15hp Briggs Smokes While Running

[GearGuy]

15hp I/C Gold 1cyl vertical shaft OHV on a '96 Craftsman lawn tractor.

Engine was always excellent. Oil would hardly look dirty between changes and was never consumed. Changed very suddenly after an oil change to Walmart 10w30 or 30wt. I don't exactly blame the oil but after 3 weeks the level was too low. So I cahnged back to another name brand oil but the problem didn't go away.

Now the oil darkens very quickly and drops below the add mark after a couple of hours of use. Smokes lightly. And if the mower tilts towards the breather, it's like oil injection into the cylinder. Solid cloud of white smoke!
At idle with the air filter off, there is a mist of oil coming from the breather tube inlet to the air filter box. It soaks the paper filter.

Could it be simply a failed breather or something more serious like the rings are shot? It's my first OHV so I don't know if they might have a specific weakness ot not. I have no idea why it changed so suddenly...

Looking for some ideas before I tear it apart because I have about 40,000 sq. ft. of grass to cut and a push mower will be to painful...

I've been topping off with some Delo 15w40 but that only seems to have slowed down the consumption a bit.

Any help would be appreciated greatly!

 

[Rickey]

Genericly it Sounds like a crankcase breather problem. This is a wild guess on my part as I have no knowledge on that specific Briggs.
Could be a broken or stuck ring also.
Maybe it just doesn't like that particular oil. You could drain it and try another type oil maybe. In fact thats what I would try first if it were mine.
Any loose hoses on the engine?
Good luck Sir.

Rickey

 

[Rickey]

Oh...and what type oil were you running in it before?

 

[Bill Kapaun]

What are the engine numbers?

Does that have a fuel pump?
If so, I believe those are "activated by the "impulses" from the breather. A hole in the diaphragm may possibly allow thick oil vapors into the fuel??

Anyway, look there or in the breather system first. A bad reed valve in the breather may cause those problems.
IF not, I'd be concerned about the head gasket starting to go.

I don't think the different oil type was a major issue, although Briggs has some caveats about non synthetic xW-30. Maybe there really is something to that???

 

[-Clayton-]

Probably a blown head gasket. Usually blows around the pushrod and lifter valley and does the exact thing your describing, And may get worse.

 

[GearGuy]

Last night was busy so I didn't have time to pull the Engine ID.
I've thrown a variety of oils in since. Especially with the rate of consumption:
Castrol HD30 SL
Valvoline HD30 SL
Pennzoil Platinum 10w30 SM
Mobil EP 10w30 SM
Some AutoRX
Exxon 10W30 SL
Kendall GT 10W30 SynBlend SM

Before the Walmart oil, I believe it was the Castrol HD30.

FP60 added to the fuel.

Engine still seems to run good otherwise. It labors a bit more on startup cold with the Delo 400. At times, it looks like it isn't burning oil at all. Spark plug fouled up a few times due to oil burning buildup. Fuel consumption is up quite a bit, probably due to saturated air filter.

I've never had the head cleaned of carbon. Could this have led to the issue? I had hoped that doses of FP60 would help keep the carbon deposits down the I'm sure that it's current condition is beyond what FP60 can help.

Anyway to check for a stuck ring short of pulling the piston out? I'm just trying to minimize the teardown.

With the air cleaner removed, the oil coming from the breather tube is a fine mist. Like from a humidifier. I can't remember if I am getting a lot of blowby from the oil fill tube with the dipstick removed. I could check tonight.

Like I said before, a tilt of the engine towards the breather and carb side produces a LOT of smoke very suddenly. Amazing how far it will go and how long it will linger on a breezless day. This occurs mostly when the engine is first started, after topping off the oil. Probably very much like an over-filled condition??? But the dipstick is original and I've measured the oil before dumping it in to verify oil level. 48oz IIRC. As the oil burns off, the smoking seems to decrease.

Everyone's input is greatly appreciated.

 

[Rickey]

Hmmm... lower oil level= less smoke. This is tough. Sounds like rings to me. The head gasket theory is also plausable.
If some how you could do a leakdown test with the cylinder vertical, spark plug up, and with both rockers loosened so as to eliminate any leakage from the "Easy spin" compression release. This would be done with a heavy oil on top of the piston and rings.
If air leakage is present under these circumstances then the head gasket is suspect,and you will probably be able to tell that it is coming from the head/pushrod area with the rocker cover off. If the oil eliminates leakage into crankcase (even temporarily) then the rings are shot. Of course a baseline leakdown test before adding any oil would be in order.
The compression release mechanism will make accurate traditional compression readings difficult to obtain.
I believe that one method involves loosening the exhaust rocker enough (.030 ?) to overcome the exhaust valve leakage created by the compression release at low rpm.
At low RPM the compression release will prevent the exhaust valve from completley seating to allow the engine to turn more freely.
And actually I have tested similar engines by turning them over by hand with the exhaust rocker loosened and listening for leakeage, srark plug wire disconnected for any tests such as these of course.
If it is a tiny leak that cannot be located by testing, retorqueing the head bolts may give a clue, by temporarily eliminating or reducing the symptoms. Thus confirming a head gasket problem.

