20 HP Johnson lower crank seal (spring loaded)

[58BigTwin]

Hello,<br /><br />I have removed the powerhead to replace base gasket and exh. cover gaskets, when I noticed that there was an oil-water emulsion in the ehxaust housing (where driveshaft resides) directly under the crank seal. It is a film on the housing, looking like custard, not too thick, but visible.<br /><br />The engine runs great (after I fixed the carburetion problem). <br /><br />Question is this: If that seal was leaking, engine function would be affected, right? Also, how does that seal work, being that it spins along woth the shaft? I would think that a lip seal that rides in the bore and doesn't spin would be more effective. Should I replace it or let it ride. <br /><br />As I said, it runs well throughout the rpm range and idles well.<br /><br />Thanks for any input.<br /><br />Tom E

 

[58BigTwin]

Re: 20 HP Johnson lower crank seal (spring loaded)

It is a 1969 20 horse Johnson, model 20R-69B<br /><br />TE

 

[Paul Moir]

Re: 20 HP Johnson lower crank seal (spring loaded)

Replace it! If it's leaking then at idle your either running the bottom cylinder lean or the top cylinder rich. You will notice a much better idle when you fix this problem. At high rpms it seems that most of the fuel-air mixture stays trapped in the crankcase. But when you fix it it should make for smoother running at full throttle (since both cylinders are doing equal work). <br />The seal itself is not supposed to spin - the spring is supposed to hold it enough to stop that. Mabey that's where you should be looking. The seal (a quad ring, like an o-ring but four) should peel out of the seal carrier (black part). Watch out - that carrier is a little delicate.<br />Oh - the other problem with a leaking bottom crank seal is it tends to suck up exhaust into the crankcase. Crud that comes up through there ends up wreaking the bottom crank bearing. I actually worked on one engine that had seized up from this. <br /><br />Besides - it is really easy to fix this problem. <br />Good luck!

 

[R.Johnson]

Re: 20 HP Johnson lower crank seal (spring loaded)

The seal is a carbon ring with a o-ring inside.When you remove the snap ring, brass or stainless spring retainer, and spring you will see two recess cuts in the carbon ring. Use these to carefully remove carbon ring from crankshaft with a couple of wire hooks, you will see the o-ring inside the carbon ring. The carbon ring has a raised ring on one side that rides on the machined face of lower main bearing. Just replace the o-ring. This seal is quite affective, and causes very little problems if the carbon ring does'nt get broke. This ring is quite fragile so don't force it. Use oil or grease on new o-ring.

 

[58BigTwin]

Re: 20 HP Johnson lower crank seal (spring loaded)

Thanks for the replies.<br /><br /> It surely looks easy to fix, in fact I took it off to look at it. I don't really see how the thing wont spin though. The spring and retainers are attached to the crankshaft (obviously). If they are spinning with the crank, then there has to be friction between the lower retainer and the carbon ring and seal which should be stationary.<br /><br />I'll see if I can find the seal. I'm kind of curious because the engine seems to run and idle pretty well.<br /><br />Thanks again<br />TE

 

[R.Johnson]

Re: 20 HP Johnson lower crank seal (spring loaded)

I have to jog my memory on this, but let me see if I have it right. There is a o-ring around the lower crank bearing, thats one seal surface. There is a inner o-ring around crankshaft, thats two. Carbon seal has raised lip to crank bearing, thats three. Carbon ring, spring, and retainer turns with crank. When you put in the seal, turn crank with flywheel, and watch seal. Jeez! now I'm not sure.

 

[58BigTwin]

Re: 20 HP Johnson lower crank seal (spring loaded)

I replaced the seal ($13), and this one spins too. I don't see how it could do otherwise. The engine runs great, especially in the 30 degree weather we have been having. Don't know if it runs any better than before I changed the seal, but hey, don't have to worry about it.<br /><br />Thanks for the replies.<br /><br />Tom E<br />Coeur d'Alene ID

 

[rodbolt]

Re: 20 HP Johnson lower crank seal (spring loaded)

hello<br /> the seal assy is designed to spin with the crank. the carbon carrier does the sealing against the block and the quad ring against the crank. the seal worked well but sometimes the quad ring gets cracked or hard. like they said its very delicate and I am not sure you can still get them.<br /> good luck glad ya fixed it up

 

[58BigTwin]

Re: 20 HP Johnson lower crank seal (spring loaded)

The dealer I got the seal from had some old stock. The seal I bought was in a small box, looking about 15 years old or so. My usual dealer said he could order the seal too.<br /><br />It was a strange system, and it seems to me that a lip seal that rode in the 1.5" bore sealing the 1" shaft would have worked too. That would have been my back up plan if the original was unavailable.<br /><br />Thanks for the replies all.<br /><br />Tom E