# perkins 4-108 questions



## pdxsailor (Mar 18, 2007)

hey folks,

need some advice. looking at a boat that has the perkins 4-108 motor. haven't talked w/the mechanic yet, but his assistant told me that the mechanic said the motor hasn't really had the routine maintenance done that these motors need. i don't know what specifics that entails. the mechanic did say the motor ran well, sounded good and there is no smoke. 

can anyone tell me more about these motors and their experience with them. what is the routine maintenance? how detrimental can it be? anything else you can offer i'll listen.


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## btrayfors (Aug 25, 2006)

The Perkins 4-108 is one of the best-known and most reliable auxiliary diesels aboard sailboats worldwide. It is very rugged and, if treated kindly, should outlive most owners.

Routine maintenance consists of checking for leaks, being sure the fluids are sufficient (coolant, engine oil, transmission oil, v-drive oil if one is fitted), checking belt tensioning, keeping the fuel clean by proper filtering, changing the pencil zinc in the heat exchanger every year or two, changing the oil at regular intervals, etc. All the normal stuff you'd do with any diesel.

These engines have a couple of quirks: (1) they are known to leak oil a bit; and (2) they are typically WAY overrated in terms of real HP output...often billed as 50hp or 47hp or 42hp, etc....but really about 30hp.

The engines are easy to work on, and parts are available worldwide.

I'd want to know more about why the mechanic said the engine hadn't been properly maintained (cosmetic or other).

Bill


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## jr438234606 (Apr 25, 2006)

I have a Perkins 4.108. It runs like a champ, but I have had a quirk or two:

Clogged filters tend to either cause it to loose power or idle too high.

Air filter is pretty much useless. It gets burned up by the cold-start device.

Cold-start device (Thermostart) has a tendency to be left on and cause premature failure and melting of the housing. I replaced my key switch and added a manual push-button for the cold-start.

My engine is extremely sensitive to temperature upon starting. It basically will not start without the cold-start device.

It leaks a lot of oil. 

If you get air in the lines, the bleeding process is complicated.

If you remove the cam-driven raw water pump, there is a special, undocumented procedure you must adhere to for lining up the pump connection. Failure to do so will immediately break this coupling EVERY TIME.

Now that I've "learned" my engine, I never have any problem with it. Sort of like a woman, huh?


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## TSOJOURNER (Dec 16, 1999)

jr438234606 said:


> I have a Perkins 4.108. It runs like a champ, but I have had a quirk or two:
> 
> Clogged filters tend to either cause it to loose power or idle too high.
> 
> ...


John - Please enlighten us. What is the undocuemented procedure on the raw water pump? I have a 4-107, but I beliove it would be the same.


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## jr438234606 (Apr 25, 2006)

When I was purchasing the boat, my boat yard replaced the raw water pump before the sea trial. They destroyed THREE pumps in the course of two hours before figuring out there is a special procedure to prevent it.

The Perkins WORKSHOP manual states, verbatim:

"Should it be necessary to remove the sea water pump adaptor plate, it must be alighned on refitting by means of the tool shown in Fig. M.4.

To line up the adaptor plate, loosen the holding nuts and insert the tool in the water pump drive position to centralize the adaptor plate to the sea water pump driving shaft. Once the tool is located, the adaptor plate securing nuts should be tightened. The tool can then be removed and the sea water pump fitted.

To cover donditions where a centralizing tools is not available, the following interim measure can be taken.

Loosen the adaptor plate securing nuts so that they just support he weight of the sea water pump. 

Rotate the engine two or three turns by hand: this will ensure that the adaptor plate/sea water pump will centralize to the fuel pump gear shaft. Then retighten the aaptor plate securing nuts.

It should be remembered that the latter procedure should only be used as an interim measure as it is not as accurate an alignment when using the tool previously described."

This info is not in the owner's manual, only in the WORKSHOP manual. Oh, and you have to be holding your mouth correctly while balancing on one foot in the light of a blue moon. Ridiculous.

Basically, if the coupling is not aligned before tighting down the screws, it sets up a situation where the shaft coupling flexes as it spins. After only a few minutes, metal fatigue causes it to fail. Mine was aligned using the engine-spin technique and I've not had any problems.


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## pdxsailor (Mar 18, 2007)

*hi there. talked w/ the mechanic*

first, let me say thanks again to everyone for their responses. there's always good info here and good folks too. looks like the motor is in good shape. but, it needs some serious forgotten routine maintenance. oils changed, fluids changed, new heat exchanger, clean the air intake, install new filters, alternator and belt, possibly a new oil/tranny cooler, etc...the alignment [of the shaft i presume] is a touch off but he said it didn't worry him. oh and the shifter is a little out of adjustment. in my opinion nothing serious to worry about. i can do a good portion of this work myself, thankfully.

next step is the rigging survey.


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## TSOJOURNER (Dec 16, 1999)

jr438234606 said:


> When I was purchasing the boat, my boat yard replaced the raw water pump before the sea trial. They destroyed THREE pumps before figuring out there is a special procedure to prevent it.
> 
> The Perkins manual states, verbatim:
> 
> ...


John - I do not doubt you. You have obviously done the research borne out by experience. I do have to say that I have had mine off a couple of times and didn't need to worry about this. I can only assume that the 4-107 and 4-108 have different raw water pumps. My questions was only for my edification.

Thank you.


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## DeepFrz (May 9, 2006)

Have you priced out the items you are talking about replacing? I think you have a fair expense to look forward to. Also good price bargaining points.


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## pdxsailor (Mar 18, 2007)

*to: deepfrz*

i haven't priced out anything yet. i just found this out today. and yep, if we make through the next two surveys i will be using the repairs as a bargaining point.


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## cardiacpaul (Jun 20, 2006)

PDX,

before they change the engine oil, get an oil sample done. 
I've found that most marinas will give you the "doe-eyes-in-the-headlamp look". They are available from ANY construction equipment dealer, or heavy truck dealership that does service. The cost is minimal, about 15.00. 

The engine oil sample will tell you many things. Fuel dilution, ash content, what type and how much of any metals that are wandering around in your engine. 

For example, Chromium - piston rings. Lead/tin - main/rod bearing wear, Boron- cyl wall wear, Butyl, gaskets/seals/o-rings. 

2 weeks ago, I did a survey on an almost perfect 38ft Scarab with twin 502 Merc's with less than 300 hours on the engines. The oil sample revealed severe fuel dilution (leaking injectors @ 140.00 each x 16) and more importantly Copper, indicating crankshaft thrust washers were going south quickly, also hurting the crank and main&rod bearings. As I write this, one engine is being replaced and the other is being rebuilt at the dealers expense, not the prospective owner. The estimated repair bill is 38,500.00. On a 95k boat. 

Little guys like UPS, Roadway Fed-ex, Caterpiller, Cummins, John Deere and Detroit Diesel use oil samples as a matter of policy.


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