I have purchased a 038 AV that is in good shape for $65.00. I want to change it to a 038 Magnum I have a 038 Magnum and I love it. Mine 038 AV has a magniesum tank and handle. i read Mad Professor's line that with a new piston and cylinder and a little creative work with a dremel it was possiable. I have also noticed that the carbs are different. If anyone has done it I would appericiate your experience. I have read that the AV can be modified to run as good or better than the stock 038 Magnum. Would be interested in that also if it is cheaper. Sincerely, Waddodiggs
Well you would have to slot the cylinder bolt holes and try to keep everything in alignment which would be a good trick if you could do it .Some say they have and I won't dispute that but it would be simpler to get a mag to begin with .
As far as an AV running with a mag most likely I was the one that said that .I have one that will .
You have to jack the compression and re-port the thing .I won't go into how to because everyone who reworks one thinks they are the only ones that know how and that's the farthest thing from the truth there is .Fact being I just don't feel like arguing about it .My suggestion is to research it a tad bit by surfing the net .Sites like MacDizzy and others pretty well cover reworking two cycles .
The AV used an HK-42 carb Walbro whereas the mag used some model of Bing but they interchange .
The Bing is supposed to be the better of the two from what they say .I own both and with the exception of rebuilding both really have had no trouble with either .
Get a 038 shop manual. It mentions potential problems going from 038 to 038 super (might have to grind cyl mating surface on crankcase). Not Rocket science here, stuff a rag in the case and get the dremel out....
The conversions I have done did not require this, but I started with super bottom ends.
Regardless you will have to slot the Mag Cyl mounting holes to match the case. Then may have to grind where there the cyl bolts seat on the cyl and/or turn the bolt heads down. Finally you need to open up the access holes in the cyl fins so your T-27 long torx will get to the bolts.
DO NOT slot the cly too far or you will get close to the bore, you also need to slot a Mag base gasket ) if using one). Using a super base gasket will work, bit the gasket will hang ~ 1mm into the bore area and hamper gas flow.
Be careful when slotting the cyl base mounting holes, keep the bore centered, a 038 base gasket is a good template to locate the holes.
For carbs the Tilly from a 038S or the Bing have the same venturi size, I've tuned the same saw with both carbs, and the settings (Hi/Lo) were identical, but I might have gotten lucky....
The Stihl manual suggests upgrading to the 038S Tilly carb, when they go from 038 to 038S. I've not played with a 038 carb to Mag conversion. Might flow enough? Don't know for sure.
Finally, open up the exhaust or go to a 3-port optional 038 Mag muffler. The dual port opened up to the limit of being able to retain the spark screens seems to work well. The ex port will be bigger on the mag cyl , match the muffler intake to the same size, then remove or open up the baffle with a 5/16" drill. Chamfer filings/drillings on the muffler so loose crap does not get sucked into your new P/C assy.
Muffler mods are a whole other topic. I just posted what has worked for me, I always leave spark screens in, or add a screen, to a "new" port. A piece of pipe welded into a new hole works well, if you size it right a Stihl blower muffler screen will clamp on.
P.S. Listen to Al too, he has been inside a whole lot of 038 saws.
P.P.S. Use OEM Stihl parts (gasket seal set, etc...) , if the P/C assy is too pricey, I can recommend TECOMEC, quality italian parts, a suppiler for Ducati bikes. Also on a saw that old, fuel line, impulse line, crank seals, check intake manifold very well.
The best simple advice to make that 038 AV cut better then a stock 038 Mag is take the cylinder to a machinist, have them take .020'' off the base. File .040'' off the piston intake side skirt [straight across]. Round off edge of piston at exact 3 points where the floor of the exhaust port and the ceilings of the transfer ports meet piston top edge at bottom dead centre. This compensates for the .020'' cylinder lowering. With the machined cylinder and base gasket installed the exhaust port can be easily scribed with a felt marker. After removing piston, round off the marked exhaust edge, then slide piston into cylinder at point where exhaust edges meet. Then mark transfers edges on piston with a sharp curved dental pick. File marked piston edges. Clean up piston, install new rings and base gasket. Reset carb.
