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I am helping a friend on his riding mower with a B&S Power Built 500 cc Engine. He said it was running poorly and was smoking.

This is what I found.
Spark plug was loose and sooty
Battery cables were loose
One bolt on the valve cover was missing (broken off) and oil was leaking out and dripping on the muffler
The valve lash was in spec.
I removed the head and inspected it. The head gasket seemed ok. It is original. The head was sooty. The push rod chamber seemed relatively cleab. It did not appear the gasket was leaking in there. The bottom of the cylinder was slightly scored.

I need to check the head for flatness. If it is off a bit what can be gotten away with. Is there a thicker gasket available to make up for some warp? I am thinking ahead in case it is off a lot.

I never saw it run. I assume there is some higher oil burning. Probably livable. The smoke he observed is likely mostly from the oil dripping down on to the muffler from the valve cover.

What is causing the oil to turn grey? Is it all exhaust blowing by the rings? He has been using SAE30 and changed the oil every year. He has not changed it this season yet. I am thinking to change the head gasket, fix the broken bolt and put a gasket on the valve cover. New plug and oil change. I would put in 10w-30 and change it after 1 hour to make sure all of the grey oil is oil. Then put in 15w-50 synthetic. I have read it burns less. Not sure if that is practically true?
A leak down test would be good but don't have one.
He said it ran with reduced power but good enough to mow his lawn. Even with a loose spark plug. I was amazed. He can not spend a lot of money right now. He just wants to keep it going good enough.

Thoughts?

nbpt100 said:

I am helping a friend on his riding mower with a B&S Power Built 500 cc Engine. He said it was running poorly and was smoking.

This is what I found.
Spark plug was loose and sooty
Battery cables were loose
One bolt on the valve cover was missing (broken off) and oil was leaking out and dripping on the muffler
The valve lash was in spec.
I removed the head and inspected it. The head gasket seemed ok. It is original. The head was sooty. The push rod chamber seemed relatively cleab. It did not appear the gasket was leaking in there. The bottom of the cylinder was slightly scored.

I need to check the head for flatness. If it is off a bit what can be gotten away with. Is there a thicker gasket available to make up for some warp? I am thinking ahead in case it is off a lot.

I never saw it run. I assume there is some higher oil burning. Probably livable. The smoke he observed is likely mostly from the oil dripping down on to the muffler from the valve cover.

What is causing the oil to turn grey? Is it all exhaust blowing by the rings? He has been using SAE30 and changed the oil every year. He has not changed it this season yet. I am thinking to change the head gasket, fix the broken bolt and put a gasket on the valve cover. New plug and oil change. I would put in 10w-30 and change it after 1 hour to make sure all of the grey oil is oil. Then put in 15w-50 synthetic. I have read it burns less. Not sure if that is practically true?
A leak down test would be good but don't have one.
He said it ran with reduced power but good enough to mow his lawn. Even with a loose spark plug. I was amazed. He can not spend a lot of money right now. He just wants to keep it going good enough.

Thoughts?

Click to expand...

Loose plug = lower compression
Lower compression = less power
Simple as that
grey oil will either be water or metal
Water is no problem
Metal means some thing is wearing out very rapidly

Thanks, what are your thoughts on using full Syn 15w-40 or 50 to reduce oil burning?

IMHO
Synthetics are a complete waste of money for mower engines
Oil burns because it gets past the rings &/or valve stems and enters the combustion chamber
Standard oil burns & leaves a carbon deposit
Synthetics blow out the exhaust un noticed till there is not enough oil left in the sump = bang .
Synthetics are designed for high output modern engines not anchient mower engines that have really not changed in the past 30 years .

bertsmobile1 said:

IMHO
Synthetics are a complete waste of money for mower engines
Oil burns because it gets past the rings &/or valve stems and enters the combustion chamber
Standard oil burns & leaves a carbon deposit
Synthetics blow out the exhaust un noticed till there is not enough oil left in the sump = bang .
Synthetics are designed for high output modern engines not anchient mower engines that have really not changed in the past 30 years .

