This is a fairly common issue on these opposed twins.
You would need to post the Code number from the engine as Briggs made a production run change in the configuration of the governor beginning 1979, 11/07. If the Code number of your engine is 791106 or lower (using ONLY the first 6 characters of the string) , there are no replaceable seal and bushings at all surrounding the governor shaft.
If the Code number of the engine is 791107 or higher (again using ONLY the first 6 characters of the string), there is a replaceable seal and bushings configured into the governor shaft assembly.
Now for the bad news. The seal (if present) is only a "foam material" DUST/GRIT blocker type of seal and is not an actual oil seal meant to keep oil in. Replacing the seal may help as a short term fix (how long unknown) but the long term repair involves replacing the governor shaft and bushings.......which requires that the engine be removed from the chassis and then the sump must come off to replace the governor bushings. Send me an e-mail if you want a PDF service manual.

IMO, if if is enough of a leak to be concerned with, you may want to pull and reseal the engine along w/ governor parts due to the age. Be careful as less and less of these OP twin goodies are available each year.

First thing I would do is check that the crankcase breather is functioning properly. One purpose of it is to create a partial vacuum to pull oil back from leaking at such places. Disconnect the rubber tube from the air cleaner, alternately suck and blow on it. It should suck virtually unobstructed but be considerably restricted when blowing and switch over quickly. Also check the vacuum line from crankcase to fuel pump for cracks, leaks. And of course there is always the possibility that the rings are worn until there is little crankcase vacuum.

I have done many of these engines in years past and have not found this to be a common problem. I have 3 right now.

Walt Conner

This post was edited by walt2002 on Sun, Dec 2, 12 at 17:02

Thanks very much for the replies guys.

Firstly, I should say my experience with playing with engines is limited.

Walt, there is actually a bit of smoke and oil coming out of one of the breathers. I have two breathers that I know of. One is the pulse hose that connects to the carb and sucks in fuel, and the other one has no hose at all, it's just a nipple on the front of the engine. It's from this outlet that some smoke and oil come out. I suspect the hose is missing and it needs to go to the air filter or something. I put everything back together and connected a spare piece of hose. There was no obstruction sucking or blowing into it. I found out that there is air coming from the pulse hose, where it connects to this black box on the engine. I shoved it back in and now there is resistance blowing into it. I then started up the motor and oil still started coming out of the governor shaft

Mownie, I took the intake manifold off today and there aren't any seals at all around the governor shaft. The full serial number of my engine is 402707-0132-01-81101912, that's all I know about it

If it's related to the oil and smoke coming out of the breather, I took off both spark plugs and held my thumb over them and I noticed that one cylinder had less pressure than the other

This post was edited by mowerman101 on Sun, Dec 2, 12 at 22:46

A picture of the governor shaft

This photo gives you an idea of just how much oil is coming out. I cleaned it off and ran it for about 3 min idle and 1 min full throttle. This is the result

Your engine has replaceable governor bushings, I can see the upper one in your picture. There should be a foam seal disc, Briggs part number 271316 in place below the circlip e-ring retainer. But as Walt said, given that one of these engines in good order actually has a slight vacuum in the crankcase which tends to keep oil inside the confines of the case........the oil leak yours has is likely due to excessive blow-by past the piston rings causing a pressurized crankcase condition.

Thanks mownie

So what exactly would be causing this excessive blow-by? Also, yes there was a circlip, I took it off and that was it, I didn't see any foam seal disc. Is it missing? Because it looks like something should be sitting between the housing and the shaft. Or is the foam seal disc inside the engine?

Thanks!

Yes, the seal is missing, but as has been pointed out, that is not the CAUSE of your leak.
The foam seal would fit into the cavity above the bushing and under the e-ring clip. It's not inside the crankcase.
On this engine excessive blow-by might be caused by wear to the piston rings and cylinder walls.
Stuck piston rings can also cause excessive blow-by.

"So what exactly would be causing this excessive blow-by?"
Piston movement in a motor will cause vacuum/pressure. As Walt mentioned, the breather has a valve that helps create a vacuum in the crankcase - regular pressure is vented into the air intake, where it's burned in the combustion process.
As piston rings get worn, the combustion process will push some of that explosion past the rings and into the crankcase. That's a little too much pressure for the breather to handle, so those gases look for other places to vent - in your case, by the governor shaft. If only gasses, you probably wouldn't notice, but the gases are helping to push-out some of that crankcase oil, hence your leak.

Thanks again guys

Next question: If I replace the piston rings will that remedy the problem or is my engine ruined?

First, vertical shaft L head B&S twins have only one breath, the other is simply a cover. Horizontal shaft L head B&S twins do have two breathers for some reason. I am not clear from your description if the breather valve was working or not.

