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Oil intrusion.

#1

P

Picknlittle

Command 17.5 CV491S engine. Last use, the engine began smoking heavy, and engine choked out. Owner thought the head gasket was blown. I replaced the head gasket, (but found no evidence of damaged gasket) and upon startup it smoked heavy, then began to clear after several minutes. I moved to mower to all it to clear completely, then started smoking and stumbling again. Under no load it would clear, only to repeat.
After it cooled, tried again. Runs perfectly for about 5 minutes, then starts smoking, losing power.


#2

R

Rivets

Check the oil level, I’m willing to bet that you will find that it is overfilled and smells like gas. If I’m correct your problem is that the float needle in the carb is not seating properly, allowing fuel to flow through the carb into the crankcase. Time to clean and rebuild the carb.


#3

P

Picknlittle

Rivets said:
Check the oil level, I’m willing to bet that you will find that it is overfilled and smells like gas. If I’m correct your problem is that the float needle in the carb is not seating properly, allowing fuel to flow through the carb into the crankcase. Time to clean and rebuild the carb.
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I'll check that, but would expect fuel rich exhaust. Oil level was in safe range before I replaced the head gasket, and after topping off before startup, it still is.
I am wondering if the mechanical fuel pump could be allowing intrusion, but the cool/warm conditions puzzle me.


#4

R

Rivets

If the oil level is correct, I will lose the bet. There are there ways for oil to enter the cylinder. One, past the rings, which I doubt given what you post. Two, through the carb, which is not happening if I lose the bet. Three, head gasket failure, possible if not installed or torqued correctly.


#5

P

Picknlittle

Rivets said:
If the oil level is correct, I will lose the bet. There are there ways for oil to enter the cylinder. One, past the rings, which I doubt given what you post. Two, through the carb, which is not happening if I lose the bet. Three, head gasket failure, possible if not installed or torqued correctly.
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Well, it's a mystery indeed. Oil level is fine, no rich fuel condition at any time. Original head gasket was intact, and showed no signs of leakage. Certainly not the kind of leakage to allow this level of intrusion. Starts immediately cold or warm. Starts acting weird 5 to 7 minutes after startup. Raw oil is intermittently getting into the intake somehow.
Just very odd!


#6

R

Rivets

When you changed the gasket, how did the valves look? Any oil residue on the intake valve? If no, what did you torque the head bolts to?


#7

P

Picknlittle

Rivets said:
When you changed the gasket, how did the valves look? Any oil residue on the intake valve? If no, what did you torque the head bolts to?
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Looked good. Required very little cleaning of head or piston. No scoring on cylinder wall. Nothing out of the ordinary. And, at startup, it's immediate. No wind up as you'd expect with low compression. This is baffling! I thought about my earlier fuel pump question. But if that were true, all fuel in the outlet line and in the carb bowl would be contaminated! Something else is going on.


#8

P

Picknlittle

Picknlittle said:
Looked good. Required very little cleaning of head or piston. No scoring on cylinder wall. Nothing out of the ordinary. And, at startup, it's immediate. No wind up as you'd expect with low compression. This is baffling! I thought about my earlier fuel pump question. But if that were true, all fuel in the outlet line and in the carb bowl would be contaminated! Something else is going on.
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Add:. The intake and carb had lots of oil within, so yes there was oil on the intake valves. Specs called for 15 then 30 lb/ft. That's how they were torqued, and if the new head gasket was the issue it would lag at startup from compression loss.


#9

R

Rivets

If oil is in the carb, the only way it can get in there is through the breather tube. Try two things for me please. First, unhook the breather tube from the carb and run the engine. If the engine runs clearly, you will probably find oil being blow out the breather tube. If this happens, you are building too much pressure in the crankcase. Normally two possible causes. Failure of the breather or blown head gasket. Then try this, unscrew the dipstick and allow it to sit loose on the dipstick tube. Start the engine and observe the dipstick. If it starts bouncing around, this would be an indication of blown head gasket.


#10

P

Picknlittle

Rivets said:
If oil is in the carb, the only way it can get in there is through the breather tube. Try two things for me please. First, unhook the breather tube from the carb and run the engine. If the engine runs clearly, you will probably find oil being blow out the breather tube. If this happens, you are building too much pressure in the crankcase. Normally two possible causes. Failure of the breather or blown head gasket. Then try this, unscrew the dipstick and allow it to sit loose on the dipstick tube. Start the engine and observe the dipstick. If it starts bouncing around, this would be an indication of blown head gasket.
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Thanks. I'll check that tomorrow.
This is exactly what happened to the previous owner his last use. That's why I went straight to replacing the head gasket, but the gasket looked fine.


#11

P

Picknlittle

Picknlittle said:
Thanks. I'll check that tomorrow.
This is exactly what happened to the previous owner his last use. That's why I went straight to replacing the head gasket, but the gasket looked fine.
Click to expand...
Well indeed, there is a lot of crankcase pressure, so there is a good deal of blow-by present. I wanted to see how much oil was blowing out. Stuck the breather end of the breather tube on a bottle and started it up. After a couple minutes it started pumping a steady flow. About 8 oz in roughly 20 seconds! But no exhaust smoke, and no low compression start-up signs. Add that when this happened the first time, it was following a dealer service, and happened suddenly. Just started smoking and choking out!


#12

P

Picknlittle

Finally contacted Kohler and spoke to a fella in the tech dept. Described what the original user told me about the failure and what I'd found, or not found. He said since it happened suddenly, and there is no scoring of cylinder wall, and no blown head gasket there was one more tiny thing that might cause it. On the cylinder head is a small reed valve that may have a piece of carbon or other debris, blocking the reed valve from closing. No guarantees, but worth checking. Welp, it's running fine now. Head scratching is over for now. Thanks.


#13

Fish

Fish

I have a sister-in-law that smokes a lot when she is drinking,
but that is another subject...


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