I posted this in my engine build thread, but thought I'd do a separate post for those of you who are flathead curious and may not know/care about my build thread. ============== I've just been going through the original Ford drawings for the 59AB and the 8BA engines (from the Ford archives) - Flat32 sent them to me (thanks Ray!). I've redrawn the critical dimensions in a parametric CAD program - such that I can validate them as accurate. What I mean by this is that when I draw the key center-lines/offsets/etc. and program in all the dimensions - the 'driving dimensions' will force the 'driven dimensions' to recalculate. This means that you can't really have a wrong dimension if all the lengths, angles, etc are correct (can't be 100% sure about a drawing that is hard to read!). What I've learned is as follows: 1) The drawings are correct - the geometry, angles and dimensions do work out (this is very good news). Interesting facts (some are obvious): a) The crank centerline does drive the deck height - even though the bore centerlines are offset from the crank. This is obviously true or you couldn't have the same length pistons/rods on both sides of the engine. b) The bore angles are 45 degrees from vertical, but they are offset to the driver's side by .2651 inches. This results in the crank center-line versus bore center-lines to be offset by .1875" (in the bore center-lines) c) The cam center-line is also offset to the driver's side - by .0242 inches. d) The valve angles are the SAME between 59AB and 8BA (though different from earlier 32-41 engines. The passenger's side valve angle is 48.641 degrees and the driver's side is 51.385 degrees. e) The overall length from the center of the cam to the top of the valve seat is the same side to side (about 7.0675), but the valve angle causes the driver's side valve to be higher (at the top side) by about .044. This was validated today when I was at my machine shop, the valve guy measured the height differences (side to side) at about .040. Those of us who've worked on these engines for years can attest to the tops of the valves being up higher on the driver's side. As a side note, it is rumored that some head manufacturer's (heard Edelbrock at one time) actually made different heads side-to-side for the 24 stud center water-neck designs (to account for valve angle, valve heights and chamber volumes). Here is a PDF of the CAD design - hard to see here, but you get the point:
That's interesting...Does Ford offer an explanation as to why the offsets? Or, is this the only set of dimensions that would work for the bores and crank in a 90º engine when running? I applaud your efforts to "bring these engines to life", and the use of CAD (SolidWorks?) to verify geometry.
Nice job. A couple questions: On the left side of the drawing I assume the .8250 dim. is half the diameter of the valve head, and the .2699 is the distance from the edge of the bore to the edge of the valve? What is the .0345 dim referring to ? Do you have any idea of why the cam centerline is .0242 offset to the drivers side?
Yes - I just picked a number for approximate hard seat width (didn't have one in front of me). the .0345 number is a 'driven dimension' - it is how far below the deck the edge of the seat would be. On the other side, it is actually .009 above. Keep in mind, the stock Ford only used 1.5" valves - so these numbers were just for me to check the height differences side-to-side . . . adding them together gave me my .044 height difference. I don't know what the purpose of the cam offset was? I may ask a couple folks I know . . . but if there are any answers, might just be old wives tales! B&S
Flathead crankshaft offset was recently discussed on Fordbarn. If you read thru this thread you will find out why. It's even mentioned in a 1932 Ford engine video. http://www.fordbarn.com/forum/showthread.php?t=158402&highlight=crankshaft offset
There is a lot more to the offset than that, and even the short introduction in the Ford beginning textbook on engineering goes way further. Offsets of various types have a long history (Ford started with the Model A) and offsets are still being actively discussed in very high tech circles like motorcycle racing and formula one. That is an advertising film, and pretty clearly the PR guy put in what little he could understand or remember when he explained an esoteric feature.
I totally agree - not within the scope of this post to even get into it. My main purpose was to share some key dimensions, angles, etc - to validate that the prints I was looking at are correct and to show that some of the documents we refer to are wrong (like the 1939 diagram - must have transposed the offset to show .168 instead of .186+). Much appreciate you weighing in! B&S
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