O38AV Magnum rebuild questions

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IHRed

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Hey guys! Got a newbie here and rank amateur chainsaw enthusiast. A little history on me: I recently took up chainsaws as a hobby and have dabbled with a few rebuilds just to teach myself the inner workings. Been cutting firewood since I was a kid but never learned much about the saws except how to use them. Grew up on a farm, and row crop farm for a living now. I've gone through a few small block chevy and fords and overhauled several diesel tractor engines. Also do all my own equipment repair so I have a little experience at figuring stuff out. Got an old O24 and an O28WB that I went through just to learn. Found both of them in the back of an old barn buried in a dirt floor by groundhogs. Owner said they had been there at least 20 years and didn't run when put there. Got both of them fixed up and running great.

My dad bought this O38 Magnum new in 1986. He was never real good at maintenance, just pick it up and use it. Any way 20 years later The thing still cut like mad, IF, you could get it started and then if it ever died not a chance it would restart. In 2008 he gave up messing with it, put it in the back of the shed, and bought a new MS390. 390 has been a good saw for him but he still talks about how that O38 magnum would cut. He loved that saw! Well last week I dug it out from under all the crap that has been piled around it the last 10 years and brought it home to fix it up for him for Christmas. Easy enough to just freshen it up but I want to get all I can out of it within reason. It's still going to be just a firewood saw. Falling trees and bucking them up. So, just looking for direction from you guys to really make this thing bite but still keep it manageable and reliable. Dad is 71 now but in great shape and can still work right alongside my brothers and I.

I didn't do a check but still seems to have good compression. It still ran very strong last it ran, just couldn't get it started and would not idle if it did start. From what I can see through the intake and exhaust ports the piston and cylinder are in great shape. Had good spark at the plug when I checked that. I'm betting new fuel line, filter, impulse line, and carb rebuild would get it going again but also thinking about doing some porting. Also thought about planing the cylinder down a little to raise compression but would need some input from you guys on that. I'm a machinist by trade and have access to use a local machine shop. I build some plastic injection molds for him once in a while and he lets me use his shop for my hobby and farm projects.WIN! He has a Haas CNC machining center in there that I'm familiar with. I did some mild porting on the O28 that I went through just as a learning experience. Not sure if I did it right or not but it sure seems to run strong for an O28?????

Anyway, not wanting to spend a bunch of money, just make this thing into a good stout saw for my dad and learn some stuff on the way. Any tips, pointers, info,or help you guys are willing to give would be greatly appreciated so let me hear what you have to say.

Thanks fellas


Joe
 
In my opinion the saw ran well enough without doing any mods to it. Just clean the carb and put a kit in it, maybe a new fuel line and fuel filter and a new OEM air filter. That would probably please your dad more than a port and muffler mod. We older guys just want them to run dependably...I have an 038 Magnum and it's plenty good as is..
 
You can go all the way and do what i did
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Hey guys! Got a newbie here and rank amateur chainsaw enthusiast. A little history on me: I recently took up chainsaws as a hobby and have dabbled with a few rebuilds just to teach myself the inner workings. Been cutting firewood since I was a kid but never learned much about the saws except how to use them. Grew up on a farm, and row crop farm for a living now. I've gone through a few small block chevy and fords and overhauled several diesel tractor engines. Also do all my own equipment repair so I have a little experience at figuring stuff out. Got an old O24 and an O28WB that I went through just to learn. Found both of them in the back of an old barn buried in a dirt floor by groundhogs. Owner said they had been there at least 20 years and didn't run when put there. Got both of them fixed up and running great.

My dad bought this O38 Magnum new in 1986. He was never real good at maintenance, just pick it up and use it. Any way 20 years later The thing still cut like mad, IF, you could get it started and then if it ever died not a chance it would restart. In 2008 he gave up messing with it, put it in the back of the shed, and bought a new MS390. 390 has been a good saw for him but he still talks about how that O38 magnum would cut. He loved that saw! Well last week I dug it out from under all the crap that has been piled around it the last 10 years and brought it home to fix it up for him for Christmas. Easy enough to just freshen it up but I want to get all I can out of it within reason. It's still going to be just a firewood saw. Falling trees and bucking them up. So, just looking for direction from you guys to really make this thing bite but still keep it manageable and reliable. Dad is 71 now but in great shape and can still work right alongside my brothers and I.

I didn't do a check but still seems to have good compression. It still ran very strong last it ran, just couldn't get it started and would not idle if it did start. From what I can see through the intake and exhaust ports the piston and cylinder are in great shape. Had good spark at the plug when I checked that. I'm betting new fuel line, filter, impulse line, and carb rebuild would get it going again but also thinking about doing some porting. Also thought about planing the cylinder down a little to raise compression but would need some input from you guys on that. I'm a machinist by trade and have access to use a local machine shop. I build some plastic injection molds for him once in a while and he lets me use his shop for my hobby and farm projects.WIN! He has a Haas CNC machining center in there that I'm familiar with. I did some mild porting on the O28 that I went through just as a learning experience. Not sure if I did it right or not but it sure seems to run strong for an O28?????

Anyway, not wanting to spend a bunch of money, just make this thing into a good stout saw for my dad and learn some stuff on the way. Any tips, pointers, info,or help you guys are willing to give would be greatly appreciated so let me hear what you have to say.

Thanks fellas


Joe
Carb rebuild as palmer said, the air filters are a SOB on these. Use a genuine one if replacing. Really easy to work on and replace. I take it on a hot restart you are just starting it from the run position (no coke position).

I have 2 and have had three, the choke flap set up is a nightmare to get right, the lever gets worn, the flap gets stuck etc.
 
Welcome!

Check or replace all the rubber and filters (if OEM air filter is stihl good don't replace with aftermarket), carb kit (bing kits are $$$), check rubber AV mounts. Clean up everything, especially behind clutch cover (while in there check oil pump drive gears). Dress the bar (take it to the shop and use vertical belt sander) ,and replace the chain/drive sprocket , if needed.

Base gasket delete and muffler mod will wake it up a bit. Match muffler to ex port and polish port. If you have cyl off a set of OEM or caber rings.

Others will know more about port work, Mastermind did one a while back and it was a screamer, search for the thread.

I try to stay away from Chi-Com parts. Lots of used/NOS OEM stuff around for these. A parts carcass or three come in handy.
 
Just wanted to say I've decided to take some of the advice given and fix it up stock for now. easy enough to go farther in the future. Gonna put in new fuel line and filter, new impulse line and freshen the carb. got a new oem air filter for it and needs a new clutch. Here's a couple pics just to show you what I'm working with. She's seen some neglect but sure was a runner that I remember. Spent the last few evenings cleaning it up getting ready for reassembly.

Thanks

Joe
 

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I'm sure not against the muffler mod and base gasket delete. Can anyone point me towards some videos or threads here with more info on those mods?

Thanks


Joe
 
Joe -

The muffler mod depends on the saw, but most folks take the muffler apart and either remove the inner baffle or drill out the holes a bit. And then maybe add another outlet and/or enlarge the existing outlets.

Base gasket delete is just what it sounds like -- delete it, and seal the jug to the case with one of the recommended liquid sealants (Yamabond, etc). You have to check piston to jug clearance just to make sure you have enough clearance.

You can find LOTS of details on both by doing a search here.

Good luck.

Scott
 

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