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??? minimum combustion chamber and piston crown thickness.......
« on: June 28, 2014, 09:13:45 am »
what say ye

......could not find any info on minimum combustion chamber thickness.

piston crown thickness possibly around 0.200 inch....... but could not find any hard/fast rules.

would tend to believe that values will vary based on comp ratio, piston diameter, chamber cc, etc.

there are some exotic engineering design formulas out there..... hoping to avoid that route.

-joe
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Re: ??? minimum combustion chamber and piston crown thickness.......
« Reply #1 on: June 28, 2014, 09:31:56 am »
Saw through a bunch of old bad cylinders to measure the thickness.

Form your own conclusions and post them on here?
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Re: ??? minimum combustion chamber and piston crown thickness.......
« Reply #2 on: June 28, 2014, 12:45:00 pm »
only cylinders i have belong to 3 running saws... not quite ready to sacrifice those just yet.
wondering if this will help with folks choosing/mixing/matching/machining pistons/cyls in some way is all.

the only sectioned saw cylinders i have seen were photos:

page 10:
http://servicesupport.stihlicademy.com/documents/ssd/Emission_Control_2012-75cb1c07f6b019b960b41f2e55e8343b.pdf

from the looks of those, possibly the the thinnest section is less than the threaded length of a typical spark plug hole?

-joe





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Re: ??? minimum combustion chamber and piston crown thickness.......
« Reply #3 on: June 28, 2014, 01:02:50 pm »
The hottest place on the cylinder head is adjacent to the spark plug towards the exhaust
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Re: ??? minimum combustion chamber and piston crown thickness.......
« Reply #4 on: June 28, 2014, 04:59:10 pm »
I must be reading into the question.  Are you asking for minimum ring land area left for making a pop up piston. If so I cant remember but maybe some of these videos tell.

Brian username Timberwolf has a real good one.









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Re: ??? minimum combustion chamber and piston crown thickness.......
« Reply #5 on: June 29, 2014, 05:58:24 am »
......along those lines that 660 and you have mentioned including heat, top ring land thickness, etc.

from what i read, smokey and grumpy jenkins both figured, that 0.125 inch was about the min. limit for the top land....for water cooled 4ST. 

must be some kind of limits out there that the kart guys/MX'ers use.

interesting to me what tim and walt and others are doing with mixing off the shelf parts... wanted to expand on this idea when machining is involved.  would like seeing more possibilities for fitment.

hope to put together a calculator that can figure out machining limits when mixing different motor combos.

-joe
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Re: ??? minimum combustion chamber and piston crown thickness.......
« Reply #6 on: June 29, 2014, 10:46:44 am »
I machined an ms880 piston to just below 90 thou. and the ring hitting a widened transfer port tore the top of the piston off at both transfers. Cleaned up the cylinder, used a bigger base gasket and it worked fine with a stock piston
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Re: ??? minimum combustion chamber and piston crown thickness.......
« Reply #7 on: June 29, 2014, 11:23:27 am »
Joe, that would be cool beans. It would be great to have a spread sheet that did all the math for you!
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