Stihl 041 AV FB Rebuild / Restoration

[ReliableRust]

My buddy gave me this Stihl 041 AV Farmboss. He said "it doesn't run, probably needs a rebuild". I guess when he went to get parts to fix it himself the salesman talked him into a new saw. I tried to tell him I didn't want it because I know myself, I can't just let broken stuff sit around, I've got to rebuild it and if it's all taken apart, well then I might as well restore it. He threw it in my truck anyways.



I brought it home and let it sit for a few days before I couldn't resist. I gave it a few pulls and decide my buddy was probably right about it needing a top end rebuild. So I checked compression and sure enough it's only at about 48psi. Spark looks great, very strong. Carburetor seems to be carburating.

It wasn't very well taken care of though, my buddy got it at a pawn shop, so probably not his doing. The rear shroud/handle is cracked near the AV mount. This seems to be common on these.

I'm hoping I can tig weld it without any filler because the magnesium filler rods cost about as much or more than a replacement part.

There's lots of missing screws and I'm not sure the chain catch is fully intact.


It's also missing the starting throttle lock and compression spring.
I can 3D print a new throttle lock and scrounge up a spring for it. Can anyone tell me how the lock is retained? Is there supposed to be a c-clip in the grooves on the pin or what?

 

[ReliableRust]

I tore it apart and found that as suspected the piston and cylinder are scored and the ring is seized. The cylinder doesn't seem too bad but I went ahead and ordered up a new piston/cylinder kit from ebay anyways just to be sure.

 

[ReliableRust]

Got it all blown apart yesterday. Gave everything an initial scrub down with hot water and dish soap.

The chain tensioner is bent so I got a new one ordered.

The bearings look pretty rough, got a lot more rust on them than I'd like to see.

The threads got rolled over on the end of the crank, I had the nut about half way on and was hitting it with a hammer to get the flywheel off. Oops! The rod bearing seems a bit crunchy anyways so I'm thinking about grabbing another crank.


A special delivery from Prismatic Powders has arrived, RAL 9010 & RAL 2004.
Today I'll be prepping the parts for powder coat by further de-greasing them and sandblasting.

 

[Bob Hedgecutter]

Well, on the plus side- the front handle looks to be in good condition!
Recoil starter handle looks nice.
Bucking spikes are in fairly good condition.

 

[ReliableRust]

All the parts to be powder coated took a bath in the boiling Simple Green Extreme and then got rinsed in with water. I like my chainsaw parts extra crispy so I cranked the shop oven up to 550F and threw them in till they stopped smoking, some of them where in there for hours. Hopefully this has burned off any remaining oils and compromised the powder coat enough to make it easier to blast off there. Powder coat can be a real PITA to sand blast off. They'll probably get baked once more after blasting and prior to coating, just to be sure there's no oil/water hiding anywhere. Here's some pics of the first batch fresh out the oven.

 

[ReliableRust]

Well I got the broken tab stuck back on, but it's not pretty, definitely won't be going on my Instagram as #weldporn. It's not terrible considering it's my first attempt at tig welding magnesium. I think it would have gone better with filler material so I could build it up to fill in the Swiss cheese then grind back down. I've never welded anything that bubbled up so bad as this did.


Looks a little better after grinding it down and sandblasting again.

 

[Woodslasher]

Well I got the broken tab stuck back on, but it's not pretty, definitely won't be going on my Instagram as #weldporn. It's not terrible considering it's my first attempt at tig welding magnesium. I think it would have gone better with filler material so I could build it up to fill in the Swiss cheese then grind back down. I've never welded anything that bubbled up so bad as this did.
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Looks a little better after grinding it down and sandblasting again.
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I'd liberally apply jbweld to the joint to fill in the holes and possibly even re-enforce it.

 

[ReliableRust]

I'd liberally apply jbweld to the joint to fill in the holes and possibly even re-enforce it.

Thanks for the tip, I didn't know there were fillers that could be used with powder coat. I'm still new to the powder coating game. Research shows people have had success with JB Weld but there's also a product called Lab-Metal that's made for this purpose. Lab-Metal is a bit expensive though so I might give the JB Weld a go.