If you don't want the machinist expense, leave out the base gasket and use a thin layer of YamaBond sealent. But I prefer the machining for ease of cylinder removal later and the spot on marking of piston edges .
Willard.
Something I should have mentioned in my last post is there will be a ridge of carbon at the very top of the cylinder wall. Remove this carbon before running the saw after these mods. A folded piece of fine emery cloth will do the job
Willard.
Quote from: HolmenTree on November 11, 2010, 03:46:01 PM
Something I should have mentioned in my last post is there will be a ridge of carbon at the very top of the cylinder wall. Remove this carbon before running the saw after these mods. A folded piece of fine emery cloth will do the job
Willard.
You should check the squish with the above mentioned mods.
You can do the same type of mods. with a magnum cly assy: there is no substitute for displacement!
P.S. I'll run my super to mag conversion (decribed above) , against your 038 AV hot rod with the above mentioned mods.
Quote from: Mad Professor on November 11, 2010, 07:55:18 PM
P.S. I'll run my super to mag conversion (decribed above) , against your 038 AV hot rod with the above mentioned mods.
P.S. to the P.S. I'll top that one. Hows about an 38 Mag that started out life as an 038 mag to begin with ,with enough guts to outcut a stock 066 over the blocks . 8)--It's kind of slow though,only runs at 14,600 . ;)
Quote from: Mad Professor on November 11, 2010, 07:55:18 PM
Quote from: HolmenTree on November 11, 2010, 03:46:01 PM
Something I should have mentioned in my last post is there will be a ridge of carbon at the very top of the cylinder wall. Remove this carbon before running the saw after these mods. A folded piece of fine emery cloth will do the job
Willard.
You should check the squish with the above mentioned mods.
You can do the same type of mods. with a magnum cly assy: there is no substitute for displacement!
P.S. I'll run my super to mag conversion (decribed above) , against your 038 AV hot rod with the above mentioned mods.
I was just giving the author of this thread simple basic information how to make his 038 Av cut faster then a "stock" 038 Mag.
I know the squish on these older 038 AVs. You're good to go with .020 lowering and have room to spare.
I own [ 3 ] 038s since brand new. 038AV, 038 Super II, 038 Mag. Only my SuperII is modded with my above description plus 4 deep finger ports and a 056 Mag carb on it. I did these mods in 1983, I bought my 038 Mag a few years later , didn't bother modding it because my Super II was fast enough.
If we ever cross paths....... sure I'll run my Super II against your Mag, hell my 038 mods are 27 years old.
Willard :D
You've got lots of room to lower the jug like Willard said .An 038 has something like 45 thou clearance stock and 101 degree opening on the exhaust stock .The base gasket is 20 thou thick .
I sincerely thank you gentleman for your responce. You have given me some really good ideas on what can be done. No one has mentioned a longer piston rod or a modifyed piston rod. I don't know if this is possiable. It just came to mind while reading your solutions to my desires. I like all your ideas. I have decided to completly rebuild the saw and use the stock parts modified to increase compression and performance. I see levels of testostrone rising here.he he he. My wife thinks I have better things to do with my time,but nothing like undertaking something new and bring it to completion with success.
Now do any of you have pictures or manuals of 038 AV. Links to such. Sincerely Waddodiggs
A longer connecting rod wouldn't do anything but jamb the piston through the head deck .Besides that the thing is a pressed together crankshaft and even if you could or would put a longer rod on it for whatever reason how pray tell would you get the job done . ???
Now granted they do knock apart 3120 Husqvarnas ,stroke them and use an 084 Stihl rod but you are talking 5,000 dollar race saws not a hundred dollar used 038 Stihl firewood cutter .You've got to be a little practical here now .It isn't like souping up a 350 Chevy .