I mention this last but really this should come first... eliminate the easy stuff early in the troubleshooting process. If there is a reed or other type crankcase breather,change that first no questions asked.
I would much rather do the easy stuff first than last.


Good luck Sir.

Rickey

 

[GearGuy]

Ok, here's the engine ID;
Model: 28N707
Type: 0161 01
Engine IPL

Carburetor is a gravity feed float type.

Engine running at idle. Still light oil mist with the air filter off. Increases noticeably when the oil fill tube is opened. Seems to suggest that the breather is functioning to some degree?

I'll see if I can do a leak down test, but I'd have to by one. I've already have a good compression tester. I'll have to find the time to play with it...

I see what you mean now about the head gasket. Looks like a weakish design. That could be a good possibility and would explain why it happened so suddenly? It's condition should be obvious after I pull the head off.

Thanks again!

 

[Rickey]

"I see what you mean now about the head gasket. Looks like a weakish design. That could be a good possibility and would explain why it happened so suddenly? It's condition should be obvious after I pull the head off."


After looking at the parts list...
Agreed.
Especially the suddenly part.
I still Hope its something simple though.

Rickey.

 

[White 03]

I have the same engine on a old craftsman mower; probably the same as yours. Mine says 15.5 HP but is a 28N707 like yours. I went through all the same things as you, including just having done a oil change with some new oil I can't remember. Mine had a great cloud of smoke on start up then increasingly more smoke while running. After replacing the breather and other things I took the engine apart but found it was the head gasket. I think head gaskets are common weak spots on these. As I remember the breather was pretty fool proof and B&S guy said they were usually not a problem. I can't remember any compression release on mine but I may have missed it.

I don't remember where the gasket failed now but I remember it was real hard to see. Also as I remember it ran pretty good except for all the smoke.

I also remember a bucket full of sparkly stuff after the next oil change. Might have been there before rebuild also.

 

[Bill Kapaun]

"I don't remember where the gasket failed now but I remember it was real hard to see."
They tend to fail right next to the push rod galley, where the sealing area is very narrow.

 

[White 03]

Quote:

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"I don't remember where the gasket failed now but I remember it was real hard to see."
They tend to fail right next to the push rod galley, where the sealing area is very narrow.

---

That sounds like it. Maybe accounts for the engine running pretty good inspite of the bad gasket.

Seems odd but you mentioned up above about the multi grade oil and B&S. Mine happened right after I change the oil to 10-30, if I remember right, just like the OP. But I can't think of any correlation between the oil and the head gasket.

 

[GearGuy]

Thanks White 03. I'm leaning towards a head gasket issue.
Well, the head/valve gasket set is on order...

Meanwhile, I've been mixing Delo 400 15w40 and Pennzoil HD30 to keep the oil heavy. Adding a bit of LC20 now and then. I had a slight overfull (just over the full mark) which resulted in quite a bit of smoke while stationary, so I had to pull the plug and bleed some off. Engine started missing a bit, so I knew the plug was fouling.
Next day I pulled the plug and it was one solid lump of buildup. Spent some time chipping it out.
Filled the tank with gas dosed with FP3000.
Engine ran GREAT! Real nice. Smooth with power.
It was late so I couldn't really tell if it was still smoking. But if it was, it couldn't have been that bad.

Even if it does, by chance, 'fix itself', I'm going to pull the head and de-carbon the chamber. It's way over due. And that automatically means a new head gasket.

I'll report what I find...

 

[GearGuy]

Took the head off last night and the head gasket is shot between the combustion chamber and the pushrod chamber.
I took some pictures that I can work on posting later. Pretty good sized "hole" about 1/8" to 3/16" wide.

Summary of observations from this problem:
- Burning oil while running.
- With air filter off, mist of oil blowing up from the breather tube entering the air filter housing.
- Air filter saturated with oil.
- Oil seepage past seals and gaskets.
- Oil darkening very quickly.
- Happened fairly suddenly.

Carbon build up was not as bad as I had expected.
Any suggestions on carbon removal other than scraping?

Anything else I should do while I'm in there?

Thanks all again for your help.