B&S burning a lot of oil - most probable cause?

[Tobi09]

The engine is a 28N707. It ran (probably) for about an hour with a lot of gas mixed in the oil (due to defective carb needle). Could this already be enough to damage the piston rings to a degree that oil gets combusted in rough quantities afterwards?
I know this looks like the obvious cause. But before I change the piston rings I would like to know if these symptoms concur with it:

- at low rpm it smokes a lot more than at high rpm
- high load smokes a lot more that no load
- at the highest mark on the oil level rod, it burns a lot more oil then on the lowest mark

Especially the last point doesn't make any sense to me, how can this be explained? Does the cylinder wall gets so much less lubrication if the oil level is lower? The compression still seems good and I didn't recognize any loss of power. Could it also be the head gasket or maybe something with the crankcase breather? Because with all this gas in the oil, the level was way too high and it also blew a lot of it out of the breather tube. Maybe the breather valve or breather filter is clogged? The air filter is already replaced with a brand new one.
I just want to prevent to disassemble the whole engine and then realize it didn't fix the problem. Could there be another cause that I am overlooking or do these symptoms completely concur with raddled rings?

 

[mechanic mark]

http://faculty.missouri.edu/~schumacherl/276781SingleCylinderOHV.pdf see if this helps, since you have already posted engine model 28N707, post type xxxx, trim xx & code number for more information. also adjust valves with engine cold, procedure section 1 page 21, specs. section 12 page 170. carburetor is problem, rebuild kit or new carb.

https://www.briggsandstratton.com/n...nemanuals.html?searchrequested=28N707-0166-01

 

[bertsmobile1]

You have either done the rings or a head gasket.
And if you are really lucky, both of them. :laughing:

 

[Rivets]

Personally, I don't think you did much damage to the rings or cylinder. Have seen this more than once in the last few months, years. I just rebuild the carb and have not had any returns yet with major internal damage. You must also change the oil and filter. Many are going to disagree with me, so read my signature.

 

[Tobi09]

Thanks.

@Rivets
But how should rebuilding the carb do something against massive oil consumption? Maybe my description was not perfectly clear. It is not the jet needle for gas control but the float needle that didn't seal correctly when the engine stood still for a while. A lot of gas went past into the cylinder and ultimately into the crankcase and the engine oil (and raised the level significantly). The engine ran for a while under this condition. That did something to the engine which causes it to consume massive amounts of oil now, with correct oil and oil level of course, and with a in-line shut off valve for the gas to prevent it from happening again.
I think the carb is ok except the defective float needle, which is at least fixed by the shut off valve for now.

@mark
28N707
Type: 0166 01
Code: 9604014A

If I order new rings I am not so sure about which one to buy. Page 11 shows two different part numbers. 696403 is the first entry (Used After Code Date 01041800) and 495854 (Used Before Code Date 01041900)
http://bsintek.basco.com/BriggsDocumentDisplay/18hnxKXAnfBhU7y.pdf

Both are still available to be ordered. I am not sure if they fit both? I found Part No. 499996 to be the cheapest I can get, which, according to some stores, is compatible with 495854 (the older number)
http://www.dlastore.com/e_store/chr...31-mm-3-4375-392331-495854-499996-391780.html

I am not sure if the older number is only compatible with pistons with the older date as well?

 

[Rivets]

When the fuel mixed with the oil in the crankcase it raised the level of oil and thinned it out. This did two things, which increase the amount of oil consumed. First, the higher level and thinner oil allowed oil to pass past the rings with greater ease. Because it is the thinner the oil rings had no control over it, as it was longer a spray, but a constant liquid laying on the bottom edge of the cylinder. Second, the breather was able to suck excess oil mist in the crankcase directly into the carb. Both conditions contributed to the high amount of smoke you observed. You must realize that normal oil level is below the cylinder and most internal parts are lubricated by either spray or splash, not oil bath, this includes cylinder walls. I my opinion, replacing any internal parts is not needed, but it is your money. Only part which might need replacing is the head gasket, if it was blown out by an excess amount of fuel/oil in the cylinder when the problem first occurred. Leak down test would give you a good indication of any problems.

 

[Tinkerer200]

I would look for the hose between the crankcase breather and the air filter air box, disconnect it from the air box find away to alternately suck and blow on this hose still connected to crankcase breather. You should be able to suck freely but quickly change over to very restricted blowing. IF that is the way it works, the crankcase breather is working OK. Probably not it but costs nothing, no tear down and eliminate that.

Next I would pull the head and check the gasket on both sides in the area between the cylinder and the push rod gallery. It doesn't take much of an imperfection to burn a lot of oil and yes, your compression may seen to be normal. This will also give you a chance to examine the cylinder wall for scoring. IF scored, not practical to fix but I doubt it is. IF head gasket appears damaged, replace it, install a new carb float needle kit but form the habit of continuing to turn off your inline fuel shut off valve and DO always check you oil level before starting your engine before using. Too high may be as bad as too low.

I can send you a Service Manual (Overhaul Manual) for your engine IF you like, address below, put in proper format, remind me engine model number and what you want.

Walt Conner
wconner5 at frontier dot com

 

[Tobi09]

@Rivets
Understood. I think both conditions you describe took place to some degree. But the oil burning continued, even after I replaced the bad oil/gas mix with normal oil to a normal level.

@Tinkrerer
Yes, thanks, I will definitely check the breather the way you described. When the engine is running, there is a lot of air pushing out of the breather tube, this probably is already a indication that combustion gasses pour through ether bad rings or a blown head gasket.

Somebody an idea what the dates in the parts list mean? (Used After Code Date 01041800) (Used Before Code Date 01041900) ? I cannot interpret these codes and still uncertain which one is correct.

 

[Tinkerer200]

Your engine will have 3 sets of numbers stamped into the valve cover. Model, type, code. You need to compare you code number with those specified in the parts list, example below.

The following is an example of interpreting date Code 99011556:

The first two digits (99) denote the year of manufacture. In this case it is 1999.
The next two digits (01) are the month of the year, which is January.
The following two digits (15) are the day of the month. In this case the 15th.
The final two digits designate the plant and assembly line.
Therefore, this engine’s manufacture date was January 15, 1999.

You need to do a bunch of checking yet before ordering rings.

Walt Conner

 

[Rivets]

If you are still burning oil, I suspect you blew the head gasket. You are going to have to pull the head anyway, so why not start there and only go deeper if you have to.