'How To' Yamaha oil pump testing

[Arrow]

The cams can be worn out if specification, but drastically different rates of wear on the two lobes is quite rare. More like a sticking condition for some reason.

Sent from my SM-G973F using Tapatalk

[so-cal-sdr200]

I wonder if I could push the pump by hand
on the short stroke?
Need another guy, or, a third hand.
One to hold the drill, one to hold the throttle and
 one to push the pump piston.
 Or take it apart for inspection...
Thank you again.

[Arrow]

Sure, take the nut off and the large washer. Turn the shaft by hand. Gives you more time to see whats going on. Please report back, does it stay in or spring back?

Sent from my SM-G973F using Tapatalk

[so-cal-sdr200]

Yes. It seems to be sticking on every other stroke.
 On the short stroke, I can push it in / down with my fingers.
This is with the throttle plate turned to max.
 The stroke does not feel smooth.
I assume on the down ( pump ) stroke I should be able to
cycle the shaft in and out freely.?
I am guessing at idle, up to maybe 1/2 throttle the pumping
should be roughly equal. Am I of the right mind?
Guess it's got to come apart.
EBay has a NOS one for $300!!! Yikes.
 I'll get back in a day or two.
Cheers, Jeff

[Arrow]

I assume on the down ( pump ) stroke I should be able to
cycle the shaft in and out freely.?
I am guessing at idle, up to maybe 1/2 throttle the pumping
should be roughly equal.

Yes, and;

Should be equal at all throttle settings.
Most unusual how there is so much difference in 180°.
My work is never done......

Sent from my SM-G973F using Tapatalk

[Arrow]

I'll be honest with you, I don't see issues like this after pump builds. All the parts are reworked and inspected/measured. The pumps are built like a mathematical formula, always the same. Formula's are always the same, unless changed. Once we have the same formula, and measured values within specification, the end result is always the same. Only if the formula is changed or a measured value out of spec. is the end result different.
2+2=4, Always.

Sent from my SM-G973F using Tapatalk

[so-cal-sdr200]

Thanks.
 I want to apologize to Chuck for hi-jacking his thread.
 Was not my intent.
 I will create a new post for any follow ups.
 Arrow, you did not rebuild my pump, so no fault of yours.
 I am curious what the issue is and anxious to learn the inner
 workings of these things.
 As a retired aerospace engineering designer I guess it is in my
nature to dissect problems and figure out solutions.
  on....

[Arrow]

Correct, I didn't build your pump. Chuck won't mind useful dialogue, I'm sure. All helps.

I'm in Aerospace myself. For now anyway.
Covid has caused many issues for us. Might loose my job shortly......

Sent from my SM-G973F using Tapatalk