Need help with stihl 041 av pressure test problem

[Robert Kugler]

Hi,
I have an older stihl 041av saw that will not start. It has spark and a new carburetor with new fuel and impulse tubing. I eventually wound up doing a pressure test (with both the intake and exhaust ports sealed up. When I pumped pressure into the impulse fitting on the crankcase, I found that it would not hold the 7psi that it should. I searched for ant other passages to block, and found that when I put a sharpened dowel stick into the bar oiler hole, the pressure buildup would start to hold, although it still leaks down fast.
I thought that there should be O rings sealing the oil pump from the crankcasde, but I am not sure. does anyone have any ideas about my troubles?
Thanks

 

[Bob Hedgecutter]

Crankcase pressure is getting into the oil tank.
Could be loose case screws, damaged case gasket, or cracked case.

 

[hotshot]

The boot (rubber ring) seal on plastic the front of the oiler body & the o-rings on the orange adjuster screw stem can commonly leak by.

Additionally, you also have to have the oiler worm gear installed, & held down in, to properly leak test the PTO side crank seal & little worm gear seal. Of course the clutch needs to be pulled off to bubble test there.

As Bob stated, the crankcase/oil tank gasket can leak internally & cause the oil tank to be pressurized, bubble test the vent hole in the oil fill cap to check for that.

Those 041s can be a real bear to P&V test, as there’s literally a dozen potential air leak points if you include the stack of three intake gaskets, the case gasket, & jug gasket.

Search for an old thread “041 Vacuum specs” & the old link below for some info on the same topic.

http://www.arboristsite.com/community/threads/041-problem-and-theory.261143/

Good luck, both the crank seals & oil pump ring are common leakers.

 

[Robert Kugler]

Thanks for the help, I will check these things.
Hotshot wrote "As Bob stated, the crankcase/oil tank gasket can leak internally".
Can you tell me where this internal gasket is?
Thanks

 

[Bob Hedgecutter]

Thanks for the help, I will check these things.
Hotshot wrote "As Bob stated, the crankcase/oil tank gasket can leak internally".
Can you tell me where this internal gasket is?
Thanks

Um- between the case halves. Look up on your search engine for Stihl 041AV IPL, that will explain it better with exploded parts diagrams.

 

[Vintage Engine Repairs]

Should be fairly similar to the 076 Super I just rebuilt - here was a list of things I checked, they should apply to your saw too. Tick them off as you go.

Whilst under pressure and vacuum, test the following -

All three oil seals (confirm that the oil worm gear is seated correctly keeping it pressed in when pressure testing. Spin it too as this actuates the oiler drive shaft and the o-ring that’s there), the lower o-ring on adjustable oiler shaft, the o-ring within the oil pump (mentioned above) and the rubber grommet on the oil pump.

If they check out, check all the gaskits between the carb and the cylinder flange and the gasket between the muffler and cylinder flange, the cylinder gasket and case gasket.
Check the oil tank valve too.

if they check out fine, then test the spark plug threads, decomp and threads at the top of the cylinder and the bolt at the side of the cylinder.

If they all check out fine, check again because one of them is leaking

 

[hotshot]

Those two o-rings on the 041 oil pump shaft have nothing to do with an air leak.

 

[Vintage Engine Repairs]

Those two o-rings on the 041 oil pump shaft have nothing to do with an air leak.

If the 041 is the same set up as the 076, The single o-ring and rubber grommet does. The o-ring on the shaft maintains atomspheric pressure in the crank from the oil lines and galley and the grommet maintains crank pressure from air seeping through the end of the oil pump body

and number 6 is what stops the crank sucking in oil and or air from the oiler or galley

 

[Robert Kugler]

Bob/Tom,
I finally got the crank and cylinder assembly cleaned up (what an oily/saw-dusty mess!). I did a bubble test on the two crank seals, which were ok. I also did a bubble test on the crankcase seam. That was ok too.
The bubble test failed on the O rings around the oil control shaft. it was a fast leak. I think that's the problem. I will get new O rings and see if that fixes it. It is definitely a problem (even if there are others). I replaced the bushing on the end of the oil pump body for good measure. There were no metal sleeves in the bushing holes. Should I put them in anyway? The bushing alone was a tight fit. I had to oil the bushing and tap the pump in with a dowel and small hammer.
After I remove the oil control knob (and the pump again ), does the metal control shaft under the knob just lift out?
I really appreciate the help guys!
Bob

 

[Vintage Engine Repairs]

Bob/Tom,
I finally got the crank and cylinder assembly cleaned up (what an oily/saw-dusty mess!). I did a bubble test on the two crank seals, which were ok. I also did a bubble test on the crankcase seam. That was ok too.
The bubble test failed on the O rings around the oil control shaft. it was a fast leak. I think that's the problem. I will get new O rings and see if that fixes it. It is definitely a problem (even if there are others). I replaced the bushing on the end of the oil pump body for good measure. There were no metal sleeves in the bushing holes. Should I put them in anyway? The bushing alone was a tight fit. I had to oil the bushing and tap the pump in with a dowel and small hammer.
After I remove the oil control knob (and the pump again ), does the metal control shaft under the knob just lift out?
I really appreciate the help guys!
Bob

I too had a leak there mate, the small o-ring 7x1.5mm I think it is? The lower one is to maintain internal pressure, the higher one is there to simply stop the oil control adjuster from spinning.

The manual suggests the metal sleeve for oiler installation, but I couldn’t order one and installed it without with no issues. Ensure it’s lubed well and the oiler holes align with the galleys (You have to remove the two bar mount / clutch cover screws and the metal plate to see the oil galley).

The two metal bushes should be there, are you sure you didn’t drop them? They help direct oil to their intended route. They just sit there and are held by the rubber grommet.

