Replace Perkins 4-108 Rear Main Seal - How To?

[BozSail]

Does anyone have detailed instructions on how to replace the rear main oil seal on a Perkins 4-108 diesel engine? I'm hoping this can be done without removing the engine, as I do not want to do that. I have reasonable access to the rear of the engine, and I believe I can remove the transmission (Hurth) and have room to access the rear oil seal (if this can be done with the engine in the boat, and the boat in the water). I am willing to haul the boat to do this if it cannot be done while in the water. I do not have room to remove the oil pan without removing the engine from the boat, so I'm hoping the oil pan does not have to be removed to replace the rear oil seal.

Not looking forward to this job, but it has to be done. This engine starts and runs great... it just leaks oil beyond any reasonable tolerance level.

Any help will be greatly appreciated.

[model 10]

You need to get a service manual! Unless you are the most amazing mechanic, you will never get the new seal installed properly in the seal housing.

Sure you can change the seal if you can remove the bell housing etc. Very straight fwd project. I would go ahead and get a new drive plate for the flywheel cause your old one is probably shot.

[DougR]

Here's the basic drill:
- block up the rear of the oil pan, because the rear engine mounts are probably going to be removed
- remove the gearbox
- remove the flywheel housing
- remove the damper plate from the flywheel ( as Ecos mentioned it might be good to have a new one on hand before starting the job)
- remove the flywheel
- remove the two piece seal carrier from the block and rear main bearing carrier and clean up the old gasket and seal halves. My recollection is that the seal carrier halves can be removed without removing the flywheel housing mounting plate.


Here is where it's good to have the service manual to follow the instructions on replacing the two piece rear seal. It's a rope type seal and needs to be installed per the instructions or you will get another try at all of the above.....

You can find a manual on line no problem.

DougR

[Lepke]

The are 2 seals. The stock one is the usual rope seal. It needs to be presoaked in oil. Hot oil works best. Then there is a newer seal with braided PTFE. It's still worthwhile to grease the new seal where it rubs on the crank. Without the oil or grease, the seal can be pulled partially out of position on the first start and you have the oil leak all over again.

[Greg Mason]

I have done it. The flywheel housing most likely has the rear engine mounts on it. As posted block up the engine. Remove the flywheel, you may want to replace the dampening springs at this point. The new seal came in 2 pieces as I recall, and it was just wrenching after that. Because my engine was reverse mounted, it was easy to see everything. I remember when enough oild leaked into the bell housing, it fouled my starter, then I was forced into action. Good luck.

[BruceS]

Hytork seal?
https://www.foleyengines.com/tech-ti...sel-rear-seal/

[Wainui]

After you get the seal off check the crank where the seal rubs to see if there’s any scoring.
Or better get a Betamarine 50 and replace!

[model 10]

Originally Posted by Wainui

After you get the seal off check the crank where the seal rubs to see if there’s any scoring.
Or better get a Betamarine 50 and replace!

What are you talking about? That area of the crankshaft is serrated and feeds oil back into the engine. If someone changed an engine because of that groove, they were an idiot.

[Lepke]

If you're going to buy the new type seal, get it from www.parts4engines.com for about $30. Foley as I remember is about $100 for the same thing. It's not that expensive to ship small packages from the UK.

[donradcliffe]

I've done the seal successfully with the engine in the boat, but blocking the engine on the oil pan ruined the cork gaskets on the pan. The engine leaked more oil than ever until I hoisted the front and back of the engine up far enough to drop the pan and replace the pan gaskets.

Eventually got tired of the oil and repowered with a Beta 50.

[Argyle38]

I did it winter before last. Not too hard, just a lot of steps. DougR's description pretty much sums it up. Only you can decide whether you have enough room to do the job. Was not a problem for me, but all boats are different. I just used a simple car scissor jack to lift the back half of the engine. Used a short piece of 2x4 between the jack and the engine and lifted against the back end of the block instead of the oil pan.

I do recommend getting one of the new, teflon and graphite impregnated rope seals from parts4engines or Foley. I ended up with both so I used the Foley. It has a tighter weave than the parts4engines one, but I think both would work and the British one is a lot cheaper. I also coated the seal with graphite grease (recommended by Foley) on the bearing surface.

Get a shop manual and torque correctly on re-assembly. Use standard torques (based on thread and bolt size) where the torque isn't specified in the manual. If you can't find the manual on line, send me your email in a PM and I'll get it to you.

I found this PDF useful for the project:

http://www.vetiver.org/Perkins%204108.pdf

[oleman]

The Perkins 4.108 is probably the most widely used 1.8 ltr diesel ever and therefor the best supported with the best technical resources available. I believe my service manual was downloaded from a member on this site several years ago. Maintenance documents should be free or very low cost for the life of a product, let's keep them that way.

[oldcal46skipper]

Originally Posted by oleman

The Perkins 4.108 is probably the most widely used 1.8 ltr diesel ever and therefor the best supported with the best technical resources available. I believe my service manual was downloaded from a member on this site several years ago. Maintenance documents should be free or very low cost for the life of a product, let's keep them that way.

Ma Perkins built over 500,000 4.108's. Why? Because they are good!
In the last 15 years we have rebuilt almost 300 Perkins 4.108 Long Blocks. Parts are readily available at a reasonable price. We refuse to work on the high revving stuff.
Been there - done that! WE have nine 4.108's patiently awaiting us to lay hands on.