Oil Pump Anatomy

[Wheelman-111]

Greetings:

Scooterwerx said he'd "fudged" his pump attempting to disassemble/inspect it. (Despite Honda-san's stern warning "do not attempt to dismantle.... said pump.) What did you learn? Has anyone else tried to do this, and what did you discover? The Service Manual is no help at all. Honda engineers probably figured the less we knew, the better...

How long does/did a tankful of oil last on average, in relation to tankfuls of fuel? That would give me some idea of what Honda's 2-Stroke mavens believed was the ideal fuel/oil mixture ratio.

[mousewheels]

The oil pump is clever piece of engineering. I took apart a non-variable pump last year, and its been sitting in a bag as 'spare parts'. So tonight, out came the bag for a photo.

--- How it works ---
The entire cross shaft oscillates. At the left end of the cross shaft is a cam. On this pump, the cam bears on a little steel pin in the pump housing. The metering piston stays fixed against the steel end cap by the spring. There's 2 oil ports internal to the shaft bore that the rotary valve operates as it turns.

The entire rotating/oscillating shaft gives the pump and intake an exhaust stroke once per revolution of the cross shaft. But with that worm drive its much reduced from the engine revolutions.

I recall from past threads, the oil pump is around 40:1 to 50:1, with adjustable types going up to 80:1-100:1 at idle. But don't go on my memory - do the search!

[Wheelman-111]

Greetings:

Nice job! Thanks!

[scooterwerx]

the oil tank lasts for a long time...depending on how much riding you do couple months probably. i filled mine once, rode it for about a month and a half then killed the pump and went premix.

[Wheelman-111]

Greetings:

So nearly impossible to calculate the volume of that oil squirt from the tiny piston, and even more uncertainty due to the unknown gear ratios from crank to cross shaft and worm-drive to cam. Wow! Honda-san keeps his secrets.!

And last, the squirt of oil is deposited as a droplet of unknown volume into the air intake near the reeds, there to be aspirated with the incoming mixture stream from the carb? What a way to run a railroad. Curiously effective nonetheless.

[mousewheels]

So nearly impossible to calculate the volume of that oil squirt from the tiny piston, and even more uncertainty due to the unknown gear ratios from crank to cross shaft and worm-drive to cam. Wow! Honda-san keeps his secrets.!

Direct way is to measure consumption.

Substitute the fuel and oil lines, prime the lines, then attach a container with 100ml of gas, and use a disposable syringe (5-10cc) filled to an appropriate starting point for the oil side. Start it up and drive flat out (under 2mi at 70mpg) until the gas down to the bottom of the container, and measure the level left in the syringe.

[Bear45-70]

Or just remove the pump and use a drill motor (the drill will have an rpm rating) to run the pump and measure the results. Then calculate for any rpm you like. I however would use oil and not gas as the oil is what lubes the pump when it is running and is much denser than gas and won't explode if it gets hot from being pumped.

[maddog]

did you know there is a filter screen at the oil tank exit which biulds up bacteria, now you no bra cuz if it don't flo from the tank da pump no can pump- shoots you gettm now

[noiseguy]

I think that the oil consumption for the engine as a function of RPM is listed in the service manual for the scoot.

[Wheelman-111]

Greetings:

I have a paper copy of Honda-san's 85-'87 Aero Service Manual. I have found no reference to oil consumption therein.