Three cylinder 4 strokes have a rocking couple due to the power
strokes, 4 cylinder 4 strokes have a 2nd harmonic - and the latter is
said to be more smooth than the former for that reason

Brian W

On Thu, 17 Jul 2003 00:22:30 GMT, "Ken Coit"
wrote:

If I read Brian's references correctly, having opposed cylinders is good as
they are balanced. If 3 cylinder engines were smoother than 4, why wouldn't
most small engine manufacturers use them? Seems like Saab is the only one
in recent memory.

I'm no expert, but I think the 4 bangers are smoother for a given level of
output. I do wish the referenced article had addressed that question.

Keep on sailing,

Ken


"Jim Woodward" wrote in message
m...
I have lived with the 4-108 for about ten years (twenty years ago) and
took the Yanmar's big brother, a 4JH, around the world in our Swan 57,
Swee****er. I'd pick the Yanmar in a second.

Among other things, a 3 cylinder has inherently less vibration than a
4. (In a three, the pistons are 120 degrees apart, while in a four,
they are 90 degrees apart, so that when one hits top dead center, its
mate is at bottom dead center.)

Jim Woodward
www.mvfintry.com


"Ken Coit" wrote in message
r.com...
Presuming you were looking to buy a used boat, which engine would you
rather
see in her:

Remanufactured Perkins 4-108
New BetaMarine 1505
New Yanmar 3JH3E

These are all adequate to the job of pushing a 16000 # boat at hull
speed,
so the question is one of your personal preference.

Thanks in advance,

Ken Coit
S/V Parfait
Raleigh, NC