"I have two breathers that I know of. One is the pulse hose that connects to the carb and sucks in fuel, and the other one has no hose at all, it's just a nipple on the front of the engine. It's from this outlet that some smoke and oil come out."

I think you need to have me send you a Service Manual. Sounds to me like and the first picture looks like the fuel pump is connected to the crankcase breather and the nipple that you say has no hose on it is where the fuel pump vacuum line actually needs to connect to. Address below, put in proper format and remind me, model number and what you want. You did not give the code number but I can tell from the Intake Manifold that this is an old engine, 80s model.

We'll worry about rings when we get the crankcase breather thing lined out. IF that nipple is not connected, you will have very low crankcase vacuum pulling oil back in.

To clarify, I should have said the first picture in the set of pictures, not the single one. Also, a vacuum hose should come out the bottom of the fuel pump on the carburetor, curve down under and around the Intake Manifold and connect to a nipple screwed into the engine block. With the arrangement you appear to have, there is virtually no crankcase vacuum created plus there will be pressure created pushing oil out as that nipple is not large enough to relieve enough pressure. That larger hose coming from the crankcase breather has been cut off. It should plug into the bottom of the air cleaner.

Walt Conner
wconner5 at frontier dot com

This post was edited by walt2002 on Mon, Dec 3, 12 at 21:59

Hi Walt

I just read your edit.

The full serial of the engine is 402707-0132-01-81101912. I was wrong to say I have two breathers, as in actuality I only have one. Currently, the fuel pump is indeed connected to the crankcase breather. I'm going to reconnect the hoses in way you specified and run the engine again. However I'm busy with work and it may take a few days to get back to you

If you could send a service manual that would be appreciated: coreyboy301@gmail.com

Thanks

This post was edited by mowerman101 on Mon, Dec 3, 12 at 22:40

It looks to me that below the governor, the sump gasket is trying to claw its way out.... Am I wrong?

I'm quite sure it's just because of all the oil that has leaked around that area, it was a mess before I cleaned it a little. However, I'll give it a better clean and see. If it is trying to make its way out, what does that mean?

Well the way it generally works is I gave my address encrypted and you contact me. The reason being that "crawlers" constantly harvest email addresses from these forums for spam but I will make an exception this time.

"Currently, the fuel pump is indeed connected to the crankcase breather."

This completely defeats the purpose of the crankcase breather.

Walt Conner

This post was edited by walt2002 on Tue, Dec 4, 12 at 9:47

As said in above Edit, connecting the fuel pump to the crankcase breather COMPLETELY defeats the purpose of the crankcase breather AND the size of the crankcase breather hose MUST not be reduced but continue full diameter to the air cleaner housing.

For test purposes, to see if leak continues, the crankcase breather hose can be left open to the atmosphere. For permanent repair a replacement hose needs to run to the hole in bottom of air cleaner housing so that filtered air is drawn back into the crankcase.

Walt Conner

This post was edited by walt2002 on Tue, Dec 4, 12 at 10:02

This is what I see when I look at the pic. If you look straight above the engine mount bolt and between the sump bolt- it appears that there is gasket material protruding out from the block. Gaskets get brittle, break and will do that. OP twins will mainly leak oil at the sump or the rear cover. Once you are venting at a gasket- the crankcase can have pressure issues. Certainly, rings could be worn, the breather not working as it should etc. - being only 30 years old :) The thing with an air cooled engine and finding oil leaks is to realize that the flywheel fan moves hot oil around- in addition to the venting issues noted above. If you are going to fix it anyway, give the gasket there a tug and see if a fine wire or feeler gauge will make its way into the block. Or maybe I'm looking at dirt....

Hey again guys

So today I got around to replacing the oil sump gasket at tomplum's advice. During this I noticed some scoring on the crankshaft. I can run my finger over it and not feel anything but running my nail over it gets a little caught. Is this serious? I'm assuming something is worn out (a bearing?) and needs replacing. How do I fix this?

Thanks

This post was edited by mowerman101 on Sat, Dec 8, 12 at 18:50

Pic of the sump cover

The sump on these are NLA. I myself would gently clean it up w/ crocus cloth, reseal and hope for the best. Unless you can find a donor. I suppose someone with the knowledge and tooling could make it perfect again. Seems to be a $$ question on a 30y/o mill. Of course as Walt pointed out- verify the breather itself is working and unhooked from the pump. Really with the engine out, it is a good time to replace all the gaskets/ seals/ hoses- clean up the combustion chambers etc. How about the governor itself? Was the sump gasket deteriorated?

