Craftsman riding mower with 21hp Briggs motor

[ruSSrt]

Purchased it used couple of months ago and it ran good with no issues. Used it last week to mow the lawn for about 45 minutes with no issues. Today I decided to change the oil and used some Chevron 10w-30 conventional oil I had sitting around. After filter and oil change I went for a ride and thing started to smoke like crazy! Huge plumes of smoke at times, but then it would run okay. On lower RPMs it'll smoke a little, but at full RPMs it would be fine.
Reading up on those mower sounds like Briggs and Stratton 21Platinum motors are notorious for bad head gaskets. Could new oil do something with head gasket? Or was it just perfect timing?
It has half of tank of 5 month old fuel with stabilizer. I also just added a little MMO to make it more "fresh".

 

[Bailes1992]

Sounds like you've overfilled it.

 

[Lubener]

I believe it is stated in the manual that using 10w-30 will increase oil consumption but yours is somewhat extreme. Headgaskets have been known to fail, hard to believe yours could have failed so quickly after an oil change. I haven't had any head gaskets fail on my Briggs 24 HP after 12 years yet. I use SAE30 in mine and use very little oil.

 

[CharBaby]

Possible overfilling of oil?
Too much MMO in the fuel?

Just asking,

CB

 

[FT92]

sure sounds like overfilled the oil check that first

 

[Eddie]

I have the same 20hp B&S twin in my JD. I run 10w30 T5 oil and no smoke. That engine takes ~ 2 quarts of engine oil. ed

 

[metroplex]

FWIW the newer B&S use synthetic 5W-30.

 

[MParr]

Could be you over filled it. The B&S manual calls for SAE 30 HD. It says that using 10W30 can result in oil consumption.

 

[jeepman3071]

If you have noticeable amounts of smoke something is wrong like overfilled oil, a leak, or blown head gasket. The whole "10w30 can result in consumption" wouldn't make that much of a difference, unless this engine smoked before and the previous owner filled it with 75w90 gear oil.

 

[WyrTwister]

Originally Posted by Bailes1992
Sounds like you've overfilled it.



That would be my first guess .

 

[tig1]

I have a 9 year old Craftsman with the 21 HP engine which has had a blown head gasket. There is a narrow area in the head and gasket that will separate and causes the smoke. I had mine replaced, but when, not if, it blows again I will do it myself. There are U tube videos on the subject.

 

[Eddie]

The latest B&S recommendations are 5w30 Synthetic. Other options are 10w30 or 30 or 15w40? for commuscal use. I oped for 10w30 Synthetic Rotella synthetic and my engine uses a few ounces between 40 hour oil & filter changes. As said before, you may have over filled or someone had put a very heavy oil in to mask a consumption problem or ??? Ed

 

[gman2304]

Just run it at WOT for a while, it should clear up. Next oil change run 30 wt or 15w40 HDEO.

 

[4WD]

Originally Posted by metroplex
FWIW the newer B&S use synthetic 5W-30.


Got B&S syn in my 19HP and 7.25 walker (both Sears/Briggs) … I'm running low (it was clearance oil) and will use only in pull start so 19 HP goes back on Delo 10w30 this summer.
I get a little smoke if it has not been started for a month … but even my 44 hour Yamaha does that.
If I run it weekly there is no smoke ever.
(sidewinders engines, all)

 

[ruSSrt]

I checked oil when filled and didn't look like I overfilled. I only put about 1.6 quart.
I thought if possibility of glug of MMO getting straight in to the carb. I will double check it all today and see.
Also one thing I forgot to mention is steam/smoke coming from oil fill tube after it runs for a bit.

 

[CT8]

I also just added a little MMO to make it more "fresh". How would MMO make the gas more Fresh?

 

[JTK]

Yep. Like said, the vertical shaft V-twins tend to tell you right away if the sump was overfilled. Oil gets blown out the valve cover breathers, into the intake and into the carburetor.

I've seen situations many times where if the machine is parked nose-down for any period of time such that the valve covers and heads are positioned lower than the oil sump, the cam covers load up with oil and it gets blown into the carb upon restart. Sometimes I takes a few seconds or longer to present itself.

 

[Astro_Guy]

I've found that my B&S V-Twin needs to sit on level ground for two days before it gives an accurate oil level reading. If you top it up right after running it then you will overfill it.

 

[ruSSrt]

Originally Posted by CT8
I also just added a little MMO to make it more "fresh". How would MMO make the gas more Fresh?

I have nothing to base it on and it's what makes me feel better

but my thought it MMO is detergent and lubricator. So if gas been sitting for a while I think MMO will help with lubrication of the carb/cylinder while gas is not being burned 100%. Plus I think if there is anything stuck in carb then hopefully MMO will break it loose and clean it out

 

[ruSSrt]

Originally Posted by Astro_Guy
I've found that my B&S V-Twin needs to sit on level ground for two days before it gives an accurate oil level reading. If you top it up right after running it then you will overfill it.

Leaving it in the garage for couple of days while my new gasket is on the way. And double check it when it arrives. Checked it this morning and it was perfectly halfway where is suppose to be