Need some images.
The first thing that comes to mind is crankcase breathing. The pressure in the crankcase varies as the pistons move in their stroke, so you will have pulses of pressure and decrease(not likely vacuum, but a definite bump). That can cause oil to be forced out the weakest spot.
tom

 

1st picture is under cyl. 1 and the 2nd is under cyl. 2. Unfortunately I wiped the mess up. Ill get another picture after I run it again.

 

Looking at this image:

Briggs Stratton 42A707 18.5 HP ENGINE BLOCK CRANKCASE 498583 CYL HEADS & FLYWHEL | eBay

P/N: 498583. Briggs Stratton 42A707-2238-E1. Block, Cyl Heads & Flywheel. GOOD USEABLE CONDITION.

www.ebay.com

There seem to be no 'places' to leak oil except a flaw in the casting or coming from the exhaust port(bad or loose valve guides?). Other option is the drool method, where oil comes from up high and drools down the block.
A final would be an upper leak that is being blown down the side of the block caused by the airflow from the flywheel blower.
I don't think it is a fun task, but maybe consider removing the 'tins' - the shrouding that directs cooling air to see if there is a leak that is flowing down, assisted by airflow. There is nothing under pressure to cause a 'spray' of oil, so the only 'mover' would be cooling airflow. I think.
tom

 

Looking at this image:

There seem to be no 'places' to leak oil except a flaw in the casting or coming from the exhaust port(bad or loose valve guides?). Other option is the drool method, where oil comes from up high and drools down the block.
A final would be an upper leak that is being blown down the side of the block caused by the airflow from the flywheel blower.
I don't think it is a fun task, but maybe consider removing the 'tins' - the shrouding that directs cooling air to see if there is a leak that is flowing down, assisted by airflow. There is nothing under pressure to cause a 'spray' of oil, so the only 'mover' would be cooling airflow. I think.
tom

That's what I'm coming up with as well. There's nothing to "leak" on the engine except the sump.

I like your idea about the airflow causing the spray. I'm going to clean the area today and put some flour or whatever similar I can find on the area and try running again to pinpoint it.

The only reason this is puzzling me is because it's black oil rather than the fresh stuff I put in and the immediate area.

I inspected the block and rest of engine when I had it apart, I didn't find anything out of the ordinary. The back of my head says a cracked cylinder but this is an Iron Sleeved block so I'm thinking likely not. It had to have gotten super hot and other damage would have surely occurred to consider a cracked cyl.


If you look at my Cyl #1 Picture you can see some leakage running down the exhaust towards the top of the photo. Something else to look at? The fit on the flanges wasnt particularly great when I installed it but didn't think it would cause a problem.

I inspected the valves as well and cleaned up their seats when I had the engine apart. Nothing seemed out of the ordinary and the engine doesn't smoke like it's burning oil.

Thanks for your help!

 

I don't want to attempt to mess with what the site did with my above post, but it should be referring to an image of a 42A707 engine block, looking at it end-on from the side where you can see the exhaust ports for both cylinders, looking into the crankcase. Visually and logically, there's nothing to deliver oil anywhere near the exhaust ports.
I do not know what it will show if you click, so I added this...
tom

 

Have you checked the gasket on the valve spring chamber cover? Checked that there is good drainback(open) from the chamber? That area on both sides likely could have some old black oil... if the drain was obstructed. I do not know these engines up close & personal, just the generic style. If there is a problem with crankcase ventilation, the chambers are often a source of leakage as the gaskets used get tired over time and seem to allow for relax of the fit and then seepage.
tom

 

I replaced all gaskets and seals with new around the engine, top and bottom. And I strongly believe I installed the notches on the gasket/cover plate the right direction but if nothing else seems to be the culprit I may have to take another look.

When I had it apart I ran wire through all the oil galleries leading to and from the valvetrain(s). I'd say the only thing I skimped on cleaning at all is the area on the bottom of the back cover plate on the block, there's 2 small voids down there with some galleries, not really sure what purpose they actually serve but thats the only thing that didn't get made spotless. The rest of the engine was cleaned very well.

To tomw's point, I had an unexplained oil leak on my opposed twin. It ended up being the top oil seal on the crankshaft. It was dripping/being blown down.

I'll have to take a closer look at the flywheel side. The only confusing part about my issue is the concentrated area where this "black spray" accumulates. I need to bust out the talcum powder or flour and look closer.

I haven't had the time lately sadly. Old man winter has been pretty lax this year but that just opens opportunities to do other chores and not play with Tractors haha

Thanks for your help guys.

 

To tomw's point, I had an unexplained oil leak on my opposed twin. It ended up being the top oil seal on the crankshaft. It was dripping/being blown down.

 

The valve gallery breather can not be put on upside down, screw holes will not match. The distance between the fiber disc in the breather and its' seat is a max. of .040". Do not push on the fiber disc or it will ruin it! Be sure disc is moving freely. Bleed hole in breather is open AND drain from chamber and crankcase is clear.
Walt Conner

 

I didn't say anything about installing the breather the wrong way. The leak isn't coming from that area anyways. It's all Cyl.#2. The breather checked out fine when I had it off the engine. Thanks for the idea though.

 

Going a little off-topic here but to those who installed a fuel cut-off valve on a twin cylinder engine~ Have you ever encountered 1 plug reading lean and one reading rich after killing the engine by fuel starvation? I didn't notice this difference before I installed the cut-off and used the key to turn the engine off.

 

Did not read all of your replies, but for oil leaks that are hard to determine their starting source you can go to O-Reillys and get a little bottle of DYE for motor oil, call dye kit
Also get a pair of UV glasses and the UV flashlite if this is not in the kit and run the motor until you see little bit of oil and inspect immediately in a dark room. Do not wait too long to clean off the dye, it dries fast. The reason you need to remove the dye fast is because you may want to test again after doing repairs. If the dye dries before you get it removed just use some fast dry spray paint over the dye for a re-test.
Be aware that their are dye kits for coolant, AC, transmissions, motor oils, so get the correct kit. Kit is about $15.

 

Following up.

The spray seems to have just quit. I imagine there was some sludge leftover inside when I rebuilt and cleaned the engine and worked it's way out of the block.

Thanks everyone for your help.

 

thanks for coming back to let us know

john