SteveSr
Addicted to ArboristSite
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Well not all back together. After cylinder went back on. Held 8 psi for approximately 10 minutes. With no air bubbles anywhere.
Did I miss something? I figured they were good so leave them alone based on the pressure test. I can take it back apart and replace the seals, but they seemed fine. My assumption was if the OEM seals were good let them be rather than replacing yet. As for the air leak where would the air leak be? In the top? Im a bit confused honestly. Sorry if these are noob questions. This is my first chainsaw rebuild.
SteveSr
Addicted to ArboristSite
That should be good. Did your test include the intake boot and impulse line?
If the saw didn't originally die from an air leak it might have died from fuel starvation. Did you replace the fuel line and especially fuel filter? Next step is to pull the carb and take it apart (5 screws). What you are looking for is a stiff metering diaphragm and/or junk in the inlet screen. post photos of any interesting finds.
It still may be the questionable AM top end.
What did you use for piston circlips AM or OEM? Did they have ears on them? How were they oriented in the hole i.e. where was the gap pointing? This could be your next disaster if not correct...
that original cylinder looked fine in the pictures, I would read upon how to clean it up and spend a lt of time looking at pictures of how far the damage can get before its considered ruined then get a oem piston if it works out. Those damn fixed jet carbs can ruin a piece of equipment in a heartbeat! All it takes is a little bit of trash to block a port inside the carb body when in use, the saw starts to sound off but the user can not adjust it so it just gets ran to finish and the damage is done. On stihl carbs they like to use a clear plastic fuel pump diaphragm, they work good for x amount of time then the carb body starts punching holes into it where its supposed to seal sometimes resulting in plastic entering the carb body ports but always resulting in fuel delivery issues.
My problem with chinese cylinders/pistons is not the lack of power but instead the delamination of the cylinder wall coating when you run it hard and hot their cheap pistons deform, rings loose tension and ring pins fall tf out. Do not try to adjust it to the oem's listed max rpm in the service manual, it must be kept rich and likely maxed at 500-1000 rpm under oem specs even if attempted to lean out.
Here is a tidbit no one ever seems to mention, know about or simply ignore if known. There is supposed to be a second "flapper" one way check valve that is mounted inside the fuel tank through the vent port, it has a "tit" that is pulled through the case with a bulge in the center of the tit that locks it against the inside of the tank sealing it. One can tell that it can be fitted by looking down into the vent port, if it can be installed the hole through to the fuel tank will have a opening with the center having a spot to lock the valve in place. Check your ipl for a vent and its part #, this may not be the correct part # but it can be googled to see what it looks like. Stihl OEM Tank Vent Stem 1110-353-1600
That vent is often missing and it prevents the older style push screw vents from leaking fuel and fuel vapors profusely
My problem with chinese cylinders/pistons is not the lack of power but instead the delamination of the cylinder wall coating when you run it hard and hot their cheap pistons deform, rings loose tension and ring pins fall tf out. Do not try to adjust it to the oem's listed max rpm in the service manual, it must be kept rich and likely maxed at 500-1000 rpm under oem specs even if attempted to lean out.
Here is a tidbit no one ever seems to mention, know about or simply ignore if known. There is supposed to be a second "flapper" one way check valve that is mounted inside the fuel tank through the vent port, it has a "tit" that is pulled through the case with a bulge in the center of the tit that locks it against the inside of the tank sealing it. One can tell that it can be fitted by looking down into the vent port, if it can be installed the hole through to the fuel tank will have a opening with the center having a spot to lock the valve in place. Check your ipl for a vent and its part #, this may not be the correct part # but it can be googled to see what it looks like. Stihl OEM Tank Vent Stem 1110-353-1600
That vent is often missing and it prevents the older style push screw vents from leaking fuel and fuel vapors profusely
It did include the boot. I plugged it between carb and boot. And the impulse line I did nothing. Which now that I think about it doesn’t make a lot of sense because the impulse line connects to the bottom of the carb which means it should have breathed. Filter has been replaced. Top end was replaced. The clips had ears and were placed in the groove upon installation. I’m not sure how their orientation would cause a failure. Please elaborate. Thanks y’all.
SteveSr
Addicted to ArboristSite
Something isn't right. It should have leaked... like a sieve. Did you test for junk in the impulse line and nipple on the crankcase? with the carb removed you can put a dab of grease on the impulse connection and turn the motor over. The spark plug doesn't need to be installed. The grease should be spat out or sucked in depending on if the piston is going up or down.
