4 cylinder or 6 cylinder?

[O C Diver]

So I'm looking hard at a boat that I may repower. Boat has a Cat 3208 natural 211 HP. At cruise it burns 2 to 2.5 GPH which equates to 30 to 40 HP. Was thinking about a Cummins 4BT 150 HP. Talked to one of the local dealer / rebuilders who said the 4BT tend to have much more vibration than the 6BT 220 HP. His comment was that 6 cylinder motors are much smoother in general than 4s. Had a 6BT in my boat and have one in my Dodge pickup. They are smooth running engines in the ideal RPM range. Any thoughts on how much rougher the 4BTs are, or 4 cylinder diesels in general?

 

[Codger2]

O C Diver wrote:
*6BT 220 HP. His comment was that 6 cylinder motors are much smoother in general than 4s.

*I can't comment on the 4s but I've had 3 Cummins 6BT 5.9s and never had one problem with any of them.

single************************* twins


-- Edited by SeaHorse II on Friday 2nd of December 2011 09:18:11 PM

 

[sunchaser]

Yes, 4s vibrate more. But with a good install (Barry mounts, right shaft coupling, good*cutlass alignment) and a new counter balanced Cummins or JD you may be just fine. Why not keep the Cat running? You will easily spend $25K on a new 4 install.

 

[FF]

I have a CAT 1160, the non throwaway version of the 3208 with 150,000 miles or about 3000 hours.

For $1500 bucks it might be worth yanking your old engine , removing the marinization ( Wet exhaust manifolds) stuff and installing it on my engine .

With no turbo its an ideal boat engine rated 210hp at 2600.

New heat exchanger , new damper plate for your tranny , new motor mounts and exhaust hose , and your gone $10,000 cheaper .

However the 4 cyl has an excellent rep as a bulletproof motor and would be more efficient at 2 gph cruise.

Vibration at cruise , no problem , only the idle might shake more.

 

[jleonard]

Go with the 6bt. Simple, easy to get parts for, easy to work on and maintain. You alrady KNOW that engine (and it's quirks).

No aftercooler so no issues with crudding things up if you run slow. Will have some extra ponies for those times you need it.

*

 

[psneeld]

Noted that a Cat 3208 isn't the most fuel efficient engine...but it isn't so bad*that a repower would ever make up the diffrence in fuel burn unless you are a running 8 hrs a day 365 a year.

Now if you are looking at major maintenance...different story...but unless you are nearing 10,000 hours and the motor is showing a sudden rise in fuel or oil consumption...not quite sure why the expense and headache of a unnecessary repower...

So if you are deadset on the repower...I'll interpret that money isn't the object and therefore I would go with the 6 cyl for the same reasons already stated.

 

[O C Diver]

Ok, here is the situation. The Cat is 23 years old and the engine hours are suspect, likely 5,000+ hours. Without dissassembling it down to the block, it woun't fit through the floor hatch and it won't go through the cabin door to the deck. Not sure it will even fit through the cabin door dissassembled. If I rebuild it in place, there is no option to have the block cooked or do any machining work other than running a hone through the cylinders. Also, you end up with a pretty crappy paint job.

While I could run the engine as is or do a so so rebuild in the boat, engine reliability is what I'm after. My plan is to do a lot of Southern cruising during the winters and I don't want to get stuck somewhere having to do a repower and pay through the nose.

My feeling is if I'm going to cut a hole in the floor and ceiling of the cabin to pull the engine in and out to rebuild it, then I'll put in what I want new and have peace of mind going forward. Also, if any of the water, fuel, or holding tanks need to be replaced, it's a simple matter with the open holes.

As I will be doing much of the work myself, the engine install would be under $20K.

 

[sunchaser]

Do you have the ER length for a 6BT? A certified Cummins 6BT rebuild is*likely the better price vs a 4 cylinder and a wonderful engine as Seahorse and JayN suggest. About 5 issues ago, PMM had a great article on the Cummins rebuild factory.

Contact Tony Athens' shop in CA for details. You may want to order the engine and all associated parts (fuel system, mounts, controls)*through them for best price and install guidance.

 

[O C Diver]

sunchaser wrote:
Do you have the ER length for a 6BT? A certified Cummins 6BT rebuild is*likely the better price vs a 4 cylinder and a wonderful engine as Seahorse and JayN suggest. About 5 issues ago, PMM had a great article on the Cummins rebuild factory.

Contact Tony Athens' shop in CA for details. You may want to order the engine and all associated parts (fuel system, mounts, controls)*through them for best price and install guidance.

