Poorman's guide to Vacuum Testing

[Jbevs]

Thanks to four paws and the guys that made it in to a PDF.

 

[teatersroad]

I was just here a couple days ago, yup, thanks fourpaws.

Poorer man's test kit ended up being: I had a gauge, picked up a 60mL syringe at the feed store for a buck fiddy, some hose and a tee fitting for another buck. Pulls 6" of vacuum and pushes 5 psi on my 60cc saw.

 

[pippin5267]

This is one of the most informative and easy to read posts I've ever read on this site. Its very easy to understand and has good clear pictures. Heres a rep for you.

 

[Jaberwky]

For Stihl saws?

The exhaust seal is simple, but on my Stihl 460 I can't bolt the intake seal on like in the photos. I'm stuck with the big long carb-mounting studs with only the ends threaded. I need some kind of plate/washer and super long sleeves to go over the studs enough to press the seal and also allow me to tighten the bolts down.

Suggestions from Stihl owners?

 

[USMC0802]

The exhaust seal is simple, but on my Stihl 460 I can't bolt the intake seal on like in the photos. I'm stuck with the big long carb-mounting studs with only the ends threaded. I need some kind of plate/washer and super long sleeves to go over the studs enough to press the seal and also allow me to tighten the bolts down.

Suggestions from Stihl owners?

I went to the local hardware store and picked up a pair of these. I think I took the tank handle or even the entire saw carcass with me to check the size (length and diameter of the opening) for the carb studs. I also grabbed a few washers. Picking up some aluminum stock would be a good idea as well. It's easy to cut with a hacksaw and it's cheap.

 

[briantutt]

The exhaust seal is simple, but on my Stihl 460 I can't bolt the intake seal on like in the photos. I'm stuck with the big long carb-mounting studs with only the ends threaded. I need some kind of plate/washer and super long sleeves to go over the studs enough to press the seal and also allow me to tighten the bolts down.

Suggestions from Stihl owners?

maybe cut off an aluminum arrow shaft?

 

[kam]

The exhaust seal is simple, but on my Stihl 460 I can't bolt the intake seal on like in the photos. I'm stuck with the big long carb-mounting studs with only the ends threaded. I need some kind of plate/washer and super long sleeves to go over the studs enough to press the seal and also allow me to tighten the bolts down.

Suggestions from Stihl owners?

In electronics, they use stand offs to lift a circuit board away
from a metal chassis. Buy from electronics parts stores, or possibly Home Depot hardware section. Or salvage from discarded equipment.

Mine are pictured between the two gauges. (silver tubes)

 

[RENNIE]

USMC
What the hell is that between the 2 & 2 1/2" mark??????

 

[K5krawler]

Go have a beer then come back in 5 minutes or so, and check to see if your vacuum gauge is reading the same as when you left it.

It takes you 5 minuets to drink a beer lol! J/K!!! Do you or anybody else here have any type of condemning limits for a leak down test. As in a drop of XXX in/Hg over X:XX ?

K5

 

[mifirewoodguy]

The only problem with a vac-only test is that it's often really hard to find where it's leaking.

Pressure testing is real good to find big or hard-to-see leaks... just keep pumping and get your ear down to the saw, or squirt with soapy water. I aways pressure test first, then vac.

When vac testing, and you have a slight leak that's hard to find, flip the saw on its side and drop light oil into the seal area. If it vanishes or stops leaking, that's your problem..

I also have a low pressure regulator to feed 3-5psi air to the saw under test - much easier to find the leaks that way than pumping - you can even dump the entire power head into to a 5 gallon bucket of water!

Gosh! I love you guy! lol!

 

[o8f150]

fantastic thread,, i just learned something too

 

[thook]

Great thread!

I gotta a question not covered here in the thread.

I don't have an impulse line on my Makita 520i. So, I'm gonna have to rig something up to test vac and pressure. I'd just recently installed a new ring because the piston and cylinder scored. Not a lot of transfer....easily cleaned up. The cylinder's smooth as silk except just below the exhaust port on one corner. Even then, barely noticeable.

I'm still reading and learning as to why this may have happened and what to do to prevent it from happening, again. I read somewhere about the saw running lean. So, I figure check the vac and press. test to make sure no seals were leaking.(It was having some running problems before getting serious and not running hardly at all). But, I just put in the new ring. Should I break in the new ring first before running the tests, or just go ahead do it?

 

[thook]

Well, since no one answered and I couldn't find any definitive info, I thought about it and I'm gonna guess it doesn't matter. Ring or no ring, neither vac or press. should be leaking past any seals in the case or cylinder head. Given part of the instruction is to rotate the crank several times over, the ring question is moot. Is this correct?

