Poorman's guide to Vacuum Testing

[PogoInTheWoods]

Guerilla tape! Genius! Many thanks!

I have a mighty vac 8000 (the one that only does vacuum for brakes). Might have to upgrade to make the pressure test easy.

When using the spark plug adaptor, the piston would need to be at the bottom of its stroke, right? That way the transfer ports are exposed/open?

Can't take credit for the Gorilla tape. Read it somewhere else and just happened to have some to try. Was surprised, though it works better for vac than pressure for obvious reasons. For pressure testing, there are easy ways of doing that from a bicycle pump or a blood pressure bulb to just cranking the regulator down to around 5~10psi on an air compressor.

As for the piston position when using a spark plug adapter, I'm usually testing without a piston during a rebuild just to make sure the case and seals are tight before I even commit to installing the piston. Otherwise, I'm not sure it matters where the piston is. You should rotate the crank when doing a vac check looking for intermittent leaks on older seals anyway. Then again I've heard that not having the crank at BDC using a plug adapter renders the test useless. Not sure why it would. Guess it doesn't matter if you're using a block-off plate with a barb on the intake for testing or the impulse passage, tho.

 

[CoreyB]

Interesting and youake it seem simple enough.

 

[cruxmon]

There are several different pressure/vacuum test kits available for chainsaws on eBay, including OEM.

 

[Deleted member 135597]

There are several different pressure/vacuum test kits available for chainsaws on eBay, including OEM.

Let me guess, you have some for sale and that's why your pulling up all these old threads. One thread would have been enough

 

[SeMoTony]

So I'm sorta new to vac testing. Got my 346 sealed up, it will pass pressure but not vacuum. So obviously a leak somewhere. How do you find the vac leak? Smoke? Dunk the whole saw in water (really don't wanna do this one), or something else?

water dunk is 2 show pressure leak, vacum would pull water into crank or other area ya don't want(-; my $.02

 

[Big_6]

I just picked up the harbor freight model, $25.

 

[Baconaman]

There are several different pressure/vacuum test kits available for chainsaws on eBay, including OEM.

I haven't looked through the entire thread, but the original pictures are no longer showing up in the beginning. Does anyone know how to access them?

 

[Okie]

I haven't looked through the entire thread, but the original pictures are no longer showing up in the beginning. Does anyone know how to access them?

I also noticed some more of his 11 year old pic's are not showing.
Did the Kodak instamatic film go bad/evaporate? (anyone got any good negatives they can re-post the pic's/)

 

[HarleyT]

All of the old pics and vids are long gone.

 

[teacherman]

So I'm sorta new to vac testing. Got my 346 sealed up, it will pass pressure but not vacuum. So obviously a leak somewhere. How do you find the vac leak? Smoke? Dunk the whole saw in water (really don't wanna do this one), or something else?

I use Gorilla tape on the carb flange and the exhaust port, and put the vac pump on the imppulse line. A bit of vaseline on the impulse connection if that is suspect. If it leaks, I'd say the seals are the next step. Any opinions?

 

[Paragon Builder]

I use Gorilla tape on the carb flange and the exhaust port, and put the vac pump on the imppulse line. A bit of vaseline on the impulse connection if that is suspect. If it leaks, I'd say the seals are the next step. Any opinions?

If it leaks, find the leak. Often pressurizing and some soapy water will tell you. Sometimes pressure holds and vac doesn’t. Lay the saw on its side and pour a little 2stoke oil on the seal. Either vac leak will stop, or it’ll suck the oil in.

On occasion case gasket fails between oil and crankcase.

 

[Okie]

I use Gorilla tape on the carb flange and the exhaust port, and put the vac pump on the imppulse line. A bit of vaseline on the impulse connection if that is suspect. If it leaks, I'd say the seals are the next step. Any opinions?[/QUOTE]

If the saw is not holding pressure/vacuum, I do not just assume it is the crank seals. I try to confirm exactly where and how many leaks.
If it is leaking I go to pressure and use soap and look for bubbles. I've found leaks in several places other than crankshaft seals.

 

[kz1000]

Four Paws has moved on to become the resident vacuumologist at Husqvarna since the posting of this thread and all pictures have been archived at the United Nations museum for the preservation of chain saws.