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Old 08-08-2009, 20:29   #1
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Perkins 4-108 vs 4-236

The saga continues. I am having my Perkins 4-108 removed next week and sent up to Transatlantic Diesel. Thanks all who recommended them. Jennifer on the phone very helpful, and they will give you prices, unlike the company in houston that my mechanic wanted to use, that only would given round estimates if that....

Anyway TAD recommends a max of 120 amp alternator off the 4-108 even with the serpentine belt option. So I wonder, what about going up to a 4-236 ? It maxes out at 84 hp at 2800 rpm. So running a high amp alternator should be no problem, and should power better into rough seas.
Of course it will use more fuel, but what about the size and footprint of the mounts ? anyone know if it will fit ? What about the size of the exhaust ?
I'll call TAD on Monday to find out, but a little foreknowledge form the group would be nice.
Thanks,
Bob
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Old 12-08-2009, 12:22   #2
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bob i have a 4.236 perkins engine which i have just fully overhauled my self i have twin 90 amp alternators fitted and would not have any larger on the engine , and i purhcased all my parts from the usa from a company called Maxi force who make genuine perkins parts for perkins themselves my engine which had done 10,000 hrs was in great shape when i stripped it down the complete overhaul engine kit cost me 650 the only prob i did find was the serck g/box oil coolers and engine coolers where slightly corroded in which where repairable but i dedcide to replace which cost me another 523 .

I would never have a 4,108 has the cylinder heads seem to fail a lot and my 4.236 will give me another 10,000 hrs of trouble free running
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Old 12-08-2009, 15:15   #3
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Bob,
The 4.236 is physically larger than the 4.108 and it mounts on 22" centers which is wider than any of the mounts for the 4.108 which were generally 18".
Measure very carefully before committing to a larger engine.
Stanley
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Old 12-08-2009, 15:37   #4
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I'd stick with the 4-108 and use a smaller alternator but I'm a minimalist. I've never heard of head problems with 4-107/4-108. Is that a common thing in GB?
regards,
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Old 12-08-2009, 16:24   #5
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The 4-236 is maybe the best recreational boat diesel ever made. The 4-108 is good, but the 4-236 is bulletproof.... and yes I still have one!
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Old 12-08-2009, 16:45   #6
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Call Balmar. They can tell you which alternators will fit on which engines. Just tell them you want to get the maximum charge possible with one (or two?) of their alternators. They have already figured out the engineering for lots of different marine engines.
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Old 13-08-2009, 06:01   #7
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David,
Fitting a larger capacity alternator to an engine is easy. The reason that engine manufacturers limit the size of alternator that they fit to their engines is really quite simple. They take into account the side load of the belt on the circulating pump and this is usually the limiting factor. When everything is properly engineered, these last and the owner is impressed with the reliability. When someone fits too large a capacity alternator, they then make the belt tighter to try and deliver the power from the alternator and when the fresh water pump fails they blame the engine manufacturer, not themselves.
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Old 15-08-2009, 07:21   #8
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Seems that I have to stay with the 4-108 due to the core exchange. TAD can only exchange like for like engines.
No worries though. The 108 is plenty fine.
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Old 15-08-2009, 09:23   #9
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Since this thread has evolved into a alternator discussion, I would like to ask does anyone know how to tell the amp rating on a given alternator.......are there any numbers or codes stamped into the unit? Also how does one tell if the alternator is internally or externaly regulated?
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Old 15-08-2009, 15:43   #10
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bob there is a web site which has a large listing of perkins engines for sale they are listed as either industrial or marine if you go to www. dieselenginetrader.com there is a large listing of perkins engines for sale in the states
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Old 17-08-2009, 10:31   #11
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An externally regulated alternator will usually have a small receptacle on the back with what looks like two spade terminals (flat terminals about a 1/4" wide) The regulator wires attach to a plastic plug that goes in here.
re: alternators amps... one belt ...100 amp max and realistically, you will be tightening your belt a lot with a 100 amp alternator and a regulator that works it good and hard.
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Old 17-08-2009, 12:38   #12
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If you have the space you can mount a bracket on the front of the engine which supports an independent shaft, bearings and a coupling. The coupling isolates and takes care of any missalignment problems. The alternator or anything else is mounted on this bracket.
The you can take off as much power as you want as the side load is carried by the bearings of the bracket and not by the engine.
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Old 17-08-2009, 12:43   #13
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Mesqua Ukee, Would like to see a photo or diagram of this setup..it sounds intriguing to me.
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Old 17-08-2009, 15:05   #14
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One of the things I would like to be able to do is PTO from the front of the engine but not sure what is the best way to do it.

I would like to add a jabsco trash pump to the engine for the next (hopefully never ) time I have a water ingress issue. They can pump a heck of a lot of water. But the pulley is 1/2 inch dual belt, and I think I will be changing over to a serpentine belt from tad for the water pump and alternator.
Also you could power a CAT pump for a watermaker that way as well....
Any ideas ?

bob
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Old 18-08-2009, 03:18   #15
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Originally Posted by captain465 View Post
Mesqua Ukee, Would like to see a photo or diagram of this setup..it sounds intriguing to me.
I do not have a photo but I have attached a crude sketch.
It is basically made of 2 metal plates that support 2 pillow blocks and the shaft. Angle iron connects the 2 metal plates to the engine. Obviously the frame should be sized to convenient bolts holes on the front of the engine and out of the way of the water pump belt.
A stack on pulley or plate having a shaft welded onto it is bolted on to the pulley on the engine. A coupling is used to transmit the power to the shaft on the above frame. Alignment is easy as the pillow blocks can be moved side to side and up and down.
Any equipment is easily mounted on the above frame. Any amount of power can be taken off the engine up to the power rating of the diameter of the shaft stub at the front of the engine. The vibration of an engine is primarily around the axis of the crankshaft.
As the belt for the water pump and primary alternator is now captured in this frame a spare or spares should be looped around the shaft before the frame is bolted onto the engine.
On one boat I did some work on this frame extended for close to 2 feet and drove a high output alternator and the compressor for a cold holdover plate system. The engine was a perkins 4-108.
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