Stihl 034 big bore upgrade

[James Sawyer]

I'm new to the site, learning a lot from this group. I have a 034AV that had some issues , which originally started this project. I've since fixed the original problems (Fuel/ Carb) but at the time I thought it needed rebuild since it was last produced in early 90's. This has evolved into more of an performance upgrade/fun project since I already bought the rebuild parts. It’s the only way to justify the cost of the tooling & additional parts is to turn this into a learning experience. I purchased aftermarket cylinder 48mm to replace the original 46mm stock Stihl. Basically I kept the same cylinder timing, widening the intake and the exhaust to flow match. The ports at the cylinder wall I cleaned up just enough to improve the transfers not opening much more than originally casted. It was surprising how much restriction the exhaust had between the muffler and cylinder. I used the exhaust gasket as template for the end results. My next project is to match the baffle area to the exhaust port cylinder wall area. I order the husky deflector and screen but I think I’m going design a slide plate to adjust the exhaust opening when tuning this to performance. I hoping to a get a back pressure reading so I’d have reference on a ball park value to use on other saws. I have a 034 super…hope this 034AV runs better guess we'll see. Please see the attached photo if interested.

 

[TRTermite]

Was your original p/c in bad condition?? I have been watching (LURKing) threads like yours and I am still too unsure of where from and how much material to remove and then there is all of the different dynamics involved. Nice post for pics I for one will be keeping tabs on this thread Thanks

 

[James Sawyer]

No ... this cylinder is going on a good working saw. I really don't have a reference as to what factory or aftermarket cylinder look like. This was cheap cylinder. Sounds like I'm at the same level as you...read...read some then bought the equipment and did it. Worst case I'm out $35 if it blows up. I did not change the timing (drop the roof or the floors of the ports) I basically widen the ports a little at the cylinder wall and smooth & blended the ports. I open the intake and exhaust ports out from the cylinder wall to the carb and muffler, plus leveled all the ports at the cylinder. I used the ring moving it with the piston in the cylinder to get my ref. lines draw for grinding. You have to pay attention to where the ring gap are so you don't widen the port where the ring will catch. Same with the piston skirt, the piston needs to close off the port. I then used a diamond round bit to slightly chamfer the edge of ports so the ring would not catch. The double cut burrs leave the ports a bit rough, I used Diamond burrs and sanding sleeves to smooth things back up as much as possible. You have to be careful not to chip the coating on cylinder bore also. The exhaust is the most important as to how smooth the port is because of the carbon buildup, the intake and transfer aren't as important from what I've read. Once done I washed the cylinder and cleaned really well using brushes, I built enough motors to know you can't get them to clean. I've found there a lot of opinions out there but no follow up testing on performance (porting to function same saw) or how to measure the results. I've yet to run across these full processes. Louder doesn't mean faster chain speed or more torque. Anyone can lean out the saw and spin it up but it won't last long I think. I'm hoping for little fast rev, little more torque keeping the chain speed a little faster than a stock saw with a proper adjust carb running at the correct fuel ratio. I like the weight of this saw (12lbs) and want it to pull a 25" bar. Learning what I know now I should have bought a MS361 for the time and effort ...I think that would have been a better choice over all. These 034's are old saws but good ones for the days... still cuts as well as it ever did. I'm not making living with my saws so really this is just a hobby something fun to do. I'm no expert, I have no reference so I'm fully aware this saw could run worse then stock so take what its worth.

 

[TRTermite]

No ... this cylinder is going on a good working saw. I really don't have a reference as to what factory or aftermarket cylinder look like. This was cheap cylinder. Sounds like I'm at the same level as you...read...read some then bought the equipment and did it. Worst case I'm out $35 if it blows up. I did not change the timing (drop the roof or the floors of the ports) I basically widen the ports a little at the cylinder wall and smooth & blended the ports. I open the intake and exhaust ports out from the cylinder wall to the carb and muffler, plus leveled all the ports at the cylinder. I used the ring moving it with the piston in the cylinder to get my ref. lines draw for grinding. You have to pay attention to where the ring gap are so you don't widen the port where the ring will catch. Same with the piston skirt, the piston needs to close off the port. I then used a diamond round bit to slightly chamfer the edge of ports so the ring would not catch. The double cut burrs leave the ports a bit rough, I used Diamond burrs and sanding sleeves to smooth things back up as much as possible. You have to be careful not to chip the coating on cylinder bore also. The exhaust is the most important as to how smooth the port is because of the carbon buildup, the intake and transfer aren't as important from what I've read. Once done I washed the cylinder and cleaned really well using brushes, I built enough motors to know you can't get them to clean. I've found there a lot of opinions out there but no follow up testing on performance (porting to function same saw) or how to measure the results. I've yet to run across these full processes. Louder doesn't mean faster chain speed or more torque. Anyone can lean out the saw and spin it up but it won't last long I think. I'm hoping for little fast rev, little more torque keeping the chain speed a little faster than a stock saw with a proper adjust carb running at the correct fuel ratio. I like the weight of this saw (12lbs) and want it to pull a 25" bar. Learning what I know now I should have bought a MS361 for the time and effort ...I think that would have been a better choice over all. These 034's are old saws but good ones for the days... still cuts as well as it ever did. I'm not making living with my saws so really this is just a hobby something fun to do. I'm no expert, I have no reference so I'm fully aware this saw could run worse then stock so take what its worth.

Thanks for the details I have too many saws (???I NEED MORE??) And they do not make me a living but my living would be tough without at least a few saws. I like the idea of how you are "experimenting" and you have said some things I have read in the past and yet I still gleaned some small yet important details such as the diamond vs. burrs....

 

[rarefish383]

James, this forum is for milling saws. We do play with them. But, if you drop down the menu to the “Chainsaw” forum you will find the guys that get serious about rebuilding. There are some guys on the firewood forum that can hold their own on rebuilds too.