Mailing List flyrotary@lancaironline.net Message #63754
From: Lehanover@aol.com <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: RX-8 Oil Pump Replacement
Date: Sat, 30 Sep 2017 13:05:48 -0400
To: <flyrotary@lancaironline.net>
Part of the answer is oil pump wear. I suspect that Mazda does not make some of the equipment found in Mazda engines. Years ago I found that oil pump end play could be way out of spec. So I started with new pumps (when we still used stock pumps) and shortened the pump body to the minimum allowed dimension.
 
The other part of the problem is that the rotors in the engine tend to foam the oil to excess. So from a long period where entrained air has escaped the oil over a night or a week of no use. Then you see good oil pressure on start up, then as you see oil temperature come up and oil foaming comes on during climb out, the oil pressure drops away.  Foam in oil is air bubbles. Air is compressible. So the peak oil pressure is no longer available. Also air in the foamed oil in the pick up expands to satisfy the lower pressure in the suction side of the pump. This reduces the volume of oil the pump can acquire to pressurize.
 
There are a number of items in play here. One is the oil brand, pour weight, recipe, and application of the oil.
Racing oils have additional additives that reduce foaming. Racing oils have additional anti scuff compounds.
Better for cold starts and engines that sit for long periods between uses. Racing oils have much higher film strengths than conventional oils. Racing oils absorb heat and give it up more quickly than conventional oils. Do you see a pattern here? Remember that duty cycle thing? Start the car engine. Drive away on ice cold oil. Don't turn over 1,800 RPM ever. Listen on shutdown as the condensate from the warm engine runs down into the sump. The first to be pumped to the bearings just before the cold oil on the next start.
 
Or, start the rotary powered plane. Warm the oil a bit. Take off and climb out with the front rotor never quite full of cooling oil, and the rear rotor over filled and foaming like crazy. Now turning up 3 times the street RPM
all of this was designed for. Synthetic racing oils can be used in rotaries. You must premix the fuel as  synthetic sump oil will not burn without gumming. Use a synthetic 2 cycle oil as a premix or inject it with a modified pump.  I use RedLine 50 weight in the sump (Dry sump) and 2 cycle RedLine in the premix.
 
While inspecting at annual, you can remove and inspect the stationary gears. Just do not move the prop while the gears are out (one at a time). Then at least you can inspect and measure the main bearings, and reinstall the stationary gears. Metal in the filter makes the hair on my neck stand up.
Not one oil relate failure since 1980.
Lynn E. Hanover
 
     
 
In a message dated 9/30/2017 11:35:07 A.M. Eastern Daylight Time, flyrotary@lancaironline.net writes:

Has anyone experienced low oil pressure due to wear of the Renesis oil pump?

 

My Renesis engine on my RV-7 has had decreased oil pressure for a while.

 

I changed the oil pump and now my oil pressure is back to normal.

 

I have 780 hours on the engine and about 2500 engine heat cycles – most of my flights are very short.    On takeoff with relatively cool oil the pressure went to 80 PSI but as the oil heated up the pressure decreased to as low as 65 psi on a hot day during climb out.

 

I change the oil at 50 hours  I always inspect the oil filter material and had some very small shiny flakes in the pleats.  The particles appear to be non-magnetic

 

A month ago I decided to remove the engine and replace the oil pump.

 

I found the aluminum oil pump housing had a slight amount of wear where the steel  pump gear seals against the housing.   Replacing the oil pump has resulted in much better oil pressure.

 

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