big twin engine balance theory?

[pcrussell50]

regarding big twins, [i have a, '59 35hp rds21b]...as i mentioned in a previous post, i build automotive v8 engines for road racing, [but i'm brand new to outboards], and a thought came to me while reading my seloc manual. in a 4-stroke automotive v8, if a cylinder has a dead misfire, [not firing at all], it's very obvious, because there is a noticeable shake. but looking at the diagrams of the big twin, being an inline deuce, with a 180 degree crankshaft, and a two stroke at that, if a cylinder stopped firing, would there be any obvious shake? Would there be any indication at all, other than lost power?

Obviously, you'd have half the power , but engine theory and particularly balance theory are fascinating to me, and my engineering text does not cover the case of an inline two with a 180 degree crank.

 

[jbjennings]

Re: big twin engine balance theory?

when my RD-15 was firing on one cylinder, I didn't notice an unusual amount of shaking like one might expect. Some, but not bad at all.
Just an observation. Other than that, I have no idea.
JBJ

 

[steelespike]

Re: big twin engine balance theory?

There is almost no noticeable difference except for the guttless performance.
Many don't even know it is on one cylinder .

 

[DJ]

Re: big twin engine balance theory?

There is almost no noticeable difference except for the guttless performance.
Many don't even know it is on one cylinder .

Exactly. Typically, the only way you will know is that power will be less than half. Idling in a barrel, you probably wouldn't know unless you unhook the plug wires-one at a time.

 

[jay_merrill]

Re: big twin engine balance theory?

I've owned a variety of OMC, two and three cylinder, 2 stroke outboards. My experience with them is that there is next to no perceptable change in balance/vibration with a cylinder that is not firing at all. As others have said, the clue is in a lack of power under load.

Where I have felt an "off balance" or vibrating condition, is when misfiring is occurring. As a cylinder cuts in and out, there a bit of a shake in the engine that is mildly noticeable. There is also a subtle change in sound coming from the motor.

Because the symtoms of a non-firing or misfiring condition are subtle, and often related to ignition, my favorite way of confirming the problem, is to make use of an inductive timing light to find the offending cylinder.