SonexBuilders.net

Hi, all
Yesterday my Sonex #1430 flew for the first time. Steve the test pilot said the plane performed very well and is easy to control. After about 7 minutes in the Air at 1800 feet a low oil pressure alarm came up. The Engine oil pressure went down to below 20psi. Steve was only 3 miles from the airport and did a straight in landing. He came in vast and height but with side slipping he dropped the plane down quickly and landed safely. (That is the reason I have an experience test pilot) Just after landing the oil pressure came good. Today I had a look at the 2 plunger for the Minimum and Maximum oil pressure. I had some trouble to get the rear plunger out. It was sort of stuck a bit. The plungers had some wear markings on it. One of the things I notice both plunger springs are almost the same diameter as the plungers. The plungers got a flat bottum hole in it, I was wondering if the spring should have been smaller and fit in the hole. During the flight the oil pressure went up to max 42psi. I am planning to make the plungers slightly smaller (0.001"). Max. CHT 200C. No damage done on the Engine.
Has anybody has this problem?

Peter Bakker,
Aerovee 2.1, Sonex #1430
South Australia

You probably need to polish the rough edges on the rear plunger. Mine got stuck and sent the pressure high enough to cause a leak in the oil cooler which lost all the oil and seized the engine and forced an off field landing. On tear down I found the rear oil pressure plunger stuck in the closed position to the point that i had to use a screwdriver to wiggle it free. I used some scotch bright to smooth the plunger until it would not stick in the galley. On the second rebuild (Nicasil cylinders) the plunger fell free when I pulled the plug and spring.

Thanks Bill, can you remember what size spring is fitted on/in the Punger. Is the spring sitting on the bottom edge or in the hole of the plunger? I had low pressure problem. The spring what is sitting on the edge of the plunger can scrape and damage the galley, this can make plunger to stick causing loose of oil pressure.

I'm pretty sure the spring didn't fit inside the plunger but rather pushed on the shoulder of it but frankly it's been a while since I had it apart. Remove any burrs you find on the spring as well as the plunger. I don't recall any problems with the spring, just the plunger.

wlarson861 wrote:I'm pretty sure the spring didn't fit inside the plunger but rather pushed on the shoulder of it but frankly it's been a while since I had it apart. Remove any burrs you find on the spring as well as the plunger. I don't recall any problems with the spring, just the plunger.

I've seen some springs with sharp edges where the wire ends ... I clean them up on the grinder wheel so they don't protrude
wider in diameter than the spring itself.

RT

Good Idea

I do believe this topic needs to be addressed at some depth as I do believe that it represents a safety issue. The under mounted oil cooler is directly downstream from the oil pump. I believe that it renders the oil cooler very susceptible to rupture due to do over pressurization during startup especially at lower temperatures. Because it is directly downstream of the well pump, elevated pressure within the under slung oil cooler is not well protected by the bypass valves within the engine. My wife and I recently had a near miss in which we had lost approximately 1.2 L of oil and only noticed it upon landing. The topmounted oil cooler, I believe is the only safe way to go.

We designed and built our own top mounted adapter plate incorporating the BDO oil pressure sender. It seems to function very well and although we do observe an approximate 3-5° C increase in operating oil temperature, by closing off the under mount oil cooler ports, I believe we are seeing lower cylinder head temperatures due to increased differential pressure between the high and low pressure sides of the engine cowl.

Rory Belanger
Sonex 1102

wlarson861 wrote:You probably need to polish the rough edges on the rear plunger. Mine got stuck and sent the pressure high enough to cause a leak in the oil cooler which lost all the oil and seized the engine and forced an off field landing. On tear down I found the rear oil pressure plunger stuck in the closed position to the point that i had to use a screwdriver to wiggle it free. I used some scotch bright to smooth the plunger until it would not stick in the galley. On the second rebuild (Nicasil cylinders) the plunger fell free when I pulled the plug and spring.

That was my experience on a rebuild. I previously couldn't get more than 31 psi, and usually it was around 29 psi (20 psi while taxiing) for well over 100 hours of operation with no ill effects. Still it never seemed like enough. When I rebuilt the engine after a prop strike I did notice that one of the two plungers was sticking. I polished it, and the hole in the case, with emery cloth and then Scotchbrite. Now I get 38-39 psi, which isn't as high as some, but far better than it was, and plenty for a VW.

May not be related to your problem but you should check the pressure with a manual gage as well. The vdo oil pressure senders aren't exactly known for their reliability.

Keith
#554

[quote]That was my experience on a rebuild. I previously couldn't get more than 31 psi, and usually it was around 29 psi (20 psi while taxiing) for well over 100 hours of operation with no ill effects. Still it never seemed like enough. When I rebuilt the engine after a prop strike I did notice that one of the two plungers was sticking. I polished it, and the hole in the case, with emery cloth and then Scotchbrite. Now I get 38-39 psi, which isn't as high as some, but far better than it was, and plenty for a VW.
Mike Smith

I would suggest either an adjustable plunger(available from Great Plains) or experimenting with a few washers under the spring to boost the cruise oil pressure.