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Stihl 024AV Trouble

ses0030

ses0030

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My buddy has an old West German Stihl 024AV that he gave me (and a bunch of other random weed eaters) to fix up for him. According to my friend, the saw ran fine until he started messing with the carb, and then it sat for a while.

Since he indicated carb troubles, I first adjusted all the carb settings back to stock but couldn't get it started. I then cleaned the carb but it was obvious someone had already been in the carb since the head on the needle screw was rounded slightly. I bought a replacement carb off of eBay and used that but still couldn't get the saw started.

I've verified that I've got spark, I've cleaned the spark arrestor on the muffler, replaced the impulse line, replaced a worn fuel cap gasket, and replaced the fuel line. I inspected the flywheel but couldn't verify that the flywheel key was good since I don't have a flywheel puller and I couldn't persuade the flywheel off by tapping with a hammer.

I finally got a hold of a compression tester today and compression was ~90psi which is low. I wanted to ask what my next step should be. I feel like it's a piston and rings but wanted to ask the experts first. Haven't had a two-stroke be this stubborn before...
 

rd35

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Did you try pouring a dribble of gas down the carb throat to see if it will fire? That series of saws had a big problem with air leaking past the choke flap on air filter. If it starts up and runs good with a few drops of gas in the carb then I would recommend taking a good look at (or just replacing) the air filter assembly.
 
irhunter

irhunter

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To review: unknown cause and 90 psi.
That says to me, pressure and vac test the saw then pull the cylinder.
Do not order any parts until you have done the press/vac tests and have the jug off.

Roy
 
Bob Hedgecutter

Bob Hedgecutter

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If you have established fuel is getting to the carb and through the carb to the cylinder- eventually after pulling the rope for 10 minutes it is flooding out the exhaust, then think about using the poor mans lack of compression definer.
Take out the spark plug and throw some oil down the hole the plug came out of. You can use a syringe, a teaspoon, pump oil can - whatever you have at hand and whatever oil you have at hand- I have used bar oil before, but if you have a bit of 4 stroke engine oil laying about, use that.
For an 024 you want about a teaspoon or so of oil, down the plug hole and then swilled around to coat the top of the piston/cylinder wall.
Now try to start the saw normally- if it fires it will be running a bit rough and smoke like a mosquito fogger- but it will confirm low compression is your answer.
The reason for the suggestion is your reported 90psi reading- might be true, or it might be a reading from a gauge not designed to give a true reading off of such a small engine cylinder- automotive gauges hardly ever give a true reading of a chainsaw engines compression.

Certainly photographs of the piston scoring and the ring land area, from through the exhaust port will confirm if it is really roasted- because at this stage we are all guessing a diagnosis.
 
ses0030

ses0030

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PXL_20210908_010733504.jpg PXL_20210908_010715998.jpg PXL_20210908_010709094.jpg

Here are a few pictures of the piston. I have not done a wet compression test or a presure/vac test yet but those are good ideas.

I did try dribbling gas in the carb but could not get it to run.
 
Crispexx

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View attachment 928575 View attachment 928574 View attachment 928573

Here are a few pictures of the piston. I have not done a wet compression test or a presure/vac test yet but those are good ideas.

I did try dribbling gas in the carb but could not get it to run.
Oh yea man, that is a well used piston! if you have the ability to, next step is to vac/pressure test it to see if it has an air leak. best to try and find the source of the scored piston before just slapping another one on.
 
Bob Hedgecutter

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Yep, I would say the gauge you used was probably fairly accurate, piston is toast- cylinder more than likely toast- but might be able to be saved.
You can dribble mixed gas into that until the cows come home- it aint likely to ever run in its current state,
 
a. palmer jr.

a. palmer jr.

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Yes, I would replace the top end on that saw but be sure to pressure/vac test it afterward, before it's started to make sure it doesn't have an air leak. Since it's an older saw it wouldn't hurt to replace the crank seals and at least check the intake boot.
 
irhunter

irhunter

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next step is to vac/pressure test it to see if it has an air leak. best to try and find the source of the scored piston before just slapping another one on.
+1

I like to vac and pressure test before pulling the jug. That way, your to-buy-parts-list is more complete before you even think of buying a piston, or whatever.
 
a. palmer jr.

a. palmer jr.

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There is a post in AS on this, the 024 and 026 do not share the same piston stroke but the 024 Super and 026 do. If you have a regular 024 you cannot change it to an 026 just by changing cylinders, you have to also change the crankshaft and rod, piston and cylinder. I've owned both and there's not that much difference between the two, I'd just rebuild it back as stock 024.
 
irhunter

irhunter

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After finding cause, check to be sure if it's a 024 or 024 super, top ends are different and pretty sure 026 parts will fit the super

There is a post in AS on this, the 024 and 026 do not share the same piston stroke but the 024 Super and 026 do. If you have a regular 024 you cannot change it to an 026 just by changing cylinders, you have to also change the crankshaft and rod, piston and cylinder. I've owned both and there's not that much difference between the two, I'd just rebuild it back as stock 024.

However, this goes...in my mind, one thing is certain...it is always a good idea to measure the diameter of your piston before ordering anything for just about any saw.
 
ses0030

ses0030

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Finally got some free time (and the tools) to do a pressure/vacuum test. Surprisingly the saw passed with flying colors. No leaks under either pressure or vacuum. Hopefully, I'll get some time soon to take apart the cylinder and pull the piston.
 
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