I have studied many pictures of the Commer Diesel engine but I can’t figure out how the pistons can travel in the same cylinder yet the crankshaft rods are offset on the crank. I assume the rockers offset the two rods or the piston rods are not in the center of the pistons. Does anyone know?
tropes
The diagrams I’ve seen seem to show the rockers are offset from the center of the pistons and connected to the rods with a simple side by side connection. Those are diagrams though, not construction plans. But it shouldn’t matter how the offset is constructed. There will be some additional stress on the bearings in the mechanism, but overall should be generally balanced by the two pistons operating in unison. It probably adds some degree of vibration and wear in the whole crankshaft, rod, and rocker mechanism.
Never mind.
linked example to look at?
http://www.oldengine.org/members/diesel/Rootes-ListerTS3/TS36.jpg
Is there something specific you’re not getting. In my mind, it doesn’t seem like there would be a problem with this setup.
http://www.sa.hillman.org.au/TS3.htm
See especially animation at bottom.
Nice way of getting good end-end scavenge without requiring an operable valve for exhaust.
I don’t think it should be a problem having the rockers angled to allow the pistons and camshaft throws to be offset. For example, take a look at these VW valve rockers.http://www.vdubn.com/sandrailing/engine/vlvetrn1.jpg
Interesting design but if you applied the ideas behind it you could make a diesel out of a rotary engine using a roots blower to raise cylinder pressure.
Not a problem; just wondering how the offset is achieved on the crankshaft. The center of the piston and the center of the crank rod are not on the same plane. It must be either with the rockers or the piston rods.
Tropes
The rockers are not angled but the rods (piston rod and crank rod) might be attached on opposite sides of the rocker.
Tropes
I don’t know about this particular engine, but harley’s have connecting rods that fit one inside the other, so no offset is required.
The Commer has a separate journal for each rod but I find this Harley rod idea very interesting. I may try this on my next Sotropa Motor http://www.youtube.com/watch?v=N8Eq4D2c7VQ&NR=1
Tropes
or one side could be a fork and the other a single rod, so that no offset is needed.
see post #11 
I think I remember an interesting feature about this design; variable compression ratio.
The engine is at idle and the turbo is producine minimal boost, the comp.ratio os something like 22:1.
At power, with the turbo at full boost, the rocker arm (somehow :rolleyes:) reduces comp. ratio to 18:1.
Any industrial engineers confirm this?
Because the rocker arm is fixed in position, I see no way it can affect the compression ratio.
Wow…I just totally figured out what this whole thread is about. I think. It just hadn’t clicked earlier on.
Could the connecting rods be offset like this wrench?
I bet that sounds awesome idling but Kevbo’s diagram shows the two pistons being on different crank throws. they are on opposite sides of the crankshaft but are both “up” at the same time.
I like my design better. 
Since the rockers are on opposite sides they would all be the identical (angled) part.
You remember right, but not with the Commer engine. The engine in question is the Rolls Royce K60, which you can Google but it’s hard to find much real information on it other than in engineering message boards. It was (and possibly still is) used for military vehicles and can accept a wide variety of fuels.
The K60 has two seperate crankshafts on either side (actually top and bottom - the cylinders are vertical) and the phase angle between them can be varied. Check out other twin-crank designs here: Histo Mobile – The home of vintage cars!
