Crankshaft offset
- Thread starter russcc
- Start date
ford38v8
Well-known member
I read a while back that a machine shop mistakenly decked both deck heights the same, so apparently they found that mythical reference point!
This thread seems to be generating more questions than answers...
I read a while back that a machine shop mistakenly decked both deck heights the same, so apparently they found that mythical reference point!
This thread seems to be generating more questions than answers...
I once, many years ago, had a flathead bored by a guy with a Rottler (sp?) Boring bar. He said the bock attached to the machine via the mains, and 'referenced' the mains (?). I always wondered if he 'cockeyed' bored it to force the cylinders to line up with the crank center. This, especially after comments about the bore being worn quite a bit on one side, and his machine 'corrected' it. How the Rottler works is a question for another thread at another time. (He was NOT a flathead guy.)
Ken/Alabama
Well-known member
I use a Sun Machine to setup my distributors and they fire 45 deg apart. And thats what the instruction book calls for.
Straightpipes
Well-known member
Rule #1: Never let a "non-flathead" machinist machine your block........
" I called you to tell you that your block has some serious problems. The valve seats are at different angles from one bank to the other. Weirdest thing I ever saw! So, hope you don't mind but I went ahead and cut the deck surface so they would match."
" I called you to tell you that your block has some serious problems. The valve seats are at different angles from one bank to the other. Weirdest thing I ever saw! So, hope you don't mind but I went ahead and cut the deck surface so they would match."
Maybe you could let the rest of us in on the joke.
OLD...BILL
Well-known member
The more I read,,, my flathead will never run again ????..............OLD......BILL
Bored&Stroked
Well-known member
Hey Gang - for those of you who are looking for dimensional details . . .
I've just been going through the original Ford drawings for the 59AB and the 8BA engines (from the Ford archives). 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 centerlines/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.
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 bitmap image and a PDF of the CAD design - hard to see here, but you get the point:
View attachment FlatheadFordEngineCrossSection.PDF
Enjoy!
B&S
I've just been going through the original Ford drawings for the 59AB and the 8BA engines (from the Ford archives). 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 centerlines/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.
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 bitmap image and a PDF of the CAD design - hard to see here, but you get the point:
View attachment FlatheadFordEngineCrossSection.PDF
Enjoy!
B&S
Last edited:
ford38v8
Well-known member
B&S, that's all good information, but it still leaves a question in my mind about deck height. Bear (bare?) with me please:
The driver side deck being lower than the passenger side, should mean that the drivers deck must extend quite a bit farther up to meet the intake deck than the higher passenger side. Disregarding the valves position, the deck from the bore CL to the intersection at the intake flat has got to be considerably farther on the driver side, or else the intake flat would be leaning toward the driver side like the whole car leans on many old Fords! B&S, can you verify this, with dimensions to show how much difference should be visible on the deck itself?
The driver side deck being lower than the passenger side, should mean that the drivers deck must extend quite a bit farther up to meet the intake deck than the higher passenger side. Disregarding the valves position, the deck from the bore CL to the intersection at the intake flat has got to be considerably farther on the driver side, or else the intake flat would be leaning toward the driver side like the whole car leans on many old Fords! B&S, can you verify this, with dimensions to show how much difference should be visible on the deck itself?
BillM
Well-known member
I think we are back to the original question; from this thread on another forum http://forums.autosport.com/topic/126663-cylindercrankshaft-offset/
If I can be indulged. In explaining the desaxe design to apprentices I would use a bicycle crank as an example.
With the crank positioned at 12 0/clock it is difficult to push to get going.
With the crank positioned ie at 1 O/clock it becomes easier to proceed
The offset crank, or in other engines the offset wrist pin provides this principal.
Elmo Rodge
Senior Member
Yep. Wayno
rheltzel
Senior Member
Here's Henry's explanation*:
"The piston bore is offset by 3/16th's of an inch from the centerline of the crankshaft, which increases the smoothness of the engine by reducing the angularity of the connecting rod on the power stroke".
* quoted from the Ford-produced film I referenced in a post, above.
"The piston bore is offset by 3/16th's of an inch from the centerline of the crankshaft, which increases the smoothness of the engine by reducing the angularity of the connecting rod on the power stroke".
* quoted from the Ford-produced film I referenced in a post, above.