Hmmm 4 cyl vs 3 cyl: better take a look at this...

http://autozine.kyul.net/technical_school/engine/smooth1.htm

Regards

Brian Whatcott altus OK


On 14 Jul 2003 14:04:33 -0700, (Jim Woodward)
wrote:

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 .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

Jim,

Finally, a dissenter from the Perkins crowd. I have been quite surprised at
the loyal Perkins support here. It has about convinced me that we should
stick with her.

I have had others comment elsewhere that the Yanmar is the rough running
engine and I don't understand why a three cylinder engine running at roughly
20% faster for a given power output, could be quieter and smoother than a 4
cylinder engine at that same power level. This is especially true if the
4-banger has greater displacement and would be running at, say, 3000 RPM at
max continuous rating of 37 SHP when the 3 banger is running at 3650 RPM at
a similar power level.

Of course, we would normally run much slower, say 2500 on the Perkins and
3000 on the Yanmar, easily reaching hull speed in most conditions.

I'm not sure I understand why having pistons at opposite ends of their
throws simultaneously would increase the vibration, but then, dynamics was
never one of my favorite courses. If you have a quick explanation, I am all
ears.

Thanks for your reply, the quest is interesting to say the least.

Keep on sailing,

Ken
S/V Parfait
Raleigh, NC



"Jim Woodward" wrote in message
...
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
.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

I'll try for an answer: the pistons are moving fastest not when the
crank is at ninety degrees to the vertical but with the crank a little
closer to cylinder - so the crank and con rod are at 90 degrees to
each other.
This has the effect of introducing a vibration at twice crank rotation
rate.

Brian Whatcott Altus OK

On Wed, 16 Jul 2003 23:51:01 GMT, "Ken Coit"
wrote:
//
I'm not sure I understand why having pistons at opposite ends of their
throws simultaneously would increase the vibration, but then, dynamics was
never one of my favorite courses. If you have a quick explanation, I am all
ears.

Thanks for your reply, the quest is interesting to say the least.

Keep on sailing,

Ken
S/V Parfait
Raleigh, NC

I installed a new Yanmar 3JH3E two years ago and just got back from a 5000
mile, one year trip to the Bahamas and back to Salem MA. We motored almost
all the way, down the ICW and back, early 1000 hours. Boat is an 1968 Apache
37 at 15000#. Prop is 17 X 12 three blade sailor.

The engine was great. Other than things I did to try and mess it up (flooded
four times due to faulty exhaust, fuel in the crankase due to incorrect fuel
line tightening) it performed flawlessly and tolerated my abuse. Quiet and
smooth enough, great mileage, nothing broke. Parts available everywhere.

Check the web page for details on the trip.

Dave Erickson
Apache 37 "Second Sojourn"
www.djerickson.com

To send email, remove the xx from my email address.






"Ken Coit" wrote in message
. 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

Dave,

Thanks for the report. What reduction gear are you using and what is your
"cruising" RPM? The 17x12 seems like a large prop, I don't think I could
fit a 17 to Parfait without some surgery. She currently swings a 15R13
three-blade which is more than adequate.

Keep on sailing,

Ken
S/V Parfait
Raleigh, NC



"Dave Erickson" wrote in message
news:RGdRa.78327$ye4.52992@sccrnsc01...
I installed a new Yanmar 3JH3E two years ago and just got back from a 5000
mile, one year trip to the Bahamas and back to Salem MA. We motored almost
all the way, down the ICW and back, early 1000 hours. Boat is an 1968
Apache
37 at 15000#. Prop is 17 X 12 three blade sailor.

The engine was great. Other than things I did to try and mess it up
(flooded
four times due to faulty exhaust, fuel in the crankase due to incorrect
fuel
line tightening) it performed flawlessly and tolerated my abuse. Quiet and
smooth enough, great mileage, nothing broke. Parts available everywhere.

Check the web page for details on the trip.

Dave Erickson
Apache 37 "Second Sojourn"
www.djerickson.com

To send email, remove the xx from my email address.






"Ken Coit" wrote in message
. 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

"Ken Coit" wrote in message .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

I have both a 4-108 which is getting harder to repair or rebuild cost
effectivly, and a Beta marine 1505 which is the Kubota 4 that is
everywhere in the world and still in production, and Yanmar being a 3
makes it a little to shakey for me, so I chose the Beta, and it is
amazing.