Bump...HolmenTree reference in the "Those wonderfull old Husqvarna's...model 61 Ranchers thru 272XP's" post I believe
Quote from: weimedog on December 29, 2010, 10:39:54 PM
Bump...HolmenTree reference in the "Those wonderfull old Husqvarna's...model 61 Ranchers thru 272XP's" post I believe
You got it. :P
Willard.
Back to the guys original question .You can make a 60 cc 038 Av run as well or better than a stock mag with a little massaging . I've done it and I'm no wizard of chainsawdom .
Hi, I am new to this forum but have been reading post for a while now.I have a stihl 038 super and was wanting to ask HolmenTree a question about how to put a 056 mag carb on my saw.If any help with this would be highly thankful.Thank you
It's got enough carb on it already .Unless you get to opening the ports up gigantic a larger carb won't do you much good .
I see what you are saying.I am wanting to get the 038 mag cylinder kit and put on it and shave the head and port the piston to the head as stated in the eariler post.I can't afford a real big saw so thought I would mod my saw to cut some 2 and 3 foot logs pretty fast.I have a husqvarna 272xp stock that does good and want to get my stihl up to cut faster than it.Thank you for your info on this. :christmas:
Hi it took me a while but I got an 038 mag cylinder kit cut .020 off the base and .040 off the piston intake side and polished the exhaust and intake ports and ported the muffler.I have a 056 mag Carb I want to put on it but it don't fit.Can you tell me how to mount it on my saw.Thanks
You're kind of spinning your wheels if you don't have a large enough intake tract to accomidate a larger carb .It's kind of like stuffing 5 pounds of potatoes in a 3 pound sack .
I have been watching this post with interest as I have a stock 38 super that I would like rework to better than a stock magnum,
I was thinking of a mag cylinder/pot & skimming.
This leads me to my questioning in order to do this right.
I Can take the .508mm/.020" off the base no problem but I don't understand the following.
Quote"File .040'' off the piston intake side skirt [straight across]. Round off edge of piston at exact 3 points where the floor of the exhaust port and the ceilings of the transfer ports meet piston top edge at bottom dead centre.
or.
With the machined cylinder and base gasket installed the exhaust port can be easily scribed with a felt marker. After removing piston, round off the marked exhaust edge, then slide piston into cylinder at point where exhaust edges meet. Then mark transfers edges on piston with a sharp curved dental pick. File marked piston edges. Clean up piston, install new rings and base gasket. Reset carb."unquote.
If someone could help me understand I would be most appreciated.
Thanks
You don't need to shave the bottom off the piston for one thing .If you drop the cylinder say 20 thou you've effectively not only increased the compression but also have changed the intake by 20 thou.At the same time though you've increased the degrees the exhaust opens if you don't raise it . That by the way is 101 degrees after top dead center on a stock 038 series .If want any more speed you have to raise it a few degrees .If you don't leave it alone .
Quote from: rj on October 14, 2013, 06:20:47 PM
I have been watching this post with interest as I have a stock 38 super that I would like rework to better than a stock magnum,
I was thinking of a mag cylinder/pot & skimming.
This leads me to my questioning in order to do this right.
I Can take the .508mm/.020" off the base no problem but I don't understand the following.
Quote"File .040'' off the piston intake side skirt [straight across]. Round off edge of piston at exact 3 points where the floor of the exhaust port and the ceilings of the transfer ports meet piston top edge at bottom dead centre.
or.
With the machined cylinder and base gasket installed the exhaust port can be easily scribed with a felt marker. After removing piston, round off the marked exhaust edge, then slide piston into cylinder at point where exhaust edges meet. Then mark transfers edges on piston with a sharp curved dental pick. File marked piston edges. Clean up piston, install new rings and base gasket. Reset carb."unquote.
If someone could help me understand I would be most appreciated.
Thanks
I think I gave a little too much information here :D
Quote from: Al_Smith on October 14, 2013, 07:20:01 PM
You don't need to shave the bottom off the piston for one thing .If you drop the cylinder say 20 thou you've effectively not only increased the compression but also have changed the intake by 20 thou.At the same time though you've increased the degrees the exhaust opens if you don't raise it . That by the way is 101 degrees after top dead center on a stock 038 series .If want any more speed you have to raise it a few degrees .If you don't leave it alone .
