Stihl 024 to 026 Needs Some TLC

[Wood Doctor]

I recently upgraded a non-running Stihl 024 to an 026 top end and added a new carb, new air filter, new plastic. I cut a truckload of wood with it today:


The engine always starts and runs rather well except (1) it lacks WOT power and (2) it smokes a little too much. Running on the same fuel, my 026 PRO does not smoke and will cut circles around it. It seems that no carb adjustments have much effect. The amazing thing is that it's idling OK, accelerates OK, and always starts. Any suggestions for improving (1) and (2)?

 

[stihl saws]

Was it a standard 024 or a super? The crank is shorter on the standard 024 vs the super. You have to have the 024 super crank to make a 026 top end work.

 

[Chris Zautner]

 

[Wood Doctor]

As originally built in West Germany, this saw was a Stihl 024 AV Wood Boss. Serial number is 115606185.

I really do not expect it to run with my 026 PRO, but it seems like it could be delivering more grunt and less smoke.

 

[T.Roller]

As originally built in West Germany, this saw was a Stihl 024 AV Wood Boss. Serial number is 115606185.

As stated the 024 non super has a shorter stroke, with a 026 top end you will have a hard time getting much out of it

 

[DSS]

I thought you had to start with a super or you had issues with case clearance?

 

[T.Roller]

Check the clearance on the piston. Bet it has tons. Check compression. The shorter stroke will make it a real turd. It would run much better as a 024

 

[paragonbuilder]

Have you checked squish? If it's an 024 with a stock 026 top end you will have 2mm extra squish which is like .08"
If you machine the cylinder it would help...


Sent from my iPhone using Tapatalk

 

[Wood Doctor]

I was told that a Stihl 024 AV Wood Boss is the same engine as the 024 Super. That means it had a 44.3 cc displacement, a 42 mm bore, and a 32 mm stroke. The stroke is the same as an 026. I increased the bore to 44 mm when I installed the larger top end.

If the squish were 0.08", I really don't see how the engine could start and run as well as it does. However, it could be the shorter stroke. There was an 024 AVS Wood Boss made, and that S on the end of AV would then indicate a Super. Anybody know?

 

[paragonbuilder]

I was told that a Stihl 024 AV Wood Boss is the same engine as the 024 Super. That means it had a 44.3 cc displacement, a 42 mm bore, and a 32 mm stroke. The stroke is the same as an 026. I increased the bore to 44 mm when I installed the larger top end.

If the squish were 0.08", I really don't see how the engine could start and run as well as it does.

If it has the same stroke as the 026 then you are right it should be good. Easy to check. Also check compression. Maybe a pinched fuel line restricting flow at full throttle, or aftermarket ones sometimes collapse under vacuum.


Sent from my iPhone using Tapatalk

 

[jacob j.]

Did it get new rings? Lack of power, combined with more than normal smoke is a classic symptom of worn out ring(s).

 

[Wood Doctor]

Did it get new rings? Lack of power, combined with more than normal smoke is a classic symptom of worn out ring(s).

Yes, the whole top end was replaced, including new rings. I have a feeling I have the shorter stroke engine, so the new jug is looking for 1.26" (32 mm) rather than the 1.18" (30 mm) that's on board. Does that seem reasonable?

Looks like lots of fuel is not being burned, that produces the smoke, and that's what is starving the engine for power. Is there any other easy fix other than a whole new top end? Machining the cylinder may be the only other possibility. Am I right?

 

[T.Roller]

Yes, the whole top end was replaced, including new rings. I have a feeling I have the shorter stroke engine, so the new jug is looking for 1.26" (32 mm) rather than the 1.18" (30 mm) that's on board. Does that seem reasonable?

Looks like lots of fuel is not being burned, that produces the smoke, and that's what is starving the engine for power. Is there any other easy fix other than a whole new top end? Machining the cylinder may be the only other possibility. Am I right?

Correct

 

[jacob j.]

I don't think there's enough meat on the base of the cylinder to machine it down that far. The easiest fix is to get the correct crankshaft and just split the case halves and throw it in there. That way you can address any other parts that need replaced.

 

[Wood Doctor]

Correct

Well, it does also seem reasonable to check the squish to be sure before I tear it down. I rebuilt an 024 AV Wood Boss with the same new top end kit and the owner says it runs flawlessly. Also, if compression were really that bad, it seems like it would not start and idle correctly. I'll check compression also. This one is still somewhat of a a mystery to me.

 

[T.Roller]

Well, it does also seem reasonable to check the squish to be sure before I tear it down. I rebuilt an 024 AV Wood Boss with the same top end and the owner says it runs flawlessly. Also, if compression were really that bad, it seems like it would not start and idle correctly. I'll check compression also. This one is still somewhat of a a mystery to me.

Check compression than check squish. You may be correct, I have made many mistakes lol just the first thing that came tomind

 

[odin]

The IPL that I have lists the following numbers for 024 cylinders:

024 - 1121-020-1200

024S - 1121-020-1201

Just cross-reference your takeoff cylinder to know for sure what you're 024 really is.

 

[Gunn]

Has the debate about 024 vs 026 crankcases ever concluded?

Some people claim a crank swap is all that's needed with the 024 to use the 026 top end.

Others claim there's differences between the 024 vs 026 crankcases and the rod angle is incorrect is you swap in an 026 crank?

 

[T.Roller]

Has the debate about 024 vs 026 crankcases ever concluded?

Some people claim a crank swap is all that's needed with the 024 to use the 026 top end.

Others claim there's differences between the 024 vs 026 crankcases and the rod angle is incorrect is you swap in an 026 crank?

My 026 has a 024 super complete bottom end. Works just fine until I crushed it lol

 

[Wood Doctor]

My 026 has a 024 super complete bottom end. Works just fine until I crushed it lol

The 024 AV that I rebuilt (the one that works flawlessly) was run over by a pickup truck. The case survived but almost nothing else did. New tank housing, new plastic, new top end, new bar studs, new shock mounts, new chain brake, new outer handle, new trigger, etc. The owner wanted too see if I could restore it because his late brother bought it (and ran over it). Total cost of all parts was about the same as a new MS 240.