STIHL The Official Stihl Chainsaws Thread

[spencerdiesel]

Thanks! It’s the first fastener I’ve come across that siezed on the way out. I’ll try heat first

 

[Yukon Stihl]

Take a candle when you have it heated up and melt it on the threads it will wick it's way down and provide sliptivity even if its cold.

 

[PogoInTheWoods]

It seems to me that a decent penetrating product would work better simply due to the lower viscosity. ' Course neither approach will do much if the the parts are bound up vs. crusted together. Now if the fastener can be turned back in with some gentle persuasion, it may be a different story for both approaches.

 

[spencerdiesel]

Thanks you both I’ve still yet to access that saw but my 1st chance I’m trying all of the above one at a time!
This other 046 I’m working on (same one I was cleaning the scored jug for) has the paint in the crankcase all bubbles up. I’ve run across this once before but what causes it? Why do they paint the inside of the crankcase anyway?

 

[spencerdiesel]

I’m vacuum and pressure testing this same saw right now. With pressure, it dropped from 5 to 3 psi in 4 minutes. Vacuum showed essentially the same loss rate. What is considered acceptable for loss in these tests?

 

[PogoInTheWoods]

It shouldn't leak. That said, small leaks at the spark plug or decomp can usually be tolerated since they're not actually affecting air/fuel considerations. They're also common. Anything associated with the integrity of the intake assembly and/or bottom end should be identified and fixed, imho. If you can see the leak on a gauge, you can find it and fix it with enough patience. Some are just a lot more difficult to pin down than others.

 

[Woodslasher]

It shouldn't leak. That said, small leaks at the spark plug or decomp can usually be tolerated since they're not actually affecting air/fuel considerations. They're also common. Anything associated with the integrity of the intake assembly and/or bottom end should be identified and fixed, imho. If you can see the leak on a gauge, you can find it and fix it with enough patience. Some are just a lot more difficult to pin down than others.

In the Stihl book for my 461 it said that "you should not have a pressure loss greater than blah blah blah in 30 seconds" and something similar for vacuum too, fyi. So, while it's not great to have a pressure loss Stihl might allow a slight loss.

 

[PogoInTheWoods]

Certain service specs seem to allow for some degree of leakage just as a "time to repair" fudge factor and Stihl is no exception. That started to change when vacuum testing entered the picture and guys figured out that just passing a pressure test was just that -- passing a pressure test. A bad seal can hold pressure all day long and not produce a bubble under enough PSI. Put some vac to it and it opens right up.

The reality, of course, is that a crankcase only needs to be so tight to create the pulses to drive a carburetor accelerator pump. And other intake leaks can effectively be tuned out if not real bad or unless there's a significant seal leak. Hence, some wiggle room in a shop manual for a fast track bench or a lazy tech.., or both. Some older saws also have lower tolerances for seals in their specs and are only rated for holding so much pressure. Push too much over the spec and they will leak. Back off to whatever the spec is and they hold.

Ideally, a saw should hold vac and pressure all day long..., because it can. At least that's the way I look at it and how I approach my repairs. They don't all turn out that way, but my +/- margin is sorta in the "how long is the saw gonna be running and what's the demand gonna be before it gets shut off" method of arbitrarily allowing a saw with any leak out the door and into a customer's hands -- with full disclosure, of course. Some saws aren't worth the trouble and will just keep on running anyway. Others can be time bombs just waiting to finally lean out hard into an expensive meltdown.

I do my best to eliminate leaks. Not pretend they aren't bad enough to mess with.

 

[northwest saws]

Here's the page from an ms460 service manual.

Sent from my SM-N970U using Tapatalk

 

[spencerdiesel]

Thanks you all! This saw is not a customer saw and I originally designated it as a parts saw in my mind.
I snugged the intake clamp (I’m very conservative when tightening things with no torque specs) and tested again. This time it took over 2 minutes to drop from 5 to 4 psi. The decomp was intact for this as well. Thanks again you all

 

[PogoInTheWoods]

So, while it's not great to have a pressure loss Stihl might allow a slight loss.

Ironically, they originally considered a crankcase airtight if there was no drop in pressure. Any drop in pressure required diagnosis and correction. They still gave some wiggle room to vacuum. Then they loosened their standard to holding o.5 Bar (7.25psi) for 20 seconds during a pressure test..., which is dubious at best if it leaks at all. They now again consider any leak unacceptable, including vacuum.

To put this into perspective, the first thing that needs clarification is how the measurement terms are tossed around and how they relate. So let's clarify that. After initially using kp/sq. centimeter as the form of pressure/vac measurement, they transitioned to the bar method and still use it today, but with PSI and in/Hg now also being referenced in some technical documentation. To more easily understand what our MityVacs are telling us, we generally need to convert what's in the shop manual to what's on the gauge.

0.5 Bar = 7.25psi and 14.76 in/Hg -- vacuum. So if your vacuum rises from o.5 bar to 0.3 in 20 seconds, you've lost nearly 50% of the seal -- in 20 seconds. Make no mistake -- it will continue to leak down to 0 within the next 30 to 60 seconds in almost every instance unless there is a specific seal tolerance that stops the leak at around 0.3 bar / 7~8 in/Hg. (I have actually had that happen on an 045 I recently rebuilt and wrote it off as the proprietary NOS seal that I used.) The same will hold true for pressure in nearly every instance. And while 0.3 bar / 4.3psi may still run a fuel pump diaphragm, anything much less will eventually become a problem.

