Pressure test setup on Husky 372XP

I'm trying to pressure/vac test my 365/372 XP XT.

I have the exhaust side gasketed off with rubber/cork sheet.

I wanted to do the same between the carb and intake boot, but there are tabs inside and outside of the boot face that block me from inserting a flat sheet in between.

What's the trick to setting up this test on this saw?

 

Other side of the carb or make a rubber piece to clamp on the intake neck.

 

I did the other side of the carb and it won't hold any pressure for even a moment. I could see/hear fuel blowing out on the e-clip side of the throttle butterfly shaft.

I can put a boot/cap over the cylinder but I was hoping to include the intake boot since they are a common failure point and visual inspection is not said to be enough.

 

Here's what I ended up with: a bottlecap from a Stihl 1gal premix bottle and my 20mm Craftsman short socket. If I lined up the cap just right it sealed off.



Now for the result: it leaks in pressure from 7psi to 6psi in 30 seconds. It leaks in vacuum from 10in Hg to 0 in about 30 seconds. Per the Husqvarna manual, the pressure test is good and there is no spec for vacuum test. Now the question is: is that acceptable?

 

I do not think that is good enouph. If it is sealed properly it should hold at least 12 psi for 60 seconds or longer with out dropping and it should do the same for the vacuum. Not only does the crankcase pressure have to push mixture up through the transfer ports but it has to work the diaphragms in the carb too. Just my personal preference.

 

I'm going to put new crank seals in it and see what happens.

I hadn't noticed this before, but the screws for the oil pump are tapped right through the housing into the crankcase. Definitely going to add some sealant to those threads!

David

 

Use some Yamabond or similar product on the screws. Gas and oil will not bother it.

 

I have the test setup going now - and it's leaking at the spark plug crush washer. It loses a psi over about a minute - so right on the limit. I tightened the plug further and got no improvement. Then I tried a new plug and no better. How should I fix this?

 

Put a round of Teflon tape on the plug for now to see if that seals it for the test. The vacuum test should hold longer than that before it drops to nothing.

 

It wasn't dropping to nothing - it would go from 8psi down to 7psi in about a minute. Soapy water showed it was leaking around the plug ring. In vacuum it lost a similar amount.

I could take an old plug and replace the crush washer with an O-ring and "solve" the leak but I assume it will leak when a real plug is in place.

 

Same spot for vacuum?

 

I assumed so, since this seal is entirely metal and would behave the same regardless of the pressure direction.

I'm going to head out and repeat the test using an o-ring from my compression tester on an old spark plug in place of the crush washer.

 

I took a much closer look at where the spark plug seals on the cylinder head, I decided the head surface wasn't machined cleanly enough. The head surface was "torn" by the machine tool and so I polished it down. Now I apply 10psi and it takes a full 2 minutes to drop to 9 psi. I'm also not seeing bubbling when I spray soapy water around the plug. I'll call that success.

 

So I am curious how much that is going to leak when your pumping a 150 psi on the compression.

 

Might not leak at all when there's heat to warm it up and swell.

 

Well, I did install the piston rings.

I can't detect any leakage on the top of the head anymore, so it's safe to say I'll lose nearly nothing.