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Discussion Starter · #1 ·
I'm doing a top end rebuild on a 440EX and was talking to a ATV mechanic, and he recommended I replace the oil pump as well. Do you usually replace them on a rebuild? A little more back ground for yah. I just bought this 400 off of a friend not sure of the maintenance that has been done previously and also I had a float issue when I bought it causing the fuel to get in the oil when it sat and the fuel was left on. I have done 3 oil and filter changes since I bought it to get the oil back to a normal color. It was a dark grey/milky color due to the fuel in the oil. I see the internals of the pumps are metal and not sure how often they need to be replaced. Thx in advance.
 

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I am a mechanic also - here's my personal opinion:

Starting with the gas in the oil; gas will not turn oil a milky color. It just thins the oil and will, with heat and over long enough time, most of the dilution will eventually evaporate out of the oil, but draining and refilling is the best solution. On the positive side, it will really clean the inside of the motor.

Now for the "milky" oil; water causes the oil to turn milky. The detergents in the oil cause the water to emulsify into the oil, trapping it so it will be carried out of the engine when the oil is changed. The emulsified water can also be evaporated out of the oil during normal long term operation. There is a vent hose on the engine connected to the carb air duct. Vapor from the crankcase is drawn through a baffle box, connected to the intake tube and ultimately passed through the combustion chamber. Keep the water out of the oil by regular oil changes using with the JASO rating or having an API rating of SJ or lower.

I have replaced only a few oil pumps in 40 years of working on motors where the replacement was necessitated due to damage, wear or lost parts. The rest of the 15 to 20 oil pumps I have replaced was for performance or just because I thought it was a good idea. Most oil pumps will outlive the life of the engine unless damaged by lack of maintenance or foreign material (dirt). If it makes you feel better, put a new pump in.

By the way - fuel can get in the oil even if you don't have a float issue. The petcock was installed so you can stop the flow of fuel to the carb - use it.
 

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Discussion Starter · #3 ·
I am a mechanic also - here's my personal opinion:

Starting with the gas in the oil; gas will not turn oil a milky color. It just thins the oil and will, with heat and over long enough time, most of the dilution will eventually evaporate out of the oil, but draining and refilling is the best solution. On the positive side, it will really clean the inside of the motor.

Now for the "milky" oil; water causes the oil to turn milky. The detergents in the oil cause the water to emulsify into the oil, trapping it so it will be carried out of the engine when the oil is changed. The emulsified water can also be evaporated out of the oil during normal long term operation. There is a vent hose on the engine connected to the carb air duct. Vapor from the crankcase is drawn through a baffle box, connected to the intake tube and ultimately passed through the combustion chamber. Keep the water out of the oil by regular oil changes using with the JASO rating or having an API rating of SJ or lower.

I have replaced only a few oil pumps in 40 years of working on motors where the replacement was necessitated due to damage, wear or lost parts. The rest of the 15 to 20 oil pumps I have replaced was for performance or just because I thought it was a good idea. Most oil pumps will outlive the life of the engine unless damaged by lack of maintenance or foreign material (dirt). If it makes you feel better, put a new pump in.

By the way - fuel can get in the oil even if you don't have a float issue. The petcock was installed so you can stop the flow of fuel to the carb - use it.
Thank you, oil pump will stay.
 
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