The dimensions on the drawing do not work - if you plug in all the offsets, centerlines and angles - you cannot possibly have the dimension value of ".168" - so I don't trust anything about the drawing at this point (other than the valve angles, which I've measured).
Joe Abbin in his Ford and Merc Rebuild book has this same diagram and while it's not relevant to the assymmetry issue, he also points out that the engine has the Ricardo "Turbulent Head"
Part of the problem is figuring out what to measure, essentially defining center... Crank location is revealed via relation of bore center, then I guess cam location should be measurable from crank... The picture posted in the "asymmetrical" thread is of course from the service bulletins, and I think it kicked off Jim's quest for more detail. Those bulletin pictures exist for multiple ages of flathead, including 99 and 59 types, and I think there is a somewhat different '49 drawing too. Following and comprehending the many lines is a chore... Crank offset at least is thoroughly documented in drawings and in engineering theory in the English Ford engineering book...I hooked up Jim with that one, and that's all thoroughly worked out...pictures there are generic geometrical studies on piston movement, not specifically flathead. All of that of course overlaps heavily with modern practices on offsets obtained in various ways. I think Ford started offsetting with the Model A. Cam offset would seem to me to be only meaningful in terms of relation to valve ( a thought kicked up by the Model A, which has no engine center to discuss) and I am assuming here that cam followed crank over to the offset position for neatness's sake and that valve angles are just Ford's way of aligning axes. Ford changed angles slightly with the 59 (only published explanation I have ever found said it allowed better water passage around valves) but kept them pointed at cam center, so that's not an issue here. Note that Ford used the same cam from '42-8 in both types of engine. My head hurts when I start figuring out which line does what.
The real question is where is the centerline and how much is the crank and cam offset . . . and in precisely what direction? Based on the drawing, the bores are shown as symmetrical in that the center-lines are shown as 45 degrees from the block center-line. What doesn't jive is that their true deck height from an imaginary center would have to be different in order for the deck height from crankshaft center (if it is offset) to be the same. I've got to do some additional CAD work to "test" a few scenarios - to see if I can end up with approximately what I believe we're seeing.
The drawing shows the overall bore centerline is offset by .265 (which is the same as the crank centerline) and you're right, the cam is only .024 off of that. I'm going to redo my CAD drawings with the bank centerlines coming off the crank centerline, plug in all the dimensions and see if it works! Good catch by you! More work by me to get this right . . . be back to you all! B&S
I think you are saying what I extract after staring at the pic...centerline for a non-offset would be intersection of bore angles measured through centers of bores...the .265 line.
Correct! A .168" offset at 45 The bore centrelines are only offset .265 from vertical. The true offset should be measured at 45° from vertical. .168" at 45° gives a vertical offset measurement of .237 The .237 offset plus the cam offset is close to .261 [ if they got their math the wrong way round] so the math is wrong [unless it is measuring something we don't see on the drawing]
Control piston slap is right. I have seen an ad for a 1913 car that mentions the cylinders being offset compared to the crankshaft, for this reason. It was standard practice on all engines, not a Ford feature. At some time in the fifties they started making the block symmetrical, and offsetting the wrist pin in the piston. This is the modern way, and the reason pistons are marked to go in one way.
If you think about it.... when the piston is coming up on compression the rod is at an angle, pushing the piston against one side of the cylinder. When the piston passes tdc the rod angles the other way, and the piston pushes against the opposite side of the cylinder. This quick reversal at tdc causes piston slap. By offsetting the crankshaft, the rod straightens out just after TDC and the piston reverses as it is going down, smoothing out the action.
Odd that the CL of the cam is called the "Centerline of the Engine" in BillM's drawing above. I'd bet that everything in the chassis is measured off the middle of the crank, and the crank is actually in the middle of the chassis.
On Ford drawing shown, line goes right up through center of visible stuff like fuel pump. With scale and lines only .02 apart I think it's pretty hard to tell whether crank or cam center is meant as center! Crank is in middle of car, anyway. If you want to discuss offsets you need another center, and if you take that to be where things would be with no offsets I think best reference is the meeting point of the centerlines of L and R cylinders.
Even at the low resolution of the 32 engine drawing it shows that the centerline of the engine does not line up with the cam, it is off to the left looking at the drawing (or to the right in car terms).
Yep - the two drawings are very different. In the 1939 one, the dimensions for degrees and angles are off of the camshaft centerline, on the 1932 one above, they are off the center of the engine. I have no clue as to which is right, but I will rework my parametric drawing to see if I can figure it out - it is highly unlikely that both are correct for their respective years . . . heck, they both might be wrong!
Just a thought but why would we not agree the true center line would be the crankshaft. If it is not the true center line than all these years the drive line has been offset and we all assumed it was centered. Since the motion of the motor begins with the crank any other add on is driven from that point seems to me those locations come after the center of motion has been established.
