Briggs 21 HP Single Cylinder. Bad rings?

Just got this Craftsman mower for free. Nothing is free.....
Engine: Model 331877, Type 1371 B1, Code 100405ZD
Started right up after I cleaned the totally fouled plug.
Burns oil blue smoke.
Has 60 psi compression.
But runs pretty well.
Just wanted to get a second opinion that there's no way this is a valve seal oil leak.
The cylinder looks great except for that stain (see photo) where I think some dirty oil sat for a couple years. It's a horizontal cylinder so that is where any fluid would pool. The stain feels as smooth as the rest of the cylinder.
Spark plug and intake valve all oil crusted. (see photo).
Would an intake valve have this much crusted on on the top side of the valve if it was an oil leak through the rings?
I don't see oil leaking down the valve stem.
Also it blows a lot out of the dip stick hole.
Exhaust valve stem is flat black and dry. (That photo won't load)
 
Ok, it's obviously bad rings, but I'm still open to somebody else saying Duh!
 
If I replace the rings, do I need to clean up that stain even if you can't feel it there?
 
Thanks
:)

You do have an oil seal on only the intake valve..
 
With the valve in the head, just off the seat, is there any back and forth play?
If so, (probably not), that would help with oil getting past the seal and burning oil.
 
You could do a "Leak down test" to ascertain the health of the engine however
I think you correct with the diag of worn piston rings.  After cleaning the head, 
flip it over, spark plug installed and fill with say seafoam-Let it sit.  If the valves are leaking
the fluid will pass the valve(s) and into the runners.
 
Re the staining.  As long as you don't have any scrapes (usually vertical), I
would just hone the cylinder before the new new rings are installed.  
 
I have a similar engine from 2005 (18HP Briggs) which needed a head and piston (dropped a valve)
A new head, honed block and new piston/rings, runs like a top (no damage to the block). 
 
Honed and new piston installed:

 
 
 

 

Thanks for the info.

Got the engine all apart. Can you tell me where the little pin in the photo goes that fell out when I turned it upside down?
 
And there's a lot of cross hatching still. Do I need to hone anyway?
 
And how do I tell that the rings are actually bad? I don't know what I'm looking for.
 
I have photos, but nothings loading right now.
 
thanks

Are you referring to the two solid pins, showing in the top of my block?  Their just alignment pins.
 
Re honing, yes, I would give it a light hone for the new rings to seat.  
 
As for ring wear, put both the compression rings in the cylinder (about 1" down from the top)
and measure the end gap...
 
 
From another thread:
Service doesn't have minimum end gap but .010" should be a target as .030" is the maximum allowed.
 
 
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It's not an alignment pin, it is smaller and was loose. I didn't see it when I flipped it to drain the last oil.
 
What stone number do you use for that level of honing?

This is the hone I have and used (for literally decades).  For 2" bores to 7" bores.
There is no "grade" of the stone listed.  You may be able to borrow one from your local 
auto parts store...
https://www.summitracing.com/int/parts/shc-94633/overview 
 
 
Can you open a free acct at Post image: https://postimages.org/login  
Upload your pic, then copy and paste the link for FORUMS.
A pic of your "pin" may help find where it goes...
 
That and some more detail, how the engine was positioned when this pin came out.
 
Admin may take a couple of days to allow it to post (for new folks).
 
 
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I'll give that a try if the photos continue to not upload.
 
The main body of the engine was how it would sit on the mower, with the bottom cover off. It's about 1/2" long and maybe 3/16" diameter.

Any updates?
 
 
 
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I got the parts yesterday. I'm hoping to do the work tomorrow.

UPS lost the cutting fluid I ordered for honing the cylinder. I finally got started today. Honing went really quick, in like 25s it was crosshatched. It brought out some wear marks I couldn't see before. Took half the day to clean off the gaskets and clean the engine block etc. So what do you use to clean carbon off the valves? Other than that it should go back together tomorrow.

With the valves removed, gasoline and or a round wire brush
in a drill motor will remove carbon real quick.  Brake cleaner/carb cleaner will work as well.
 
Once done and the head assembled, flip it upside down (spark plug installed) and
fill with say Seafoam.  If the valves are leaking (over night), you'll see the Seafoam go 
past the valve seats and come out the ports...
 
If so, some valve seating compound, along with the tool will help seal those up 
fully...
 
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Won't the wire brush damage the valve mating surface? What about the combustion chamber, can the valve seat handle the wire brush?

Just go nice and easy and with a cleaner(gas, brake cleaner, etc), won't hurt anything.
I'm talking a 1/4" shaft brush, used on a hand drill motor-NOT a super heavy duty brush on a large grinder.
 
Works fine on the head, piston, etc.
 
A piston top & block pic(18 HP Briggs) cleaned after 15 years of service. 
Damage is from a dropped valve that destroyed the head and piston
(piston & head WAS replaced due to valve parts impacts).
 

 
 

Another delay. The valve seal I got in the gasket package just falls into place. No resistance. Now I'll have to order another seal and wait :(.

You just have the one seal, on the intake valve, correct (part # Briggs & Stratton 690968
SEAL, Valve ) ?
 
 
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Hey, I'm getting mixed answers for how to orient the piston rings. These are inside beveled rings. Both look identical. Right now I'm seeing videos that say bevel goes up on the first ring and down on the second ring. The guys I bought them from say both go up. First they said both go down.  Can you tell me what the real truth is?
 
