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  #1  
Old 12-05-2015, 11:15 AM
Scremm's Avatar
Scremm Scremm is offline
 
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Location: Eliot, Maine
Posts: 83
Default FP to CS Conversion Unintended Consequences

I recently converted from FP to CS and ran in to a bit of a problem?. I am sharing this in case someone else runs in to similar symptoms and in also to get community feedback.

Engine: O-360-A1A (one regular mag, one pmag, overhauled, currently w/ ~460 hours)
Governor: Jihostroj (New)
Stainless steel prop governor oil line (New)
Prop: Whirlwind 74 RV (New)

First and second ground runs had expected engine behavior and oil pressures. Logbooks updated, FSDO notified and first flight was ready to go.
On first flight, the oil pressure was initially normal on initial take off roll but after 160 seconds post take off start the oil pressure alarm went off while engine still maintained power. (The oil pressure alarm was set to go off at 25 psi.) I immediately reduced power and returned to land but before I could land the oil pressure got as low as 6 psi but then recovered to about 30. I?m thinking I would have an aircraft covered in oil but there was not a drip to be found. Therefore there could be an issue with the oil pump, prop governor, oil pressure sender, bearing or something entirely else.

In order of diagnosis over several weeks:
1. Inspect oil pressure relief valve bearing and spring ? looked normal. Adjust oil pressure relief spring by adding washers and going to heavier spring. The idle pressure was now 50 psi but adding power resulted in oil pressure drop, not rise.

2. Swap out oil pressure sender. No change in readings.

3. Disconnect prop governor oil line from prop governor adaptor and perform pressure leak down test. Results 39 over 40 and probably closer to 40 over 40. This is definitely outside the 3 to 36 acceptable range.

4. Drain oil and inspect oil filter, oil sump screen. No particles found. (I change the oil and inspect filter with every oil change and the filter has always been very clean.)

5.Remove prop governor and installed cover plate. Reconnected prop governor oil line. Ran up engine (with new oil and filter of course). The PSI at idle was stable (~50 psi with heavier spring) but adding power resulted in lower oil pressure dipping down to the 20s. Also, at high manifold pressure settings, the prop maximum rpm was ~1300.

6. Disconnected and capped off the prop governor oil line and capped off the prop governor adaptor. Now the oil pressure to the prop can only come from the #1 main bearing oil passage. Ran up the engine with the same results as before. This time I noticed that after the engine was shut down that the prop remained in full course pitch. The crank was not releasing the pressure.

7. Remove prop and inspect crank plug. Still solidly there.

My diagnosis:
After takeoff the main bearing shifted causing the oil from the #1 main bearing oil passage to have a free pass in to the sump, when the PSI reached the minimum, the bearing assumed another position resulting in a higher but still unacceptable oil pressure. Tests 4 and 5 isolated the issue to the front of the crankcase. With the current position of the bearing, the oil coming through the #1 oil port is pressurizing the prop but the clearance is so tight that it is not allowing pressure to be released. The bearing is also in such a position that it is also sapping PSI. Although the bearing has been seated fine for the prior ~460 hours, the additional oil pressure coming from the prop governor imparted a new force caused the bearing shift.
My problem seems to be very similar to this one seen by Bob Martin:

http://http://www.vansairforce.com/c...ad.php?t=45821

Next steps:
I?ve already talked to an engine shop but they haven?t yet reached the same conclusion.
Step back and take a break for a while?..Then likely remove engine and determine root cause and damage. I think the likely cause is an undersized bearing. The damage may be crank case halves may need to be reworked, crankshaft may be damaged, and the main bearing is most certainly junk.
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N221Z RV8A Maine 600+ hrs

Last edited by Scremm : 12-05-2015 at 11:18 AM. Reason: Change title
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  #2  
Old 12-05-2015, 11:34 AM
Pat Stewart Pat Stewart is offline
 
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This may be a dumb question but is the front plug removed and the back plug still in.
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  #3  
Old 12-05-2015, 12:00 PM
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Yes. The front plug was removed and the back plug is in.
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  #4  
Old 12-05-2015, 12:14 PM
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Adding graph of first take off. Ten second intervals.



Adding graph of final engine run w/ prop governor disconnected.
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  #5  
Old 12-05-2015, 05:28 PM
aerhed aerhed is offline
 
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Have you verified this with an analog gage?
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  #6  
Old 12-07-2015, 07:49 PM
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I used two different pressure senders and got the same readings. With the other symptoms I am pretty confident the problem is at the front of the crankcase.
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  #7  
Old 12-07-2015, 09:03 PM
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RV6_flyer RV6_flyer is offline
 
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Default Lycoming SI 1462A

Typically I would do Lycoming Service Instruction 1462A when the governor is unable to maintain set RPM.

I do not understand your reduction of oil pressure so would end up doing SI1462A just to make sure that the rear plug is sealed correctly.
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  #8  
Old 12-07-2015, 09:20 PM
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Quote:
Originally Posted by RV6_flyer View Post
Typically I would do Lycoming Service Instruction 1462A when the governor is unable to maintain set RPM.

I do not understand your reduction of oil pressure so would end up doing SI1462A just to make sure that the rear plug is sealed correctly.
And make sure the orifice in the compression tester used is sized at 0.040 to use the go/no go numbers in the SI.
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  #9  
Old 12-08-2015, 04:31 PM
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Scremm Scremm is offline
 
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The governor was able to maintain set RPM when it was installed. When I removed the governor from the engine it was to try and isolate the issue and that is when I saw the strange low RPM behavior at higher power settings. In theory without oil pressure to the prop it should have acted at fine pitch and I should have been able to reach max RPM.

I am pretty sure I have the correct diameter orifice. I've also visually and physically inspected the crank plug and it's solidly in there. Plus the prop didn't release pressure and remained full coarse when the engine was shut down so it is really keeping the pressure in the crank in place.
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  #10  
Old 12-08-2015, 05:24 PM
Pat Stewart Pat Stewart is offline
 
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I seem to remember an old discussion about the gasket for the prop governor and that it can be installed wrong and cause similar issues. This is just a guess and may not add any value.
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