041 Vacuum specs

[SpaayDawg]

So last week I finally got my 041 AV "Magnum" back together. Mild port, muffler mod, sans base-gasket, Super carb. Instead of a "here it is, it runs great" thread this is a "son-of-a-gun, thing won't run" thread".
After toying with the carb and 2 kits I did a leakdown test on it, and it failed epically. It seems to hold pressure ok (~8psi), but vacuum it will only take about 6in Hg. My question I guess is what should I be looking for out of the old girl? My 028S, and a 390 I did recently held around 12"Hg.

If I pump the vac tester up to around 10, I can watch the gauge slowly creep down until it settles around 6. Then It will hold 6 for as long as it takes to drink a cold beverage.

What'yall think?

 

[SpaayDawg]

bump

 

[pioneerguy600]

The radial seals are likely starting to wear a little on the lips, pressure pushes them tighter to the craknshaft sealing them better, vacuum opens the lips inward and allows a little air to enter, when the vac drops a little the seals will close tighter on the shaft and slow the leaksge down. If it were my say for my own personal use I would run it for a while yet but be always wary of it, if the engine starts to show signs of air leakage then shut it down and change seals. For anyone but myself I would suggest changing the seals now.

Pioneerguy600

 

[hotshot]

Vacuum Test

Stihl suggests 0.5 bar or 7.35 psig in the 041 manual, but no time factor.
This 7.35 psig roughly equals 15" Hg. Lakeside warned against going higher, as they all will start pulling air & this does not simulate the real world running conditions.

Vacuum testing is sometimes a strange process, as I can get a leak at 10" Hg one time & then it holds the next time at up to 15" Hg ...on the same seal! I think that the initial positive pressure testing will "set" or make the lip seal better.

On the older saws like your 041, you can separate (gently) the seal lip from the shaft with a small toothpick tip, then test the seal & it will not immediately reseat for the vacuum test. I'll bet the rubber is getting too stiff to quickly reseal, & do recommend changing these intermittent ones.

 

[SpaayDawg]

I should have stated before, I started this saw with a crankshaft and a piston, and procured parts from there. It has all new seals. I was just wondering if 6inHg is "good" or should it be able to hold more?

Should I have any concern with the "seal" between the oil pump gear and the crankshaft? Would this be where my "leak" is?

 

[hotshot]

Yes it can leak at the small OP worm driver seal...BTW that is the same little seal used in 028, 032, and 045/0566 oil pumps bodies too! I would get the light oil can out and see where it's sucking air in. If the shaft seals are new, then you can almost ignore them unless the shaft or the seal's external bore surface was boogered up.

I would not be satisifed with only 3-4 "Hg. The S041 is a bear to leak check, as it can also leak into the front where the large oil pump housing grommet seals the case. I would blind both the cylinder ports with sheet metal blinds to keep the leaks from coming through the intake manifold stacked/gasketed seams.

Is your spark plug torqued tight & the CC-Jug gasket brand new?

 

[SpaayDawg]

Yes it can leak at the small OP worm driver seal...BTW that is the same little seal used in 028, 032, and 045/0566 oil pumps bodies too! I would get the light oil can out and see where it's sucking air in. If the shaft seals are new, then you can almost ignore them unless the shaft or the seal's external bore surface was boogered up.

I would not be satisifed with only 3-4 "Hg. The S041 is a bear to leak check, as it can also leak into the front where the large oil pump housing grommet seals the case. I would blind both the cylinder ports with sheet metal blinds to keep the leaks from coming through the intake manifold stacked/gasketed seams.

Is your spark plug torqued tight & the CC-Jug gasket brand new?

Spark plug is new, and tightened, no base gasket just permatex. I took my air hose and a spray bottle of windshield cleaner and checked all around the cylinder for bubbles and there were none. Both the intake and exhaust ports are blocked with plates and inner-tubes pieces. I have not wanted to pull the clutch or the flywheel but I guess I will have to.

 

[Diesel Pro]

With the clutch and flywheel off could a guy do the oil trick like you would to seal piston rings for a compression test?

 

[hotshot]

Yes that's the only way I know of to check the seals, so you're looking right at them. On the PTO side, you'll have to use the clutch spider & a piece of pipe (I cut a deep "V" on the end of a 3/4" PVC stub) to keep the oiler gear in place during presure testing. If you don't, it will pop out & hit the wall or something of greatest value on the work bench...

The V in the stub end lets me see the small oiler gear seal while pressure bubble testing. It also let's me see if it is sucking in the Singer sewing machine oil (light oil for testing) for finding vacuum leaks

 

[james fletcher]

Stihl suggests 0.5 bar or 7.35 psig in the 041 manual, but no time factor.
This 7.35 psig roughly equals 15" Hg. Lakeside warned against going higher, as they all will start pulling air & this does not simulate the real world running conditions.

Vacuum testing is sometimes a strange process, as I can get a leak at 10" Hg one time & then it holds the next time at up to 15" Hg ...on the same seal! I think that the initial positive pressure testing will "set" or make the lip seal better.

On the older saws like your 041, you can separate (gently) the seal lip from the shaft with a small toothpick tip, then test the seal & it will not immediately reseat for the vacuum test. I'll bet the rubber is getting too stiff to quickly reseal, & do recommend changing these intermittent ones.

would you have a 041 manual you can send. only thing i could find was the parts manual.

 

[SpaayDawg]

Yes that's the only way I know of to check the seals, so you're looking right at them. On the PTO side, you'll have to use the clutch spider & a piece of pipe (I cut a deep "V" on the end of a 3/4" PVC stub) to keep the oiler gear in place during presure testing. If you don't, it will pop out & hit the wall or something of greatest value on the work bench...

The V in the stub end lets me see the small oiler gear seal while pressure bubble testing. It also let's me see if it is sucking in the Singer sewing machine oil (light oil for testing) for finding vacuum leaks

Thanks for the heads up!

 

[hotshot]

Vacuum tested

SpaayDawg,

I just re-sealed a standard Stihl 041, and it's holding -15"Hg (~7.5 pounds) steady for over twenty minutes now.

Before that, both seals were leaking badly, mag side on vacuum & the clutch side on pressure. Both seals were hard as a rock, and I liked to never got the mag side seal out...

Did you ever get your leaks fixed?