I remember seeing a diagram of a V-8 engine that used one connecting rod for each pair of opposed pistons. I suppose such an engine would be out of balance, but it would be a bit more compact. at any rate, were these ever produced?
A single rigid connecting rod? How would that follow a rotating crankshaft that’s not in alignment with the connecting rod most of its rotation?
Otherwise, I’m not seeing it.
I think the OP is thinking more along the line of a pair of piston using only one lobe of the crankshaft, similar in principle to the arrangement of the Harley Davidson V-Twin.
Well, upon looking at some images of crankshafts for V8 engines, that seem to way they are already made, one lobe per pair of cylinders…
So, I do not know what the OP means.
As I read it, the OP is describing and opposed engine, not a V configuration. The only way I am aware of that it can work with a ridged connecting rod between pairs of pistons is by using a scotch yoke, or a separate rod connected between the common rod and the crank.
In the steam age, these were never common, but not terribly unknown. Rather than having a second crank throw, it was more common to add a second pair of cylinders at right angles, giving a cross or X configuration. In those days machining multiple throws on a crankshaft was difficult.
Scotch yokes have never been too popular. Lots of force on a small area leads to high wear.
Ah, reading replies that came in while I was typing:
Yes, nearly all V engines use one crank throw per pair of cylinders. This is why 6 and 12 cylinder engines have the bores at 60 degrees, and 8’s at 90. 90 degree V6 engines (except the first ones) need split throws to give even firing, but there is some vibration left over.
A 90 degree V configuration balances nicely. With a single cylinder engine, you can put some counterbalance on the crank, but only half enough to balance the piston/rod. Beyond that you are just converting vertical shake to horizontal shake. But if you add a second rod and piston at 90 degrees, then you can double the counterweight, and it all balances out (well, mostly!)
Kevbo, I’m not sure exactly what the OP is asking about but if he is looking for horizontally opposed 8-cylinders, Porsche built some for racing models including the Porsche 904 and and the 908. I hope these help him find what he’s looking for. I’m guessing the answer isn’t that exciting though because they’re not exactly V engines and they aren’t particularly more interesting than the boxer 6-cylinders Porsche uses today.
More than a few opposed 8’s in aircraft as well, Lycoming IO-720, and Jibaru 5100 are still in production according to Wikipedia.
There are engine designs using the solid rod connecting opposing pistons and a Scotch Yoke to drive a conventional crankshaft. There is an alleged advantage to the way the power stroke drives the crank shaft with different timing than the conventional pivoting rod. See Bourke Enginefor an example.
Going by ralph124c’s history, he’ll never be back to this thread, so asking him to clarify what he means is an exercise in futility.
A “V” configuration engine does not have opposed cylinders/pistons. This is a contradiction in terms. We can try to guess what you mean, but you may not get accurate answers unless you can phrase the description properly.
ETA: “Going by ralph124c’s history, he’ll never be back to this thread, so asking him to clarify what he means is an exercise in futility.” Now you tell me! :smack:
ralph124c may not come back to clarify but what I think he’s asking is normal V8 connecting rods look like this right?
http://www.junkyardgenius.com/internal/AMCrods69-70.gif
Has anyone made them like this (but, you know, bolt on)?
http://foxrivercycle.com/wp-content/themes/auctionpress/thumbs//337011.jpg
No…what I remember was a V-8 block with two opposed pistons on one connecting rod. One piston would be at TDC while the other would be at BDC. I don’t remember if an actual prototype was built.
How does a V8, or any V engine have opposed pistons?
By opposed, I meant the cylinders on opposing each other on each bank of the engine.
Since cylinder pairs in an engine (flat or V) tend to share a journal, they have to be at more or less mirrored positions with respect to the cylinders. In a flat engine, when one piston is at TDC, the opposite piston on the pair has to be at BDC. In a V engine, top-center is only 60 or 90 degrees apart. One cylinder reaches top center, then the paired cylinder reaches it 90 degrees later. (Whether each is on a compression or exhaust stroke depends on the engine design.)
The only exception I can think of is the 1980s-era GM V6’s, which were modeled on GM’s V8. Since V8s run best with a 90-degree cylinder offset and V6s run best with a 60-degree offset, lopping off two cylinders to make a 90-degree V6 made an engine that could be machined on the same lines as the V8 (which was good because those lines were both perfected and fully amortized)… but made a V6 prone to vibration.
GM’s solution, used by other makers here and there, was a split-journal crankshaft that gave the 231 V6 an even firing pattern (effectively one every 60 degrees) but with a 90-degree cylinder angle. The crank had three piston journals, each split and offset by 15 degrees.
That’s as close to “simultaneous TDC/BDC on a V engine” as I can think of, or imagine.
Opposed piston engine is being missed used throughout this post.
An opposed piston engine has two pistons in each cylinder, and the top of the pistons face each other. The pistons come together on compression. No heads and are often the Skinner Uniflow design. Just my nit pick.
no they can’t, because the cylinders are arranged in a V. you cannot have a rigid v-shaped connecting rod shared between opposite cylinders. The pistons are constrained to traveling in a straight line, so the angle of the connecting rods has to change to enable them to do that while the crankpin revolves around the crankshaft’s axis.
those are “fork & blade” connecting rods. They work the same as side-by-side connecting rods, but one rod has “forked” journals which sit on the outside, and the opposing rod has a “Blade” journal which sits in between the forks. the big V-12 airplane engines from WWII fighters and bombers used fork & blade conrods, and Harley-Davidson motorcycle engines use them to this day. the only reason the rods in your picture don’t have bolts holding the big ends together is because they don’t need to; Harley crankshafts are pressed together.
as a cite, here is an example of the crankshaft and connecting rods from an Allison V-1710 airplane engine. note the fork & blade configuration on the “big ends” of the connecting rods:
http://www.oldengine.org/members/diesel/duxford/Allison5.jpg
At 1400 pounds dry weight, we’ll need to beef up the front suspension a bit …
Some [del]idiot[/del] [del]fanatic[/del] Brit stuck an aero V-12 in a car a few years back - think your basic 30-foot-long Can-Am car. 36 liters, 3-4000HP, dual rear drive wheels. Never heard any bad news so I assume he didn’t kill anyone else driving it.
Cool bits about the fork-and-blade connecting rods. Never been a Harley or aero engine aficionado and didn’t know such a design existed.