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Author Topic: Rebuild or replace an 038  (Read 1490 times)

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Offline ZeroJunk

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Re: Rebuild or replace an 038
« Reply #40 on: June 25, 2020, 10:01:27 AM »
Most replacement pistons are marked B.  Some of the Meteor pistons have the diameter on the box.

I assumed that they assume that an A cylinder would be worn enough that a B piston would work as a replacement.

Offline Al_Smith

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Re: Rebuild or replace an 038
« Reply #41 on: June 25, 2020, 11:09:19 AM »
 So far all  I've stumbled over has been an MS  200T piston . It doesn't have either an A or a B .What it does have is an 8 and it's on the arrow side .BTW my eye  sight is 20/20 but I have bilateral astigmatism which is the reason for the specs .Maybe the 034 stuff will be more enlightening ?

Offline Al_Smith

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Re: Rebuild or replace an 038
« Reply #42 on: June 25, 2020, 11:39:56 AM »
Let me elaborate on this a wee bit just for general info.20 years as an IBEW electrician and 29 at Ford motor and I've worked on one piston line at Honda and I've lost count how many  at Ford .
At one time before the advent of high precision machining they could not hold tolerances which is why they made grade sizes .Even Honda as late as 1988-89 had grades .Now of days at Ford they can hit every one within micro meter tolerances which is about 15 mics or so or about a half a thou  .One inch is 25400 micro meters 
So considering when say a 2100 Husqvarna  or an 81 cc McCulloch were made it makes sense they would have grade sizes . Best they could do .Stihl may or may not have been able to hold size a little better,don't really know .Doesn't really matter at the end of the day they seem to run just fine and long unless you get stingy with the oil .Maybe a review of the oil wars needs reignited again . 8)

Offline ZeroJunk

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Re: Rebuild or replace an 038
« Reply #43 on: June 25, 2020, 12:23:21 PM »
I accidentally mixed some 52 to 1  . Hope my stuff isn't ruined.

Offline Al_Smith

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Re: Rebuild or replace an 038
« Reply #44 on: June 25, 2020, 01:28:56 PM »
Only use half as much,it will be fine :D

Offline JoshNZ

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Re: Rebuild or replace an 038
« Reply #45 on: June 26, 2020, 12:43:29 AM »
Well I had another ballsup, the little mark in the seal lip I mentioned is leaking. Because I forgot to put sealant on it =/.

Don't suppose anyone knows of a way to get them out without damaging them? Why am I asking.. I'll just order another haha x(.

I tried pumping 90 psi into ccase that wouldn't blow it out. Don't want to split halves I'll do more damage to bearings than damaging seals would.

Offline Air Lad

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Re: Rebuild or replace an 038
« Reply #46 on: June 26, 2020, 03:39:28 AM »
I accidentally mixed some 52 to 1  . Hope my stuff isn't ruined.
52 to 2 may do  :D
Sorry..couldn't stop myself

Offline Al_Smith

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Re: Rebuild or replace an 038
« Reply #47 on: June 26, 2020, 06:46:54 AM »
On that seal you might try tipping the saw on it's side and use red Loctite .If you use some acetone on a Q-tip first to clean the area it might seal .If I'm not mistaken you only have to seal about 15 PSI of crankcase pressure .
I had one,038 Mag that for some reason kept blowing completely out the seal on the clutch  side .The Loctite cured the problem .

Offline JoshNZ

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Re: Rebuild or replace an 038
« Reply #48 on: June 26, 2020, 07:10:36 AM »
That probably would work but id feel better about it for the decade if I properly got some sealer around it and maybe dressed the nicks. Silly mistake =/

Offline Al_Smith

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Re: Rebuild or replace an 038
« Reply #49 on: June 26, 2020, 08:57:34 AM »
I've been on this bore grade thing like a hound on a hot trail of a fox. So far even after digging out the service manuals on microfiche which are a nuisance to read I've found exactly nothing .Not even the specs of cylinder as referenced to piston finished diameter .McCulloch BTW does furnish these specifications
Could this be one of those so called and closely guarded top secret things originated by certain manufactures ? If so they are doing a good job of it .--and the saga continues . :)

Offline Greenerpastures

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Re: Rebuild or replace an 038
« Reply #50 on: June 26, 2020, 05:53:35 PM »
My thinking is if I was turning something on a lathe and I'd come in .160mm or .0063" over on diameter I sure wouldn't want to only have emery cloth to get it there.

But now you're talking me out of it xD. The mech at Stihl shop in town says he's scrubbed for hours with 80 grit taking the ali off, according to him you cant go through it.

Can you tell if you've gone through the plating?

My concern is I have ali quite close to the ports, I guess if you spill acid over the port wall you're getting into the aluminium cylinder then?
People already said, apply the acid with caution, use an ear bud or the likes to apply just enough to the streaks of alloy on the cylinder, donít
have acid running everywhere, dry excess off with a fresh cotton bud.
It was also mentioned to use a suitable grit paper to do no damage,
and yes, you can destroy the plating a lot easier than the Stihl dealer with
the 80 grit suggests, so be carefull, clean the cylinder up first so you can
see where you need to apply acid and sand.

