Vacuum testing chainsaws

[tomalophicon]

Hi experts,
I just bought a pressure/vacuum tester.
I've been testing pressure and spraying soapy water at suspected areas to reveal the leaks.
However, I'm not entirely sure how to home-in on the areas that may fail the vacuum test? I have a vacuum leak somewhere.
I know the crank bearing seals are likely culprits, but is there a handy procedure for identifying other areas?
Cheers,
Tom.

 

[heimannm]

I put a few drop of heavy oil around the crankshaft and see that that affects the rate of the vacuum leak. Summer weight bar oil is a good option. You should see a difference in how quickly the vacuum drops with the oil.

Mark

 

[huskihl]

Hi experts,
I just bought a pressure/vacuum tester.
I've been testing pressure and spraying soapy water at suspected areas to reveal the leaks.
However, I'm not entirely sure how to home-in on the areas that may fail the vacuum test? I have a vacuum leak somewhere.
I know the crank bearing seals are likely culprits, but is there a handy procedure for identifying other areas?
Cheers,
Tom.

A common spot is the decomp button. You can hold it out manually and usually they’ll seal

 

[tomalophicon]

Thanks very much guys, I'll try some oil and the decompression valve.

 

[L34]

I use a bit of grease on seals if I think they are suspect.

 

[Vintage Engine Repairs]

Main areas to check:

intake manifold
Impulse line
Spark plug threads
Decomp plug threads
Case gasket
Base gasket
Oil seals
Exhaust flange for sealing
Intake flange for sealing
Tester hose itself
oil pump
oil flow adjuster
Outside rim of bearing pockets
Tank (fuel and oil) caps / breathers

 

[atpchas]

Hi experts,
I just bought a pressure/vacuum tester.
I've been testing pressure and spraying soapy water at suspected areas to reveal the leaks.
However, I'm not entirely sure how to home-in on the areas that may fail the vacuum test? I have a vacuum leak somewhere.
I know the crank bearing seals are likely culprits, but is there a handy procedure for identifying other areas?
Cheers,
Tom.

The only places I've found to pass pressure but fail vacuum are seals and decomp. As mentioned, a bit of oil or light grease can be the tell-tale.

 

[tomalophicon]

Great - thanks everyone - I'll report back when I can test again.

 

[tomalophicon]

So I pressure tested again and it sits on 7 psi nicely. Even when I pull the starter it jumps up and down but stays around the same pressure.

Vacuum is a different story. I can't get it over around 2 or 3 psi. It can hold vacuum fine for a 3 minute count but when I pull the starter it keeps dropping with each pull.

Is this potentially a sign of bad bearings? Is there a way to diagnose bearings without splitting the case?

Thanks
Tom.

 

[frank_]

i never bother with vac testing personally
i drop some oil down the plughole and if it runs then dies i know the piston or bore is scored
or i drop some fuel down the inlet and then down the plug hole, and if it only runs from fuel down the plug hole then there is bad vacuum

 

[tomalophicon]

i never bother with vac testing personally
i drop some oil down the plughole and if it runs then dies i know the piston or bore is scored
or i drop some fuel down the inlet and then down the plug hole, and if it only runs from fuel down the plug hole then there is bad vacuum

Thanks. Has a new piston and clean cylinder. The saw runs fine.
Edit: bought the saw with a scored piston and wanted to track down possible causes.
Tom.

 

[atpchas]

So I pressure tested again and it sits on 7 psi nicely. Even when I pull the starter it jumps up and down but stays around the same pressure.

Vacuum is a different story. I can't get it over around 2 or 3 psi. It can hold vacuum fine for a 3 minute count but when I pull the starter it keeps dropping with each pull.

Is this potentially a sign of bad bearings? Is there a way to diagnose bearings without splitting the case?

Thanks
Tom.

I'd suspect seals first. put a small bead of grease or viscous oil where the lips of the seals contact the crankshaft. Apply vac and seal if any grease is pulled under the lip. If the seal is bad, it may indicate a bad bearing or simply a seal that aged out or got too hot.

 

[tomalophicon]

I'd suspect seals first. put a small bead of grease or viscous oil where the lips of the seals contact the crankshaft. Apply vac and seal if any grease is pulled under the lip. If the seal is bad, it may indicate a bad bearing or simply a seal that aged out or got too hot.

Thanks very much.
Didn't get a chance to pull the clutch or flywheel tonight but will do over the next couple of days.
Tom.

 

[J D]

Thanks. Has a new piston and clean cylinder. The saw runs fine.
Edit: bought the saw with a scored piston and wanted to track down possible causes.
Tom.

If p/c are scored/seized best to resist the urge to tear it apart until after a pressure/vac test to find out if/where there's a leak

 

[tomalophicon]

If p/c are scored/seized best to resist the urge to tear it apart until after a pressure/vac test to find out if/where there's a

Thanks. I'll know for next time.

 

[tomalophicon]

I managed to get time to pull the saw down a bit which is a husky 365.

The clutch side o ring and seal are not holding pressure with the clutch and oil pump removed. I've read this might be normal for the 365/372? Can anyone confirm this?

The flywheel side holds pressure and i couldn't see any evidence that it isn't holding vacuum using oil on it.
Below are some videos.

 

[sled_22]

There's supposed to be a little oring behind the collar that the seal rides on behind the oil pump. Like micro oring the diameter of a nickel. I replaced the one I just rebuilt but many on here said to put some sealer on the bottom of the collar. This is where the leak is coming from on seal leak 1 video.
Also. You should have your clutch installed and tight on the collar for everything to properly seal. It's hard to see where it's leaking at that point but necessary for everything to seal correctly.
seal 2 video is coming from around the actual seal i see. Does the seal look damaged? I'd probably replace that too since you're right there.

 

[Mad Professor]

If you pull the top end might as well do seals as cheap insurance, especially older saws. Stihl gasket sets come with seals, and are cheaper than buying just seals. Not sure about OEM Husky sets.

 

[PogoInTheWoods]

Many crank seal vacuum leaks are missed because too much pressure masks the leak like a one-way valve. And while the grease and oil method can help identify a vac leak at a seal under vacuum, so will a bubble test using just limited pressure. Think of a tire bead needing x-amount of pressure before it will pop onto a rim and hold air. Same with a crank seal under pressure that only has a marginal vacuum leak. Crank the pressure down and the air will escape and be detected by a bubble test.

Personally, I always bother with a vac test when determining the integrity of a crankcase and top end.

 

[tomalophicon]

If you pull the top end might as well do seals as cheap insurance, especially older saws. Stihl gasket sets come with seals, and are cheaper than buying just seals. Not sure about OEM Husky sets.

Thanks. I have a set of seals and gaskets. It didn't come with the O ring though.