Oil pump question

[Hunterb]

I am in the process of reassembling my 1997 787 motor and I'm having a heck of a time with the oil pump. I put all new lines on and, after a mighty struggle, got the supply line bled and, eventually, the little lines to the intake bled as well. During this process I had the pump in and out of the boat and connected and disconnected several times. My question is a about the position of the cam at idle and full throttle. The way I'm understanding this pump is when the throttle is at idle the cam is rotated against the spring so there is tension in the spring. As the throttle is increased the spring in the cam causes the cam to rotate and increase flow. So if the cable broke or fell off the pump would 'default' to full flow. Is that correct? Because I've had this thing on and off and disconnected a bunch of times I've managed to confuse myself.

 

[JeremyD615]

The cable pulls against the spring tension. As you open the throttle the cable moves the arm, and when you let off, the spring returns it to idle. The safety is in that the spring has enough tension in it to move the lever past the closed position and back to the wide open position if the cable were to break. That’s a hard concept to explain, so ask away if you need me to come up with a better way to describe something.

 

[Sportster-2001-951C-Stock]

It's supposed to flow maximum oil if cable breaks. (fail safe design).

 

[Hunterb]

The cable pulls against the spring tension. As you open the throttle the cable moves the arm, and when you let off, the spring returns it to idle. The safety is in that the spring has enough tension in it to move the lever past the closed position and back to the wide open position if the cable were to break. That’s a hard concept to explain, so ask away if you need me to come up with a better way to describe something.

Thanks for the reply. I'm still a bit confused by where the cam shouid be at idle. Tomorrow I'm going to put the carbs back on and will hook up the cables and see how it looks. I hope it's right. I bought this ski from a guy who said it 'ran great last weekend but for some reason won't start now. I think the carbs need cleaning'. Turns out the rotary gear was stripped requiring the motor to be disassembled, during which I found the pistons were cooked so a total rebuild was in order. That's why I'm a bit worried about the oil pump and how it's set up. I've never seen this motor run. HaHa. Hoping to see it do so soon.

 

[JeremyD615]

They’re pretty self explanatory when you get everything back on. You’re going to rotate the arm against the spring tension and attach the cable. Then you just adjust to line up the marks at idle. Make sure that once you get the idle screw set to your desired rpm, you recheck the marks and readjust as necessary...

 

[Sportster-2001-951C-Stock]

If you question the oiling system is functioning, you can run pre-mix in the fuel tank while working out any bugs. If the carburetors are working properly, the lubrication will be carried by the fuel into and throughout the crankcase.

If the pistons were roasted, it may have been caused by carburetor issues, oiling system issues, or just too many hours. All 2-strokes will eventually destroy pistons if not rebuilt before it happens.

Most often a 2-stroke is damaged early in it's life by lean detonation (carburetor/fuel system issues), this will certainly shorten their life dramatically, especially at high power loads where great amounts of heat are generated. An overheated piston due to the lean air/fuel mixture will destroy the oil film, leading to more heat.

Lean hesitation, falling on it's face and stalling like it ran out of fuel is the primary indicator of fuel system issues. On the flip side, too much fuel is also not a great thing b/c it tends to wash away the oil film and power is reduced b/c combustion is incomplete.

Think of air/fuel mixture as dancing on the head of a pin, in terms of too much or too little fuel. It's better for the 2-stroke engine to be slightly on the fat side but not so fat it loses power due to incomplete combustion.

Fortunately if the fuel system is working properly and adjusted according to the factory settings, these engines run great and last many hours.

As an example, this image shows the 717/720 engine oil pump, the red circle highlights the alignment marks of the pump lever arm and pump body which should be parallel at throttle idle position. Adjust the oil pump cable accordingly and check it periodically, especially after adjusting idle speed..

 

[Hunterb]

They’re pretty self explanatory when you get everything back on. You’re going to rotate the arm against the spring tension and attach the cable. Then you just adjust to line up the marks at idle. Make sure that once you get the idle screw set to your desired rpm, you recheck the marks and readjust as necessary...

OK. Thanks. I was a bit confused because I watched a couple of videos and people said to hold the cam in the wide open position but if the cable is disconnected it's already in the wide open position... I think. I will hook it up today and look really closely at it to make sure it's right before I try to fire it up.

 

[JeremyD615]

With the cable detached, the cam will be in the wide open position. If the cable is attached, you will have to turn it by hand to get it to that position...

 

[Hunterb]

With the cable detached, the cam will be in the wide open position. If the cable is attached, you will have to turn it by hand to get it to that position...

That's what I figured. Now I'm totally confused on how to align the bracket on the carburetor. I disconnected the plates rather than taking the cables out and losing the adjustment. Now I have the throttle and choke cables hooked back up but the oil pump cable has me baffled. I have the throttle and choke cables attached to the Mag carb, which looks right, but the oil pump cable bracket which I assume attaches to the PTO carb, has me confused. This comes back to my original question about the orientation of the cam. If it is full flow at full throttle and full flow if the cable is disconnected then, at idle, the pump cam should be rotated against the spring pressure. Then when you accelerate the oil pump cable should actually get 'longer' in order for the cam to rotate to a 'higher flow' position.
I'm so confused.

 

[JeremyD615]

Remember that it’s a cam, and not a screw type valve. As you rotate the cam counterclockwise, it moves from no flow to progressively higher flow. If you keep rotating the cam past the point of its max flow rate, it goes back to zero and starts all over again. The static position of the spring, as if the cable broke, is at the max flow position, and as you put tension on the spring you rotate past that point to the idle, or low-flow position, and the cable pulls against the spring tension to keep the arm moving in unison with the throttle. If the cable were to break, the arm would rotate by spring tension alone and travel back towards the idle position, and then past it, back to wide open. Does that make sense?

 

[Hunterb]

Remember that it’s a cam, and not a screw type valve. As you rotate the cam counterclockwise, it moves from no flow to progressively higher flow. If you keep rotating the cam past the point of its max flow rate, it goes back to zero and starts all over again. The static position of the spring, as if the cable broke, is at the max flow position, and as you put tension on the spring you rotate past that point to the idle, or low-flow position, and the cable pulls against the spring tension to keep the arm moving in unison with the throttle. If the cable were to break, the arm would rotate by spring tension alone and travel back towards the idle position, and then past it, back to wide open. Does that make sense?

OK. That helps. Thanks for helping me out. I think the problem I'm having may be related to the pump cam and spring. I'm going to pull the pump back off and look closely at it. Right now, when I pull on the cable it will rotate a little more than 1/2 way and then it hits a hard stop which I'm not sure is right. I had trouble with the spring when I was struggling to bleed the lines and may have messed something up.
Thanks again for the help. I'll let you know what I find. Right now I'm Taking a break because I'm totally frustrated with it and that's not a good frame of mind to be working on it.

 

[Hunterb]

Success!! I had my son look at and he figured it out. The spring was in the wrong spot and was preventing the cam from rotating far enough. It's all fixed now and looks correct. Thanks to all those who replied.
After getting this done we figured out that you cant get the exhaust in with the engine in place, which it already is. Crap. It's taking me a long time to reassemble this engine.