Mentioned in a current thread, but not described, DeSaxe layout has been tried and produced in the past. I believe ST and Fox offered them up to the 1960's, possibly later. I'd be glad to hear better specifics...

In a DeSaxe layout, the shaft centerline and the cylinder centerline do NOT intersect. The cylinder is offset from the shaft centerline... usually towards the power stroke side. I expect the intent was to keep the rod more directly in line with, or parallel to, the load on the piston during the power stroke. That reduces rod side force, and piston scrubbing friction.

When the centerlines intersect, sleeve port timing is symmetrical. Ports open and close at equal angles from Top Dead Center on both upstroke and downstroke. TDC and BDC take place when the rod and crankpin align vertically.

When they do not intersect, Top Dead Center shifts slightly, depending on the dimensions - piston diameter, stroke radius, rod length and amount of offset. TDC is most likely to occur when the rod and the crankpin are in line. Similarly for BDC. That is usually at slightly less vertical distance above and below shaft centerline than with a symmetrical layout.

At a "steady" RPM - i.e., constant degrees per second (it isn't, but let's consider rotation rate steady) more shaft degrees open during the bypass (transfer) period could mean more physical time to deliver fresh charge to the upper cylinder under the lower pressure of crankcase pumping. An effect like longer symmetrical timing ( time duration) without compromising exhaust phase, which enjoys greater pressure at port opening. As port° timings can have large effect on performance, skewing them favorably may have had promise.

I did some spreadsheets years ago that found port durations were altered. MORE shaft degrees for one port phase, LESS for the other. I seem to remember more vigorous - quicker - compression stroke with extended power extracting stroke... An interesting pursuit! With the 'slanted' straight-line alignment of the rod and crankpin at max distance, it appeared that "dwell" in TDC or BDC range was also shifted to favor burn time and or transfer "dwell" around its max.

I think the most compelling reason we don't see DeSaxe engines these days is the extra cost and complication of machining, for limited gain. I may still have those XL sheets around, but we are now several XL versions later than when I did them.

Duke Fox was an innovator and tried a lot of things. Some, even many, worked well. The Garofali's may have had more methodically developed reasons.

I don't recall any ST's having DeSaxe although it's possible but the Fox 29/35 are certainly DeSaxe. All of the original Mercos (29/35/49 and 61) were DeSaxe but I seem to recall (at least with the 35) they were offset to the opposite side to the Fox. Also an SC 108 that I have is DeSaxe but the 120 isn't. There's definitely a difference in port timings either side of BDC but only a matter of a degree or so.

Just to add a bit to the dwell time at top and bottom dead centre, con rod length/stroke ratio plays a big part in this. The higher the ratio the better and around 1.8 is desireable.

I have a few Super Tigres I believe are built in that style. I've always wondered what the object is. M

Hi!
No!
That's only the carb that has been positioned to the left not the cylinder!

You can't tell a Desaxe setup from the outside unless you already know for sure its Desaxe. You have to at least have the backplate off and piston at TDC. Usually the crankpin will be off center of the crankcase and the crankshaft counterweight will not be perfectly level. Below is one of my engines that is Desaxe. This picture doesn't show the crankpin being offset to one side very well - bad camera angle. But you can see the crankshaft counterweight isn't level on both sides.

The photo I put in this post didn't work properly, so I'm digging it up on my photobucket page.



Same engine, different angles. K&B Sportster .65 from a Mig-27 RCMAT FQM-117