Looks like you need to remove the top end again to fix the piston clips. You don't want whatever is clogging the impulse to go back in the engine.
The clips are springs and the AM ones have been well known to jump out of the groove in the piston trashing an engine. The ear is just more mass on the spring making it more likely to pop out. This is why the OEM clips are earless. The correct installation is with the clip gap facing either up or down.
Best to use OEM earless clips if the same diameter wire as the AM ones. If not, grind the ears off the AM clips, install in the proper orientation, and hope for the best.
Great info thanks.
The wrist pin retaining rings will rotate in their bore when the engine is running. I think the majority of the circlips popping out come from reusing the original wrist pin in a aftermarket piston without measuring its length to the .01...over time and measuring every one you learn that very often aftermarket pistons use a different length pin than oem to match their piston design. The incorrect length pin will pop out the clips every time under load. The second reason clips come out is they were deformed by the installer or the clips with wings are left on instead of cutting them off.
I never blamed the chi com garbage for anything. I just observed a 30 some buck piston and cylinder Kit is going to be junk. You disagree with the statement?
And it's probable an air leak took that saw down in the first place.
SteveSr
Addicted to ArboristSite
Not according to multiple Stihl repair manuals that I have read. If they rotated in use Stihl wouldn't tell you specifically how to orient them on installation.
Incorrect pin isn't good but still shouldn't be the cause of a clip coming out... unless it is cheap AM installed incorrectly thus having a high likelihood of coming out anyway.
The forces acting on the circlip (spring) are caused by the constant acceleration and deceleration of the piston as it moves up and down. If the gap faces left and right the forces exerted on the top and bottom of the clip tend to compress the spring which might make it prone to leaving the groove. This is why clip mass and orientation is important.
The "ear" is just more mass on the spring which can exacerbate the situation. These clips should be made out of spring steel which should be hard to bend. The AM clips may not be quality spring steel and thus easier to abuse (bend) during installation.
The OEM wrist pin can be a bit long for an aftermarket piston, the circlips seem to go in their groove but on the end that the second clips goes in the clip is not completely seated. The OEM pin may need to have a few thou ground off one end, one should measure or match the pin supplied with the AM piston against the OEM one before just jamming them in on a rebuild.
Patrick1903
ArboristSite Operative
Quick question, not intending to hijack. If a saw isn’t getting enough fuel, how can it produce enough power to burn itself up? Or is there a fine line where it’s slightly starved for fuel, ie leaned, but still produces plenty of power to cut? Like turning your H side in? How do you avoid this, always paying attention to carb adjustment I suppose and engine sound, adjusted to 4 stroke out of the cut? And/or preventatively replacing fuel line/filter?
This is what I found measuring wrist pins^^
Fuel is not only meant to power the engine but also cool it
Lean condition is fuel starvation, less fuel and too much air. The engine will rev higher and sound hollow, less fuel will allow the piston and cylinder to heat up drastically. Unless one has a tach permanently attached to the saw its the operators ears, eyes and hands that relay the saws condition so being tuned into how a properly set up saw engine operates is the best option.
SteveSr
Addicted to ArboristSite
Thanks, I was not considering the pin being too long. You would think that the installer would catch this as there should be a little end play on the pin. If no end play start looking for partially seated clips. Just another reason that I don't mess with AM junk.
SteveSr
Addicted to ArboristSite
Since you should be taking this apart again to check/fix the circlips you also need to take a VERY close look at the chamfers on the port edges. AM cylinders are known to have poor or no chamfers on port edges. If an unchamfered port edge catches a ring it is game-over for the engine!
Is that $30 P&C kit still a good deal?
I get to see them after the carnage has occurred and have to figure out what caused it. In the last 20 years AM parts have become popular but for me I have only installed one AM cylinder during that time, all the rest come my way already broken/damaged. For me its OEM all the way as I have worked on PRO chassis saws but am in contact with many other mechanics and saw porters, we share info on what`s good or not so good.
You are right btw. When I was inspecting it prior to assembly I noticed that it wasn’t chamfered so I did it. Great info though sir. Having worked in a machine shop for years I gave it the one over. I also ordered a new Stihl piston, rings, rod, and clips. and yesterday honed the cylinder. So we will be going back to OEM. Thanks again for y’all’s help through this. I’m enjoying the forum and the info here.
