Perkins 4108 rear main seal

Marcjsmith

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Ok I k ow. It’s british engine, if it’s not leaking oil, that’s means it’s out of oil...

I think the time has come to replace the rear main seal on my perkins 4108.

My though process is doing it one of two ways.
1. Leave transmission attached to shaft, remove bell housing from engine and trans and slide shaft aft as far as possible then remove flywheel and change seal

2. Take take trans off the shaft by disconnecting coupler then remove flywheel, and seal.


I’m hoping to avoid removing the shift linkage and hoping to avoid having to realign the shaft to the engine....

That being said. I know that if I’m taking the trans off, might be a good time to service it, beyond just a normal fluid change. It has not been giving me any problems....so I’m not inclined to open it up.

I’m also aware that even though my pss seal is not leaking, but if I do option 1 I’ll have to remove part of it to slide the shaft aft... which could result in the dripless shaft dripping upon reassembly.. Do I increase the scope of the project to include a new shaft seal...

Thoughts...
 

slug zitski

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Sounds like trouble

space to work is always the issue

work quality is critical

shaft log, stuffing box will be an issue

damper plates flywheel can be troublesome

inspect for wear..groove ..on the output shaft surface

speedi sleeve solution for wear

up to you
 
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billsreef

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Unless you are pulling the engine to do the seal, you will need to remove the transmission in order to have enough space to do that job. Leaving the transmission attached to the shaft might also put a bend in the shaft, and it will only take a small oops to bend the shift linkage. It's a pain, but the only way to do this job is pulling the transmission.
 

Zonker

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Yeah 2. Undoing the linkage is usually just a little pin connecting the cable to the shift lever.
 

Marcjsmith

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space is one thing I have....compared to some boats...

good point on the bending... found out from a good source on a same model boat that I'll need to jack up the aft end of the engine to get the bell housing off... so now if I have to do that, do I start looking at engine mounts...

sheesh maybe the oil drip isn't so bad?

IMG_3533.jpg
 

longy

Overlord of Anarchy
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Is your engine not mounted horizontal or is that some camera trick? IIRC the tops of Perkins were horizontal?
edit - sorry now actually seeing picture is athwartships!
 

SloopJonB

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sheesh maybe the oil drip isn't so bad?
A leak there or in a similarly problematic area is a good case for leaving it until it becomes unacceptable, not simply annoying.

Besides, as you imply with it being British, after all that work you will only have reduced the leak, not eliminated it. ;)
 

CapDave

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Antigua
I have Volvo D2-55Fs which are basically Perkins, and we've had some trouble keeping them oil-tight recently. We replaced the rear crankshaft seal on both and, due to an original installation issue, we replaced the oil pan on both. Then we replaced the gasket on the back side of the raw water pump on both. Now they're holding oil.....though we'll see how long?

We did some of that out of the water, and since we had to lift the engines I wanted to do as much as possible. We put in all new mounts, and we replaced the 13-year old hull diaphragms on the saildrives. We were also having trouble with our Flex-o-Fold props and replace both of those.

Between the new mounts and the new props, it's a huge difference - way less vibration, and much better performance.

For me, if you have to do something not ordinary like dismount/lift an engine, it makes sense to do as much associated work as possible at the same time.
 

slug zitski

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I have Volvo D2-55Fs which are basically Perkins, and we've had some trouble keeping them oil-tight recently. We replaced the rear crankshaft seal on both and, due to an original installation issue, we replaced the oil pan on both. Then we replaced the gasket on the back side of the raw water pump on both. Now they're holding oil.....though we'll see how long?

We did some of that out of the water, and since we had to lift the engines I wanted to do as much as possible. We put in all new mounts, and we replaced the 13-year old hull diaphragms on the saildrives. We were also having trouble with our Flex-o-Fold props and replace both of those.

Between the new mounts and the new props, it's a huge difference - way less vibration, and much better performance.

For me, if you have to do something not ordinary like dismount/lift an engine, it makes sense to do as much associated work as possible at the same time.
Must be careful of excess crankcase pressure…blown seals

diesels always have somekida crankcase breather that must be kept in order
 
How many hrs on the engine? How hard is it to rig out of the boat? These are rock solid engines, I think they even have sleeved liners. I would seriously consider a full overhaul, winter is coming not a bad time to do it. This is definitely a job someone with mechanical inclination could do themselves in a garage, get a harbor freight engine stand you can rotate and have at it. It's been awhile but parts were available.
 

slug zitski

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We replaced the crankcase breathers in 2019 when we bought the boat
Don’t know why seals fail prematurely

the only seal failure I can remember was my fault …I allowed paint to contaminate the seal

I have run commercial rated diesels for ten of thousands of hours with out seal problems

possible that marine leisure rated diesels are just not as durable , high rpm or the operating environment is an influence
 
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Marcjsmith

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How many hrs on the engine? How hard is it to rig out of the boat? These are rock solid engines, I think they even have sleeved liners. I would seriously consider a full overhaul, winter is coming not a bad time to do it. This is definitely a job someone with mechanical inclination could do themselves in a garage, get a harbor freight engine stand you can rotate and have at it. It's been awhile but parts were availabl
Indicated is around 1800hrs. if memory serves. So I don’t think r&r is warranted. Although it was “lightly” locked up after sitting for nearly 10 years unused. So does puff some blue smoke on start. But otherwise runs great. Annoying leak not withstanding...

@SloopJonB had the feeling more than a few times. Still get that feeling and dopey grin when I fire up the boat and slip the lines...
 
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slug zitski

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Indicated is around 1800hrs. if memory serves. So I don’t think r&r is warranted. Although it was “lightly” locked up after sitting for nearly 10 years unused. So does puff some blue smoke on start. But otherwise runs great. Annoying leak not withstanding...

@SloopJonB had the feeling more than a few times. Still get that feeling and dopey grin when I fire up the boat and slip the lines...
When a diesel sleeps for a long time the valves may stick in position …not close completely

always a good idea to remove the valve cover and have a look
 

MiddayGun

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Don’t know why seals fail prematurely

the only seal failure I can remember was my fault …I allowed paint to contaminate the seal

I have run commercial rated diesels for ten of thousands of hours with out seal problems

possible that marine leisure rated diesels are just not as durable , high rpm or the operating environment is an influence

The Perkins 4108's are notorious for it, its a rope seal.
Fix it, and it will leak again soon after.

There are companies that offer upgraded seal kits, how effective these are, I don't know.

They are a seriously old design now, but they do seem to keep going.
 


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