Porting 101

[husqvarna addict]

I need some opinions on intake port duration. I have an older dirt bike cylinder that I am going to add boyesen ports to it to increase fuel and air into the transfers area and it has reeds on this model. I am wondering if I could add the boyesen ports to a chainsaw piston port cylinder or would it just spit air and fuel back out the carburetor? Has anyone attempted this on a chainsaw, hope to hear back thanks.

 

[weimedog]

'cause 9k rpm is boring?

Like just turn in that screw on the carb? That will get you past 9k! Then punch a screw driver through the muffler to let that mean machine breath!

 

[Way2Slow]

Nope I'm not a yankee so I guess I'm banned from the sight. I'm just a grumpy old southern redneck, born and raised in GA. Other than the near 23 years playing GI Joe for Uncle Sam and living all over the place, I've lived in GA my whole life.

Why a chainsaw, I found it laying in the woods and appeared to have been there at least a year. It was frozen up so it had to be torn down and new crank and bearings installed. Going back together, I'm like Tim Allen in Tool Man, it's gotta have more power. I don't thing I've ever built a stock anything in my life, so why start now. I've owned chainsaws since the mid 60's but this is the first one I've had to tear down. I started off with twin Mac-10's on my go cart in the early 60's. Then got into racing outboards in the late 60's and have owned high performance cars and raced cars most of my life so I got into cylinder heads at an early age also. Needless to say, I've spent a few hours with a die grinder. Too many actually, the doctors claim the vibration from them is what caused all the problems I'm having with my hands now and not even supposed to be using one.

 

[Way2Slow]

I hope that was not a question for me about dirt bikes. I know less about those than I do chainsaws. I've never rode or worked on those. Don't even know what a boyesen port is. I know what boyesen reeds are but you have to have a reed valve engine to use those.

 

[weimedog]

Nope I'm not a yankee so I guess I'm banned from the sight. I'm just a grumpy old southern redneck, born and raised in GA. Other than the near 23 years playing GI Joe for Uncle Sam and living all over the place, I've lived in GA my whole life.

Why a chainsaw, I found it laying in the woods and appeared to have been there at least a year. It was frozen up so it had to be torn down and new crank and bearings installed. Going back together, I'm like Tim Allen in Tool Man, it's gotta have more power. I don't thing I've ever built a stock anything in my life, so why start now. I've owned chainsaws since the mid 60's but this is the first one I've had to tear down. I started off with twin Mac-10's on my go cart in the early 60's. Then got into racing outboards in the late 60's and have owned high performance cars and raced cars most of my life so I got into cylinder heads at an early age also. Needless to say, I've spent a few hours with a die grinder. Too many actually, the doctors claim the vibration from them is what caused all the problems I'm having with my hands now and not even supposed to be using one.

Sounds like a lot of us got here from somewhere else...TRYING to retire! Have land in Alabama that might be a destination. Have to sell out of here first. Chainsaw & building rock walls is how I fed my racing habit as a kid. Dirt bikes & motocross until my 40's didn't leave me with much for joints. SO moved to saws as my motorsport because I can't ride as I want to. AND we cut a lot here on the farm. Pay taxes selling timber, heat with wood, fence & trail maintenance. The folks here are much less testosterone enhanced than the racing crowd therefore easier to deal with...a lot of really good folks here. instead of bragging about the 10k motor and 5k suspension, its about a 350 port job. Maybe a 1000 dollar saw with a 350 dollar port job! Much more down to earth here. And unlike the racing many here work with their saws and the hobby is an extension of their livelihood. Even though the costs are low, the financial risk can be much much higher..

And as a person who's family is from the south, but raised in the north; spend years traveling the country & even international I can tell you "Red Neck" starts around Syracuse and ends in California to the west, and south to Florida. You fit right in. Any questions....look at those maps of red and blue by county, not state; of this election. If its red....

 

[Way2Slow]

Just my luck. Finished putting saw together and stuck in a stump I left a little tall the other day from two dead pines I took down in my yard. I didn't go three inches and sparks flew big time. Every tooth on a brand new chain looks like someone spent five minutes with a side grinder on the cutting edge of them. Totally wiped that sucker out. I made a few attempts at cuts just to load the saw and see how it would do, and it's running great. Sharpen the chain and try the other stump tomorrow, or go get one of the logs I hauled off, maybe I can see how it cuts then.

