to get the proper vacuum number. Husky states 5 to 10 psi for pressure checkout. I use 7.5 psi, middle road here. If your vacuum is given in psi, not in/hg, you need to double the psi figure to obtain you vacuum target. In this example you need to pull 15 in/hg for a proper vacuum leak test. I wait 30-seconds on both test, no loss is pass.

 

[lone wolf]

Certainly doesn’t hurt, I’ve just never found it necessary.

Well, the STIHL repair Manuel recommends 20 seconds. I like to be double sure there isn't even a micro leak.

 

[Gord404]

quite often will get a good positive reading and sometimes neg is bad especially rotating the crank a bit

 

[Vintage Engine Repairs]

Well, the STIHL repair Manuel recommends 20 seconds. I like to be double sure there isn't even a micro leak.

I had a carb leak fuel past a grain of sand that indented the gasket and diaphragm and let fuel pass tiny tiny amounts and flooded the engine over night lol

 

[lwmibc]

This question has been on my mind of late--how much of a seal leak will cause destruction of a 2 stroke engine by overheating from a lean mixture?

I calculate that about 10 litres per second of air goes through a 70cc saw running at 10,000 rpm, using simple cylinder volume and volumetric efficiency (which I found surprisingly high at 80%). To lean the mixture 10% would require a liter per second leak--that sounds far beyond 'micro-leak' status, that would be detectable by just blowing (or sucking) into the crankcase and hearing a loud whoosh of air going through the seal.

If holding pressure/vacuum for under 30 seconds is considered a 'fail'--why?

 

[huskihl]

This question has been on my mind of late--how much of a seal leak will cause destruction of a 2 stroke engine by overheating from a lean mixture?

I calculate that about 10 litres per second of air goes through a 70cc saw running at 10,000 rpm, using simple cylinder volume and volumetric efficiency (which I found surprisingly high at 80%). To lean the mixture 10% would require a liter per second leak--that sounds far beyond 'micro-leak' status, that would be detectable by just blowing (or sucking) into the crankcase and hearing a loud whoosh of air going through the seal.

If holding pressure/vacuum for under 30 seconds is considered a 'fail'--why?

Because it will probably get worse. It may take it 10 years to get worse, but it’s not ever going to get better. I don’t actually wait at all when I do it. I pump it up and if I see the needle move I fix it. I have no idea what the needle looks like after 30 minutes