Stihl 024 AVS with strange symptoms

[SteveSr]

So I just did some work. The main things I did were clean the muffler and clean off/ readjust the coil - it appears to have solved the smoke, and excessive heat - hurrah! It’s running decent now. However the racing idle when tipped on its side is still there.

I went to attempt a pressure test (I have plenty of bicycle inner tube) but I couldn’t figure out how to access the impulse line with the carb installed, nor could I find another way to clamp the tube over the inlet port without a fair amount of work making/buying an adapter. The carb has a barb that goes straight into the impulse line, so it is fully covered when the carb is installed. Am I missing something?

Below is a link to a video showing how it is currently running. I’m thinking I had two problems, I solved one, and now I just have to track down an air leak?

From the video - bad crank seals. Well, the saw is only 40-45 years old! Don't try to run it (especially inder load) with an air leak. Also could be a torn intake boot.

Before going further remove the muffler cover and post a photo of the piston and rings as seen through the exhaust port. The piston might already be scored by the P.O.

For leak testing you can use a spark plug adapter and leave the impulse line connected to the crankcase and carb.

Did you use OEM seals? Did you install them to the correct depth?

 

[stihltech]

Remove the pump side of the carburetor to access the pulse hose for vacuum and pressure test. It will still hold the rubber on the intake for testing.
IF the test is OK, I would definitely check the lever height in the carb and pressure test it again. Also make sure the metering diaphragm buttons in the center of the diaphragm are the same height. Pressure test carb with the metering side on and off.

 

[Bob Hedgecutter]

During the "rebuild" did the cylinder come off the saw?
Could be your initial smoky start up was washing any residual oils and crap from the crankcase left overs from the previous owner of the garage that was having a sale.

Also, during the "rebuild" what method did you use to get the seals past the crank steps?

 

[ktpnw]

From the video - bad crank seals. Well, the saw is only 40-45 years old! Don't try to run it (especially inder load) with an air leak. Also could be a torn intake boot.

Before going further remove the muffler cover and post a photo of the piston and rings as seen through the exhaust port. The piston might already be scored by the P.O.

For leak testing you can use a spark plug adapter and leave the impulse line connected to the crankcase and carb.

Did you use OEM seals? Did you install them to the correct depth?

Seals were not OEM, but appeared to be of good quality. I know that’s not saying much, I generally always use Oem parts but they Oem seals were double what I paid for the saw, and the ones I used were well reviewed. I was careful to set them to the correct depth (or at least, matched the depth of the ones that were in there, which appeared original)

 

[ktpnw]

Remove the pump side of the carburetor to access the pulse hose for vacuum and pressure test. It will still hold the rubber on the intake for testing.
IF the test is OK, I would definitely check the lever height in the carb and pressure test it again. Also make sure the metering diaphragm buttons in the center of the diaphragm are the same height. Pressure test carb with the metering side on and off.

Good call, makes sense. How do I check the metering lever height? I haven’t been able to find a spec for this model carb.

 

[Bob Hedgecutter]

Seals were not OEM, but appeared to be of good quality. I know that’s not saying much, I generally always use Oem parts but they Oem seals were double what I paid for the saw, and the ones I used were well reviewed. I was careful to set them to the correct depth (or at least, matched the depth of the ones that were in there, which appeared original)

yes- but how did you get them over the crank step?
Cheaper seals are often only single lipped- so can be more easily damaged during installation- I had a bur on a keyway crank stub cut two brand new seals before I figured out it was there.

 

[ktpnw]

During the "rebuild" did the cylinder come off the saw?
Could be your initial smoky start up was washing any residual oils and crap from the crankcase left overs from the previous owner of the garage that was having a sale.

Also, during the "rebuild" what method did you use to get the seals past the crank steps?

No, did not remove the cylinder. As far as installing the seals, I used a socket and plastic mallet (carefully, set to the correct depth) as I saw on YouTube.

 

[ktpnw]

yes- but how did you get them over the crank step?
Cheaper seals are often only single lipped- so can be more easily damaged during installation- I had a bur on a keyway crank stub cut two brand new seals before I figured out it was there.

Gotcha, makes sense. Certainly possible. Sounds like a pressure test is what I need

 

[Bob Hedgecutter]

Good call, makes sense. How do I check the metering lever height? I haven’t been able to find a spec for this model carb.

I would have to go look through some old manuals, but pretty sure the old HU 54 carb metering lever height is flush with the diaphragm chamber floor.

 

[ktpnw]

I would have to go look through some old manuals, but pretty sure the old HU 54 carb metering lever height is flush with the diaphragm chamber floor.

Great, thank you. I will check that as we’ll.

 

[Mad Professor]

Seals were not OEM, but appeared to be of good quality. I know that’s not saying much, I generally always use Oem parts but they Oem seals were double what I paid for the saw, and the ones I used were well reviewed. I was careful to set them to the correct depth (or at least, matched the depth of the ones that were in there, which appeared original)

Gasket set is cheaper than OEM seals

 

[Bob Hedgecutter]

Good call, makes sense. How do I check the metering lever height? I haven’t been able to find a spec for this model carb.

https://tillotson.ie/wp-content/uploads/2015/07/techinfo_hu_eur.pdf

 

[flatsfisher]

So I just did some work. The main things I did were clean the muffler and clean off/ readjust the coil - it appears to have solved the smoke, and excessive heat - hurrah! It’s running decent now. However the racing idle when tipped on its side is still there.

