M20 Hydraulic Pump Flap Diagram

[Nukemzzz]

9 hours ago, N201MKTurbo said:

But it does seem to maintain a stable rate after it is adjusted. Maybe there was a method to their madness.

For some reason the engineers used a large diameter adjustable flat orifice to control the retract flow. This is very sensitive dimensionally.  The flow could have been controlled more precisely with a conical or needle valve up or downstream of the ball instead of trying to integrate it into the ball pre-load and capture system. They may have had their reasons, i just can't see it...perhaps because I haven't tested the designs that I have in mind to discover the issue they saw.

[N201MKTurbo]

28 minutes ago, Nukemzzz said:

For some reason the engineers used a large diameter adjustable flat orifice to control the retract flow. This is very sensitive dimensionally.  The flow could have been controlled more precisely with a conical or needle valve up or downstream of the ball instead of trying to integrate it into the ball pre-load and capture system. They may have had their reasons, i just can't see it...perhaps because I haven't tested the designs that I have in mind to discover the issue they saw.

What you propose would probably work better, but it would require a bigger, heavier pump with more parts and more machining operations. Maybe their goal was to save weight and money? After all we are talking about something that is done rarely, takes a minute or two longer to adjust than a more elegant solution and works perfect after adjustment.

[LantisPDX]

Thanks for all the advice that was given. I ended up on an extended trip to San Diego in the plane so I have not had a chance to work on the flaps.  I will be working with my mechanic to recoin the 3/16" ball when I return, as I agree, it really sounds like the problem spot. We had tried to recoin it at the time but I think we need to be a little more aggressive. 

I am excited to get home and to get the flaps working correctly! 

[M20F]

On 4/14/2020 at 12:15 AM, Nukemzzz said:

By uniquely qualified I mean...

I’ve been a mechanical engineer for diesel fuel injection systems for 18yrs. 6 of those years leading the development and launch of these systems into Europe. 2yrs Prior to the 18 I was a service engineer explaining to technicians around the world how to troubleshoot Diesel engines (creating diagrams and steps like attached...but more professionally done...not in PowerPoint). The 9 years before that I was a certified auto/diesel technician. My current job is an engineering reliability leader and manager for the same systems. The majority of this current job consists of engineers presentIng to me their troubleshooting of design failures trying to convince me that they know what went wrong and how to fix it (answer is often no...lol). 

I stayed at a Holiday Inn Express last night.