Had my neighbor go with me to some 30" logs we took out of my yard a couple months ago so he could run it and I tuned the carb. Then we made about a dozen cuts with the 20" bar buried the whole time and it just ripped through them and never slowed up. He commented "man! that thing is fast and light". When I put him out at his house, I told him not to forget "his" saw. I told him merry Christmas and gave it to him.
He has a small business doing yard work and trees, and someone stole his saw a month ago out of his truck and was going to cost him almost a grand to replace it. He does a lot for me and keeps my grass cut, (which I do a lot for him keeping his ragged equipment going) so I figured he would get way more use out of it than me. I will say, my 029 super couldn't hold a candle to it.

 

[volvo2før]

Anyone tried chamfering the piston skirt like this? I know a 2-stroke motorcycle guru that do this on almost every engine he's porting.

 

[LegDeLimber]

I expect that you'd need to factor in, just how much that big ramp shape, affects the intake timing.

Also curious if it might let the oil film slip into the piston to cylinder clearance, a pinch better.

 

[Chris-PA]

Anyone tried chamfering the piston skirt like this? I know a 2-stroke motorcycle guru that do this on almost every engine he's porting.

The only effect I can see of that would be to increase intake duration. You'd have to watch out for free porting the exhaust too.

 

[blsnelling]

I don't see the advantage. I want the port to open as quick as possible, allowing the max flow with the max case pressure.

 

[volvo2før]

The only effect I can see of that would be to increase intake duration. You'd have to watch out for free porting the exhaust too.

I think the advantage will be to let more oil remain on the cylinder wall, specially on the upper area. Better oil coating also improves the seal between the rings and bore wall and decrease compression leakage.

 

[Chris-PA]

I think the advantage will be to let more oil remain on the cylinder wall, specially on the upper area. Better oil coating also improves the seal between the rings and bore wall and decrease compression leakage.

How will it do that? Most pistons already have a small bevel, and oil films are pretty thin.

 

[volvo2før]

How will it do that? Most pistons already have a small bevel, and oil films are pretty thin.

Many pistons also don't have any bevel at all. The square edge of the skirt will scrape oil off the cylinder wall instead of letting it settle. When chamfering the skirt, the rings can also carry lubricant to the upper cylinder area. I know there have been much smoother idling when chamfering pistons with only one pistonring. I will surely give it a try on my next port job ☺

 

[Stihl311]

New to this forum been cutting for a little while and just got a ms 311 was wanting to port and polish and muffler mod it and tune the carb by someone who knows what there doing....wondering if after the woek is done would I gain much horsepower or enough to run a 24" .050???? My buddy has a 391 and he runs a 24 inch bar and the hp's are so close I am wondering if this mod will allow me to run that size bar no problem with a full chisel chain

 

[shorthunter]

Most people here will tell you not to waste your time with porting on a plastic crankcase saw.

The muffler mod will help if you trim the limiter tabs and retune the carb

 

[Chris-PA]

Porting on a clamshell isn't any different except it's a bit further to reach inside due to the extended cylinder, and it is harder to increase compression by cutting the cylinder. The plastic case isn't going to break due to the power increase.

 

[millpro]

I have a husqvarna 257. Doing a complete rebuild. It had scored the piston. The cylinder which is what came on it new was fine with the exception of a nick at the bottom of the exhaust window. I have ported it and took the nick out. It wasn't bad but I'm wondering if I went to far. I have ring coverage at bottom dead center. Just wondering if it's enough???

 

[blsnelling]

I have a husqvarna 257. Doing a complete rebuild. It had scored the piston. The cylinder which is what came on it new was fine with the exception of a nick at the bottom of the exhaust window. I have ported it and took the nick out. It wasn't bad but I'm wondering if I went to far. I have ring coverage at bottom dead center. Just wondering if it's enough???

BDC isn't what matters. Is the skirt fully covered at TDC?

 

[millpro]

BDC isn't what matters. Is the skirt fully.

 

[millpro]

BDC isn't what matters. Is the skirt fully covered at TDC?

Yes its git plenty of skirt below the window.