Author Topic: Deck Height Difference in XT Cases Versus XP Cases  (Read 825 times)

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Offline weimedog

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Question is if its harder to build a .040 shim or lower the intake? AND what happens to the transfer & exhaust timing by raising the cylinder .040? Not certain at that point in rotation of the crank & location of the piston how much difference the .040 lift will make. I also think there is ground to be tilled because of the windowed piston, both on the 064 and the 272 piston designed for those older two transfer port designed cylinders. But that too would require grinding the 372 cylinder some to open up the bottom of the transfers. Of course trimming the skirt on the Stihl piston is an option,just I hate doing that for a whole variety of reasons.

Offline KilliansRedLeo

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In my old age, my eyesight is not what it used to be, so making a shim is easier for me than detail grinding in the cylinder because I made a jig out of a trashed (white death) pair of 372 cases. I have a very small router that I use with a spiral carbide cutter (it is used for inlay cutting in furniture making) that has a bottom bearing that will follow the case without damaging the case and cut out the shim. I have used it on copper shim stock up to 0.060 and aluminum up to 0.080.  The port timing is difficult to measure, I have thought more that once about cutting the top off a cylinder to try to make it easier to make those kinds of measurements but have never gotten around to it.
"When the people fear the government...you have tyranny....When the government fears the people....you have liberty"

Thomas Jefferson
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Offline weimedog

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Can rough measure with a wire through the exhaust port. Measure the wire first of course! Then adjust what you get with the wire by the number of degree's it takes to rotate the piston that distance of the wire thickness. Not perfect but can ball park the numbers. Easier to get good numbers on the intake side as you can see it on the 372's. (Have just the cylinder on the cases)


I'm game to try either build concept. I can approx. the .040 with 2 base gaskets and measure the port timing. But would rather use a shim & 1194 for a real running trial.

Offline sharkey

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If you dont have a lathe, you guys may want to try fashioning a cylinder base cutter out of a piece of plexiglass or thin hardwood.  Something that has a flat surface.  Trace around the base of the cylinder spigot onto your flat material.  The spigot is the metal guide that sticks out of the cylinder base and fits down into the crankcase.  Cut out the hole making sure the spigot just fits and there is enough room for the ears of the cylinder.  Fix a piece of good quality sandpaper to the flat with some spray adhesive.  Cut out the sandpaper from the opposite side using a razor blade.  Fit the cylinder spigot into the hole of your flat over the paper and give it a couple twists.  It takes maybe 10 minutes to cut .015 inch off the base of your cylinder with good paper.  Check your spigot as it may also need trimmed but you can do this with a file.  You can now set your squish a little closer and still use a thin gasket.     

Offline KilliansRedLeo

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Good idea! Will give it a try in another situation. Right now we are dealing with a piston that is too tall for the jug by 1.5mm so we need to add not subtract from the jug.
"When the people fear the government...you have tyranny....When the government fears the people....you have liberty"

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Offline weimedog

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Post pictures and results on the 350 when it i done. Your 372 chain brake parts go out in tomorrow AM mail.

Cheers!

Roughed out the 350... no paint on the muffler, no polishing on the die grinder work. Just wanted to see if things would go together and work......they do. Will run it then go back and make things pretty if it runs WELL enough to be interesting....uploading a video of its guts and is first minute of run time. It needs a chain and air filter..... the air filter might be interesting... If it shows promise, then we can go back and tweakm& clean things up and make it right .. pretty as well. But for now... just proof of concept saw. I'll stick the video on youtube where my stuff usually resides on my afleetcommand channel  Its the "fugly Husqvarna 350...."

Offline KilliansRedLeo

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OK, I put together the Hyway BB piston from a 372 BB Kit and a stock Meteor 272XP piston 52mm. In the attached prictures you can see that the 272 piston is noticably taller in compression height, it is however noticably shorter in overall height 2.0mm. The BB kit piston has clipped corners on the skirt where the 272 does not. The BB piston is a semi 'full circle' design and is only 31mm at its narrowest point the 272 being a full 5mm wider. OH height of the BB kit piston is +2.0mm taller than the 272XP piston.

So what do you think? My thoughts are that we should pick up some in the intake timing and also come compression due to the taller CH. However we now have to deal with the impact of the 272 piston being a windowed design and the BB kit piston not. Howeve this is mitigated by the fact that the Stihl 064 Piston is windowed and runs fine in many of theses saws I have built.
"When the people fear the government...you have tyranny....When the government fears the people....you have liberty"

Thomas Jefferson
1743-1826

Offline KilliansRedLeo

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Test assembled the saw with no base gasket and 272 piston, runs hits cylinder top. Tried again with AM base gasket, same results. With 2 gaskets clears cylinder top but don't know by how much. 2 base gaskets are nominally 0.0343 uncompressed. So if 1 gasket is half that 0.0171 perhaps a copper shim and a single gasket. Got to take it apart and measure squish with two gaskets.
"When the people fear the government...you have tyranny....When the government fears the people....you have liberty"

Thomas Jefferson
1743-1826

Offline KilliansRedLeo

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There is some manufacturing tolerances between individual pairs of XP cases (don't have any XT cases to try). Same cylinder, same piston, same gaskets, first pair of XP cases, squish measured 0.0112. Substituted another pair of XP cases all else remained the same, squish measured 0.0153. In both cases cylinder was mounted and torqued to factory specs 10NM. Substituted a stack of gaskets from Northwoods saw squish now measures 0.025-0.028. Good enough to put the saw together and see what it does!
"When the people fear the government...you have tyranny....When the government fears the people....you have liberty"

Thomas Jefferson
1743-1826

Offline sharkey

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Maybe a piece of soft flashing between two thin gaskets would give you the squish your looking for?  Had you posted that you had a small router that you used on the copper shims?

 

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