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

[Just_Alex]

Thanks @openspaceman, yeah that’s the one. I’ll send them a wee message or see what happens when I place an order.  
Quite keen to get the rubber parts from L&S as they have some of the original Stihl parts (AV stuff for example). 
 

 

[Wonky]

Just saying,  Meteor pistons are the next best pistons to use other than oem..

 

but call me cheap, I’d check the skirts and probably put the piston in the cylinder and Also check the gap, as with most things there are tolerances… then I would then decide from there. 
having said this,  the rocking of the piston means as it get worse it eventually gets snagged in a port then the damage can be catastrophic.

 

But most times it comes down to not having to take it apart again because they have paid someone to do it and they want to guarantee it, Thus the time and guarantees is money in most peoples eyes, 

nobody is paying me, so I choose what and when I do things.

that’s why I’m happy to run a saw with older rings for a while..

[openspaceman]

29 minutes ago, Wonky said:

the rocking of the piston means as it get worse it eventually gets snagged in a port then the damage can be catastrophic.

 

I've never had that but I have had a 026, IIRC, where the skirt was worn so thin it was a sharp edge.

 

If the saw is just old and worn  putting a ring on the old piston restores a lot of compression.

 

I have two Husky 262s which were the last saws I bought new when I was contracting in about 1995 and they are both sound except they have poor compression, I have every intention of just replacing the rings.

 

This is why I suggest putting an old ring in the bore and pushing it square with the piston, then checking the ring gap. The rings wear much worse than the nikasil bore which hardly shows any wear at all when you measure the ring at various depths of the bore.

[Wonky]

It has to be bad and you have tobe unlucky. But either way a lot of peeps like to just replace things as it cost more money taking it apart again…

This was a heated Handle 10mm 044, I brought  for £200 in good working order…🙈🤣

after I complained 🤔 I got it for £100 🤔. Some think it wasn’t worth it, but I think it was 😉

I cleaned it all up & those main bearings got changed as they were grinding that Ali into an oily paste. and while I was there and the bearings out It got it a new all over black epoxy paint job👍
you can see in the red rings where the piston was rocking and hitting the crank at bdc  on the 044
 

But I can  say I'm not going to give a new paint job to my 038's😉

 

I will add a bit more to this thread  when I do a bit more to the 038's 👍

 

 

 

[spudulike]

On fitting a piston v new rings....If you fit new rings on a worn piston, you will possibly get good compression after 6 pulls BUT...the first pull should give at least 70psi and the new rings on their own will just not give the same compression and will be VERY noticeable when the saw is hot.

This is difficult to explain but I had an 024 pulling 180 psi once but the piston was very worn and it barely had the power to pull the chain round and hot, it was pathetic.

The piston by itself with no rings causes an initial compression (not enough for combustion) and the rings then up that and create a seal good enough for combustion. The seal of the piston to the bore is just as important as the rings in my experience.

Lastly, the piston skirts seal the inlet and exhaust port at different parts of the two stroke cycle. If the piston is worn, you will get FREEPORTING which is where the crankcase pressure or vacuum is lost out of a port when the piston should be sealing it. If your saw puffs heavy vapour out of the back end of the carb when revving it up...it is freeporting!! That is bad!!

Just fit a new piston...do the job once and correctly!

 

[openspaceman]

28 minutes ago, spudulike said:

Lastly, the piston skirts seal the inlet and exhaust port at different parts of the two stroke cycle. If the piston is worn, you will get FREEPORTING which is where the crankcase pressure or vacuum is lost out of a port when the piston should be sealing it.

Yes I'm not advocating using a piston if the skirt is worn. When I get around to stripping my 262 I will measure the piston and post pictures on here. I'm hoping the piston will not be badly worn.

[spudulike]

19 minutes ago, openspaceman said:

Yes I'm not advocating using a piston if the skirt is worn. When I get around to stripping my 262 I will measure the piston and post pictures on here. I'm hoping the piston will not be badly worn.

