Murry lawn tractor Model 40604B

[Harold2689]

Hello!

I have a Murry lawn tractor, Model 40604B, manufactured: 0272. It has a 12HP Briggs & Stratton engine. It was running perfectly, when suddenly it started running very rough, and at the same time, started blowing blue smoke out of the muffler. I removed the "hood" and shroud of the mower to gain access to the engine, and found the spark plug and the muffler both LOOSE. I also removed the upper air cooling housing from the engine, and found the cooling fins around the cylinder, and the area around the head, packed with mice nesting material! After cleaning all that out, I noticed that the bottom third of the head seemed to be "wet" with oil. After changing the spark plug, and tightening the muffler, the engine started up, ran for about 30 seconds, billowing blue smoke all the time, and gradually running rougher and rougher until it died again. I removed the cover over the valve springs, and "thin" oil poured out. By thin, I mean gasoline mixed with crankcase oil.

I'm thinking possibly a blown head gasket? What say you guys? I cannot locate a manual for either the engine or the mower.

Thanks in advance for any light you can shine on my problem, and any help or suggestions you may be able to offer.

Harold

 

[Rivets]

Sounds like you have more than one problem. From what you posted you have a blown head gasket and the float needle is not seating properly, allowing raw fuel to run into the crankcase. Please post you engine model, type and code numbers and I should be able to provide you with a service manual. Also include the name on the engine ie, Vanguaard, Intec, I/C.

 

[Harold2689]

Sounds like you have more than one problem. From what you posted you have a blown head gasket and the float needle is not seating properly, allowing raw fuel to run into the crankcase. Please post you engine model, type and code numbers and I should be able to provide you with a service manual. Also include the name on the engine ie, Vanguaard, Intec, I/C.

I wish I had that info. All I have is that the engine is Briggs & Stratton. It's marked 12 HP on the lawn tractor, not the engine. It's a single cylinder, vert shaft, electric start engine. That's all the technical specs I have right now, and that's not much to go on. I'm sure there's a plate somewhere on the engine, but I haven't found it yet. It was my mom & dad's, and I inherited it when Mom passed several years ago. They bought it used, and it ran perfectly until the last time I used it.

I was thinking head gasket, but I wanted input from you guys. It's not at my house, so I'll have to see if I can locate more info on the engine next time I go over there.

Thanks so much for your input.

Harold

 

[Rivets]

The engine numbers are stamped on the shroud, either on top by the spark plug or on the side.

 

[Harold2689]

The engine numbers are stamped on the shroud, either on top by the spark plug or on the side.

yeah, They're usually on a tag, but I didn't see them when I looked. I'll swing by tomorrow and have another look...

 

[Harold2689]

The engine numbers are stamped on the shroud, either on top by the spark plug or on the side.

Ok, I stopped by today and discovered why I didn't see the numbers before.


Here's the engine cooling shroud. I was looking for an aluminum tag riveted to it.


They were actually stamped into it...


THAT'S what I was looking for...


See the bottom quarter of the head is black? It's oil residue.


When I removed the cover over the valve springs, oil thinned with gas poured out.

I'm pretty convinced the head gasket is blown, and I'll start with that. I need to get a complete gasket kit, and we'll see if there is still a leaking gas problem. There wasn't until the head gasket blew, so I don't know if there are two separate problems, or just the one.

Any info you can provide will be greatly appreciated. Now that I have the model number, I'll see what I can find on line.

Thanks again,

Harold

 

[Rivets]

Stop, I DOUBT THE HEAD GASKET IS BLOWN!! The number of times I've seen a blown head gasket on that engine you can count on one hand. You are going to have to do a little more investigating. I'm leaning toward a bad sump gasket or seal around the dipstick tube. Clean and dry the block around the base very good and then coat the entire base area, where the crankcase and sump meet, with baby powder. Spray or puff it all around, light coat. Let it sit for a day and then check for leaks. The powder will tell you where the leak is. To check the seal on the dipstick tube, check to see if you have oil there and it is loose. Don't purchase anything until you know where the leak is, as you may be wasting money. Just my opinion. This manual might be of some help.

https://drive.google.com/file/d/0B6NaqjIxWV1ycG8wd0s3Z2Q2X00/view?usp=drive_web

 

[Harold2689]

