Hot-Rodding an 031av

[Sportfury70]

So I scored two 031av saws for $100. I posted in the you suck thread, now it’s time detail the work.

A young work buddy of mine wanted me to teach him how to modify saws, and we got lucky finding these two so close for so cheap. They didn’t run at first, but both had good compression.

After a carb rebuild and trigger chip swap (I used the silver Oregon ignition chip) mine starts and runs like new.

We will take mine down first and do all the goodies to it so I can teach him to do the same on his own. Plan is to port int/ext and smooth the transfers. Delete base gasket, advance timing a bit, and dual port the muffler. Also going to repaint them, but I’m not gonna split the case because it’s runs so well I don’t think there’s any vacuum issues.

For the paint I picked up ford light grey and kubota safety orange, I found on this site that they are a close match to the original Stihl colors.

 

[Sportfury70]

I found another porting thread and it shows a riser in the middle of the intake port. I assume that’s to increase velocity and split the mixture for combustion/ or direct mixture to the transfers.

For those of you that has ported one of these, do you keep that riser in the intake and just widen the port a bit, or can I delete the riser also?

Also, do you put the ring gap center of one of the ports, or keep it between the transfers and int/ext? I’m not yet sure if has pinned rings or not.

 

[Sportfury70]

Okay so I planned to take pics of the build, but naturally I got in the zone and completely forgot.

Anyway, the kid did a great job porting it. We widened the ports about 1/8 inch on each side of the ports. Also smoothed the bottom of the transfers, but left the uppers alone. Port timing was unchanged.

Deleted the base gasket, there was a ton of room on the squish. I think you could take a few millimeters off the bottom of the cylinder and not have to touch the squish band. At least on this saw anyway.

Coil has the points deleted, so I advanced the flywheel 3/4” forward like others have done in the forum.

I also drilled a 1/2” hole in the muffler just above the existing exit.

Everything got sandblasted and painted, except for the crankcase. It leaks bar oil but I didn’t get a case gasket and wasn’t sure if I needed a splitter, so it’ll just wear a diaper for now. The Majik ford light grey and Kubota orange are spot on.

It popped on the third pull, then lit off on the next after I opened the choke! You can tell it has a lot more power, and it’s sounds sweet!

 

[Sportfury70]

Saw a set of Stihl Duromatic bar decals on eBay, gonna have to pick those up and slap them on.

The top cover has a nasty crack, but I’ll find another one later.

 

[HarleyT]

The pic shows a Stihl chip. Is the oregon on the other saw?

 

[Sportfury70]

The pic shows a Stihl chip. Is the oregon on the other saw?

That chip was dead. I replaced it with the Oregon.

 

[Sportfury70]

The other saw has a good Stihl chip. They both had been converted from points to electric at some point in the past. They both have the points flywheel, which is why I had to figure out how to time the dang thing after I took it apart.

 

[cookies]

That paint turned out fantastic, did you bake it to harden it? how hard did it turn out and how long to fully cure? I think you addressed the major faults on that model pretty well and it should cut nicely.

 

[Sportfury70]

That paint turned out fantastic, did you bake it to harden it? how hard did it turn out and how long to fully cure? I think you addressed the major faults on that model pretty well and it should cut nicely.

Thanks! Although it’s better in pictures, the shop is dusty so there’s some contamination. The paint directions wanted 24hrs between coats, but we have a powder coat oven. I put the first coat on and then baked them at 250 for an hour. Another coat and another hour, then I was able to reassemble.

I should have preheated the parts, the cover has some bubbles from off-gassing.

I’m going to run it side by side with my buddy’s tomorrow morning to see just what kind of power I picked up.

I gotta say the P&C looked amazing. No scoring or transfer at all. Just a bit of carbon on the top of the piston.

The saw looks good, but not so immaculate that I’ll be afraid to use it. I’ll try to get a video of it running tomorrow.

 

[hotshot]

I found another porting thread and it shows a riser in the middle of the intake port. I assume that’s to increase velocity and split the mixture for combustion/ or direct mixture to the transfers.

For those of you that has ported one of these, do you keep that riser in the intake and just widen the port a bit, or can I delete the riser also?

Also, do you put the ring gap center of one of the ports, or keep it between the transfers and int/ext? I’m not yet sure if has pinned rings or not.

That ‘uvula’ hanging down from the top of the intake port help keeps the bottom ring tucked in at BDC, I wouldn’t try to remove it.

Both piston rings are pinned, so they’re in a fixed location between the transfers & intake.

Good old school rugged saws for bucking firewood.

 

[cookies]

All of the older stihls I have pulled apart have really good looking bottom ends, only the ones with mesh or flocked mesh showed piston crown edge wear and light wear on the cylinder but still fully useable with a new set of rings. And the only reasons they needed rings were loss of spring tension(age) or increased gap in the ring groove (plum worn out) seen as the piston is moved a little up and down while watching the ring, pistons can wear out there too. I think their longevity had to do with good port timing but smaller ports for max ring support and often a ring support in the intake port, larger squish, lower rpm operation and dare I say recommended higher oil ratios in the fuel.

 

[Sportfury70]

That ‘uvula’ hanging down from the top of the intake port help keeps the bottom ring tucked in at BDC, I wouldn’t try to remove it.

Both piston rings are pinned, so they’re in a fixed location between the transfers & intake.

Good old school rugged saws for bucking firewood.

Yeah we left the, uh, uvula, in place and unmolested. And I saw the pins, there is still plenty of cylinder wall where the gap rides.

Now that you say it about the uvula supporting the rings, it makes total sense.

 

[HarleyT]

With the correct Stihl chip, you do not have to change the timing.

 

[leecopland]

Saw a set of Stihl Duromatic bar decals on eBay, gonna have to pick those up and slap them on.

The top cover has a nasty crack, but I’ll find another one later.

Lot of 31's around for cheap

 

[Sportfury70]

Quick tune and cut. You can see I was trying to be careful with it, hence the chain grab. The railroad tie was not the best wood, and I ended up fattening the high jet and loosening the chain after this cut. It cuts nice though!

No go on comparing it with my buddies saw. His either has an air leak or the coil goes bad when it gets hot, because it wouldn’t start unless we let it cool down.

I also have him $20 and swapped covers. Now it has an un cracked cover.

I think this’ll be a fun gtg saw!

Edit* ugh it’s telling me the video is too large. I’ll post on YT and try to link.

 

[Sportfury70]

 

[Sportfury70]

I haven’t touched the chain yet. It looked good but was stiff with varnished bar oil and some corrosion. It took a bath in the parts washer which freed it up, but really needs a sharpening.

 

[Sportfury70]

With the correct Stihl chip, you do not have to change the timing.

Even with the non-electronic flywheel? There was no flywheel key when I pulled it. Would the one that went bad be the correct one to use and still be able to use a key? I would feel better with one in there.

 

[HarleyT]

Here is the list of saws that use that ignition module.

 

[HarleyT]

I'm not sure that there is much difference in the flywheels, it may just be missing the adjustment windows.