Porting Farmertec 372xp BB

[pioneerguy600]

Ya, Credit River Terra Cotta 2005

I never seen wood like that up in the territories, figured it was in the Ontario area.

 

[Gypo Logger]

I never seen wood like that up in the territories, figured it was in the Ontario area.

There's word of a 28' spruce log with a 24" tip, but I'll believe it when I see it.

 

[pioneerguy600]

There's word of a 28' spruce log with a 24" tip, but I'll believe it when I see it.

Maybe in Sasquatches back yard.

 

[morbius18]

I forgot that I wasn't done with the exhaust port on my 50mm oem and lowering the intake on my 48mm. I assembled the 52mm a dirkoed it. So I had to remove it. I discovered that the farmertec piston has no cutout for removing the circlips; I didn't notice when installing. This was fun to grind a slot to remove it while mounted to the saw. Multiple layers of shop towels covering the crank and bottom end...


I did some cutouts while I was grinding the piston. I used a ms461 piston for an example.

 

[logger450]

What is the advantage of a stepped exhaust port over keeping the taper all the way to the inside of the cylinder? I have never tried porting a saw yet but a few ported saws. I am mostly cutting 20-26" oak and maple and my problem with some of the ports are they have all kinds of speed but fall short when you need the torque. Could I do port work on the intake side and just cleanup the exhaust side. I believe the exhaust is where the torque comes in. No need for a cookie cutter just a strong tree cutter. I bought a 385 top end from mdavelee and it has the best of both worlds. Speed and torque.

 

[morbius18]

What is the advantage of a stepped exhaust port over keeping the taper all the way to the inside of the cylinder? I have never tried porting a saw yet but a few ported saws. I am mostly cutting 20-26" oak and maple and my problem with some of the ports are they have all kinds of speed but fall short when you need the torque. Could I do port work on the intake side and just cleanup the exhaust side. I believe the exhaust is where the torque comes in. No need for a cookie cutter just a strong tree cutter. I bought a 385 top end from mdavelee and it has the best of both worlds. Speed and torque.

I don't know the advantages, I just wanted to try it as I found a post by Mastermind about doing it. My OEM cylinders will have a regular port opening.




This is how my OEM ones look. Regular non step ported on left, same cylinder non ported on right.

 

[morbius18]

[QUOTE="logger450, post: 6744306, member: 110064" I bought a 385 top end from mdavelee and it has the best of both worlds. Speed and torque.[/QUOTE]

The best thing would be to degree this one or find the numbers from the seller. I'm not knowledgeable about most others saws. I researched the numbers for the 372 and the same kept popping up.

Sorry I couldn't help more with this.

 

[logger450]

That non step port you did looks real nice. I don't know anything about porting so I ask as many questions as possible. The 372 is a real nice saw. I just started buying them up as well.

 

[morbius18]

I finished all three cylinders; 48mm oem, 50mm oem and the farmertec 52mm big bore. I shot for all the same numbers to compare how they run.

The 52mm Farmertec big bore numbers:
Intake: 80*
Exhaust: 98*
Transfers: 118*
Squish: .037"
Blowdown: 20*

Squish is high as it came, as I cannot cut the base, no lathe. I really had to raise the transfers and the exhaust on this one to get my numbers.

 

[morbius18]

I finally got around to putting it back together. We had a big snow and a farm. Horses were having to be kept in stalls and crap mucked 2x per day. And the kids were home from school, so not much disappearing into my shop for a few hours.

I used only the top ring on the piston, and I used Dirko HT on the cylinder.

Saw passed pressure and vacuum test.

On assembly, I noticed the heat shield was hitting the flywheel side of the case. I put the muffler on with only the cylinder bolts and its skewed slightly to the flywheel side.

So either the cylinder bolt holes are slightly off or the machined exhaust/muffler mating surface is.





I put the screws in the bracket and then tightened it up and it 'centered' itself slightly.

I tested compression. I was telling myself if it wasn't at least 140psi, I wasn't going to run it. At .037" with no base gasket, I wasn't too optimistic. I was surprised that it read about 145.

 

[morbius18]

I reassembled it and got it ready to run. I couldn't get the saw to idle right. It passed pressure and vacuum less than an hour earlier.

It would burp on choke, start on half and then die. I kept thinking it was the carb. I'd pull the plug and it looked wet. Figured I flooded it. Blow out the cylinder and repeat. It was taking 10 pulls on full choke to burp.

After about 30 minutes of tweaking the carb and pulling the plug, I actually started to think. Sounds like its not getting impulse. Pulled the cover and checked, it looked good, and I was able to pressurize and vacuum the case. Carb port was good also.

I thought it has to be fuel. I drained the tank and noticed there was alot of fuel line in the tank. I took off the rear buffer screw and the cylinder/handle one. The fuel line was kinked where it makes the bend into the tank.

I pulled the 70-75 mm called for in the service manual, refuelled it and adjusted carb to 1 1/4 on both. I left the cover off.

It started right up and purred nicely. It reved well and returned to idle.

I quit at this point. Stopping on a positive allows me to not think out every 'whats wrong' scenario in my head for the rest of the evening.

 

[smokey7]

With the ehaust that high it bleeds off compression also. So if the port was at 104 it would have more trapped volume and higher comp.

 

[morbius18]

With the ehaust that high it bleeds off compression also. So if the port was at 104 it would have more trapped volume and higher comp.

I'm suprised it was that high, but the squish isn't that far off from an oem with gasket.

This one was an experiment/practice.
It was on sale at huztl for $12. I threw it in with some gaskets, seals and carb kits.

I'll be running the oem 50mm cylinder long term. It's squish is .025. Should yield a good compression at the same numbers as the 52mm big bore.

 

[morbius18]

I took my 24" bar and chain off my ms441 and did a few test cuts in some smaller cedars. In the next few days, I'm going to get a dry hardwood log of at least 16 inches to do my video test cuts on. I'll be using a 20" Husqvarna bar and a new Stihl chain.

 

[mdavlee]

I only lost 15 lbs going from 102 to 95 on another 52mm jug. 98 isn’t really high anyway for some of us.