BTW, I also read in an old-ass Stihl manual somewhere to use a screwdriver to 'gently pry' a crankcase apart. Didn't think that was very good info either! LOL

The thing is, these are usually easy leaks to find and fix. Just fix em or learn how to if you haven't chased too many yet. If you work on saws often enough, you'll find your vac/pressure test setup to be one of your most valuable investments for both fixing stuff right, and your peace of mind when you're done with a job or project. Anything else is just guessing. If you find a leak, fix it.

That's what the MS462 C-M and other new Stihl manuals now tell ya to do.

Sorry for the lengthy post. And not that it's the case here or I'm implying anything, but I just find it curious that some folks will spend more time trying to come up with reasons to NOT do a vac/pressure test than it would take to do one in the first place. Hell, I was that guy many years ago. Just trying to encourage folks to go the extra mile. It becomes routine before you know it.

 

[RI Chevy]

Anyone know if this will be available from dealers? ?

 

[Maintenance Chief]

Ironically, they originally considered a crankcase airtight if there was no drop in pressure. Any drop in pressure required diagnosis and correction. They still gave some wiggle room to vacuum. Then they loosened their standard to holding o.5 Bar (7.25psi) for 20 seconds during a pressure test..., which is dubious at best if it leaks at all. They now again consider any leak unacceptable, including vacuum.

To put this into perspective, the first thing that needs clarification is how the measurement terms are tossed around and how they relate. So let's clarify that. After initially using kp/sq. centimeter as the form of pressure/vac measurement, they transitioned to the bar method and still use it today, but with PSI and in/Hg now also being referenced in some technical documentation. To more easily understand what our MityVacs are telling us, we generally need to convert what's in the shop manual to what's on the gauge.

0.5 Bar = 7.25psi and 14.76 in/Hg -- vacuum. So if your vacuum rises from o.5 bar to 0.3 in 20 seconds, you've lost nearly 50% of the seal -- in 20 seconds. Make no mistake -- it will continue to leak down to 0 within the next 30 to 60 seconds in almost every instance unless there is a specific seal tolerance that stops the leak at around 0.3 bar / 7~8 in/Hg. (I have actually had that happen on an 045 I recently rebuilt and wrote it off as the proprietary NOS seal that I used.) The same will hold true for pressure in nearly every instance. And while 0.3 bar / 4.3psi may still run a fuel pump diaphragm, anything much less will eventually become a problem.

BTW, I also read in an old-ass Stihl manual somewhere to use a screwdriver to 'gently pry' a crankcase apart. Didn't think that was very good info either! LOL

The thing is, these are usually easy leaks to find and fix. Just fix em or learn how to if you haven't chased too many yet. If you work on saws often enough, you'll find your vac/pressure test setup to be one of your most valuable investments for both fixing stuff right, and your peace of mind when you're done with a job or project. Anything else is just guessing. If you find a leak, fix it.

That's what the MS462 C-M and other new Stihl manuals now tell ya to do.

Sorry for the lengthy post. And not that it's the case here or I'm implying anything, but I just find it curious that some folks will spend more time trying to come up with reasons to NOT do a vac/pressure test than it would take to do one in the first place. Hell, I was that guy many years ago. Just trying to encourage folks to go the extra mile. It becomes routine before you know it.

I have a mighty vac and I do alot more carburetor work with it than pressure checks ,but if I even suspect that a seal is leaking I change it now.
The cost of most of my saws are minimal so a little investment isn't going to kill a project. After all I bought my 044 for 175.00 with a bad piston and if I spend 40.00$ on a piston and 40.00$ on seals I consider it a good investment ( not that I paid that muchfor seals) But why would I risk burning up the top end? There's lots of simple tests for identifying a bad seal that work pretty good, for the weird stuff I'll break out the mighty vac.

 

[spencerdiesel]

I’m constantly learning from y’all’s feedback, thank you! Here’s the piston from that saw. HEAVY scoring on the exhaust side with nothing on the intake (barring “normal” wear).
The saw had been lean enough to burn premix on the underside of the piston.
Do y’all think this was mainly a lean condition, possibly ended with straight gassing?
The rod big and little ends still retained a decent amount of oil, so that makes me wonder.
*Also, the carb was filthy (restricted fuel flow/ lean?) and the impulse line wouldn’t hold pressure AT ALL, would leak from 5 psi to 0 in about 20 seconds. I then replaced the impulse and it held as stated a few posts ago.

 

[Yukon Stihl]

You may have found the leak that caused it.
Are going to clean the jug and get a new piston?
Vac and pressure test after you are done.

 

[spencerdiesel]

Yes sir that’s what I’m leaning towards as well, the more I think about just how bad it leaked at the impulse line.
I cleaned the transfer out of the jug, pictures are a page or two back. I’ve installed a new meteor piston and checked squish.
While on squish, any of y’all ever get “big” variation on different areas of the squish band? I use 4 pcs of soldor at each “corner” of the piston and have had close numbers with the other 4 engines I’ve checked so far.
On this one, one area measured .020”, and another ran .027”. I checked it again with new soldor and got the same things. What do you all think?

 

[PogoInTheWoods]

If the rings are sloppy (or you're measuring without them), and the .027 numbers are from the intake and exhaust sides of the cylinder, the piston could be rocking that much at the wrist pin axis. Otherwise, I think I'd be looking for debris or something else as the cause. Maybe even the piston. That's a pretty large discrepancy.

 

[spencerdiesel]

I think you’re right, the piston was ring less. I’ll put the new cabers on and check again thanks!

 

[Maintenance Chief]

Had the dynamic dou out today for some work. MS441C and the 066 round top.

 

[spencerdiesel]

Well with both rings……it’s exactly the same lol. I guess it makes sense, solder at 4 corners I guess canceled out any rocking without rings.
Top is 1st measure, left is 2nd, Right one is after installing rings