Yes, vast difference in ‘drops like a rock’ or takes ten to twenty seconds to bleed off.
Slow leak can be tuned out by richening up the fuel mix.
Slow leak can be tuned out by richening up the fuel mix.
Stihl 028 diagnosis and rebuild
- Thread starter JW51
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Cut out a piece of bicycle/motorcycle inner tube to fit the exhaust then bolt the muffler over it
Yeah, inner tube would have been my first choice, just haven’t been able to locate any in my junk piles yet.
I understand I have a leak and that’s not ideal, but as a complete newb to this, I have zero context for what that means in real life. As in, how much vacuum is the saw actually creating when running on each stroke, and how likely is this slow leak (wherever it may be) to affect anything under that vacuum condition on an engine cycle that lasts a tiny fraction of a second.
The one gentleman thinks I’m in the clear, others seem to suggest I need to get the saw completely tight.
————-
Side note - I was searching other threads for a vac loss spec and came across one that mentioned a test on the Stihl 041. Someone mentioned in that thread a couple places in the oiling system that could cause a vac/pressure leak.
Does the 028 oiling system have a similar setup that can be the culprit? I mention that only because a bar oil leak is another issue I need to solve while the saw is torn down.
I understand I have a leak and that’s not ideal, but as a complete newb to this, I have zero context for what that means in real life. As in, how much vacuum is the saw actually creating when running on each stroke, and how likely is this slow leak (wherever it may be) to affect anything under that vacuum condition on an engine cycle that lasts a tiny fraction of a second.
The one gentleman thinks I’m in the clear, others seem to suggest I need to get the saw completely tight.
————-
Side note - I was searching other threads for a vac loss spec and came across one that mentioned a test on the Stihl 041. Someone mentioned in that thread a couple places in the oiling system that could cause a vac/pressure leak.
Does the 028 oiling system have a similar setup that can be the culprit? I mention that only because a bar oil leak is another issue I need to solve while the saw is torn down.
Sam R
8mm Socket
It's the same, plus or minus - should not lose more than 3 psi in 20 seconds. If it's a slow leak and you determine it to be your seals - I can't remember if 028 is a clamshell or not, 291 is if that means anything - you can decide whether to do the seals and crankcase if you're tearing it down anyway.
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The oil pump is driven by the gear on the sprocket.
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271/291 is driven by a worm gear driven by the sprocket.
Sam R
8mm Socket
I have seen those small screw holes leak before - drives you mad trying to find that leak...
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Oil pump mount screws?
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On the ms291?
Or the 028?
Or the 028?
I’m talking 028, but I can’t answer for what the other guy is referring to.
Sam R
8mm Socket
Come to think of it I believe that leaky oil pump mounting-hole was an 038 Super...
You can get trashed inner tubes from a bike/cycle shop for free. I like the one from truck/tractor tires.
028 is NOT a "clamshell"
Oiling system is not connected to crankcase for vacuum concerns unless case gasket is pooched., not likely unless case has been apart or corrosion.
Leaking oil is a worn pump or pump internals. I think seal o-rings gasket are still available from stihl
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Yeah, I was reponding to him.
The 041 has a different oiler system..
Here is a pic of the 041 off of the web...
The 041 has a different oiler system..
Here is a pic of the 041 off of the web...
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The 028....
Sam R
8mm Socket
I had an 041 once that the crankcase gasket leaked between the crankcase & oil tank. 028 is a split case too - now that you went and made me look it up; it it's losing oil that's a possibility. You can detect such a leak by opening the oil tank and looking in there when you're pressurizing the crankcase. If you see bubbling with oil in the tank, then you're crankcase seam is leaking.
That said, Stihl specs call for less than 3 PSI leak down in 20 seconds. But any leak is cause for some concern and you should seek the source of it. Because like all things they get worse if left unaddressed.
Perfect. I’m learning lots here. Looks like conversion from psi to inches Hg is roughly 2. So 6 inches in 20 seconds is spec. Bear with me as I geek out.
My saws leakdown from 20 inches took 144 seconds, which is a slower leak that 6 inches in 20 seconds.
Or are we saying “pump up to only the 6 inch mark, and see if it takes at least 20 seconds to reach zero?”
On my gauge the vac leakdown does not seem to be linear at all as I watch it.
Sam R
8mm Socket
I just went and read the 028 service manual regarding pressure/vacuum testing. Some of this is a little out of date; I don't know what purpose putting the piston at TDC really serves. If you're going through the intake port you just want your piston up enough that it's not blocking air from getting into the crankcase.
It gives measurements in BAR; it says pressurize to .5 BAR & vacuum to -.5 - then you should have no leak down from pressure & no more than .3 and hold on vacuum. It suggests that if you leak down more than that your seals need replaced. I guess I knew that, in my experience they either leak massively during pressure or not at all.
It gives measurements in BAR; it says pressurize to .5 BAR & vacuum to -.5 - then you should have no leak down from pressure & no more than .3 and hold on vacuum. It suggests that if you leak down more than that your seals need replaced. I guess I knew that, in my experience they either leak massively during pressure or not at all.
If there was a leak between crankcase and bar oil tank, wouldn’t that result in bar oil in the crankcase rather than outside in a puddle?
Come to think of it, would a leak in that area cause bar oil to move into crankcase while case is under vacuum? And perhaps fuel mix to even enter the bar oil tank when case is pressurized?
If I happen to have THAT kind of issue, this saw is going to be sold for parts. Not enough real or sentimental value for me to be splitting the case.
Sam R
8mm Socket
On the compression stroke it would suck oil from the tank which would probably find its way into the combustion chamber, you'd end with a lot of varnished parts & probably some smoking. Power stroke would probably blow a bit of fuel into the oil tank, which could in theory thin out your oil.
It was the exhaust block. Once I had that good it held from 16 inches to 13 for like 11 minutes. Took twenty minutes to leakdown to 8.
I’m moving on. Just figured out my T27 scrench is too fat for the cylinder bolts. Stuck without the right tool for tonight.
I’m moving on. Just figured out my T27 scrench is too fat for the cylinder bolts. Stuck without the right tool for tonight.
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