Piston, Revision 0
Just worked 13 days straight, so I apologize for the lack of updates on this front. Today is a rare day off, before I go into another 12 days straight, and I'll have enough consecutive weekends to tell the company they can't designate me on the weekend of the 9th and 10th, so I can go to the (very nearby) Arlington Fly-In.
Today I'll try and get some of those dimensions I posted earlier, into some semblance of working dimensions to derive other stuff from. I would like to get the master rod started, but I need other things first.
Using the dimensions I recorded from the 'real thing' a couple weeks ago, combined with existing knowledge of bore, stroke, and compression ratio, I can figure out the dimensions of the cylinder. This will theoretically help me figure out the master rod length, and I can work from there.
So one of my measurements taken was the cylinder's height, which I placed at 11.5 inches to the top of the 'intake port' (This is the point on top where the intake is bolted in. The 4360's Intake is on top of the cylinder, and exhaust on the side). The following picture shows what that measurement actually means, highlighted in yellow. I can use this to figure out the scale of the shown drawing, then work out such things as valve sizes, the height of the cylinder sleeve, etc.
My printed copy of the image the above is excerpted from, has that dimension at approx 1.65 inches, giving me a scale of 1.65/11.5 or 14.3 %. Any dimensions taken from this drawing, divided by 0.143 should give me an approximate fullscale dimension, then divided by 6 gives me my scale dimension. To confirm this, I take a measurement of the piston, which we know has a bore of 5.75 inches, measures 0.82 in the drawing printout, which is 5.734 inches using my math - close enough for government work! And I'm former Air Force, I would know ;D
I will probably use this value to go back and work out some of my other dimensions that I was sort of guessing on, like the crankshaft. This drawing shows that as .43 inches, or 3 inches full scale, so half an inch at my 1/6 scale, and... I used .435 inches, so I have some work to do. (this was for the master rod journal) And of course a change here changes my master rod, so I'm glad I checked this now.
Moving back, I have decided to do a revision 0 mockup of the piston. Knowing the piston is 5.75 inch bore, I can correlate the two drawings I have that show the piston, to glean information on the wrist pin, and one view even shows a very clear outline of the master rod, which will help me later. The piston on the R4360 is hemispherical and has 4 rings, with one additional ring at the very bottom. The image shown gives a piston height of 0.59 on paper, or 4.125 at full scale, so .6875 (11/16) at my 1/6 scale. I can't quite make out the detail on the grooves for the piston rings, so I will just use an arbitrary for now, and call it 1/32x1/32, and space them roughly where they look in the drawing. I can blow it up later and get a slightly more accurate idea if I wish. Lastly, the hemispherical part appears to extend about .06 inches, or .4195, or .07 inches at scale, I'll go with the nearby .0625, 1/16th of an inch.
One minor deviation, the 1/6th scale puts the bore at a strange 0.9583 inches. I like to work with even numbers, so I would round this either to the nearest thousandth, or nearest fractional equivalent, which lets me choose between 0.958, or a fraction of either 15/16 or 61/64 (0.9375 or 0.953125 respectively) - 15/16 sounds nice and easy even though it's further from true scale, so I will use it for now. I understand machining is easier in decimals, but for now, it's easier for me to track the numbers if they equate nicely to fractions. This is being done in CAD, so they can always be changed later
So, without much further rambling, we have a piston of 0.9375 bore, that has a base height of .6875, plus a hemispherical addition of .0625. This piston has (4) 1/32" grooves for the rings, plus an additional one near the bottom. (Some math would normally be required to figure out how to make that hemisphere, but CAD lets me just do an arc consistent with three points, and then rotate that arc about an axis to get the 3d solid
(I can then go back and get the radius of the arc if I need it - in this case it works out to 1.7890625 inch radius)
iso view:
side view to show hemispherical surface:
That will wrap up this post, but I'm obviously not done with the piston. It's all I can do from the one view in the patent that I was working from. Another view will give me the dimensions for the cutout for the wristpin, and the wristpin itself... and that will be my next post. perhaps later today, we shall see ;D
As always, comments are highly welcomed, as I don't have the machining experience to know if my decisions are wise! Would you have done something differently? Did I forget something important? Note this is Revision 0, or not-for-production; it's intended to get the basics down, and will not be made as-is. Rev0's are expected to be changed as other parts of the engine are designed and force changes in existing parts.
- Ryan
(edited to correct typos. who needs proofreading when there's a 'modify'?)