.040 off the 038's intake skirt plus the .020 with the cylinder lowered works fine Al. Simple tricks Madsens first did to my 038s back in the early '80s . Mind you we were boring out the carbs venturies also or just swapping bigger carbs, plus for race GTG s 4 finger ports were also a good way to get even more air/ fuel mix through the unit..
On my 137cc 090AV 's we were taking 2 mm [.080] off their intake skirts. Experimenting on a piston only was a lot cheaper then ruining a good cylinder.
My advice is try .020 off the piston's intake skirt first, then go from there.
Walkers made some good robust saws,I've ran a few .
There's several trains of thought on this cutting the skirt business .While it might cause it to take a bigger "gulp " on intake by lowering it the intake would happen lower in the cylinder regarding degrees past bottom dead center .Now this could be good or not so for several reasons .
For one if it where slightly delayed by only allowing say 20-23 thou you lowered the cylinder the piston would have created a lower pressure by virtue of the fact it had taveled farther up the cylinder .This is turn would create a higher differential of pressure between the crankcase and the atmospheric side of the carb and as such would be at a slightly higher velocity .--more--
Conversely though by opening the intake port sooner it could possible that during the transfer and exhaust there is some point where it's open clear back to the carb .If things were just right and if the carb was large enough to supply fuel it might be possible to get a suction clear through the thing .
Now I'm not saying which is best but there are options and different trains of thought on this stuff .Some of the gurus say to get your port time open parameters by first widening whatever port you are dealing with first before you raise or lower the respective one .Who is right or who is not so who is really to say if the end results are the same ?
As general conversation the same applies with regards to transfer ports .Some are gaga over finger ports .Some prefer externals some just redirecting the uppers with a domed piston .Then again some prefer to use a flat top piston and achieve great results .--twenty ways to skin the same cat --- ;)
I found the mods I explained are not rocket science. I did the exact same mods on my brothers Jonsered 670 as my 038 and the 670 proved to be faster. The Jonsered took the mods better :D
Well on a work saw they'll all be enhanced somewhat .Now the part nobody can explain .
I know some of the top race saw builders in the country who have forgotten more already than I will ever know .What none can explain is that on identically reworked saw for reasons unknown one will have a slight edge over the other .It's a great unsolved mystery .Remember though on a racer a slight edge is the difference between win or lose with sometimes less than 2 tenths of a second in times .
What in the heck are y'all talkin about? 8)
Quote from: mastermind7864 on October 17, 2013, 08:02:46 PM
What in the heck are y'all talkin about? 8)
Red neck repair 8)
I specialize in that.... :D
Ok guys/advisors Thank you all for your help so far.
I've taken the plunge & ordered a mag pot & piston for the old 038 super of mine.
But i want to pump up the mag setup.
I have a lathe with a milling vice & all tooled up.
I would like to try taking an offset skim from the intake skirt for accuracy also skim the pot seat.
When the kit arrives i'll check things out & make some measurements.
So i guess i'll be anoying you guys soon.
In the meantime what are finger ports how do they work, what are the losses or gains in performance & how are they created?
What exhaust/exhaust port mods should i consider?
Okay here is the theory behind finger ports ,boost ports ,secondaries or whatever you want to call them .
In the transfer of fuel following the power portion of the downward piston travel the hardest portion of the cylinder to purge the partially unburned gasses is right above the intake port .This is what they are for .
They aren't some new inovation invented by a crazy man in California .The concept is as old as a two cycle engine istelf just done in many different ways .
AL_SMITH,Thank you.
What are the bad points?
Is there a suggestion as to the position of them?
What depth & shape should they be?
How many?
Forgive my ignorance but i'm learning on the fly here.
HolmenTree talked about squish.
In regard to compression, what size squish should i look for?
