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Old 10-26-2012, 10:35 PM   #37
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06 WRX 30r 6 speed
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Originally Posted by oem View Post
Aboothman, thanks for agreeing with me and showing the problems with Crystal's torque plate assumptions.

Now I will explain why torque plates are not needed for gaping the rings.

aboothman calculated .0015" as the max circumfrence difference so I will use that number.

Ring gaps are measured with a feeler gauge (thickness gauge), which is a go/no go gauge. Feeler gauges come in .001" increments and do not measure the gap. The user can only tell if the gauge fits or does not fit. i.e. a .015" gauge fits too loose, a .016" gauge fits ok, and a .017" gauge does not fit. For this example, that means the gap is greater then .015" and less then .017". Only by feel can one determine how close the gap is to .016". So with practice one can get closer to feeling what he believes is .016" but it is not exact.

So now when a max circumference difference of .0015" is used the most the ring gap will be off is one feeler gauge. If it is not the max the difference will be between a tight .016" and a loose .016". If we were building F1 engines, this would matter. But for 99% of the Subaru engines built here by members, the difference will not matter.

Just because a process is more complicated does not make it right.
This is THE BEST thing you have posted to date, and it makes real sense!! But it is making an assumption based off theoretical numbers that I pulled, for the most part, from my arse. I should not have said max, because it is completely possible to have a bore distortion of .001 or greater. Without EXTENSIVE testing we do not really know how much bore distortion is possible, or what shape it will take.

With out actually having YOUR block in front of you, with all of the required tools, before and after a plate hone, it is pretty much pointless to speculate too far...but I was bored This is why I finished with "Do it right (hard/expensive way) or do it wrong (easy/cheap way). We could extend the "it will be fine" mentality to no end.

Furthermore the .001 used to derive everything I posted above, used as the difference on ONE AXIS of a theoretical distorted bore, is based off of a test with completely different methodology. That piece of math alone has so many variables and possible error to discount ALL of the math I posted.

I wouldn't really call what either of us posted fact...more like armchair engine building. I simply wanted to fill in the gaps in OEM's statement that Crystal's math was wrong since he cannot be bothered to support any of his statements.

And then the JE tech's statement that ALL of it is wrong Considering what the tech said about "bumps", and how they can affect the cylinder, it becomes clear that a cylinder honed WITH a torque plate must be gaped WITH a torque plate (old news). In my mind these theoretical bumps will take the cylinder out of round negatively (inward) when the cylinder is relaxed without the plate, which actually could affect the end gap more than on a cylinder that has NOT been plate honed. Such a cylinder would have a positive flex (outward) with a torque plate as the tech suggested, which would not affect the end gap as the rings do not follow minor changes in cylinder wall diameter. More speculation for thought....and hopefully verification!!

In my opinion, if you are not that concerned with getting the tolerances as close as possible, then buy an OEM block and drop in some pistons. That is an attitude that has been taken advantage of by crappy engine builders for years, especially in Subaru land... which is why you see so many built engine horror stories. Now that we have some engine builders taking the time to get it right, and rightfully charging a little bit more for their time, it seems ass backwards to revert to the "its good enough" attitude now...especially if you are building it yourself. It can affect parts of your build: Cleanliness, main tolerences, PTW clearances, EVERYTHING.

This discussion is clearly aimed at those of us building engines at home...even in our kitchens on occasion!! Personally I have all the time in the world to do things the hard way. If the results are the same, great!! But why take the chance, when you have the time to spare, because "it is complicated"? If I did not have the time, I would have paid someone else to build it for me with the money I spent on tools and measuring instruments.

As for "more end gap on higher boost engines" it assumes that we are all building high boost engines. What about higher compression engines, whether turbo or N/A?
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Last edited by aboothman; 10-26-2012 at 10:54 PM.
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