Hey Ronnie - thanks for chiming in! I really don't care what is center - just want to know what the dimensions are, and where they are dimensioned from. I've heard that the cranks were offset all these years - probably from folks who looked at these drawings (which don't jive) - but the deck heights are consistent when you measure them with a crank, rod, piston, so the bores must be aligned with the crank (side to side) - or how could the rods and pistons be the same lengths? Unless of course the driver's side bore had a different length than the passenger side? Then you have the valve angle and how they align with the deck - obviously different on the 52 degree side from the 49.5 degree side. The valve seats are all the way up to the deck surface on the driver's side and sunk on the passengers's side. I'm just curious as to what the real "truth" is . . . now back to CAD I go!
I made a quick drawing to check the crank to cylinder offset; the 1932 drawing looks right but the other one doesn't.
Piston slap was not the main reason for offsetting engines on A's and V8's, though it is closely related. To quote the Ford engineering text that I sent Blown '49 when he was doing the updated drawings, "The principal object of this [Desaxe] offset is to diminish the obliquity of the connecting rod during the power stroke, so that the mean thrust of the piston on the cylinder walls during this stroke when the bearing loads are greatest, is reduced." Getting rid of such thrust would help piston slap, but that's not a hot issue...slap is only going to happen on slightly loose engines when stone cold. This is to get rid of power wasted wiping the piston against the wall. I believe.
Well, center of engine in the Ford car is obviously actual crank location...that and the whole drivetrain are straight down the middle, and in the drawing shows the visible stuff up top on that center. A's and B's are also offset...I mention that because there isn't really any other central point to discuss with them, just a vertical block that is different on each side to contain the works and hence not really centerable itself. On the V8, the block has two sides that are just about the same, so if you wanted to you could discuss centering that or worry about the differences brought about by valve angles and offset crank, but still the crak is at the center of the car. Offset is only in relation to bores in either case...offset of crank then has to be related to the hypothetical location of a crank with its axis centered where the bore centerlines would meet. On the A and B you could measure crank offset fairly directly with a plumb bob down the bore and a ruler, more an illustration of what's what than a practical technique, on a V8 level the side under study and do same. Turning this into practice would really require making fixtures to center in bore and a dummy straight crankshaft allowing center measurement, kind of like fixtures used to set up hypoid rear axles.
Power wasting, not so sure. It used to be a common speed trick to put pistons in backwards, to reduce friction and pick up a few free HP at the expense of piston slap when cold. This was done on a lot of engines in the sixties and seventies.
Using the simple Pythagorean theorem, the 1932 one is correct on the offsets - the 1939 one cannot be. I haven't got back to my CAD model, been too dang busy with XMas stuff - will have to wait for the New Year I think
How does all this compair to the Lincoln V8 that Ford built before his 1932 V8. I've always though the fork & blade rods were a nice feature. Bob
You make a point here that I hadn't considered before. With the offset you describe it would mean that the piston is beginning its downward power stroke ever so slightly before the rod goes overcenter in the bore. Everything else being equal, this seems like it would cost you at least some small amount of power by trying to make the engine run backwards for just that tiniest split second. Though I could see the effect being at least partially offset by slightly retarding the timing or some other tune up adjustment. Hmmmm... I'm going to have to run all this through my giant brain for a while and see what happens.
I think the point is, when the piston reached TDC and starts back down it must stop dead for a split second. If the piston flips from one side of the cylinder to the other at this time you get piston slap if the piston is not a perfect fit. If the piston is moving this happens slowly, cushioning the blow.
Always amazed by the engineering feats of old. The stuff the figured out is cool. Check the notes out in the print. Defines valve centerlines for both sides. Definitely a cool picture for the man cave. Posted using the Full Custom H.A.M.B. App!
My head hurts, along with my eyes, and I find myself scribing lines on xeroxes of the service bulletin cross sections... now, as I thrash around, I note on a diagram of a small block Chevy that piston pins are offset towards passenger side, moving the TOP of the connecting rod thataway. Looking at a '39 Merc cross section, seems like BOTTOM of rods are effectively moved toward passenger side. This seems...DIFFERENT. Ford talks about greater distance and hence greater velocity of travel on downstrokes over upstrokes as part of this. I hate it when they nearly derail my brain, then add in "it will be obvious..." We are looking at triangular vector pics here... It's all starting to remind me of hell in the back row of 8th grade geometry.
Issues to be thrashed: effects of piston offset, as engineered and as commonly reversed by rodders... Ford's crank offset vs common use of piston offsets...same, different?? Purposes same, different? Have not yet figgered that out...I suspect different... Effects on TDC dwell...this is discussed by Yunick...flatheads, like SBC, have a lot of dwell there...builds pressur...how effected by offset? Research continues. Running out of fingers for the math, need to draw vectors triangles...
Y'all are assuming these are engineering drawings, which they are not. These are illustrations for service catalogs or other purposes (ie; advertising). You need to look at the engineering drawings to get the accurate dimensions.
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