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Old 18-12-2015, 06:26   #1
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Perkins 4-108 rear seal replacement

Has anyone replaced the rear engine seal on their Perkins 4-108, which has a well-deserved reputation for leaking as it ages? Also, if you've replaced this seal, did you use the Foley Engines seal?

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Old 18-12-2015, 08:43   #2
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Re: Perkins 4-108 rear seal replacement

It took me 2 tries to get the stock real seal installed correctly. It seemed impossible the first time and it had a weep. Followed the directions the second time.
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Old 18-12-2015, 14:15   #3
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Re: Perkins 4-108 rear seal replacement

My front seal is the one leaking.
Previous owner broke a belt & used a stocking to get home with it. Only problem was the stocking got wrapped around the pulley & chewed out the seal & damaged the shaft where the seal runs.......
Not a big leak & a correctly placed fruit tin catches the odd drip. Newspaper soaks the rest up. lol
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Old 18-12-2015, 14:47   #4
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Re: Perkins 4-108 rear seal replacement

[QUOTE=BruceS;1991369] damaged the shaft where the seal runs.......

That is a pretty easy repair should the leak become worse. There is a part called a "speedy sleeve" sold at bearing houses just for damaged shafts.
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Old 18-12-2015, 15:40   #5
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Re: Perkins 4-108 rear seal replacement

I have an old 4108 generator engine. I've rebuilt a lot of engines, but the seal replacement should be no problem for a careful worker.
I have a Foley seal and it hasn't given any problems. When assembling the 2 halfs, the seal should protrude slightly. Trim accurately with a single edge razor blade. It's better to have slightly too much seal protruding than too little. The book calls for graphite greasing the seal where it rubs on the crank, and after combining the 2 halfs, rotate the seal on the crank to ensure it turns smoothly. If it binds it can pull the seal out of position.
Any assembly lube works on the seal. The factory rope seal works ok, but doesn't last as long and has to be soaked in oil first. It can dry out from heat, light use and the rope seal tends to get hard. In an emergency I have used stern bearing packing.
The 4108 is an easy engine to overhaul. My only complaint is the British system of machining items oversize that require the pistons be installed twice.
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Old 18-12-2015, 15:45   #6
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Re: Perkins 4-108 rear seal replacement

Quote:
Originally Posted by Lepke View Post
My only complaint is the British system of machining items oversize that require the pistons be installed twice.
How do you trim the piston tops in the field?
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Old 18-12-2015, 16:15   #7
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Re: Perkins 4-108 rear seal replacement

A lathe is the best way. I've never been anywhere in the world I couldn't find a proper machine shop. The goal is to have 4 cylinders producing the same power and an engine making rated power.
In the field, w/o proper tools, you can measure with a feeler gauge and a proper straight edge. I have a bench drill press and mount the piston in a 2 way vice. With a homemade tool I get the piston top square, 90° to the spindle. Again using feeler gauges and the depth control I crank the piston across the cutting jig, making several passes to slowly reach the finished height. It takes several hours to do 4 pistons. Cutting tooling and or a grinding attachment can be purchased at a machine supply or maybe Harbor Freight. Probably on Ebay, too. Grinding leaves a better surface, but it's hard to mount on a drill press. If you could mount a grinder so the stone is down, you could use the 2 way vice and so the same thing if everything was solid.
It's a lot of trouble, so after marking the pistons, find a machine shop and have them do it. It's easy on a lathe.
My father was a chief engineer. He taught me many things. He could finish poured lead bearings with a file taking .0005 off every stroke. I suppose you could file, but keeping square and having 4 the same would be hard. I use to cast and machine my own pistons, but not Perkins. I can make pistons that don't require secondary fitting. I don't know why Perkins can't make standard blocks and pistons.
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Old 19-12-2015, 12:30   #8
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Re: Perkins 4-108 rear seal replacement

Suggestion, get the tel# for Complete Yacht Service, the Yanmar/Perkins dealer in Ft. Lauderdale and ask for the owner Marc ( USMC), tel him Pat N now in Tampa told you to call.
Marc knows everything there is to know about Perkins and their seals..............
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