Stihl 038 AVS Farm Boss (late ‘80s) worth saving?

[Just_Alex]

@Stubby Thanks, I try! Although the rat could be winning this one, jury’s still out!😂

Good thing I have a 5L container of WD40, because: more cleaning today. It’s starting to look like saw parts again, and not like a pile of muck.

I could not see any perishing or cracks on the boot, my guess is this saw has sat for a decade or two and has not seen much action and the oily gunk has preserved it like the precious fossil it is! 😄
 

Carb is a BING 48A / 101A and I’ve decided to make a list of potential spares to order first before placing a bunch of orders. As tempting as it is. 
 

@spudulike is the breather hose materially different from the 038’s impulse line hose? It looks like a red (maybe was clear once?) hose. Was super clogged with gunk all around so not sure if it needs replacing or if that’s a non-issue. Or maybe I can just use a bit from the meter-length black hose L&S sell….

 

Here’s another million dollar question: how does one go about shifting the head gasket off the crank case? It’s pretty much baked on there I think. I don’t want to make any marks on the aluminium so for now I’ve just gently shifted one side of it and when I couldn’t move the rest I soaked it in WD40. Will that do to soften the material? Any tricks of the trade?

 

Pictures below. Aside from the head gasket and flushing the whole crank case and the crank bearing with methylated or pure WD40 to flush out any potential gritty bits that may have made their way down there, I feel like it’s at least at a point now where I can start to plan ordering the components and then have a few weeks of sleepless nights worrying about whether or not I’ll remember how to pit this old hornet back together again….

 

 

 

[spudulike]

The breather pipe is usually clear and usually have two very coarse grub screws in them to stop fuel pissing out but allow air in. Check and you will need pipe of similar internal bore and the screws will need to be reinserted.

 

On the gasket, remove as much as possible and I use a very sharp wood-chisel to remove the residue - obviously at a very flat angle to the surface like you are taking off a very fine layer of wood and not at a vertical angle using a mallet

[Just_Alex]

<picks up wood chisel again with trembling hand> phew! I used a chisel a tiny bit but said to myself “Alex, don’t be a fool now, best ask what Spud does first!”

 

 

thanks Spudulike. Will inspect the breather tube. Clear is better, I get why it’s designed this way. 
 

Another thing I noticed is that the rubber grommet thing on the oil pump looks pretty perished, so potentially that could be refreshed too. 
 

I’ll see if I can obtain original Stihl parts for anything rubber, but yes as you point out sometimes it seems tricky to find bits for these old creatures. 
 

 

[Just_Alex]

For those with too much time on their hands (and might be interesting for @Wonky and other future readers of this thread), found this 028 service manual which according to the introduction also largely applies to the 038. Some cool info in there. 🤩

 

STIHL-028-038-Service-Manual.pdf

[Wonky]

Good morning 😉 I was busy reassembling the one I had apart this weekend.🙄

And the 038 is now a runner.👍

the bing carb was apita cleaning the gasket under the half circle 

my timing numbers were exh101 trans122  int73 squish 24thou without the gasket, just dirko sealant.

i think I do need some new rings as the ring end gap in the cylinder is 25thou, but I will run it for a while first.

 

 

the 440 piston is not gonna work, the piston pin to crown height is different to the 038 , ask me how I know 🤣 what’s more is the rings are slightly different thickness iirc 440 1.2mm thick and 038 1.5mm 

 

one other thing make sure you don’t allow the larger crank seal prolapse and the spring pop off.

if your not sure what I mean. The ridge on the crank is what makes it do it. I use a bit of thin stiff plastic to help reduce the bump.then pull it out after fitting the seal with a bit of dirko sealant around the edge.

 

 

[Wonky]

One other thing with your oil pump leak, I had mine off and had to clean the gasket off the case. 🤔

I made a rough and ready one from a bit of gasket card and rubbed a bit of dirko on both sides. 
no leaks yet 🤞

I add the ipl of the oil pump, ( although you can see this on l&s when you log in). I never took my pump apart. I just cleaned the inside & shaft and the seal where the worm gear goes. I put a bit of grease on both before reassembly

[Just_Alex]

Morning all. I have a potentially very naive question for our brain trust: How come most overhaul discussions revolve around replacing the entire piston, rather than just making sure the cylinder is in hood shape and then putting new piston rings on the existing piston? What are the reasons to go with a whole new piston & rings set over just new high quality piston rings? Surely new rings would give the head and existing piston new life?

 

I’M not trying to be a cheapskate or anything, I’m trying to understand the engineering reasoning (also if good replacement 50mm pistons are hard to come by, maybe keeping the OEM piston plus new OEM rings is mechanically a better option?).

 

Many thanks for improving my knowledge, I’m really really grateful  

EDIT: I think this answered part of my question. The part of the question around what is better- low quality piston & rings versus old OEM piston and new OEM rings I would still love your thoughts on  

 

 

Edited April 5, 2022 by Just_Alex

[openspaceman]

 If there are really no other options I'd try it. The problem is the piston skirts wear front and back, also if the piston has seized the lands that the rings sit in may be bad. The land needs to be clean for the gases to push the ring against them and seal.

 

In the old days when car engines lasted about 50k miles  there were firms that recovered then from slapping by putting an expander inside them and spreading the skirt  front to back, they would also turn them on a lathe and knurl the bottoms to bring the hatchings proud and in spec again, never heard it done for 2T pistons.

[Just_Alex]

Really useful info @openspaceman, thanks  Still trying to settle for a piston kit but the nicer quality ones don’t seem to have the 50mm available, and I look at the £10 ones and think… is this going to be decent enough? is it made of cheese?
 

I’ll keep looking 🙃

[openspaceman]

https://www.lsengineers.co.uk/piston-assembly-50mm-dia-for-stihl-038-chainsaws-replaces-1119-030-2001.html

 

NON genuine

Says it is out of stock but not that it is unavailable