 

[ReliableRust]

Well I filled the holes with jb weld last night. I went pretty conservative because I want it sanded out smooth before coating. Should be dry enough to sand it out tonight.



The first part to be powder coated!

The coating is a little thin in some of the corners but overall came out pretty nice. I measured 3-5mil on a few different spots, but the tester won't fit into the corners where it's thin. Now I'm excited to get the rest done, can't wait to see that orange! The sand blasting is slow going, but I'll get through it.

 

[ReliableRust]

Well I forgot to get some pics after sanding the jb weld. Here's some of it after powdercoat though. It came out pretty well but some of the deeper holes that were filled with jb weld, didn't seem to attract the powder well leaving blemishes in the finish.


I finished up all the powdercoating today.



Hopefully I can remember how it all goes back together now!

 

[Vintage Engine Repairs]

Really well done mate. It’s great to see you taking care and doing a good job.

 

[ReliableRust]

Really well done mate. It’s great to see you taking care and doing a good job.

Thanks! I figure if it's worth doing I might as well do as good of a job as I can.

 

[ReliableRust]

Maybe someone here could provide some feedback on my next steps here. I'm thinking of using Indian Head Gasket Shellac as a dressing on the new paper gaskets, especially the ones I hope to never disassemble again like that case halves and the fuel tank halves. I choose Indian head mostly because I already have some and it's supposed to be petroleum resistant. I'm planning to coat both sides of the gaskets. For ones that might come back apart like the cylinder gasket and the carb/exhaust gaskets, is it OK to just put them on dry? As you can see in the photos I've cleaned up the sealing surfaces using a carbide scraper, they're not 100% clean, but what is left is as flat as I could get it without removing any of the base material.

 

[Vintage Engine Repairs]

I have heard a few that use Indian head shellack but it’s often combined with, it’s a nightmare to get off. Modern gaskets don’t generally require any sealer, but those who use one often use something that may be a little easier to clear up. You never know when you’ll need to go back into the saw and using the above, will likly require you to get new gaskets. My preference is Permatex Aviation Form-a-gasket. It’s fuel and oil resistant, easy to apply, has a slow dry / long work time and is designed to allow you to remove the mated surfaces. I have found I now apply it to most all gaskets including carb to manifold gaskets and air filter gaskets found on old saws, but thinly.

Another somewhat common product on gaskets that people use is just threebond 1184. Though you better be prepared to work fast as it cures quick and I believe that it doesn’t offer you the ability to remove the mated surfaces and reuse the gasket like permatex aviation.

 

[ReliableRust]

You make a good point there, better to have the ability to get back in there if needed. I've used Permatex Aviation Form-A-Gasket on my boat and it worked well for me. Wish I could remember what I did with the bottle of it I had, oh well, what's another $10 at this point. I always feel better with that added bit of insurance that a little goo on the gasket gives or at least appears to give.

 

[ReliableRust]

Making some good progress! Forgot to take pictures along the way.

 

[ozziechainsaw]

Really nice job so far. The lower handle repair is excellent.

 

[Den]

Nice job. The 041AV is one of my favorite Stihl's.
You will love the unmistakable sound of the 041AV.
.

 

[ReliableRust]

Well I hit a bit of a snag on the clutch. During disassembly I damaged the threads on the crankshaft while trying to remove the flywheel, so I got a new crank from a local guy who sells parts. I had noticed the threads were longer on the clutch side of the crank but didn't realize it would be an issue until I got it all together. I guess some sort of spacer is required as the clutch is bottoming out on the chain sprocket (cup) instead of hitting the collar on the crank. I tried 3d printing a plastic spacer, but I feel like some metal is going to be required for a long term solution. Someone said they used a piece of 1/2" stainless tubing as a spacer, so I might try hitting up the local hydraulic supply house to see if they have a piece of tubing that will work.

Please let me know if you've got any other ideas. I was think possibly grinding down the back of the sproket so it slides down the crank further, allowing the shoulder on the crank to protrude.

 

[Bob Hedgecutter]

Are you missing or have the incorrect thickness cover washer ( 1110 030 7502 or 1110 030 7503) that goes on first before the spur drive sprocket and clutch drum?