Need Perkins 4.108 Expert

[BozSail]

I have replaced the rear main oil seal twice. First time was 5 years ago. Leaked a little, but not too bad. Replaced it again in July 2024. Now it leaks worse. What could be the problem? I'm thinking just not installing the seal properly. I welcome a ny helpful tips.

[Kello]

I'm not a Perkins expert, but an engine is an engine, and since you said you'd welcome any tips ...

My neighbor has a very old Perkins, and in one of our conversations I kinda remember he mentioned that the rear oil seal is made of flax, and since he hasn't started his engine in many years that the flax would be dried out and leak next time he started the engine. See if your engine is old enough to have been designed for a flax seal, and if you have replaced it with a modern packing (they are Teflon now?) that may be your problem.

If your engine is newer and has a prefab rubber seal, then maybe your shaft is worn at the seal, IMO, the fix for that isn't worth the time or trouble, put an oil diaper under the transmission and go sailing. Also, did you grease the shaft (and seal lip) before you installed the seal?

[Harryj50]

I was told by the owner of at least two 4.108's that he put a pan under the engine, captured the leaking oil, and put it back into the engine.

[roberttigar]

I'm not an expert, but I have a 1977 vessel with the original 4-108. Yes, it leaks oil. But, here's what I have found:
The design of the vessel has the engine positioned at about 18 degree's angling to the stern in order to line up properly to the prop shaft.

If I keep the oil level slightly less than to the hash mark on the dip stick, it leaks less oil. Bob

[GordMay]

I bought some engine oil, for my boat.
But it was too thick, so I thinned it out, with some gasoline; but then it was too thin, so I added more oil; but I just can't seem to get it right.
It's a viscous cycle.
So, I went to the library, and asked where I could find books on greases, oils, and lubricants.
The librarian suggested I try the non-friction section.
So, I did, and learned that you can't use vegetable oil as gearbox lubricant,
because it doesn't contain any trans fats.

[marcjsmith]

Originally Posted by GordMay

I bought some engine oil, for my boat.
But it was too thick, so I thinned it out, with some gasoline; but then it was too thin, so I added more oil; but I just can't seem to get it right.
It's a viscous cycle.
So, I went to the library, and asked where I could find books on greases, oils, and lubricants.
The librarian suggested I try the non-friction section.
So, I did, and learned that you can't use vegetable oil as gearbox lubricant,
because it doesn't contain any trans fats.

Groan....isn't there a thread for dad jokes?

[more]

Originally Posted by BozSail

I have replaced the rear main oil seal twice. First time was 5 years ago. Leaked a little, but not too bad. Replaced it again in July 2024. Now it leaks worse.

again,but this time try buy orginal 25€ +- send email to your local dealer

[skipperpete]

Originally Posted by BozSail

I have replaced the rear main oil seal twice. First time was 5 years ago. Leaked a little, but not too bad. Replaced it again in July 2024. Now it leaks worse. What could be the problem? I'm thinking just not installing the seal properly. I welcome a ny helpful tips.

It happens ! Sometimes the spiral groove in the crank journal is full of crud, sometimes the ends of the packing are too low or the packing isn’t rolled in well enough ….and then there’s the gasket that secretly avoids sitting in its allocated position as you join and fit the seal housing halves.

[Lepke]

When you replace the packing it needs to be slightly long at the seam so it's pressed together when the housing is reinstalled. Grease the shaft where the seal rubs. If you don't grease no matter what seal material, the first engine start tends to drag the seal and opens the gap.
The best place to buy a seal is: https://parts4engines.com/collection...al-upgrade-kit
$36 much cheaper than Foley and others.

[Belesama]

Simple question. Bought a boat with an overhauled Perkins 4.108 just bolted in. Having to connect it all up. For the life of me, I can't find where the fuel return line connects to the motor.

[marcjsmith]

In this pic I highlighted in yellow the fuel line from the top of the injectors to the top of the engine mounted fuel filter and from there to the tank. I would also download the service manual for the 4108. It’s out there for free.

[Belesama]

Thank you!! I have the service manual and it is poorly detailed in this area. Assumes a base level of knowledge I clearly don't have lol. I'm not familiar enough with the function of this engine. I believe those are atomizers on top of the injectors there. The return fuel line is attached to the same port on the filter seems counter intuitive. But solves my mystery! Thanks!

[marcjsmith]

No problem. Glad to be able to help

the return to tank line and the return from the injectors are just banjo style fittings so the fuel just flows through them.

I'm sure there's a mechanical reason for doing it that way.

the OEM canister style fuel filter on the perkins is a PITA. IMO its a special kind of hell when it comes to bleeding the air after a filter change. there are products for swaping out the OEM canister with a spin on. I opted for a couple of racors upstream with a finer micron rating than the engine mounted filter. The theory being that the up stream filters will catch all the debris so I won't have to futz with the engine filter....

TAD has a good writeup on bleeding here is their current updated procedure and tips

https://tadiesels.com/assets/docs/te...hanging-v4.pdf

let me know if you need any other pics

[crosswire]

I rebuilt a 4108 about 10 years ago, including the dreaded front and rear seals. They leaked very little until about 100 to 125 hours, then the leaks increased significantly. I was using straight SAE 30 weight Shell Rotella. I changed the oil and the leaks subsided. Even though the recommended oil change interval is 200 hours, I have continued the 100 hour change interval and have had only small leaks. Oil is so much easier to change than seals.

One other possible factor was that I changed out the original stamped steel crank pan for a cast aluminum one with cooling fins. Maybe the aluminum one had a better fit.

[skipperpete]

Here’s one of the several 4-108 fuel diagrams. The preheat tank can be a stand alone that must be manually filled or the heater supply can be included in the return line.