Chainsaw Repair
Husqvarna - Stihl - Poulan - Jonsered - Dolmar chainsaws and more => Modified Ported Work or Race saws => Topic started by: bleed_limegreen on August 06, 2014, 10:52:31 pm
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Hello all, new here and would like some help with porting my first saw. A 42cc strato PP4218
how much can I open the exhaust and intake as in how much wider .... should i open the strato ports or leave them
thank you in advance
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First of all, if you are going to be doing any cutting, you need to remove the cylinder from the saw.
Measure the width of the piston skirt.
Stick a small square down in the cylinder and draw lines square with the base to the edges of the ports.
Compare the lines with your piston skirt so you can determine your limits.
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EASY BERRY PICKING
Some of the greatest benefits are typically obtained with opening up the muffler and adjusting the squish (distance from the top of the piston to the squish band inside the combustion chamber). The minimum distance is .020". The new guys typically remove the cylinder base gasket and use something like Yamabond as a liquid PVC gasket to lower the cylinder. This increases the compression. No cutting involved on the cylinder or piston. The gains are typically noticeable on a firewood saw like yours.
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The skirt measurement is VERY important, you cannot widen the IP or EP wider than the skirt width, if you do you are in a world of hurt! In fact you should subtract some off the skirt width to insure that your ports are completely covered with the skirt. If this is your first attempt I suggest that you subtract 1mm 0.03937 from each side of the skirt to insure coverage of the ports. Also, be sure to measure both the intake and exhaust side skirts because there is always some variation in the width, sometimes intentional sometimes manufacturing tolerances.
As a first attempt at modification you would be best advised to give what 660 suggested above a try, the gains might be all you need.
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Isn't a 4218 a clamshell motor? Haven't looked @ an IPL IIRC it is. If it is no base gasket to remove.
Shep
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You cannot change the squish on a clamshell motor! Unless you can find a taller piston which is a lot of searching and measuring.
Squish is easy to measure.
Use little pieces of rosin core solder. You mash them between the piston and the top of the combustion chamber at four places around the edges.
You can stick little short pieces on top the piston with some chassis grease or you can insert longer pieces through the spark plug hole and extract them from the spark plug hole after you've mashed them?
You get the small electronic solder so you are not mashing much
Keep it away from a port so you are not cutting off a little nib with the port.
Measure the solder with digital calipers or a mic.
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With a clamshell motor about all most porting people will do is to widen the exhaust port a little.
Some engines have cover plates over the intake ports and you can get to the intake transfers from the outside.
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You cannot change the squish on a clamshell motor! Unless you can find a taller piston which is a lot of searching and measuring.
Dont say cant Jim. Roger figured out a way using stock piston.
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How does that work? Machining? Stretching rod?
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How does that work? Machining? Stretching rod?
Thread in poulan board. I will see if I can find it for you.
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Adam 1st page maybe half way down http://chainsawrepair.createaforum.com/poulan/poulan-pro-295/
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Another tidbit: don't widen ports over 65% piston size. Ex:40mm piston x .65= 26mm port width. Open muffler outlet (no spark screen) to 85% ex. port (length x width x .85= size of outlet) using spark screen do 100% ex port. This is general info not hard fast rules.
Shep
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Kev, thk
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Thanks guys for all the input. I will start the project this weekend after some more test cuts is for comparison. I have already modded the muffler and re-tuned and is much better. I had an idea to boost squish on this clam shell and that is to machine the crank journals the same as the base as in if .020 is removed from the base than the same is removed from the from the journal areas..... what do you think?
also at what oint psi do you start using hi octane fuel say 100 and up? as a test just tried some 110 race fuel at 40:1 mix with klotz super techplate and not much difference only maybe a bit better throttle response....
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Just warning as I have been there. Get away from Super 80% 20% and run the Original 100%
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Just warning as I have been there. Get away from Super 80% 20% and run the Original 100%
what did you not like about it?
I know it is and can be a bit dirty, but this will not be a daily use saw more of a toy.... i will just have to watch for carbon build up..... I was also thinking good race gas would help as well...thoughts....?
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Not just me. There is a reason original is used by the racers.
I had a piston starting to caramel up like many of folks found out from hard working saw.
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You should see some improvement just by reworking the exhaust port and muffler .You may get a tad more if you shift the ignition forward a few degrees .
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also at what oint psi do you start using hi octane fuel say 100 and up? as a test just tried some 110 race fuel at 40:1 mix with klotz super techplate and not much difference only maybe a bit better throttle response....
You wont need more than 89-91 octane. Most of my saws are ported with a couple around 200 psi and they run faster on 91 than 100 octane.
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update on my project.... took it apart and did measurements. piston is 41cm ex.port was 19cm so I opened it uo to 24cm. i did nothing to the carb inlet port as it was the same size as carb bore, the strato ports i cleaned up for better flow.
what do you all think? will this make a good improvement or go bigger on the ex. port?
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mm?
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mm?..... is this good or bad?
just checked squish.... its ,056..... need to tighten that up.....
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.020" is ideal.
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got her back together, got squish down to .029-.030 not ideal but better than .056 cleaned every thing in the ultrasonic cleaner even the piston makes everything like new and shiny. got it fired up but no time to test or tune as was late here but will tomorrow
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mm?
Not sure if you're asking mm: muffler mod? If not done then probably worth while giving what else you're doing.
Or, mm: millimeters? Because if you're exhaust is 19cm then you may run into some issues. :D
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update on my project.... took it apart and did measurements. piston is 41cm ex.port was 19cm so I opened it uo to 24cm. i did nothing to the carb inlet port as it was the same size as carb bore, the strato ports i cleaned up for better flow.
what do you all think? will this make a good improvement or go bigger on the ex. port?
When you say you opened the exhaust port are you referring to where the port matches with the muffler or the opening inside the cylinder. I am thinking you mean where the muffler matches to the cylinder.
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yes made cyl side a few mm wider and the muffler side a little as well as gasket matched the muffler
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yes made cyl side a few mm wider and the muffler side a little as well as gasket matched the muffler
Did you chamfer the edges for the port opening inside the cylinder a little to help prevent the ring from hanging as it goes by.
Also a few mm is not the same as 5 cm that you previously posted. That is why you got a (mm) response.
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not that big of a deal to set up and cut squish/base then move your bearing bores up into the jug to match. more work than most builders want to do along with the fact most builders don't want to mess with clam shell engines. kinda hard for a builder to tell you $350 for porting and machine work on a saw that only costs $200-$300 new