Most here will understand this but I feel somewhat obligated to reiterate the importance of vacuum/pressure testing small two stroke equipment. Just sold a top end job on a mtronic 362. Don’t throw parts at anything before you know how it failed.
Importance of vacuum/pressure testing
- Thread starter ballisticdoughnut
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Not just small two strokes. All two strokes.
You would be surprised at the numbers of guys who seize motors several times because they didn't determine the original failure mode.
You would be surprised at the numbers of guys who seize motors several times because they didn't determine the original failure mode.
Somebody got a Stihl dealer tool box?
yes sir.
It is a guarantee that the problem will not bee a leak in the bottom end.
Yes it is nice to have a Stihl tool kit, but it is not necessary.
Many posts here and you tube on how to to it. Yes, you can buy a Harbor Freight pressure and vacuum tester and do the same thing.
And I goofed up. VACUUM and pressure, in that order.
Yes it is nice to have a Stihl tool kit, but it is not necessary.
Many posts here and you tube on how to to it. Yes, you can buy a Harbor Freight pressure and vacuum tester and do the same thing.
And I goofed up. VACUUM and pressure, in that order.
I have the stihl dealer tool box. Use the vacuum/pressure tester to test fuel lines and impulse lines is about all.
I know I am a contrarian. But , if you can't hear that a saw has a leak running it you may need to do something else.
Starter fluid with a nozzle to find it.
I know I am a contrarian. But , if you can't hear that a saw has a leak running it you may need to do something else.
Starter fluid with a nozzle to find it.
Map gas works too.
A vac/pressure test before re-building a carb is a good thing to do when testing a chainsaw. If vac/pressure test is bad, a good carb will also appear to be bad also.
barfer
I like chopping wood
Propane also… get it close… if it revs up you found the leak…
But +1 with everyone above who said you don’t need a special Stihl proprietary tool. Virtually any auto parts shop will have a compression checker that connects to the spark plug hole. Those vacuum/pressure pumps with gauge are sold by everyone from snap on to mighty-vac or cheapo harbor freight.
The compression tester is a tool that is inexpensive and I think everyone should have because even without “problems” to diagnose measuring your compression and recording it over time will tell you how your rings are wearing… how much life is left in your motor… and it really is just as easy as changing a spark plug (bwalker I know you’re thinking about sawdust falling in there right now
)Great post OP!
I've never done one yet, so I don't know. Why do them in that order?
I don’t, though it works either way.
I always test w/ pressure first to use soap spray bubbles to quickly find it/them & to keep more crap from being sucked inside the saw.
Make sure it holds 8-10 psig all day. Rotate the crank a few times if you want to. Stick an oiled up round toothpick in the seal to shaft contact area & see if the lip rebounds if you want to. Hard & old seals will keep leaking…
Then pull a 14”Hg vacuum, again should hold for hours and if it won’t hold it’s got a bad seal(s)! Squirt some light 3-1 machine oil or baby oil around the shaft to see if it pulls it in during the vacuum decay failure.
the reason for vacuum first is that a seal lip can be pushed back into place on the crank by using pressure first. Rare, but I have had it happen a few times over the years.
Will someone doing a few saws have it happen? Chances are slim. Just the way I was taught by Stihl. It works for me.
Will someone doing a few saws have it happen? Chances are slim. Just the way I was taught by Stihl. It works for me.
Good point, the rarest failure I’ve seen over 50 years of case testing is a on an 041 Super saw. Of course that saw has a dozen potential leak points listed below.
The orange oil adjuster thumbwheel’s 8mm o-ring would hold fine under pressure, but the saw would slowly fail a vac test.
A guy could have tuned around it, but it bothered me…liked to never found it.
1) PTO or Right Side Crank Seal
2) Oiler Worm Gear to shaft Seal -OR- Bar oiler gear cover seal
3) Starter/Magneto or Left Side Crank seal
4) Cylinder Jug Base to Crankcase (CC) & the Studs x4
5) Crankcase, Case halves Punch Pins (x2), & the CC Side Halves Case Gasket
Also "bubble check" the oil filler hole (Double checks the internal crankcase gasket integrity when the oil tank is a common casting). Pressure test only.
6) Impulse Line Elbow Fitting at CC & the Impulse Hose
7) #1 Lower Intake Cylinder/Shield Gasket
8) #2 Lower Intake Shield/Manifold Gasket
9) #1 Upper Intake Manifold Block Gasket
10) Bar Oiler Rate Adjuster Screw O-Ring (at rear)
11) Bar Oiler Drive Gear Front Grommet
12) Bar Oiler gear shaft brass plug (back of case)
The orange oil adjuster thumbwheel’s 8mm o-ring would hold fine under pressure, but the saw would slowly fail a vac test.
A guy could have tuned around it, but it bothered me…liked to never found it.
1) PTO or Right Side Crank Seal
2) Oiler Worm Gear to shaft Seal -OR- Bar oiler gear cover seal
3) Starter/Magneto or Left Side Crank seal
4) Cylinder Jug Base to Crankcase (CC) & the Studs x4
5) Crankcase, Case halves Punch Pins (x2), & the CC Side Halves Case Gasket
Also "bubble check" the oil filler hole (Double checks the internal crankcase gasket integrity when the oil tank is a common casting). Pressure test only.
6) Impulse Line Elbow Fitting at CC & the Impulse Hose
7) #1 Lower Intake Cylinder/Shield Gasket
8) #2 Lower Intake Shield/Manifold Gasket
9) #1 Upper Intake Manifold Block Gasket
10) Bar Oiler Rate Adjuster Screw O-Ring (at rear)
11) Bar Oiler Drive Gear Front Grommet
12) Bar Oiler gear shaft brass plug (back of case)
My limited experiences with small single cylinder engines are to get a dedicated small engine compression tester. The automotive versions, at least my Snap On has a stiffer Schrader valve along with a much longer hose. A recipe for inaccuracies if there ever was one.
Yes. You need to KNOW that your compression gauge is reading accurate on small cc engines.
I've had guys bring chainsaws to me that they had installed new piston/cylinder or rings and said that compression was lower with the new stuff and saw won't run due to low compression.
Their compression tester was not reading accurate on chainsaws.
Their gauges would read ok when checked on a air compressor tank or a automotive engine.
The saw's problem was not low compression.
Hint: The special low pressure wimpy schrader valve needs to be at the end of the hose that is connected to the engine under test.
I've had guys bring chainsaws to me that they had installed new piston/cylinder or rings and said that compression was lower with the new stuff and saw won't run due to low compression.
Their compression tester was not reading accurate on chainsaws.
Their gauges would read ok when checked on a air compressor tank or a automotive engine.
The saw's problem was not low compression.
Hint: The special low pressure wimpy schrader valve needs to be at the end of the hose that is connected to the engine under test.
If a saw will sit and idle and you don't have to turn the idle needle adjustment up. You can flip it upside down and it still idles fine. Push the nose of the bar up and down and it doesn't change the idle.
Why would you screw with it ?
Why would you screw with it ?
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