Back to the alignment - be aware that those bar mount screws go into the oil tank, so ensure that the tank is empty first!
There is a small o-ring, (again 7 x 1.5mm) inside the oil pump that may require replacing (see my post above), but mine was fine so left it, yours may be the same too. Worst case your saw will smoke a lot and won’t hold pressure so just make a mental note there
Well done!

 

[hotshot]

Fix, test & repeat! Fix, test & repeat and you’ll eventually have it holding pressure all day long.

Did you bubble test the oil tank cap’s vent hole? That will show you if you have either a failed crankcase gasket or pump shaft o-ring leaking by.

If you can find Viton o-rings, instead of the standard Buna-N, they will stand up to the heat a lot better.

 

[Robert Kugler]

Tom,
I was not aware that there is anything under the metal guard plate under the bar mounting bolts, I will pull it off and look for bushings.
I was able to order the bushings and both types of o ring from a place called "Riverdale tool" online. the parts were not expensive (about $13 for 3 sets), but the shipping was outrageous: $17 for 2 ounces of parts (@!#$%!!)
Oh Well, the saw is worth it.......

 

[Bob Hedgecutter]

Bob/Tom,
I finally got the crank and cylinder assembly cleaned up (what an oily/saw-dusty mess!). I did a bubble test on the two crank seals, which were ok. I also did a bubble test on the crankcase seam. That was ok too.

Bob

Curious as to how you bubble test the case gasket when part of it seals the back of the oil tank to the crankcase that cannot be accessed from the exterior?
A bubble test on the oil tank vent as suggested above will eliminate that area.

 

[Robert Kugler]

Fix, test & repeat! Fix, test & repeat and you’ll eventually have it holding pressure all day long.

Did you bubble test the oil tank cap’s vent hole? That will show you if you have either a failed crankcase gasket or pump shaft o-ring leaking by.

If you can find Viton o-rings, instead of the standard Buna-N, they will stand up to the heat a lot better.

I think "fix test & repeat" is good advice as opposed to my method of "guess; buy, pay & test". Fixing appear$ to be incidental . Just kidding, but I will be able to fix the saw on the spot next time.
Next time I will look for Viton o rings.
I did bubble test the oil cap and it tested ok (I think you suggested that before, and I was sure to do it).
I bought a full gasket kit, mostly to get the intake/exhaust gaskets. So I have a crankcase gasket, but I dont want to split the case unless there is no other way. I'd rather not mess with the crank bearings. I do have new crank seals also
When I reassemble the intake and exhaust, should I use a gasket sealer, or do you think it will cause me trouble?

 

[Robert Kugler]

Curious as to how you bubble test the case gasket when part of it seals the back of the oil tank to the crankcase that cannot be accessed from the exterior?
A bubble test on the oil tank vent as suggested above will eliminate that area.

Bob,
You said it....I couldn't reach the whole gasket, I just did the bottom of the case, since I think that it takes the most abuse. I would probably have split the case as the very last think I tried.
I didn't realize that the oil cap bubble test would cover the crankcase gasket (Thanks for the trick!!).
I also did not test the cylinder gasket because I couldn't get at it. I'm thinking to fix the o rings and pressure test again.
The saw will be down for another week until the o rings arrive.
Do you have any trick to get the circlip off the oil control knob? It is very hard to get anything in there.
Should the oil flow control bolt just lift out after the knob is out?
Thanks for your help....

Bob

 

[hotshot]

I think "fix test & repeat" is good advice as opposed to my method of "guess; buy, pay & test". Fixing appear$ to be incidental . Just kidding, but I will be able to fix the saw on the spot next time.
Next time I will look for Viton o rings.
I did bubble test the oil cap and it tested ok (I think you suggested that before, and I was sure to do it).
I bought a full gasket kit, mostly to get the intake/exhaust gaskets. So I have a crankcase gasket, but I dont want to split the case unless there is no other way. I'd rather not mess with the crank bearings. I do have new crank seals also
When I reassemble the intake and exhaust, should I use a gasket sealer, or do you think it will cause me trouble?

None on the exhaust, but yes on the stacked intake gaskets.

Just put some Motoseal (or Yama/Honda bond) on your thumb/forefinger tips and lightly apply to both sides before you set them on the carb/intake studs.

 

[Bob Hedgecutter]

Bob,
You said it....I couldn't reach the whole gasket, I just did the bottom of the case, since I think that it takes the most abuse. I would probably have split the case as the very last think I tried.
I didn't realize that the oil cap bubble test would cover the crankcase gasket (Thanks for the trick!!).
I also did not test the cylinder gasket because I couldn't get at it. I'm thinking to fix the o rings and pressure test again.
The saw will be down for another week until the o rings arrive.
Do you have any trick to get the circlip off the oil control knob? It is very hard to get anything in there.
Should the oil flow control bolt just lift out after the knob is out?
Thanks for your help....

Bob

I don't think I ever said anything about testing the oil filler cap anywhere and it will not prove a whole lot unless the oil tank vents through the cap.

 

[Robert Kugler]

I don't think I ever said anything about testing the oil filler cap anywhere and it will not prove a whole lot unless the oil tank vents through the cap.

There is a hole in the cap

 

[Robert Kugler]

None on the exhaust, but yes on the stacked intake gaskets.

Just put some Motoseal (or Yama/Honda bond) on your thumb/forefinger tips and lightly apply to both sides before you set them on the carb/intake studs.

Thanks Randy, I will; and thanks again for the help.
Bob

 

[Robert Kugler]

Thanks Randy, I will; and thanks again for the help.
Bob

Sorry hotshot. You were the one who suggested the bubble test on the oil cap, It does have a vent and it did pass the test (at least until the o rings are replaced on the oil control bolt).
Thanks for the tip.
Bob