Click to expand...

The reason I said full synthetic is because Brigg recommends their 15w-50 and it is full synthetic. I have only seen a few brands of 15w-50 oils and they have all been full synthetic. I agree, I would not use full synthetic in a small engine just becasue it is synthetic. It is contamination that is the issue not the oil breaking down. If you have an oil burner you should frequently check the oil and top off.
Are you suggesting leaving a carbon deposit is desirable.???? Yes? Please explain.

I can not help but to notice more and more small engine oil is synthetic.

Std oil $ 2 / bottle
Synthetic oil $ 10 / bottle
Which would you rather have 35% of ?
Synthetics are very good but putting them in an old engine will not make it run better
In fact putting it in a new engine will not make that run any better either
Being a thinner base , you will get more leaks overnight from that than from strait 30 oil
People stress about visible smoke and synthetics do not burn as easily so do not smoke thus the engine must be running better till of course it stops running al together.
Cheap oil replaced regularly is much better than expensive oil left in there for too long
Mower oil should be replaced every season , at the end of the season ( not at the beginning of the next one as most do ) .
Thus having oil good for 20 years is not any advantage
OTOH if it makes you feel better the go ahead

nbpt100 said:

Thanks, what are your thoughts on using full Syn 15w-40 or 50 to reduce oil burning?

Click to expand...

Where was this taught at? Go one level thicker on oil to combat burning, LOL. Just hit me. This is typical American logic. Engine manufacturer says SAE 30W. We all think hey go to 20W50 LOL.

nbpt100 said:

I can not help but to notice more and more small engine oil is synthetic.

Click to expand...

Around here it is getting a lot harder to get conventional oil. Most that is because they wanting to reduce inventory, plus they make more money on Synthetic. It is also push as an environmental friendly item.

Now I do use 15W50 synthetic in most small engines with oil pumps. The reason is it has a much better operating temperature range plus it reduces my need to stock multiple grades.

As the current engine problems. Loose plug was definitely a sign someone less has already been checking the engine. IF this is a 31/330000 series engine they are bad to blow the head gasket. Sometimes it may not appear to blown to the untrained eye. I tend to do a leak down test on these engine before even thinking about removing the cylinder head. It is a non invasive test that can determine if there is a cylinder problem or not. But once the head is remove it can't be without a new head a gasket. The engine could have been just running on a rich mixture due a leaky carburetor part.

Note: non invasive tests can save a lot of unnecessary work and parts.

Briggs recommends synthetic oil in certain conditions. 15w-50 synthetic in very warm temperatures. Synthetic 5w-30 in very cold to warm.



Currently, were I live the price difference between brand named dyno oils and some synthetics is about a dollar. The difference is not as large as it once was. I am not sure why? However, That is an other topic for a new thread.

I am trying to understand why this oil turned grey and what to do about it. Moisture perhaps?. How would the water get in the crank case? This is a 12 year old machine that has always been stored out doors under a tarp.
I am also trying to help him get some more use out of this engine. if in fact it is wearing out and the grey color is metal particles. Perhaps bearing journals or aluminum from the block. This engine is not sleeved.

He says it does burn some oil. That is hard for me to judge, as what does "some" means. I have read that the 15w-50 is good for oil burners. I do not know that for sure. This is why I am asking.

You can theorize that while it is in storage, more oil may leak in to the top of the cylinder and cause a lot of smoke at start up. While at temp it would not burn as much as it is at the 50 viscosity level. So it seem to be a bit of a trade off. It would lube critical engine parts better. Not smoke as badly or carbon up as badly. You know it is an oil burner so you do not need the visible and annoying reminder by having an exhaust cloud that people may complain about.

At this point, My thought process is to put the engine back together with new gaskets and solve the valve cover leak. Drain the old oil and replace with 10w-30(because it will drain better). Then run it for a short period. Observe and see if it gets grey again and how much it may smoke. Let it get hot and drain again to help flush the engine clean of any water, debris and old oil. Next I would fill with Briggs and Stratton 15w-50 or a 15w-40. I was toying with the idea of a straight 40 weight.