 

[72thing]

thook, I'm new at the vac/press testing thing, too. But, having just tested my 036, I'm confident in doing it again. If all you're doing is testing the crankcase, it won't matter if there's even a piston in it, lol--as long as the cylinder is sealed tightly to the case. Definitely pressure test it first to make sure you don't have any leaks with your blockoffs, etc. And don't forget to look for leaks around the sparkplug!! Mine leaked around the plug and it threw off my test until I discovered it. I used soapy water (LOTS of Dawn) to spray around everything. If it pressure tests ok, then vacuum test it. Make sure you have the clutch assy, etc and the flywheel off so you can actually see the oil seals. I know that's pretty obvious, just sayin'. :deadhorse:

Will

 

[thook]

thook, I'm new at the vac/press testing thing, too. But, having just tested my 036, I'm confident in doing it again. If all you're doing is testing the crankcase, it won't matter if there's even a piston in it, lol--as long as the cylinder is sealed tightly to the case. Definitely pressure test it first to make sure you don't have any leaks with your blockoffs, etc. And don't forget to look for leaks around the sparkplug!! Mine leaked around the plug and it threw off my test until I discovered it. I used soapy water (LOTS of Dawn) to spray around everything. If it pressure tests ok, then vacuum test it. Make sure you have the clutch assy, etc and the flywheel off so you can actually see the oil seals. I know that's pretty obvious, just sayin'. :deadhorse:

Will

Right'o. I'd figured all that, but I do appreciate the feedback, Will. Thanks!

 

[SkippyKtm]

Good 'ol four paws, what ever happened to him? He hasn't been here for nearly a year and a half.

Truly a great thread, he is a lost asset to Arboristsite...

 

[Edge & Engine]

We have a Mityvac pressure/vacuum pump available now for $45.95.
Mityvac [MVC MV8255] Mityvac Selectline MV8255 Vacuum/Pressure Pump - $45.95

We've been using this model in our shop for the past 8 months or so, it's a nice unit..

 

[thook]

Makita dcs520i: Vacuum/pressure test

So, I finally got around to doing the deed today. I took all the info supplied in this thread into account when figuring my methodology.

I used the bicycle inner tube gaskets......only, instead of going the somewhat more involved route of modifying a spark plug as the testing point, I cut the valve stem section of the tube and used the valve stem to hook up the testing tools.

First, I tried installing the valve stem/gasket at the intake port with the valve stem protruding through the carb boot, but that proved to be inadequate in two ways. One simply because I didn't have the right length of bolt needed to mount the carb boot over the gasket.....and consequently stripped some threading in the cylinder head.....though not beyond being able to still mount the carb. Two, and more importantly, the inner tube is thicker around the valve stem. Being that the intake port is so small, the carb boot would not sit flush enough to give a proper seal. So, I moved it to the exhaust port and made a block off plate of aluminum stock drilling a hole in the center so the valve stem would protrude. On the intake side, I simply made a flat gasket of the tube and installed the entire carb ***'y over it. As well, per Stumpyhusky's suggestion , I applied a light coat of grease to both mating flanges. It all sealed very well.

To pressurize everything, I used an old, but functional, Rock Shox suspension fork pump. It's rather slender, lightweight, and has a gauge and pressure release valve. One full pump and the case/cylinder was up to 50psi.(No...nothing blew up). So, I let some air out, and after 1 minute no pressure had escaped even after several rotations of the crank.

Then, I removed the pump, removed the inner valve from the stem, and applied the vac pump. Again, after 1 minute and several rotations, no air had escaped. All's good with Makita!

I used a schrader type valve stem. I figure, though, one could get a bit fancier and use a presta type valve with a schrader adapter if using a schrader fitting on the pressurizing tool. The presta valve would allow one to actually fasten the valve stem to a block off plate via the circular nuts normally used to tighten the valve stem to bicycle rim. Fancy, but not really necessary.

Anyway, my little addition. Thanks for the great write up!

 

[ft. churchill]

Thank you for this post as it gives ya all the needed ideas an know how to do this important check.

 

[Dan Forsh]

I've been reading this thread for a while now with the intention of getting set up to do pressure/vac testing. I never used to pay too much attention to those who would always reply to any running issue with "pressure and vac test it".

Now I realise this is really good advice and a very simple common sense starting point when working on a saw, especially for those of us who buy them broken, history unknown.

So initially I was thinking that the Mityvac was the way to go, but unfortunately these aren't the most common here in the UK and sellers seem to know this and certainly price the pressure/vac model like they're rocking horse manure.

I didn't want to have two different set ups so I found a new compound gauge with a 4" dial on ebay quite cheap and our friendly maintenance fitter at work supplied the fittings I have up to now.

Not exactly compact but I won't have any trouble reading the dial. I've bought one of those bulb type blood pressure pumps on ebay but this is gonna be a while as it's coming from China, so I should be geared up for pressure. The one thing I haven't yet worked out is what I'm going to use for vacuum.

Any ideas on a cheap vacuum pump anyone? I suppose I could look for a really cheap brake bleeder maybe? When I type in hand vacuum pump on ebay most of what comes up seems to be a pump attached to a clear plastic cylinder with inches marked on the side "From United States", go figure?

I'll post a pick of the finished assembly once I have it all together.