pkpatrick

B&S 7HP tiller getting oil into carb

I have an eight year old Craftsman tiller with a 7 hp B&S engine, no. 121402-0194-E1, which ran great ubtil this spring. As usual, I changed the oil and air filter and began tilling. After about 30 minutes, the engine started smoking badly. I thought I may have over-filled it with oil, but when I checked it is was actually a little low but milky looking. I changed it and began tilling again and the same thing happened. The next time I tried to start it, the pull rope broke as the engine seemed locked up. I replaced the rope and removed the spark plug and saw oil on top of the piston. The engine then spun freely. I see that the oil is coming through the breather tube into the carb. I removed the rocker cover and head and when I pull the rope, oil shoots out the oil supply hole with much force. Does this appear to be bad rings or possibly a bad diaphram in the rocker cover?

cheese

Sounds to me more like a blown head gasket.

pkpatrick

Thanks. Cheese. That had crossed my mind. With the head removed I sealed the top of the cylinder with my palm and gave her a pull oil shot out the oiler port. I think I'll finish tearing it down and replace the rings and head gasket. Do you know how to tell if the diaphram is bad?Beer 4U2

cheese

Are you talking about the breather? I don't know of a diaphragm in the valve cover.

pkpatrick

Well, the owner's manuel calls it a rocker arm cover. There is a small, metallic diaphram on the inside. I was thinking it may have been damaged by the pressure if the head gasket blew. It looks like itr is integrated into the cover, so I'd have to replace the whole thing. Should I have pressure or vacuum under the cover? I picked up a new gasket today and will replace it within the next couple of days.

cheese

That's a reed valve. It should be fine. I've never seen one damaged unless someone physically tampered with it.

pkpatrick

I replaced the head gasket, fired her up, ran great for about two minutes. The the breather hose started shooting oil again. I didn't have it connected to the carb, so it continued to run until I shut it down as I was losing a lot of oil. Looks like a lot of ptrssure is building up in the crank case. I may try just plugging the hose and see what happens. Couldn't hurt as it appears the cylinder wall may be cracked anyway. Thanks for your help, Cheese.

cheese

Did you look at the condition of the cylinder walls when you pulled the head off? Also, could the engine be revving too high? Does the oil smell like gas, or is it too full of oil?

pkpatrick

I plugged the breather tube and the tiller runs fine. After about 5 minutes at a slow idle, it begins to smoke badly and oil is now oozing from several places on the engine, including the valve cover. The pressure is building quiet high in the engine as when I shut it off and remove the oil filler plug, oil shoots out. I have changed the oil again and filled to the proper levell. It becomes almost foamy when it gets hotand when it cools, the level drops in the crankcase and it again looks normal. The cylinder walls look normal and the oil doesn't smell like gas. Thanks.

cheese

The oil gets foamy? If so, that is a sign of too much oil. Does it have a dipstick? The oil should not foam no matter how hot or how long it has run. How much oil did you put in it?

pkpatrick

It does not have a dipstick so per the owner's manual, I have always filled the crankcase to the point of overflowing. It holds about 2/3 quart, and I've always used a high-grade SAE-30 ND oil such as Pro-Mix 4-cycle oil.

cheese

It should hold 20 oz of oil. The only thing I can figure is maybe the engine is being operated at a pretty good angle? I don't really recommend using ND oil. I don't know about the brand oil you are using, so I can;t say, but it could be that since it doesn't have detergents, it may also not have anti-foaming agents? Not sure. I doubt that's the problem, but thought I'd mention it.

pkpatrick

I fixed the tiller today! I replaced the motor with a brand-new one and all is well again. When I have more time, I'll throw the old one on the bench and disassemble it and see if its worth rebuilding. Meanwhile, thanks for yor suggections, Cheese.