I appologize in advance for this long winded story, but I don't know of any better way to describe the problem.

My grandfather has a Sabre lawn tractor from the mid 90's with a 17hp B&S engine. The muffler is mounted in the front of the tractor, below the engine. For the past few years, when the engine is started, translucent plumes of smelly grey smoke billow from the muffler for the first 5 or so minutes of use, then they go away. We figure that this is caused by a small oil leak, as the oil level never drops below the "full" range during the season.

A few weeks ago, my grandfather started cutting the lawn, when after a couple minutes the muffler suddenly spewed a cloud of opaque, thick grey smoke, and the engine quit. It would not restart until the engine cooled off. He asked me to take a look at it. When I started the tractor, this event repeated itself. The smoke was so thick that I thought the engine was on fire - but it wasn't. I started taking it apart and discovered that the air filter compartment was coated with oil. I figured that whatever was causing the small oil leak of the past few years had become a catastrophic problem which would be beyond my skills to fix. Then, my grandfather mentioned that he added oil after he used it last time because he thought it was too low. I checked the oil and discovered it was WAY too high. I drained the oil to the correct level, at which time the mower started working again as it had before.

Now this is where the mystery starts. He proceeded to cut the yard with the tractor without problem. However, when he went to cut the yard again a week later, the the tractor quit again after 2 minutes with the cloud of opaque grey smoke. He tried it twice more with the same result, and was ready to throw in the towel. Today, he finally told me what had happened. I stopped over to see if there was anything else I could do. I figured that the internal parts of the engine finally gave out after being subjected to the excess oil levels. I check the oil to make sure he hadn't added anymore, and it was OK. So I started it and began to drive it around and cut the lawn, waiting for that inevitable cloud of grey smoke and the engine to die. The thing is, the engine never died and the muffler didn't smoke. I cut half the lawn before deciding that the engine was not ruined.

We are not sure what to think. Anyone have any ideas what would cause the engine to quit one day, but not the next?

 

Being a 17-horse, it should be an overhead valve engine and, if so, I suspect a slightly blown head gasket. Specifically, the area between the valve chamber and the combustion chamber probably has a small breach in the gasket. Or, perhaps, your grandpappy has mistakenly added oil each use when he may not have had to. 4 or 5 ounces of overfilled oil will result in the cloud of smoke you've encountered. Post back with the engine model, type and code numbers.

 

Thank you so much for your help! I called him up and got the information you requested:

15 HP OHV ( I was wrong about 17 HP)
Model: 28N707
Type: 0635 A1
Code: 9510264A

After the first "overfill" incident, I drove home the point that he should never add oil and that I will check it when I visit at least once a month. Thanks again!

 

I was able to get the parts list for the engine and have ordered the valve overhaul kit #495992, which includes the head gasket. Do you think new gaskets will solve this problem. Thanks again!

 

I do believe that we're on the right track but this is not the only possibility of the source of the smoking. Bear in mind the difficulty in diagnosing a job unseen. For what little the cost of the upper end kit you purchased and, provided you can perform the labor, you really can't go wrong. If when you remove the cylinder head you don't think that this is the trouble, be sure to post back with such suspicion before proceding any further.

 

Thank you for your help and patience. I've finally had a chance to look through past threads with similar problems and have gleaned a lot of information about replacing the head gasket as well as other possible (but less probable) causes of this problem. I was wondering if you knew how much torque the head bolts require for this engine?

 

220 inch pounds, head torque. Valve clearances will be .005", by the way.