I want to measure then skim for my super to mag then do the inlet outlet piston skirt compensation from calculations.
Thats if i'm understanding correctly. Also finger ports look to be an option not to ignore.
To be able to run at sustained higher than stock RPMs you need to adjust the port sizes .There is a basic formula suggesting what is required in terms of port time/area open parameters based on cylinder bore .In essence what it says is as the RPMs increase the time decreases and as such they need more area .You can Google it .
You have to keep in mind every port needs changed at least a little bit .Also keep in mind the piston acts as a slide valve .You haveto leave enough area around the ports and piston so it doesn't leak which is why you mark the piston as a reference .
Also remember the piston ring end gaps ride between the upper transfers and the exhaust port .You certainly don't want to have a ring gap ride over an open port which most likely would snag the ring and turn the engine into junk in about a millisecond .
As far as marking the piston everyone has their favorite method.Mine is with an indelable sharp point felt marker .( laundry marking pen) .
Before you get to carving on that thing do some reading .You won't find much on chainsaws or go kart engines .Try RC engines ,British motorcycle sites and such .
Whew long explaination .As far as finger ports it's just one option.Keep in mind how a two cycle engineworks or transfers fuel .It's all based on differential pressures .You have atmospheric pressure on both the intake side and the exhaust it's what it done in between that causes increased performance .
The intake port can be assimulated to the intake valve of a 4 cycle and the transfers to the cam shaft and size of the valve .The exhaust likewise with a "cam" .
With a 4 cycle yu have cam lobe overlap and with a 2 cycle you have port over lap .
For example the tranfer portion is opening on a rising pressure fromthe crankcase while at the same time there is a decreasing pressure from the exhaust port opening .On most Stihls this is 20 degrees of rotation after the opening of the exhaust.As RPMs increase it is often required to allow more time and as such the exhaust port is not only widened but raised a few degrees to give it more time to transfer fuel and purge the cylinder of exhaust gasses .
The bottom transfers are widened to kind of "funnel the pressure from the crankcase in more so than stock .The uppers are modified to not only help a more easily transfer but also to direct the charge .Fingers included which is just one option .
You need to also keep in mind bigger is not always better .You must not do alterations that lead to decreased pressure because you could end up getting exhaust gasses blown clear down to the crankcase .Not good .
What you need to do is Google Gordon Jennings two stroke tuners manual .
You have given me plenty of homework to cross reference, for that i thank you.
My mag pot & piston have arrived so i'm gonna make the nessesary measurements of the existing super pison & pot then swap it for the new mag. I will then do the homework before anything else as suggested.
I'll rework the super, try it & if all is good i'll move on to reworking the mag.
It is easy to follow someone elses work & often prefferable but there is a major benefit in understanding ones undertakings.
So i changed piston & pot for the 038 mag kit.
The diference was quite noticable, however i can confirm that after some studying then some grinding & milling You can make a super eat a Magnum cause i swapped back after the super was lowered & ported.
My next move was skimming the crank seating so in the future the pot can be bolted on without skimming the base but this leaves me with an unuseable Super pot, oh well it'll get used sometime. I then went to town grinding shaping & polishing on the mag pot.
"Well let me see when she bogs with a 36" bar on an alaskan mill" was my thought.
This is now one oak eating monster. :)
(https://forestryforum.com/gallery/albums/userpics/34051/image.jpg)
Horse Chestnut tree on top & a nice Oak
Thank you Al_Smith, Thank you holmentree.
Next on the list are finger ports then reworking my 090. 8)
Why in the world would you want to rework an 0-9-0 ? They aren't the fastest thing ever made but darned few have as much torque as that big boy .That thing is like the Clydesdale of chainsawdom .
Al_Smith
Cause i have some massive oaks that came down in the big recent UK storm, no hurry & a Clydesdale saw that i intend to repot & piston. So if that clydesdale can pull an 8' home made bar through 5.5 to 7' oak for 300' before reworking then another 300' after i'll treat her to the new piston & pot in the way that seems to work best.