*Yes I'm aware of the factory rebuild program. Both the 4BT HP150 and the 6BT 220 are available, that's what I was planning on using. The 4BT and the 6BT are essential the same engines other than 2 more cylinders. While I have the room for the 6BT, I can't imagine needing more than 150 HP. Look how many 40'+ trawlers were made with a single 120 HP Lehman.

 

[sunchaser]

Diver

You seem to have the bases covered and your mind made up. Why did you start the thread - a test?

 

[FF]

Removing the 3208 would seen much easier if you yanked the heads , lifted the block and dropped the crank and rods.

Still a 500+ lump of iron to remove , but lots less hassle.


Since its all steel scrap, no problem , just unbolt and carry out.

The 4 cyl might fit in with no woodwork requirements , by simply stripping the extras , alternator , starter water pumps?

150 rated HP is still plenty for a 2-5gph trawler crawler.

 

[O C Diver]

sunchaser wrote:
Diver

You seem to have the bases covered and your mind made up. Why did you start the thread - a test?

*I was looking for opinions on how smooth running 4 cyl. diesels in general and the* 4BT in specific were compared to 6 cyl. diesels. Figured there had to be some people here with 4 cyl. diesels and maybe a 4BT that would post there opinion / experience.

Thought that was pretty clear from the last sentence in the first post.

 

[Island Cessna]

OK, I'll bite*and attempt*the original question.

A 6 cylinder engine can be dynamically balanced without any additional balance shafts or other "tricks". An in line 4 cylinder engine cannot be inherently balanced, hence the lingering concern about smoothness with*4 cylinders. The cure for this is to add balance shafts to the engine that offset the imbalance. These can make the 4 cylinder close to perfectly balanced. I believe certain models of the Cummins 4B have balance shafts and others don't.

My*1962 Willard 36 has a smooth Gray Marine 4 cylinder engine. It is based on*a Continental Diesel with*a Lanchester Balancer (he was the inventor of balance shafts according to Wikipedia) and a 150 lb flywheel. It*squeezes an amazing 50 hp continuous out of a svelte 1440 lb package. It also has special "Cushioned Power" combustion chambers (I believe they are called Lenova Cells) that Continental claim make the engine smoother. With good polyflex engine mounts and close to perfect shaft alignment it is as smooth as any engine.

If you go with a 4-banger be sure it has balance shafts. They don't seem to call a 6 cylinder a 6-banger. Must be a reason for that!

Any engine will vibrate if not aligned or*with worn out mounts.

Bill

 

[FF]

Sad we cant get 3 cylinder diesels in the 100hp range.

Smooth and would be more compact , even at the same displacement.

The larger cylinders and longer stroke might even be more efficient .

 

[psneeld]

Not sure I would treat the 3208 as scrap...as a working takeout there may be more than a few people interested in it...sure there's plenty out there...but it may still be worth more as a takeout than scrap.

 

[O C Diver]

Island Cessna wrote:
OK, I'll bite*and attempt*the original question.

A 6 cylinder engine can be dynamically balanced without any additional balance shafts or other "tricks". An in line 4 cylinder engine cannot be inherently balanced, hence the lingering concern about smoothness with*4 cylinders. The cure for this is to add balance shafts to the engine that offset the imbalance. These can make the 4 cylinder close to perfectly balanced. I believe certain models of the Cummins 4B have balance shafts and others don't.

My*1962 Willard 36 has a smooth Gray Marine 4 cylinder engine. It is based on*a Continental Diesel with*a Lanchester Balancer (he was the inventor of balance shafts according to Wikipedia) and a 150 lb flywheel. It*squeezes an amazing 50 hp continuous out of a svelte 1440 lb package. It also has special "Cushioned Power" combustion chambers (I believe they are called Lenova Cells) that Continental claim make the engine smoother. With good polyflex engine mounts and close to perfect shaft alignment it is as smooth as any engine.

If you go with a 4-banger be sure it has balance shafts. They don't seem to call a 6 cylinder a 6-banger. Must be a reason for that!

Any engine will vibrate if not aligned or*with worn out mounts.

Bill

*The mechcanic who rebuilt my chater boat engine, also mentioned these balance shafts or something similar. He said all the 4BT coming from cummins now had them along with the new heat exchanger / exhaust manifold combination. Will have to contact cummins to verify this.

 

[Conrad]

FF wrote:
Sad we cant get 3 cylinder diesels in the 100hp range.

Smooth and would be more compact , even at the same displacement.

The larger cylinders and longer stroke might even be more efficient .

