Skymaster Forum  

Go Back   Skymaster Forum > Messages
Register FAQ Members List Calendar Search Today's Posts Mark Forums Read

Reply
Thread Tools Rate Thread Display Modes
  #1  
Unread 12-12-21, 09:52 PM
Jhogan0101's Avatar
Jhogan0101 Jhogan0101 is offline
Registered User
 
Join Date: Mar 2019
Location: Philadelphia
Posts: 121
Jhogan0101 is on a distinguished road
Gear Issues 337B

Having some gear issues…

-Gear started to cycle slowly.
-This plane has the optional rear gear pump installed
-Took plane out of service for some avionics replacements, its been out of service for about 11 months.
-Trying to get the plane back up and running now.
Recently:
-Both front and rear hydraulic screens were cleaned, not a lot of debris.
-Front nose door actuator was leaking, actuator was removed, rebuilt, reinstalled
-While actuator was removed, alot of hydraulic fluid came out of the system
-New hydraulic fluid was filled after actuator was reinstalled, filled until started to pour back out.
-Manually pumping the doors open/closing is normal, no leakage.
-While doing some test runups, no flights, after shut down, there is quite a bit of hydro fluid on belly coming out of the hydro vent on the front/belly of the plane. This was without touching the gear handle at all.
- Next time running up, while idling at 1200 rpm on both engines, i pressed the gear handle down. It took any where from 5 to 10 secs for it to snap back up to down neutral. During this, hydraulic fluid was dripping from the vent, i confirmed before that the fluid was halfway on the site glass in reservoir.
- While flying i had to physically hold the gear lever up to complete the gear retraction, had to hold gear handle down to complete gear deploy.

Not really sure whats going on here, my a&p and ia are also stumped. Any ideas as to what might be happening? The power pack was rebuilt about 100 hours ago by previous owner.
__________________
337B
Philadelphia PA

Last edited by Jhogan0101 : 12-12-21 at 10:04 PM.
Reply With Quote
  #2  
Unread 12-13-21, 12:51 AM
wslade2 wslade2 is offline
Registered User
 
Join Date: Feb 2016
Location: none
Posts: 184
wslade2 is on a distinguished road
I also have front and rear engine driven pumps. Had a similar experience. Long story short, air was getting sucked into the system. If seal is leaking at either pump, it can suck air in, mix it with the fluid and foam it up. Foamy fluid compresses easily and makes actuation soft. Foamy fluid appears to “boil over” out vent tube. Beware possible leak on suction hoses and any fittings on the suction side. O rings Teflon backup rings also suspect. Also learned these pumps are not self priming. Be sure they’re primed while going through everything. Lastly discovered the backup of having twin pumps was no good because the check valves had 50 yrs of crud in them. Imagine a failed pump with check valve that won’t completely close allowing pressure to bleed off.

I would examine both pumps carefully. I created a vacuum device with hand brake bleeding vacuum pump to assess for suction leakage. But didn’t get to use because I discovered my front pump running dry after a run up where I had primed it. Ended up having both pumps rebuilt not simultaneously which lead to discovery of check valve problem. After pumps and suction side examination, do the check valves. One in rear wheel bay and other by power pack interior side of firewall as I recall.

For good measure I replaced all pump hoses, o rings and backup rings.

Last edited by wslade2 : 12-13-21 at 03:54 AM.
Reply With Quote
  #3  
Unread 12-13-21, 01:15 AM
wslade2 wslade2 is offline
Registered User
 
Join Date: Feb 2016
Location: none
Posts: 184
wslade2 is on a distinguished road
You can ground test each pump by observing system performance rear engine only and then front engine only running.

Also as I recall, manual recommends 3 cycles of gear after service on jackstands to be sure air is out.

I also rebuilt front actuator and had to top off multiple times.

You can also run the pumps while on jackstands using a drill. Splined socket from harbor freight fits the pump shaft.

While looking at that front wheel well area there other actuator in there that can leak, the uplock actuator and main gear actuator. If one is leaking, the others may be in same shape too.

To prime the pumps, I filled them manually while turning the prop. I put a hose on the power pack exterior vent and blew on it while cracking the suction line at each pump. Don’t run the pumps dry and unprimed. It’ll ruin the seals and you’ll have to start all over again. (Ask me how I know.)

Last edited by wslade2 : 12-13-21 at 04:01 AM.
Reply With Quote
  #4  
Unread 12-13-21, 04:20 PM
Jhogan0101's Avatar
Jhogan0101 Jhogan0101 is offline
Registered User
 
Join Date: Mar 2019
Location: Philadelphia
Posts: 121
Jhogan0101 is on a distinguished road
Ok thanks for the info wslade2, we’ll try the things you mentioned. Hopefully thats it.
__________________
337B
Philadelphia PA
Reply With Quote
  #5  
Unread 12-14-21, 12:40 PM
Jhogan0101's Avatar
Jhogan0101 Jhogan0101 is offline
Registered User
 
Join Date: Mar 2019
Location: Philadelphia
Posts: 121
Jhogan0101 is on a distinguished road
Update:

When front engine only running handle/doors behave normal

When rear engine only running, doors will open/close slow. Handle will not snap back to neutral.

Check valves were opened/cleaned no debris.

Swapping hydraulic pumps (front with rear)today to see if problem follows pump
__________________
337B
Philadelphia PA
Reply With Quote
  #6  
Unread 12-14-21, 08:26 PM
Jhogan0101's Avatar
Jhogan0101 Jhogan0101 is offline
Registered User
 
Join Date: Mar 2019
Location: Philadelphia
Posts: 121
Jhogan0101 is on a distinguished road
Problem solved:

Rear intake/return fitting on rear pump was loose. The nut holding the o ring was not tight. The pump was sucking in air and mixing it with hydraulic fluid. We replaced the o ring and resealed. Crisis averted.

__________________
337B
Philadelphia PA
Reply With Quote
  #7  
Unread 12-14-21, 09:34 PM
wslade2 wslade2 is offline
Registered User
 
Join Date: Feb 2016
Location: none
Posts: 184
wslade2 is on a distinguished road
Awesome! Cheap and easy. How did it get loose? Not tightened enough first time? Or aging of the o-ring and back up ring made it loose compression/tightness. Maybe a prophylactic front o-ring change due too?

In the video....is that fitting not exactly straight and lined up or is that just an illusion? Could that be contributing to the initial failure? Doesn’t look like the compression nut is completely flat. Might just be my imagination not seeing it in person.

Last edited by wslade2 : 12-14-21 at 09:39 PM.
Reply With Quote
  #8  
Unread 12-14-21, 09:43 PM
Jhogan0101's Avatar
Jhogan0101 Jhogan0101 is offline
Registered User
 
Join Date: Mar 2019
Location: Philadelphia
Posts: 121
Jhogan0101 is on a distinguished road
Smile

I think illusion, definitely wasn't cross threaded when removed. I think the nut got loose overtime, hoses were replaced in 2019 annual, possibly wasnt tightened down 100%. That Annual was 85 hours ago, noticed gear slowing down maybe 15 hours ago. But yeah, im glad its an easy problem to fix and didnt lead to a catastrophe. Thanks for your help with this.

Have a Merry Christmas and a Happy New Year!
__________________
337B
Philadelphia PA
Reply With Quote
Reply


Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is Off
HTML code is Off
Forum Jump


All times are GMT -4. The time now is 04:49 PM.


Powered by vBulletin® Version 3.6.9
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.