I wasn't commenting on your answer or opinions and more on what I do and have found in my experience and was answering the OPs question. We all have our ways ...no offence......but have found a new Meteor or Hyway piston is often not really much more costly than a set of OEM piston rings so go that route.

I usually take the rings off, push the piston up the bore, stick my finger over the plug hole and see how easy it is to pump up and down. I then put the piston so its base is close to the open end of the cylinder and see how much clearance there is from the skirts to cylinder by pushing it back and forth across the bore with my thumbs.

Very subjective but after you have done a few....it works for me. 

Comparing new against old is the best way but isn't often able to be done. Ring wear is measurable and if the ring is done...the piston is likely to be the same.

[Just_Alex]

Thanks everyone, this has been super helpful and I’m glad I asked. L&S will be glad too, since this has resulted in a rather lush order of parts 😊🤩 The only thing I really couldn’t find on their site was a Bing 48A carb repair kit, so sourcing that is the next mission. I’m keen to see how rebuilding the carb goes, those components look finicky and it’s very possible I might mess it up the first time. 
 

I’m starting to get a little bit concerned I won’t be able to put it all back together without having a dozen bits left over🙈. Is there a general rule of thumb in terms of the order people put the saw back together? Put piston and cylinder back on case with new gasket, then put carb (once rebuilt) back into the handle part and then marry the handle part back up with the crank body?
I want to add a few things which others may think of as “cosmetic” such as new fuel line, fuel filter, air filter, air prefilter (won’t be able to do a new oil line or oil filter because we are keeping the case closed), the carb rebuild of course…. My assumption is it’s pointless to fit a new shiny piston and then mess it up with contaminants from ancient intake components. Is this a good approach?

 

Oh and should I bother with a new exhaust, or try to get it to run first? I’m not sure what to look for in terms of criteria too judge a muffler etc by, I can’t see much rust for example. Any tips on this?

 

Anyway, wishing you all a pleasant evening 🙂
 

[spudulike]

5 hours ago, openspaceman said:

I've never had that but I have had a 026, IIRC, where the skirt was worn so thin it was a sharp edge.

 

Yup, they do slap a bit when old and worn, I have had a couple that have slapped so hard, the skirt has shattered - just what they do and guess the piston and bore design just allows it with high use!

The pic Wonky put up with the paper in the bore is one of those, so much slap the piston skirt has shattered! Sort of shows my "Wobble Check" for piston wear as well.

Edited April 5, 2022 by spudulike

[spudulike]

Just now, Just_Alex said:

Thanks everyone, this has been super helpful and I’m glad I asked. L&S will be glad too, since this has resulted in a rather lush order of parts 😊🤩 The only thing I really couldn’t find on their site was a Bing 48A carb repair kit, so sourcing that is the next mission. I’m keen to see how rebuilding the carb goes, those components look finicky and it’s very possible I might mess it up the first time. 
 

I’m starting to get a little bit concerned I won’t be able to put it all back together without having a dozen bits left over🙈. Is there a general rule of thumb in terms of the order people put the saw back together? Put piston and cylinder back on case with new gasket, then put carb (once rebuilt) back into the handle part and then marry the handle part back up with the crank body?
I want to add a few things which others may think of as “cosmetic” such as new fuel line, fuel filter, air filter, air prefilter (won’t be able to do a new oil line or oil filter because we are keeping the case closed), the carb rebuild of course…. My assumption is it’s pointless to fit a new shiny piston and then mess it up with contaminants from ancient intake components. Is this a good approach?

 

Oh and should I bother with a new exhaust, or try to get it to run first? I’m not sure what to look for in terms of criteria too judge a muffler etc by, I can’t see much rust for example. Any tips on this?

 

Anyway, wishing you all a pleasant evening 🙂
 

Piston back on..make sure it is the correct way round - arrow to the exhaust port and make sure the circlips are 100% located - gaps to the top on Stihls. Sometimes the base gasket needs fitting prior to fitting the piston.

Fit the manifold to the cylinder and then refit the cylinder and pull the manifold through the air box back plate. A nice smooth pair of long nose pliers work for me NOT a sharp screwdriver....seen the result of that too often.