Chainsaw Repair
How To Basics - Carb Fixes + Mods - IPL and Service Manuals => How To Basics and Fixes => Topic started by: 05_sprcrw on May 23, 2011, 07:42:57 am
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I am wanting to woods port my 394xp nothing over the top just a nice simple port to give it a little more life. How do I begin to take measurements so I know where and how much material to remove.
Right now my plan is to taper the bottoms of the transfers towards the bottom of the cylinder, clean up the piston, and widen the exhaust and intake a generous amount, don't want to change timing so floors and roofs would stay where they are.
I know that I don't want to lower the floor of the exhaust at all or raise the roof of the intake either. This will be the first time I have ever ported so all pointers and tips no matter how basic would help a lot. Thanks!
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I am very much a beginner also. But what i do when i have a saw opened up is i will put the piston into the cylinder (without the ring). Take a pencil, draw around the exhaust port. Take the piston back out and see where your lines are. That tells me how much i can grind out of the port. you need to stay away from the piston skirt edges about 2mm on each side. I make sure i champfer the port where i ground so i don't snag a ring. I don't do anything with the transfers but clean them up. I also tighten my squish by removing the base gasket. Then depending where my compression is i may take the gasket thickness off the roof of the exhaust and the same off the bottom of the intake. Then of coarse port matching the exhaust port and muffler. Than lastly a muff mod. This definitely wakes the saw up but i am by no means an expert. Just my 2 cents.
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If you are going to experiment it might not be a bad idea to first tinker with a lesser expensive saw first .
Now if all you do is rework the muffler and some port polish ,maybe widen just a tad ,you will see results .You haven't really changed the porting scheme any just allowed it to "breathe " better .
The port time area opened really doesn't need much correction unless you can raise the compression which will allow a higher exhaust opening .Now if you do that the time area opened for the tranfers will need some correction ,the intake etc . As the speed increases the time allowed for each portion of the cycle decreases and thus the port sizes will need to be altered to compensate for this . It's complicated but simple in principal .
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Thanks guys, I have already lowered the jug and have .02" of squish now it has plenty of compression it will support the saws weight and slowly drop down as the piston cycles when I hold the starter chord and let the saw go (with a 28" bar and chain full of fuel and bar oil so fairly heavy).
So I would want to raise the exhaust port the .034" (thickness of my gasket) and lower the intake the same as well. I thought I read some where that if I left the exhaust port lower like that it would move the power band a little lower and keep more torque in the motor? I definitely want it to have more pull then super speed, I will be using it almost exclusively in hard woods like elm, ash and lots of oak.
I don't want to do too much up front just polish it up and maybe widen the intake and exhaust ports. Would I benefit from opening up the bottom of the tranfers and tapering them to the bottom of the jug? I have read of guys doing this/ suggesting it be done. I am a beginner to porting but I was planning on only using files to do the work so I won't take to much material at any one time. I understand it will be a much slower and tedious process but figured it is safer that way. So I have no problems setting a fairly ambitious but safe goal for me to port this cylinder. I will definitely do a muffler mod, and match the exhaust opening to the ported cylinder, do I need to do that with the intake as well?
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Because of the angle involved with the position of the rod and piston it's not just as simple as raising the ex port the thickness of the gasket .You'll either have to use trig to figure it or use a degree wheel .Both actually .
You might have to do it a couple of times but just don't carve too much off at a time because once it's gone, it's gone . If you are going to raise it don't go bonkers . Just take it back up to about stock and go from there .
One thing you have to keep in mind is that WOT rpms' out of the wood is just noise .Sounds impressive but does nothing else .It's in the wood that counts .What it can sustain when under load is what gets-er-done .
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Thanks I have been doing some more research and have decided that I am going to leave the roof of the exhaust where it is at. I have the general idea of what to do now its just a matter of keep reading and re reading to make sure I have a firm grasp. I am going to order a new piston and clean the under side of it up and get it ready for the ported cylinder. Then I will also have the muffler modded, thought about having a small metal plate that I can swap out for a spark arrester screen on one of the openings so I can make it quieter if I am cutting in residential areas. Other then re-tuning the saw would it ill affect it in any way doing that?
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Do what you want but were it I ,I'd just let the thing beller with an opened up exhaust . It can't be any more annoying than some kid with a big speaker in his car trunk going boom, ka boom ,boom . Lawdy rattles the windows and shakes the fillings out of your teeth and that's supposed to be cool . ::)
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Do what you want but were it I ,I'd just let the thing beller with an opened up exhaust . It can't be any more annoying than some kid with a big speaker in his car trunk going boom, ka boom ,boom . Lawdy rattles the windows and shakes the fillings out of your teeth and that's supposed to be cool . ::)
Fair enough lol I was thinking the same thing but figured if it were worth the time I would keep a plate on hand.
What about opening up the top of the transfers towards the intake side of the cylinder? I have herd a lot of guys doing this but I am still trying to figure out why it is beneficial? I am really trying to understand the concept behind it, I know it obviously works but what is the driving theory behind it?
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The transfers themselves are designed to "sweep" the area above the intake as that is the most difficult to purge of exhaust gasses .
In addition to that ,directing the flow away from the exhaust helps prevent a condition called "short circuiting " this is when too much of the transfered fuel and air mix is blown right out the open exhaust port .
A slight widening of the upper transfers is one way to achieve a better condition of transfer among several methods .Don't get too carried away though, bigger is not always better .
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Thanks, I have a Meteor piston ordered and once that comes in the saw is going on the work bench to start this port.
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Well I ported it last night :o.
I have to wait for a round ball stone to add the bevel back in but I think it turned out good for a first porting job. I know it has a few flaws but over all it is as good as I can personally manage.
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Well I got the jug back from having someone mill it down for me. I have a ball hone on order to help the rings seat quicker. I got the ball stone in so I can bevel ports now so I will be doing that this evening. I don't think I will get to start the saw up this evening probably most likely is tomorrow.
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Go easy with that hone else you'll grind right through the plating .
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I was going to do it like this video suggested
http://www.youtube.com/watch?v=u9mZClv5Nfo
Will that be too much?
And I fired it up last night with the old rings and this thing is very snappy, it has great throttle response and very good compression. I have not tested the compression yet but I am willing to guess its over 180 psi.
I only ran it for 2 1 min cycles and I didn't snag a ring as of yet so I think I did good? If I didn't I would have assumed something would have happened by now but maybe not. I still need to muffler mod it at some point.
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Looks okay to me .
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The ball hone is back ordered but its no big deal I am going to just run it until it comes in then pull the jug to re-check everything and hone it, and put new rings in.
I ran about 1/2 tank through the saw last night and I am very happy with how it cuts. It has good throttle response and seemed to pull like a freight train in the wood. I am hoping to test it out in some larger wood soon. I will make sure to grab video of it then.
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If it runs great with the old rings why change them ? It will take a while for new rings to seat you know .
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The rings are pretty worn already so I know it will take a while for the new rigns to seat and I will run the saw for a while like this until the hone comes in.
I made a quick video of the saw making its first large cuts last night. I only ran it for a few min and still have it set a tad fat. It was running an 8 tooth rim, 28" bar and full skip oregon jgx chain. Roughly a 32" elm is what I am cutting in this video.
http://www.youtube.com/watch?v=oakLgRcMzGM