I went to attempt a pressure test (I have plenty of bicycle inner tube) but I couldn’t figure out how to access the impulse line with the carb installed, nor could I find another way to clamp the tube over the inlet port without a fair amount of work making/buying an adapter. The carb has a barb that goes straight into the impulse line, so it is fully covered when the carb is installed. Am I missing something?

Below is a link to a video showing how it is currently running. I’m thinking I had two problems, I solved one, and now I just have to track down an air leak?

the carb should be off, and the intake blocked to do the pressure and vacuum tests.

 

[Bob Hedgecutter]

the carb should be off, and the intake blocked to do the pressure and vacuum tests.

unless- you have no suitable material to make an intake blocking device that works properly and you do not use the method described by @stihltech above, then the carb kind of has to be there to hold a simple piece of flat rubber against the manifold.

 

[ktpnw]

https://tillotson.ie/wp-content/uploads/2015/07/techinfo_hu_eur.pdf

Thank you! Very helpful

 

[ktpnw]

Well I tore it all apart today and there’s good news and bad news. Good news is that the cylinder head gasket looked pretty terrible, I’m guessing that was the source of the leak. Bad news is the piston and cylinder are lightly scored. I say lightly because I can barely feel it with my finger, but I can feel it (and see it). It still seemed to have pretty decent compression (can easily hold it up with the pull rope) but it’s definitely not perfect. I think I will put it back together with the new gasket and see how she runs, not sure a $25 saw is worth a $200 piston and cylinder.

I did check the metering lever (it was very very close but I tweaked it a tad) and the intake boot which seemed fine. So hopefully once I get a new gasket I’ll have at least a pretty functional little saw, and I’ll keep my eye out for a lightly used piston/cylinder. Thanks again to all for the help and advice.

 

[Bob Hedgecutter]

Well I tore it all apart today and there’s good news and bad news. Good news is that the cylinder head gasket looked pretty terrible, I’m guessing that was the source of the leak. Bad news is the piston and cylinder are lightly scored. I say lightly because I can barely feel it with my finger, but I can feel it (and see it). It still seemed to have pretty decent compression (can easily hold it up with the pull rope) but it’s definitely not perfect. I think I will put it back together with the new gasket and see how she runs, not sure a $25 saw is worth a $200 piston and cylinder.

I did check the metering lever (it was very very close but I tweaked it a tad) and the intake boot which seemed fine. So hopefully once I get a new gasket I’ll have at least a pretty functional little saw, and I’ll keep my eye out for a lightly used piston/cylinder. Thanks again to all for the help and advice.

Make a gasket- or delete the gasket and use liquid gasket maker if squish allows.

Lets see some photos of the "scoring" is it scratches or transfer of smearing aluminium up the face of the cylinder?
The transfer needs to be cleaned up while you have it apart, piston needs checked over to make sure the ring grooves are good and clear- allowing the rings full movement.

 

[ktpnw]

Finally had a chance to do a pressure test, and the prognosis is grim. It is leaking from the crankshaft side seal, but the metal to metal contact (outside of the seal) not the seal to crankshaft contact. Either I or the previous owner (probably me) must have scored that part while removing the old seal. That seems like a hard issue to solve. Does this saw sound like it is a wall ornament (or part out)? I did only pay $25 for it, so if so that’s not a huge deal.

Attached are a couple photos of the piston and cylinder. The rings do move freely in the grooves, and again it does feel like it has good compression.

Thanks again for all the help and advice.

 

[Bob Hedgecutter]

Finally had a chance to do a pressure test, and the prognosis is grim. It is leaking from the crankshaft side seal, but the metal to metal contact (outside of the seal) not the seal to crankshaft contact. Either I or the previous owner (probably me) must have scored that part while removing the old seal. That seems like a hard issue to solve. Does this saw sound like it is a wall ornament (or part out)? I did only pay $25 for it, so if so that’s not a huge deal.

Attached are a couple photos of the piston and cylinder. The rings do move freely in the grooves, and again it does feel like it has good compression.

Thanks again for all the help and advice.

Well, leading with these photos or a clear shot of the top of and ring area of the piston could have erased a couple of pages of guessing.
But, you did due diligence and found your problem.

Cylinder should clean up, new piston and rings, new seals installed properly and you are good to go again are you not?
If pocket is scored- lets see it- aerobic sealer applied when installing seal may cure it- might just be you drove the seal in out of square.

Or did you pop the old seal by trying to drive a tool in from the outside to pry it up?

 

[ktpnw]

Well, leading with these photos or a clear shot of the top of and ring area of the piston could have erased a couple of pages of guessing.
But, you did due diligence and found your problem.

Cylinder should clean up, new piston and rings, new seals installed properly and you are good to go again are you not?
If pocket is scored- lets see it- aerobic sealer applied when installing seal may cure it- might just be you drove the seal in out of square.

Or did you pop the old seal by trying to drive a tool in from the outside to pry it up?

Yes, I started with a seal puller, which got the non-flywheel side out, but instantly broke on the flywheel side, so I popped it out with a screwdriver, which was difficult. I'd seen it done on youtube, but I'm sure I scored the inside somehow. I can't really see (or get a photo) until I get this seal out. Aerobic sealer might be the way to go. I will figure out how to properly remove and then get a new seal. Good to know that the cylinder is looking ok but I'll probably not replace the piston until I'm sure the seal problem is solvable.