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Old 27-07-2017, 11:40   #1
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Perkins 4-108 oil leaks solved

My friend's Perkins 4-108 always leaked oil. Two years ago he took it to a yard, they pulled the engine and replaced all the gaskets and seals. It started leaking badly again in few months. I have installed a nice fiberglass pan under the engine, so the oil doesn't end up in the bilge. Oh my hubris. I pulled the engine again, replaced all the seals and gaskets. Looked beautiful. Started leaking all over the front few months later. I don't give up. Pulled it again.

Aside. I put myself through college fixing MG at the local British Leyland dealership. I have rebuilt few Perkinses over the years since I switched to sailing and sailboats and always noticed how superficially similar the design of the 4-108 was to an MGB motor. The relevant similarity is that the front motor mounts are attached to the front plate. When I disassembled the 4-108 this time, it finally struck me. The front plate on the MGB went on the front of the block over two big locating pins. The Perkolator has no such pins. It weighs twice as much and (some owner refer to them as "rock crunchers"): add shock loads and vibration. What really drove the concept in was noticing the Perkins engine block had provision for hefty motor mounts brackets, forward and aft, unused in the marine version. I bet the famous London cabs use THOSE to mount the engine. Not the front plate.

Before you install the timing cover, the front plate is held to the block by five or six measly 5/16" bolts. A bunch of 1/4" and 5/16" bolts go through with the installation of the timing cover, but the torque specs and common sense prevents you from honking down on those. The timing cover is easily distorted and leaks would be all but guaranteed. The gasket set you get these days is all of one material and it is foam of some kind. So, as the engine bounces around and shakes, the block starts twisting behind the front plate coming to stops on the threads of those measly five bolts.

The proper answer would be to install sturdy locating pins. A machine shop could probably do that. You would need to find suitable location as not to compromise the block.
As I didn't have the time or money for the machine shop, I came up with different solution. First I made a hard paper gaskets instead of the foam one in the gasket set to go between the block and the front plate and one for the timing cover. I used hard setting Permatex on the block to plate gasket. Tightened the aforementioned 5 or 6 measly bolts, but temporarily added all the timing cover bolts as well without the timing cover and tightened everything lightly and evenly and in a fanciful sequence, so the gasket got compressed evenly. Let it set overnight.

Before installing the timing gear and cover, I tightened the 5 bolts properly.
Now the hard part. Out of some high tensile Al alloy plate, I cut and drilled a frame in the shape of the timing cover gasket, but narrower. I used 1/4" plate and made it in two pieces because I didn't have enough material for the complete circuit. Thicker and one piece would be better. I used it instead of the good-for-nothing original oval washers when installing the timing cover.

Anyone confident enough to install the timing gear and set the backlash probably knows the timing cover is made to float a little and has to be positioned just so, so the front crank shaft seal is concentric with the shaft. There was a special tool for that operation for the MGB, A ring, temporarily installed instead of the oil seal, before the bolts of the timing cover were tightened. Now to be sure, after centering the timing cover by feel and tightening few of the bolts lightly, I drilled and tapped two #10-24 locating screws through the timing cover into the front plate.

With the proper paper gasket and the stiff aluminum frame instead of the handful of oval flat washers, the timing cover can be tightened down (with longer bolts of course) as much as the bolts and threads can handle, providing the extra needed support for the plate to block joint. To say nothing of the now leakproof timing cover gasket.
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Old 27-07-2017, 12:11   #2
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Re: Perkins 4-108 oil leaks solved

Let me try to ad photos. Ooops, windows 10 doesn't let you resize photos.
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Old 27-07-2017, 12:32   #3
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Re: Perkins 4-108 oil leaks solved

photos, one of bedding down the front plate, the other: after the timing cover went on
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Old 27-07-2017, 13:07   #4
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Re: Perkins 4-108 oil leaks solved

perkins are brit engines. brit engines always leak. leaks make em run. pretend it is a diesel mg B. hahahahaha
even brand newly rebuilt will leak. buy oil absorbant engine diapers and place one under engine. run engine.
breathe and live life. engine will leak oil.
if it stops leaking, it will blow up.,
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Old 27-07-2017, 13:31   #5
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Re: Perkins 4-108 oil leaks solved

ZeeHag, you are completely right. But I can't help myself, I got the engineering bug and a Zen and the Art of Sailboat Maintenance complications. I occasionally manage to sail somewhere, too.
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Old 27-07-2017, 13:34   #6
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Re: Perkins 4-108 oil leaks solved

i keep the dideez under engine while sailing. is only time my gorgeous perkins needs em. ha ha ha

are you new at the fine art of oil containment???
helped that i had vws and other drippy cars so i know how to cruise with a spare set of all fuel and oil line bits and oil absorbant dideez.
ha ha ha ha
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Old 27-07-2017, 14:14   #7
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Re: Perkins 4-108 oil leaks solved

I don't think what you did is necessary. I see what you are saying but I think you need to up grade your gasket sealant to something more modern. The real problem area is behind the mount plate with the front pan gasket.
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Old 27-07-2017, 17:09   #8
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Re: Perkins 4-108 oil leaks solved

Quote:
Originally Posted by sv.antea View Post
What really drove the concept in was noticing the Perkins engine block had provision for hefty motor mounts brackets, forward and aft, unused in the marine version. I bet the famous London cabs use THOSE to mount the engine. Not the front plate.
Might it have been easier to engineer mounts using the "hefty" locations?

My MGA forward mounts do use 2 bolts directly to the block, along with 2 on the front plate, but most of the load is directed to the block. Any chance that the Perkins has a similar provision?
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Old 28-07-2017, 08:49   #9
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Re: Perkins 4-108 oil leaks solved

I always thought Perkins were externally lubricated!
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Old 28-07-2017, 08:57   #10
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Re: Perkins 4-108 oil leaks solved

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Originally Posted by coloradohi1 View Post
I always thought Perkins were externally lubricated!

Hilarious!
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Old 28-07-2017, 09:25   #11
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Re: Perkins 4-108 oil leaks solved

Yeah, but they run and run and run. Due to the low compression, that engine is just about bulletproof, IMHO. I loved that 4-108 on my Irwin 52.
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Old 28-07-2017, 09:44   #12
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Re: Perkins 4-108 oil leaks solved

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Yeah, but they run and run and run. Due to the low compression, that engine is just about bulletproof, IMHO. I loved that 4-108 on my Irwin 52.
I think the Perkins has a high comprssion ratio, like 22:1 Some other engines have ratios down around 18:1.
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Old 28-07-2017, 12:47   #13
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Re: Perkins 4-108 oil leaks solved

Hiya. That should kill the leak. Nice one. You got the tool to centre the water pump">raw water pump drive flange so the drive doesn't snap.
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Old 28-07-2017, 14:57   #14
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Re: Perkins 4-108 oil leaks solved

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. You got the tool to centre the raw water pump drive flange so the drive doesn't snap.
Just about nobody does because it isn't needed. That kind of drive is pretty much self aligning.
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Old 28-07-2017, 15:12   #15
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Re: Perkins 4-108 oil leaks solved

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Just about nobody does because it isn't needed. That kind of drive is pretty much self aligning.
Really. You got a 4108. After re fitting my timing cover and not aligning the raw water pump flange, the ear snapped off the impeller shaft and dropped into the drive gears. Fortunately the gears survived but it did stick a hole in the timing cover.Which is when I found out about the need to align. So in my mind I would say to not bother aligning is somewhat fool hardy. Nobody needs that T shirt, I certainly didn't.
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