I hope you have the manual now.
The fine scoring of the crankshaft itself does not appear to be too bad. You would want to polish that up a bit with some 500 grit (or even finer) emery or carborundum paper.
You can make your own strips of extremely fine polishing grit paper by placing 3/4" wide masking tape or fiberglass reinforced shipping tape lengthwise on the unsandy side of automotive "wet or dry" sandpaper. Then cut the strips off using a box cutter style razor knife and a good straight edge. I usually use 600 grit for what you have to do.
Though your crankshaft is serviceable, the plain bearing in the sump cover may be worn to the point of needing to have DU replacement bearings installed.
Converting the plain bearings to DU bearings requires a machine shop type reaming to counterbore a relief for the DU bearings to be pressed into. This is not a DIY operation as it requires special tools.
You can measure the existing bore to determine if it needs bearing replacement.
Your pictures to compliment the posts are quite good (and helpful).

Hi mownie. You mentioned a 'plain bearing'. I can not see any bearing on the sump side of the crankshaft. I also didn't remove any bearing. It seems this side of the crank just sits inside the sump housing and uses the oil in it as lubrication. Looking at the parts list of the engine I can't see any bearing that is supposed to exist on this side of the engine. Am I missing a bearing? Or is this plain bearing on the other side of the crankshaft?

tomplum - I've reconfigured the hoses so that they are connected correctly. While its out I'm replacing the head gaskets and I'm going to clean off the carbon deposits. The hoses themselves are fine. I've already replaced the fuel line and filter. The sump gasket didn't appear too bad but it was somewhat deteriorated. It was hard getting it off as the last person who replaced it used a sealant. As for seals, I've ordered the governor shaft seal but that's it

This post was edited by mowerman101 on Sat, Dec 8, 12 at 21:02

In this case "plain bearing" means the sump cover IS the crankshaft PTO end main bearing. Same for the crankcase being the crankshaft magneto end main bearing.
When the plain bearing bores are worn beyond service limits, the case and sump cover bearing bores can be reamed out with a precision reamer to accept replacement DU bearings to be pressed into the counterbore cut by the reamer.
If you will read section 10 in the service manual it explains the configuration, and you will see why it is not a DIY repair.

This post was edited by mownie on Sat, Dec 8, 12 at 23:36

From the pics it looks like the small amount of transfer will clean off the crank and being the lower end the sump bearing wasn't damaged too bad. One can verify that. Depends on the end result desired VS $$ put into it. Lots of techs use sealant along w/ the gasket on these. I take my high tack stick and zip around the gasket on install. Excess sealant is not your friend however. Sometimes both sides on certain engines get done. You don't like pulling them down a second time for free! BTW Briggs tells you to use sealant in the areas which may have been marred on clean-up , but it isn't necessary on the whole surface. Resealing the rear cover, breather and other cover is a good thing whilst you are this far.

This post was edited by tomplum on Sun, Dec 9, 12 at 0:20

Yes, I too use High Tack. Briggs sumps have a habit of "losing grip" on the sump gaskets on a lot of their engines after many hours of operation.
Another "trick" I do is to use an "automatic center punch" and make a line of very light punch marks along the entire bolt pattern gasket perimeter. I make the punch marks about 1/2" apart (in the center of gasket surface) on the sump cover. These punch upsets provide just the right amount of grip to stop the gasket from "wiggling" during engine operation when there is a significant torque load borne by the sump cover. That was something I learned from working on motorcycles back on the '80s.

Hey guys. Thought I would update you: I threw everything back together and ran the engine, which now has the hoses connected correctly. Still, oil comes out of the governor shaft, but it is much much less than the amount that came out before

This post was edited by mowerman101 on Fri, Dec 14, 12 at 3:10

Did you check the oeration of the crankcase breather?

Walt Conner

Yes I did, resistance blowing in, none when sucking in

You seem to be back at square one. The best you can do is know that the breather is working and the engine is sealed. Beyond that- would you want to go further dollar wise? Any question on the breather, replace it. The mouth test is good providing you get a quick response from the reed. In my experience, things as simple as a missing dipstick seal will exasperate an oil leak condition.

It's funny that you say that because I don't have a seal on my dipstick tube. Anyhow, I've ordered a governor shaft oil seal so hopefully that will at least stop the leak. It still may burn oil up rather fast though

Dipstick TUBE oil seal.....item # 524 in Briggs IPL for 402700 series. Briggs part # for seal 271157.
In order for the dipstick and tube to effectively do its part in controlling engine crankcase pressure the dipstick must close tightly to the dipstick tube as well. Any looseness or sloppy fit at that juncture will affect crankcase pressure.

Actually, the upper ring on the dipstick is what ends up missing some of the time. It is PN 691870. I had a horizontal twin Vangard that had that seal missing. It would pump oil through the breather enough to where I was thinking it may have bigger issues- but a new seal put a smile on his face.... BTW 692532 is the new PN for the outer tube seal Mownie had listed.