Don’t Miss This Step In Your Rebuilds..

[Vintage Engine Repairs]

Real time pressure and vacuum test, it’s really this easy and will save you so many potential running problems

 

[Canyon Angler]

Thanks for this. I bought a tester but haven't used it yet, so this helps.
It looks easier than I expected. For some reason I was thinking the crankcase vacuum test would have to be done somewhere else than at the spark plug, but I guess turning it over will equalize the pressure in the crankcase and cylinder...and/or the piston will move up as you draw the air out of the cylinder, creating vacuum in the crankcase, as well.

 

[pioneerguy600]

Thanks for putting this vid up, it will help so many newcomers that have never seen the vac/pressure tools or how to set up and do the tests. These tests save so much time and energy , many times unnecessary guessing and parts swapping.

 

[cookies]

this needs to be sticky'd in the chainsaw repair page
I see you got the 3/8 drive m12 stubby impacts I rave over, makes clutches and crank nuts a breeze eh?

 

[Canyon Angler]

Question: Will an engine ever pass a pressure test, but fail a vacuum test ... or vice-versa? And if so, why?

It seems like if it passes one test, it should pass both ... and vice-versa. But I bet there's something I'm missing.

 

[Brufab]

Thanks for the valuable knowledge shared

 

[gary courtney]

Question: Will an engine ever pass a pressure test, but fail a vacuum test ... or vice-versa? And if so, why?

It seems like if it passes one test, it should pass both ... and vice-versa. But I bet there's something I'm missing.

There are several factors that can cause it to fail vacum and not pressure. Seals and decomp are 2 that come to mind that can pass pressure and fail vacum. Spark plugs, cylinder gaskets, case gaskets will fail both test. The intake boot has sometimes passed pressure but failed vacum on me. I look at the seals first.

 

[pioneerguy600]

There are several factors that can cause it to fail vacum and not pressure. Seals and decomp are 2 that come to mind that can pass pressure and fail vacum. Spark plugs, cylinder gaskets, case gaskets will fail both test. The intake boot has sometimes passed pressure but failed vacum on me. I look at the seals first.

Yes, seals can leak under pressure but seal under vac. Pressure pushes the lips outward causing a leak, vac pulls them in and helps seal them tighter to the crank.

 

[Vintage Engine Repairs]

Question: Will an engine ever pass a pressure test, but fail a vacuum test ... or vice-versa? And if so, why?

It seems like if it passes one test, it should pass both ... and vice-versa. But I bet there's something I'm missing.

Old or worn seals will most often fail on vacuum because the sealing lip (the one with the spring) lifts up and away from the crankshaft when a vacuum is drawn . Note that pressure will actually push the sealing lip down on a seal unless they are dry and hard and thus leak both pressure and vac. Old dry seals = fail on both pressure and vacuum tests. Old weak seals = fail on vacuum but will generally hold pressure.

The front sealing lip is just a dust seal, the one that really does the work is the one with the spring and faces inwards (it’s also the reason it’s easy to prolapse on a crank shaft machined step on the clutch side) if it faced the other way it wouldn’t.

 

[HumBurner]

Bookmarked and hoping to be able to save the video for offline viewing.

Thanks!

 

[gary courtney]

Old or worn seals will most often fail on vacuum because the sealing lip (the one with the spring) lifts up and away from the crankshaft when a vacuum is drawn . Note that pressure will actually push the sealing lip down on a seal unless they are dry and hard and thus leak. Old dry seals = fail on both pressure and vacuum tests. Old weak seals = fail on vacuum.

The front sealing lip is just a dust seal, the one that really does the work is the one with the spring and faces inwards (it’s also the reason it’s easy to prolapse on a crank shaft machined step) if it faced the other way it wouldn’t.


View attachment 969355

Like the illustration.

 

[Vintage Engine Repairs]

Thanks for putting this vid up, it will help so many newcomers that have never seen the vac/pressure tools or how to set up and do the tests. These tests save so much time and energy , many times unnecessary guessing and parts swapping.

Thanks Jerry, for your comment and all your help over the years!

 

[Vintage Engine Repairs]

this needs to be sticky'd in the chainsaw repair page
I see you got the 3/8 drive m12 stubby impacts I rave over, makes clutches and crank nuts a breeze eh?

I love the m12 stubby! I love both driver and wrench, took me a while to get use to them, but they’re great. The stubby especially, the 4th setting to avoid cross threading & over tightening is so useful nipping them up before swapping over to a ratchet.

The driver, I do really like it, but I prefer the feel and smoothness of the motor in the stubby.

Have you got the 90 degree die grinder? I absolutely love that tool!

 

[Vintage Engine Repairs]

Like the illustration.

Thanks, it’s not mine but was useful to show the profile of how they sit

 

[Canyon Angler]

Old or worn seals will most often fail on vacuum because the sealing lip (the one with the spring) lifts up and away from the crankshaft when a vacuum is drawn . Note that pressure will actually push the sealing lip down on a seal unless they are dry and hard and thus leak both pressure and vac. Old dry seals = fail on both pressure and vacuum tests. Old weak seals = fail on vacuum but will generally hold pressure.

The front sealing lip is just a dust seal, the one that really does the work is the one with the spring and faces inwards (it’s also the reason it’s easy to prolapse on a crank shaft machined step) if it faced the other way it wouldn’t.


View attachment 969355

Good stuff, thanks, Tom (and others). That illustration makes it clearer.

 

[cookies]

I love the m12 stubby! I love both driver and wrench, took me a while to get use to them, but they’re great. The stubby especially, the 4th setting to avoid cross threading & over tightening is so useful nipping them up before swapping over to a ratchet.

The driver, I do really like it, but I prefer the feel and smoothness of the motor in the stubby.

Have you got the 90 degree die grinder? I absolutely love that tool!

yes sir I have the 90' cut off, the m12 grease gun is the kitties ******* if you own or work on anything with grease fittings. No more hand cramps and it uses very little battery power to empty a entire grease tube.

 

[5155]

Sometimes I check while carb and exhaust are removed, gorilla tape is my friend. Not my original idea.

Diagnosing carbs with this tool next?

Going to test my suspect power brake booster on the truck one of these days.

 

[Jasonrkba]

Good video. Seals can last for a very long time but if the saw is 10-15 years old I replace them. Seals are cheap, piece of mind is priceless.

 

[Vintage Engine Repairs]

Sometimes I check while carb and exhaust are removed, gorilla tape is my friend. Not my original idea.

Diagnosing carbs with this tool next?

Going to test my suspect power brake booster on the truck one of these days.

That’s a really good idea, sure, why not! Watch this space.

 

[Mad Professor]

Tom did you make up the plug adapter? Snap us a picture.