Offline Greenerpastures

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Re: Rebuild or replace an 038
« Reply #51 on: June 26, 2020, 06:08:44 PM »
Let me elaborate on this a wee bit just for general info.20 years as an IBEW electrician and 29 at Ford motor and I've worked on one piston line at Honda and I've lost count how many  at Ford .
At one time before the advent of high precision machining they could not hold tolerances which is why they made grade sizes .Even Honda as late as 1988-89 had grades .Now of days at Ford they can hit every one within micro meter tolerances which is about 15 mics or so or about a half a thou  .One inch is 25400 micro meters
So considering when say a 2100 Husqvarna  or an 81 cc McCulloch were made it makes sense they would have grade sizes . Best they could do .Stihl may or may not have been able to hold size a little better,don't really know .Doesn't really matter at the end of the day they seem to run just fine and long unless you get stingy with the oil .Maybe a review of the oil wars needs reignited again . 8)
Reminds me of Vauxhall / Opel cars with colour coded cams, you ordered
the colour that you saw under the rocker cover when you removed it.
Other manufacturers of the same era didnít have this system, yet seemed to have no failures either, the color coding for the slightly different finished tolerances definitely solved the problem of fitting out of spec parts.
I guess White Yellow and Red was another version of the ABC.

Offline Al_Smith

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Re: Rebuild or replace an 038
« Reply #52 on: June 26, 2020, 11:27:02 PM »
Oh yes there was variation some years ago .For example you might have a Ford cast iron V8 with 4 different bore grades in the same block .You'd never know unless you rebuilt it  after 150 thousand miles or more because they would do that if you changed the oil .See it all goes back to the oil again  :D

Offline JoshNZ

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Re: Rebuild or replace an 038
« Reply #53 on: June 27, 2020, 05:01:18 AM »
I'm back in business with this saw anyway. 3rd or 4th pull it fired and spluttered then opened choke and away it went.

I didn't read anything in the manual about setting ring gap? I did poke the piston in there before putting it together the gaps looked plenty big enough to my eye.

One thing this saw always suffered from was hard starting after sitting more than 10 days or so (needed squirt of fuel through plug hole no amount of pulls started it). Glad to see that problem is gone with the rebuild. Carb looked good inside so I didn't touch it. I assume either fixing compression or replacing seals/impulse tube is what fixed hard starting.
Loctite around the seal fixed the problem, it held pressure and vacuum as long as I bothered to wait.

I'll let the rain pass then go get stuck into some logs. I've got a tank of 40:1 mixed, I assume that's all that's really required for running in?

Offline Al_Smith

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Re: Rebuild or replace an 038
« Reply #54 on: June 27, 2020, 08:41:48 AM »
You might tune the high speed just a tad rich for 4-5 tanks then lean it out and flog it like a rented mule .Run in is another debated issue .
What you will  find after a bit of run time .It takes a little run time to fully seat the rings .As you go along you will notice it improves a little bit .After a period it will run much better than the first few start ups .With any luck you might not have to fool with that thing for the next 20 years .The 038's are tough old buzzards .

Offline Mad Professor

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Re: Rebuild or replace an 038
« Reply #55 on: June 28, 2020, 09:09:45 PM »
From p. 26 038 shop manual

Note: If a new cylinder is to be installed, always fit the matching piston.  Replacement cylinders are only supplied complete with piston for this reason.

From an old 028, 038 manual p.17

If only the piston is to be renewed, every replacement piston (marked "B") can be used with any cylinder.

I assume the above piston would be a slightly loose or tight fit?

I know that Stihl did start marking replacement pistons "A/B", I've used those in 036 rebuilds.

Offline Al_Smith

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Re: Rebuild or replace an 038
« Reply #56 on: June 29, 2020, 10:54:09 AM »
Thanks for the info .I'm not sure if I have the manual in printed form but I do on micro fiche and may on CD .
An odd thing I noticed ,on some models they listed a piston plus a cylinder and piston as a unit  with no listing for just a cylinder .Then on the other hand Mahl made some pretty tough cylinders than can stand a lot more abuse than some realize .

Offline Air Lad

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Re: Rebuild or replace an 038
« Reply #57 on: June 30, 2020, 03:44:13 AM »
From p. 26 038 shop manual

Note: If a new cylinder is to be installed, always fit the matching piston.  Replacement cylinders are only supplied complete with piston for this reason.

From an old 028, 038 manual p.17

If only the piston is to be renewed, every replacement piston (marked "B") can be used with any cylinder.

I assume the above piston would be a slightly loose or tight fit?

I know that Stihl did start marking replacement pistons "A/B", I've used those in 036 rebuilds.
How (for example) would an old/worn A cyl go with a new ( presumably slightly larger) B piston/ring setup ? Could this pair keep a good tolerance and work well for a few more years?
And to the original question. Yes..Rebuild smiley_thumbsup

Offline Al_Smith

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Re: Rebuild or replace an 038
« Reply #58 on: June 30, 2020, 05:51:31 AM »
I found the above in just one paragraph on a micro fiche  slide .The question arises,just how is one supposed to "fit" a piston in a plated cylinder ? With a cast iron liner you can hone it to size but there really isn't much you can do on a plated cylinder . I never found anything that gives max diameter,taper or ovality .
I'll just go with my original.you're not trying to build a part for the space shuttle .It either runs or it doesn't as far as I'm concerned  .In my case everyone I ever overhauled did run and most very well .Some needed a bit more attention though than others. 

Offline Mad Professor

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Re: Rebuild or replace an 038
« Reply #59 on: July 01, 2020, 01:57:47 PM »
How much better is a modern 72cc 038 equivalent, than the 038? I imagine it's a bit of a stupid question, rebuild or replace, but I've never known anything else other than this 038 mag.

I got it back from a friend wrecked, scored piston and galling on cylinder I don't know if he did something stupid or if it was time.

The cylinder and piston kit looks pretty available, affordable, aftermarket though.

Would you put a new top end on it, split it and do bearings/seals etc and top, or wreck it and buy brand new? Mostly firewood and for tidying up logs around mill


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