Also angles between gaps, seems like there's more than one opinion on that.
 
thanks
 

There should have been directions included with the rings.
 
In any event, look at approx the 15 minute mark below:
https://www.youtube.com/watch?v=4VnNDUOsxEM 
 
The rings (both upper compression rings staggered about 180 (the end gap), from each other, to help with sealing.  You DON'T want them in-line as compression will now blow straight past them.
 
Same for the oil rings. As there's 3, I set mine so the end gaps are about opposite each other BUT 
above / away from where the oil level would be once assembled..
 
A Briggs shop manual specific for your engine would give you what the factory recommends..
 
(I work on most every engine make/model, etc, so having a shop manual for all is not practical....)
 
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There were cryptic directions with the rings. Not very clear. And after getting two answers from them I don't know what to trust.

Also, I had watched the video you referenced yesterday and the rings don't have bevels in that one so I'm still unclear how to orient the bevels.
 
thanks

 I found this on another site and believe it to be credible and make sense:
 
 
Rings rotate in the grooves unless they are pegged .
The spring of the ring does not create the compression, it is the gasses trying to get past the ring which forces them out to make the seal with the oil on the bore & in the ring groove .
This is why on 4 strokes champhers always point up.
When new the rings have not made their seal against the bore so spacing them 120 degrees helps the initial compression.
 
Of course a shop manual would give you conclusive answers...
 
 
 
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That is the most intelligent thing I've heard all day about the bevel. I'm an engineer and it's really good to understand why you're doing something, not just knowing you are supposed to do it. I pointed them both up.
 
One thing I'm not confident about is how deep I installed the main seal on the drive side. First I put it in flush, but the flat part of the crankshaft was right at the edge of the seal, so watching another video where the guy drove it all the way in, I just did that. I can't see how it would hurt, but the shiny part of the shaft that is now showing tells me that the original seal was probably flush. I have a second seal if that was not a good idea.
 
Also, the bolts holding the two halves together had some kind of lock tight or sealer on them. Is that needed for putting it back together?

There's an oil hole in that recess that CANNOT be covered up,
IE; seal NOT PUSHED DOWN FULLY INTO THE HOLE..
 
Anywhere in the cover leaving the oil opening clear AND the working part of the seal fully intact with the crankshaft. 
A little oil between the crank and seal wouldn't hurt Flush is fine and you should still be able to see the opening... 
 
*As a side note, on my 18HP Briggs, that seal started leaking after 5 years. 
I took a short cut and pulled it with the engine in the machine
(drill and use sheet metal screw to pull the seal-
Ultimately nicking the crankshaft.) 
Now THAT FIX- Pulled the engine and cover
and seal.  I had about 1/4 crankshaft NOT damaged on the end not damaged.
I put the seal into the case, JUST ENOUGH to catch the case and ride on the 
un-damaged part of the crank.  Used Yamaha case sealer on the outer edge of the seal.
There was just enough "good crank" and just "enough cover" -
Re-assembled, stayed and is currently nice and dry..
(A major screw up with a positive ending)
 
 
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Believe it or not, the engine started right up and runs smoothly and no smoke and no leaks.
 
Ran it for about 25 min and still good. 
 
Thank you for your help!!
 
Then the mower started dying when I put it in reverse and then quit altogether. No voltage on the starter side of the solenoid. So now I have to figure out what switch etc. is not working.
 
But I think the engine is good.
 
Thanks.

Also, I started the engine with the mower blades engaged and ran it for 20 min at medium rpms. I didn't realize the blades were spinning. I didn't drive or mow. Would you expect that to effect the rings breaking in? Or anything else?
 
thanks

Glad to hear the engine is good....  
 
Check voltage, while running at the battery and make sure it's 13-14 volts. 
If more than that you may have popped a fuse.
 
I do think it's more than that, as you said, a bad safety switch somewhere.
It shouldn't have cranked with the blades engaged.   
 
As for break in, you want load on the engine to help seat the rings.
Varying RPMs, hot and cold heat cycles as well.. 
 
With that said, that engine is very forgiving (Including break in) if assembled correctly
(as it seems to be).  
 
I'd be re-checking the engine install itself itself, the WIRING.  Make sure nothing got 
pinched, blew a fuse, etc. Physically follow every wire about the engine (shouldn't be many)
to make sure all's. clear..
 
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I checked the ignition switch, clutch/brake switch, reverse switch, attachment clutch switch and the seat switch. All are fine. I put it all back together and it starts right up and runs smoothly. But it only starts with the blades engaged. It will not turn over with the blades dis-engaged. No click, or any response. But once started it will run in both positions. And according to the manual, the blade lever is physically backwards. But there's no way to mess that up so I'm clueless how that could be.
 
The blades engage and spin just fine. But, the belt feels like it's not tight enough when engaged.
 
And I think full throttle is not fast enough. I think I can rig up a tach to measure that, but I don't know what full rpm should be.
 
It also dies if I put it in reverse with the blades disengaged, but keeps running if the blades are engaged, and there's an ROS position on the key switch that allows it to run in reverse with the blades disengaged. That is clearly backwards.
 

Max RPMs:
 
https://www.engine-specs.net/briggs-and-stratton-engines 
 
 
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