Stop, I DOUBT THE HEAD GASKET IS BLOWN!! The number of times I've seen a blown head gasket on that engine you can count on one hand. You are going to have to do a little more investigating. I'm leaning toward a bad sump gasket or seal around the dipstick tube. Clean and dry the block around the base very good and then coat the entire base area, where the crankcase and sump meet, with baby powder. Spray or puff it all around, light coat. Let it sit for a day and then check for leaks. The powder will tell you where the leak is. To check the seal on the dipstick tube, check to see if you have oil there and it is loose. Don't purchase anything until you know where the leak is, as you may be wasting money. Just my opinion. This manual might be of some help.

https://drive.google.com/file/d/0B6NaqjIxWV1ycG8wd0s3Z2Q2X00/view?usp=drive_web

Wow! I was all set to go for the head gasket! Would a sump gasket cause the same symptoms as a blown head gasket? I'd have thought if that gasket was a problem, it would just allow crankcase oil to spew oil all over the place, but wouldn't cause the engine to billow blue smoke. Somehow, I think engine oil is getting into the combustion chamber, and from the amount of smoke, I'd say quite a bit. The engine was running just fine when this happened quite suddenly, as if something actually failed. The spark plug, when I removed it, was actually loose, and the business end was wet, and fouled with oil.

I don't have any specialized tools to do some of these tests or replace some of the parts, except for a torque wrench to torque the head bolts. I don't have the leak-down tester, but do have air compressor. I wonder if I could find the leak by just pressurizing the combustion chamber via the spark plug hole and listening/observing for leaks.

Thanks for the link to the manual. It's a LOT more info on this engine than I had.

This may turn out to be a bigger project than I first thought...

 

[Rivets]

Remember I said you may have a couple of problems, well I was wrong. I think you only have one problem, that is a bad carb float needle and seat. It will explain all your symptoms. When the needle stop sealing off the flow of fuel into the float bowl, the engine started running rich. Stumbling, smoking, and getting so rich it killed the engine. All the while you were tightening the plug, muffler and cleaning the fins, raw fuel kept running through the carb into the crankcase, thinning the oil. When you started it up again the breather sucked up the misty mixture and pumped it into the cylinder, giving the smoking situation to start again. That being said I would suggest you have the carb cleaned and rebuilt, changing the oil and filter while it is being done. Clean the cooling fins, which was probably the cause of the plug and muffler coming loose, reassemble everything. That should solve your problem. If this unit came into the shop with these symptoms, that is what we would do. That carb is not one I would recommend an amateur try to rebuild. Just my opinion which some members think is to expensive and you should just put a band aid on it, by installinga shut valve in the fuel line. Your choice.

 

[Harold2689]

Remember I said you may have a couple of problems, well I was wrong. I think you only have one problem, that is a bad carb float needle and seat. It will explain all your symptoms. When the needle stop sealing off the flow of fuel into the float bowl, the engine started running rich. Stumbling, smoking, and getting so rich it killed the engine. All the while you were tightening the plug, muffler and cleaning the fins, raw fuel kept running through the carb into the crankcase, thinning the oil. When you started it up again the breather sucked up the misty mixture and pumped it into the cylinder, giving the smoking situation to start again. That being said I would suggest you have the carb cleaned and rebuilt, changing the oil and filter while it is being done. Clean the cooling fins, which was probably the cause of the plug and muffler coming loose, reassemble everything. That should solve your problem. If this unit came into the shop with these symptoms, that is what we would do. That carb is not one I would recommend an amateur try to rebuild. Just my opinion which some members think is to expensive and you should just put a band aid on it, by installinga shut valve in the fuel line. Your choice.

Ok, I'll look more at the carburetor. What you say makes sense, and does provide an answer as to why the oil is diluted with gas. I'll start by taking the bowl off of the carb and check the float to see if it cuts off the fuel flow. There is a manual fuel shutoff valve and an in-line fuel filter between the fuel tank and the carb, but I never use it to shut off the fuel flow.

This problem seems a lot simpler than the head gasket, etc., and if it is the problem, I'll leave well enough alone, and won't take the head off at all. I will need to buy or make a few gaskets to replace those for the intake, exhaust, and the one for the breather cover over the valve springs. It will be a few days until I can get back there to work on it, but I will definitely keep this thread updated.

Thanks so much for all of your help and advise.