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B&S V Twin smokes on startup.

I just bought an older (around 2012) Craftsman riding mower with a 26 hp Briggs and Stratton. It emits a bit of blue smoke when it starts. Then there is no smoke for a moment until the muffler starts smoking because the there is a bad oil leak and oil is sprayed onto the muffler. I have not used it enough to know if it puffs smoke on a warm start. I will look at that.

I am going tear the engine down and replace all the gaskets.

What could be causing the puff of smoke on startup? Is there anything I could do to figure this out?
Several forum posts indicate that this may not be a real problem, but I would like to think about it before I open up the engine.


I have written a long post with all the details, see below.

tldr



All the details on my B&S V Twin engine that leaks oil and smokes.


I have an older (around 2012) Craftsman riding mower with a 26 hp Briggs and Stratton. It has problems and I am going to tear down the engine.

1) Leaks.
It leaks oil, and leaks and leaks. The man I bought this from said his mechanic said it is a head gasket. But I see no oil pooling under either of the heads. It could be the crankshaft seal. In any case, it leaks badly enough that oil is sprayed onto the muffler (and everywhere else underneath the mower). There is also evidence of leaks around the oil filter. Within a minute of starting it, the muffler gets hot enough to start burning off the oil. A new gasket set is on order. I may clean the engine and run it to see where all the leaks are, but this may not be necessary.

2) Cam shaft.
The compression release does not work. I checked the valve clearances. All four are at .007. The manual calls for .005. Several internet sources give .005 to .007 as the spec (I read it on the internet, so I know it must be true). So that is not enough to cause the compression release not to work. It can be started by rotating the engine by hand just past the compression stroke and then it starts right up. A new cam is on order.

Here is a link to a video on diagnosing and fixing the compression release:

3) It runs well and I have used it a couple of times. I notice a puff of blue smoke from the exhaust (not burning off the muffler) when it first starts, but that goes away very quickly and no more smoke until the two and a half quarts of oil on the outside of the muffler start to cook. I have never worked on small engines, but in auto engines (horizontal crank), smoke on startup would point to valve stem seals, or other things and smoke while running points to rings. What could cause this puff of smoke on startup?


Any advice on this would be appreciated, especially on the puff of smoke issue.


Thanks.

First, trying to diagnose a small engine problem basing on your knowledge of automotive experience will get you in trouble very quickly. They are close in operation, but far apart in the cause of a problem. Second, I would start by removing the plugs and look to see if they are oil and/or carbon fouled. Oil would indicate to me you have a blown head gasket on one or both cylinders. A blown gasket could also cause oil to spray on the muffler.and other parts of the engine. If you report back be sure to include all engine numbers so we know what you are looking at.

Rivets, thanks for the reply.

I looked at the plugs before buying the mower. Both looked relatively clean, as if they were used, but not fouled. I did this because I was told the head gasket was blown.

I used it around the yard a couple of times before checking the valve clearance. They looked the same, leading me to believe that they were not just replaced.

I saw no oil spraying anywhere with the engine running, mower parked.

I think the oil is getting flung onto the muffler after dripping onto the pulley (and what I am guessing is an electric clutch) underneath the engine during driving, but have not confirmed this.

Stamped into the valve cover:
Model 445877
Type 1565G5
Code 110920YG

@Rivets
If it is a blown head gasket, would I be able to tell when I take the heads off?

A trained eye would be able to see a blown gasket very quickly. You should never reuse a gasket so if you decide to pull the heads have new gaskets available. Personally I doubt if the oil is being thrown from the PTO pulley onto the muffler. Also, did you measure valve clearance, looking the same tells you nothing.

Ok thanks.

The problem I am most concerned about is the puff of smoke on start. I will address the others in a separate post later.

What are the most probable causes for the puff of smoke? How can I track it down? If it's not the rings then I don't want to pull the pistons with all that entails. I would rather know if it is a problem before hand.

If I do decide to pull the pistons, the manual gives good instructions for checking clearances.

Head gasket or crank seal..

Ok. That's two people with more experience than me who think it is the head gasket. I have a complete gasket set on order, so I think it will be fixed either way.

How can I tell it's the head gasket? Should I clean the engine and test for leaks? Or would I be able see it spray out under certain conditions?

On the cam...

I did measure the clearance: .007 on all four valves. Slightly over the .005 spec in the B&S manual, but not enough to cause cranking problems. So I am confident the new cam will fix that.

Because I’m not standing next to you to see your problem, I must go by what you have posted and my past experience. You can do what you want, but that’s not how I would proceed. I would be pulling the heads and replacing the head gaskets. I’m guessing that the oil is being drawn into the cylinder through a bad part of the head gasket between the valve galley and cylinder. Why, because from what you say oil is getting into the cylinder and at startup it is being burned and pushed out the muffler causing the smoke at startup. After you have the engine running excess oil is being pushed up of the cylinder through a blown section of the gasket. Remember I can only make my guesses using the info you provide and based on my past experience. As you sound like you have your mind how to proceed I’m getting out of this thread and wish you luck.

@Rivets
Thank you for the advice. It has ben helpful in understanding the engine. I will look at it carefully before tearing it down.

It will be a couple of weeks before I can get to this again, but I will try to post the results.

if it is an OHV engine the oil can drip down thru worn valve guides. It is a 10 year old mower. If you can live with it just be sure you keep an eye on the oil level. Otherwise this may become the plumber story of the bad faucet seal that led to a new valve that led to replacing a pipe, which led to opening the wall, which led to replacing the run which led to replacing the main.........