Stihl West German O24 AV Restore / Upgrade to Ported 44mm

[Paul Fithian]

Thanks again, Doc. I was just trying to replicate how it was on the NWP cylinder.

When I port the 44mm Mahle cylinder for this, I'll do that. But practice first with the scorched one I have!

 

[Paul Fithian]

Finished assembly, started right up and ran great, but one or more bearings have a bad groan and need to be replaced.



Stripped it back down to the case, need to acquire a case separator and some bearings. Any suggestions?

 

[Agent Smith]

For a case splitter, I use this style. Fits 026's and many other saws. Always worked well for me. Available on ebay and other places.

 

[drf256]

Finished assembly, started right up and ran great, but one or more bearings have a bad groan and need to be replaced.

View attachment 361628

Stripped it back down to the case, need to acquire a case separator and some bearings. Any suggestions?

What kind of groan?

If there is no side play the bearings are probably good. How is the clutch drum bearing? The bar tip roller move easily?

I’ve just never heard a bearing make a sound that let me know it was bad. Either the seals went prematurely from too much movement in them, there was grey residue in the saw from the metal actually getting ground up, or the piston got all sorts of scratches in it from metal debris.

Its not the worst idea to change out the bearings. You’ll need another oem gasket and seal kit. They are pretty large bearings for that size saw, that’s why they rarely fail.

 

[Paul Fithian]

Sounds like a dull roar. After running for a minute, you can see smoke in the exhaust from bearing heat building up.

I thought these might be bad. The saw was seized when I received it, and the miracle of Aerokroil got it moving. It did make some noise after rinsing out the case with mineral spirits, with dark gray matter in the solvent.

More to follow after I receive a splitter and bearings and can do an autopsy.

 

[drf256]

That’s different. If it was locked up, the bearings were probably rusted, packed with metal residue or both.

 

[Paul Fithian]

The Mahle 44mm cylinder went to the Doctor's office and lost 0.016" from the base. He included a very nice chamfer augmentation as well:


Thanks for the metal surgery, Doc!

 

[Paul Fithian]

Split the case and removed the crank. Corroded flywheel bearing was source of noise.

Crank and rod big end bearing in good shape for re-use.

 

[Paul Fithian]

Case assembled and shaved cylinder installed, here are new timing numbers:


Next step is to layout new port timing numbers and grind on the cylinder. Maybe these?
Exhaust - 105
Transfer - 124
Intake - 76

 

[Paul Fithian]

Been away at Porting Practice to further develop skills. Needed to make sure I didn't screw up the Mahle cylinder @Agent Smith restored and Doc shaved for me.

Very happy with how the ports turned out:





Timing numbers were pretty close to Doc's target suggestion:

When I washed out the cylinder, water flow from the lower to upper transfer showed excellent directional orientation toward the intake.

 

[Paul Fithian]

Assembled and ready for test run, possibly tomorrow




Doc's high flow air filter and 194 carb at the inlet, 3/4" holes on both sides of the muffler should enable adequate breathing.

This setup has the same bore/stroke as a current model MS251. I'll borrow my SIL's again and do some comparison cuts.

 

[drf256]

You need a new clutch drum sprocket Paul.

 

[Paul Fithian]

Agreed, ordered a new .325 rim sprocket

 

[Paul Fithian]

Happy to report saw runs perfect. Test cuts tomorrow.

Pictured next to the 024 AVS I upgraded with an unported 44.7mm P/C last year. Both made in West Germany a few months apart in the mid-80’s

Huge thanks to Doc, his contributions to both of these saws made them better than when they were originally built.

 

[Paul Fithian]

Ran through a tank and a half of fuel, had a bit of fun with a big red oak stump section:

Rings and piston look perfect. Saw felt stronger the longer I used it. Starts with almost no effort, first burp and it's going. Maybe the best running saw I have ever used.

Plan is to use this for edging when I set up the Alaskan mill with my newly acquired and ported G660

 

[Paul Fithian]

I've run this saw hard over the past few days, maybe 4 tanks total through it at this point.

With a 16" bar and Oregon 22LPX chain, it just rips through red oak. Starts/stops instantly, perfect throttle response in both directions. Never stalled after startup tune

This hybrid using a 44mm 026 cylinder is a great option for upgrading a vintage 024 AV.