Finally, Why change the oil in the Fall and not in the Spring? Why does that make any difference? My curiosity has me on this one.

If it gets him through the season I think he would appreciate it quite a bit.

If you wait until Spring to change the oil then all the acids in the dirty oil will eat away slowly at the aluminum and over the years this may cause problems.
Changing it after the last use of the year and then running it for a short while before storing for the Winter will eliminate this potential problem.
Crud will also build up in the bottom of the crankcase if the dirty oil sits all winter.

And to add to what Chris has said.
The detergents can only hold the tiny solid bits of debris ( usually carbon ) against the force of gravity for so long .
Leave it sitting for a long time & it will form a sludge
On a car engine no problems because the oil pick up is above the floor of the sump
On vertical shaft engines the oil pick up is below the floor so that is where the sludge will accumulate .

No oil will destroy your engine
Oil is not morgage your house expensive .
So buy some & try it .
Make notes on your computer / phone
Next year buy a different one and see how it goes
When all is said & done, it is oil in the most primative engines currently being made

FWIW: Running an engine for only short intervals will accumulate condensation internally, that can eventually turn oil grey.

Engine must be run long enough to get full heat & burn out the condensation.

grey oil can also be STP type deposits (clay or ptfe) or non-detergent mineral racing oil. I saw so much of that sh_t when working in the machine shop. It makes clay like deposits everywhere. The idea with the non-detergent racing oil is it is supposed to get changed after every race. The STP was what ever they put in it, I dunno.

Grey oil indicates metal, likely from the Connecting Rod Big end. Use Standard 30 oil. Likely a lot of oil inside the muffler causing smoke, so contamination (Aluminum Alloy) may be coming from the Cylinder Wall.
Don't over think it. Keep your eye out for a good newer model. Tis the season!

Gord Baker said:

Grey oil indicates metal, likely from the Connecting Rod Big end. Use Standard 30 oil. Likely a lot of oil inside the muffler causing smoke, so contamination (Aluminum Alloy) may be coming from the Cylinder Wall.
Don't over think it. Keep your eye out for a good newer model. Tis the season!

Click to expand...

I will thanks. Going to make a new post requesting for ideas on what is a suitable repower engine. You always need a plan B.

bertsmobile1 said:

IMHO
Synthetics are a complete waste of money for mower engines
Oil burns because it gets past the rings &/or valve stems and enters the combustion chamber
Standard oil burns & leaves a carbon deposit
Synthetics blow out the exhaust un noticed till there is not enough oil left in the sump = bang .
Synthetics are designed for high output modern engines not anchient mower engines that have really not changed in the past 30 years .

Click to expand...

Yeah don't waste money on what you do NOT need....run a good quality oil that is spec'd by the manufacturer and with any piece of equipment look it over and check the oil level before firing up! thanks for everyone's input i reall enjoy the forum and have learned so much! Thank you for all those that have served and the ones that gave all!

Update: I replaced the head gasket, decarburized the top end. Set the valve clearances, Changed the plug and oil with SAE 30. Replaced the cooling fan as it was damaged. Then I ran it for 30 minutes mowing. It ran well.

After wards I checked the oil and it looked very clean.

The engine seemed to have plenty of power. the owner was happy.

I did notice the transmission acting was funky. It is a 7 speed on a TroyBilt Pony. I am not familiar with it but it seems like a variable speed as the shifter does not have detents. You slide the shift lever any where between 1 and 7. It seems to have slow speeds and high speeds. There is no medium speeds. In 1 thourgh 5 it is slow. Some difference in speed but not much. In 6-7 it goes fast. So It is slow or fast. While in the slow speeds it has little torque. It could not drive over small bumps. Seems Like it is slipping.

I dont know much about it. Any thoughts before I make a separate post about it.?

Belts are worn
Replace both of them