*We've had two Albin 25's with 3 cylinder engines, one a Volvo and the other a Yanmar, and found both to be very smooth. I've heard that 3 cylinders are inherently better balanced than fours, but I've also heard the opposite.*

Thoughts?

 

[bobc]

As I've mentioned in another post, the John Deere 4045TFM that I've just installed is smoother and quieter than the Lehman 120 it replaced. The JD has balance shafts. They make a non-turbo version of the JD, which I think would have been fine, but I was talked into getting the turbo. The turbo is pretty simple, so I don't think it's going to change the reliability that much, and I'm not often using the extra power, so I doubt the engine is under any additional stress. Having made the switch, I have no regrets about moving from a six to a turbo four. Having said that, the JD isn't a high-strung engine like the Yanmars. I'll cruise at 1700 RPM, plus or minus.

 

[FF]

3cyl , or better multiples of 3 are the smoothest (leaving out opposed pistons like BMW bikes).

6 cyl is 2X 3cyl and 12 cyl is 4X 3 cyl.

If you want smooth and cheap a DD 3-71 from a generator would be first choice.

With good hunting you might find an aluminum block 3-71

Sure the fuel consumption would be a half gallon/hour higher than a more modern engine , but the first 20,000 hours would be nice and smooth!

The balance shafting and all the items required to smooth a 4 or 5 cyl all require power to spin.

 

[Conrad]

Thanks FF - you've confirmed what I'd previously always thought. So in theory a 9 cylinder engine would also be smooth, although I've never heard of them, other than in a radial configuration.

 

[JD]

More than you probably*ever wanted to know about a V6.

http://en.wikipedia.org/wiki/V6_engine

 

[RickB]

There are lots of 9 cylinder slow-speed diesels.

 

[Conrad]

Thanks Rick; these are larger, industrial use diesels?

 

[Baker]

I would stay with the 3208 personally but that was not our question. Those engines in the NA version are good forever if all of their vital signs are still good.

Also, the 6 cylinder Cummins was available as an NA engine producing 115hp I believe???? Does the Cummins Reman division sell these??? Or do you need more power?

 

[O C Diver]

Baker wrote:
I would stay with the 3208 personally but that was not our question. Those engines in the NA version are good forever if all of their vital signs are still good.

Also, the 6 cylinder Cummins was available as an NA engine producing 115hp I believe???? Does the Cummins Reman division sell these??? Or do you need more power?

*It is my understanding that neither the 4B or 6B (non turbo versions) are available from Cummins Remain. The boat cruises at 2 GPH which should equal about 30 to 34 HP depending on who you believe. The 4B at 80 HP would have been enough to do the job with some to spare.

 

[Phil Fill]

The commercial trawler in Everett rebuild the engine in place/frame which they take to Alaska running 24/7 for days.* So why are you concerned about doing a rebuild in place which would cost 1 grand per hole.* So for 20 grand you could rebuild it twice.* Besides most failures are the engine bloke but what hangs off them.** If your 671 need a rebuild I would have it done in place.

 

[FF]

"If your 671 need a rebuild I would have it done in place. "

Not really,

An "inframe" can be done in place , new bearings , cylinders and pistons and gasket set is possible.

A rebuild requires the block to be cleaned , surveyed , line bored for the crank and cam, the crank and cam ground (if needed)

Usually 2 sometimes 3 inframes can be done before a proper rebuild is required.

 

[davechili]

Old thread - new question

I recently looked at a trawler with two 4 cyl Lehmans. They seemed to run a lot rougher and louder than a single 6 cyl. Do ya'll think that that is characteristic, or just a badly set up pair of 4's.

 

[Nomad Willy]

With all the usual things being equal the more the cylinders the smoother w some exceptions concerning some crankshaft configurations and some cylinder configurations such as V types. Go w the six.
Also generally speaking the fewer cylinders per displacement the more torque and the greater cylinders per disp the more the maximum power.

 

[FF]

As I will be doing much of the work myself, the engine install would be under $20K

A DIY engine swop can be done for half that or less..

If you want the 6 look for an International DT 360 or 466 at the wreckers , both mechanical and electronic injected are cheap.

For better resale , I would go to the John Deere TRACTOR guy. Avoid the stupid priced marine folks.

A couple of times a year JD sells factory rebuilds ,with NO core trade in required!

The 80 hp 4 cyl would be ideal, and carries a SAE std bell housing.

Match it to a Twin Disc rebuilt , and for well under $10K you get a commercial (not yachty rated ) power plant.

Run the numbers the existing tranny, might work , might not.

FF

FF