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
- Start date
Help Support Arborist Forum:
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 ?
barfer
I like chopping wood
You’re not wrong. But *accuracy* is less important as *consistency* in the measurement.
Even if the cheap-o compression tester is 20 psi high or low or whatever as long as it’s consistently 20 psi high or low a guy who doesn’t want to invest in a dedicated comp tester will still have a “directionally accurate” tool that will allow him to make the diagnosis.
Personally I fall in the “only cry once” category when it comes to buying things… especially tools (cry the day you buy it and never cry again)
But for a weekend fix it guy who wants to know if he’s got a problem with his rings. Or to know if they’re wearing out faster than his other saws or whatnot…. Yeah those cheapo compression tools work just fine.
I mean… that type of user isn’t making his living shaving tenths of a second off lap times. He’s not running tests on a linear particle accelerator… he doesn’t need a swiss micrometer and an electron beam microscope
Even you pros… if you were on a desert island with nothing but piles of non-running saws, feeler gauges, a mityvac, an auto parts compression tester and basic hand tools there isn’t a single problem you wouldn’t be able to diagnose.
Would you want your good tools? Of course you do. You should see my toolboxes
. I could have been a doctor with all they’re worth… seriously. (Luckily a lot of them have been in my family for 4 generations) but most of them I bought. And yeah we pay a lot of money for those good tools… because they’re worth it.But not everyone needs that. Not everyone wants that. And I totally respect that.
To each, their own. If you compare say HF to Snap ON, which would I trust more? Agree, buy once, cry once. I'd rather buy consistent quality than wonder "what if"
A little off topic, but say you were building a garage etc.., with a tape measure that was missing a few inches. As long as that is the only one that is being used, no problem. But.....
Everyone's mileage may vary, I suppose
A little off topic, but say you were building a garage etc.., with a tape measure that was missing a few inches. As long as that is the only one that is being used, no problem. But.....
Everyone's mileage may vary, I suppose
barfer
I like chopping wood
Hey you and I are on the same page fella… there’s no question which tool I want. There’s no question which one I trust more.
When I left home I had six hundred bucks in my pocket, a 500cc Honda and a very tiny tool set of the very best made in USA tools I could afford at the time. Near the end of every month I was dead broke and counted the days until I could buy food again. Living on ramen ten packs for a dollar. I couldn’t afford to waste a single dollar. But when I bought tools I bought quality because I’ll never forget the frustration I felt years earlier pulling the big fasteners connecting the crossmember to the a-arm on that 68 Chevy with a socket wrench with a pipe on the end of it for leverage and seeing the socket literally break open because it was made in Taiwan.
To this day my brother tells the story of hearing me screaming as I lay on my back, throwing it as far as I could. (mad face) He thought the car fell off the blocks and was crushing me or something
I was so angry I had to stop what I was doing, clean up and get on the bike and go to the parts store to buy another socket. Napa auto parts was open late and sold the snap-on off brand unpolished tools that were made in USA. When they didn’t have it I had to ride out to monument auto parts in concord, CA… they had it all but it was a long trip.
As the years passed every time I broke one of those cheap tools I’d throw it in the same direction.
After my dad passed away and we were clearing the place out we took those bushes out and found a big ole pile of busted made in china and India tools and we laughed our heads off…
Anyway… not everyone can afford those good tools. Not everyone is a pro technician. Not everyone is “mechanically inclined” and I don’t fault those guys. Not a single bit. Maybe they’re great at math or accounting or whatever something else. For the past decade or so when I meet women in San Francisco they tell me “there are no real men here” and laugh.
So to those computer guys and non-mechanically inclined folks or folks who simply didn’t grow up with that training in their everyday lives… it’s not their fault.
And I applaud them for doing the research and getting their hands dirty and trying something new—as long as they aren’t doing anything dangerous. And maybe that guy doesn’t want to spend $300 on a set of end wrenches on his first try. At least he’s trying. He’s learning. He’s broadening his skill set.
Not everyone was fortunate enough to have mentors train them in this stuff. Not everyone went to night school at contra costa junior college while they worked 60 hours a week taking welding classes even though he’d been welding since he could hold a torch… not everyone had that training. I sure am grateful to all the mentors and folks who trained me. I’ve spent a good part of my life trying to pass that on to the younger generations. Less and less of them seem interest in it (shrug)
So… you’re not wrong. Someday they’ll learn that buying junk tools is a total and complete waste of money… but hey if it’s part of their journey I don’t look down on them for it. If anything the opposite is true.
I tell some of the other old guys (and myself) “remember… there was a time when WE didn’t know anything… we all had to learn”
Anyway… you’re not wrong. But for those beginners out there who want to learn and spend money on harbor freight tools they’re going to have to throw away if they stick with it… I think about it as the price of learning… tuition of sorts… (shrug)
But mostly I applaud them for taking the initiative to learn. We should encourage them… not dump on them for not knowing stuff… for having garbage quality tools… they’ll get there… or they won’t. But the ones who get there will get there. They don’t need us to tell them their tools suck.
We *do* need to tell them when they’re doing something dangerous… if they’re using a made in china spring compressor for suspension… that’s actually dangerous… you know what I’m talking about right?
Peace my brothers (and sisters) out there
Similar threads
