sudden INCREASE in oil pressure

[n502pd]

Maybe an old subject, but I have had in the last several hours, another incident of very high oil pressure.

I had landed after an uneventful 30 min flight after condition inspection, shut down, chatted with airport bums for about ten mins, restarted with some difficulty (probably heat soaked fuel supply as this was the first time I had stopped for such a short time), and taxied to runup and take off again. Durring initial stages of run up, oil pressure began to climb well above of 100 psi. I aborted and returned to hanger.
After cooling with a fan, I investigated pressure plunger/pistons,valves. Rear one was good as it slid right out, and wasnt stuck. However the front was different. It need to be coaxed out with a wooden dowel. I found very small particle in the bore when cleaned. Not aluminum and not steel, so I dont know what it was. Opened the oil filter...nothing inside...changed oil...again nothing.

Here is what I surmised. the spring end under the piston...not on the silver plug that is screwed into the block...sits on the bottom of the plunger in the top of the block bore, and is not centered in the bore because the bottom of the piston has a curved surface where the spring coil contacts the piston. Since the spring isnt captured on bore centerline by the piston, the top coil of the spring is free to move latterally in the bore and will contact the surface of the bore. That contact can, and appairently has, scuffed off small parts of the bore surface, and has caused the piston to hang, thereby causing higher than normal pressure. I suspose low oil pressure might be caused by the same senario, but I have not seen that personally.

So my questions here are, how many others have run across this pressure malfunction? And, what have you done about fixing it so as to not happen again, other than the careful polishing of the piston? Further, has anyone actually discovered bore particles from the cleaning of the bore, or marks in the bore, as I have on my first happening with the rear regulator piston,and again on the front piston, and what was the fix? Did the fix last? The first time was at 17 hrs tt, and the 2nd was at 30 hrs tt. Using Valvolene 20-50 vr1, and fram hp3 filter, changing at 25 hrs. Nominal press 62-70 psi hot, max temp seen 190 or so.

Thanks for any input!

Joe

[lutorm]

the spring end under the piston...not on the silver plug that is screwed into the block...sits on the bottom of the plunger in the top of the block bore, and is not centered in the bore because the bottom of the piston has a curved surface where the spring coil contacts the piston. Since the spring isnt captured on bore centerline by the piston, the top coil of the spring is free to move latterally in the bore and will contact the surface of the bore. That contact can, and appairently has, scuffed off small parts of the bore surface, and has caused the piston to hang, thereby causing higher than normal pressure.

Both of my oil control plungers are shaped like upside down "buckets" where the spring sits inside the bucket and presses against the inside of the top surface. (They look just like these. The plugs also have a raised centering ring that the spring sits around. It is not possible for either ends of the spring to touch the bore. Are you saying you have plungers with a flat bottom where the spring just sits against the surface without any centering? Are you sure you haven't mounted the plungers upside down so the spring is pushing on the sealing face?

[tx_swordguy]

Hi Joe,
James who you met in Arkansas has a revmaster with the adjustable relief valve/oil filter assembly. His two relief valves were taken out and replaced with the above set up. He had a similar occurance prior to us leaving for OSH. I pulled his relief valve and polished it up as it was a very rough ground piston. I found a similar particle as you describe. It was a particle that almost looked like a small broken pencil lead. After polishing and cleaning the valve cylinder we got it working again however I saw no marks in the cylinder. The spring fits inside the piston so it does not move around as you describe. It is designed just like the ones lutorm had a pic of. Outside of polishing and making sure the cylinder is clean I don't know of a way to keep that from happening.
Mark

[n502pd]

I am very sure I have the pistons installed with flat surfaces up, into the case bore. Pistons were polished well, and bores cleaned and inspected as well as possible. The picture lutorm showes a differewnt type than what Sonex supplies. I have reordered a second set just to make sure I have the latest parts. the new ones are exactly the same as originally supplied with my engine 3 years ago. Indeed, the bottom lip of the pistons...both front ant rear...is radisused/rounded, and the spring is ground flat on both ends in an attempt to give the spring a flat surface to rest in. the springs do not come close to fitting inside the pistons, and are free to roam from side to side within the block bore. I have no idea of how often they roam, or move, but they are not secured at all from doing so. so, because the springs are not secured on centerline of the bore, by the pistons, and are able to roam, creates the basis of my concerns.

I will look into the item shown in the picture. My current, installed fix is to have fabricated an aluminum plug fitted inside the piston, with a reduced diameter protrusion below the botton of the piston, the diameter of which tightly captured the first coils of the spring, and holds the the spring in coaxial allignment with the diameter of the piston, thusly elliminating any possibility of the spring roaming into the bore walls. To date, ground runs have shown no adverse effects. The alumimum plug has a 1/8 in dia hole drilled lengthwise to prevent any movement of the plug away from the piston due to trapped oil being heated inside the piston.Actual flight tests have been precluded by extream high temps durring the days, with todays temps around 102, heat index near 107. I most certianly plan to fly several flights to reconfirm ground run indications.

Thanks to you both for the comments, and the picture!

[Onex107]

Take a close look at the ends of the spring wire. Mine were cut off pretty sharp and if they contact the wall they could scratch it. A little Dremmel grinder touch up made them smoother.

[n502pd]

I have absolutely looked and treated the last coil end of the spring. Mine were almost knife edged, and slightly larger than the spring overall diameter. However, even with the removal of those sharp protruding ends with the Dremil tool, I still had a second occurance of a stuck piston. I will surely report back in the future with reguard to my little fix for securing the upper end of the spring. I have not securred, sideways, the bottom of the springs because they sit on the flat surface of the plug/nut item, and the spring if it does move latterly, wont scrape the side of the bore because most all of the springs compression-height change is quite further up in the bore, closer to the piston. I would have designed the spring to be of such a diameter as to fit inside the piston. However, I am reluctant to 'hunt' the world for a suitable spring and do testing, long term, while airborne, and have complete failure of the unknown spring. I am aware of the formulae used for spring design, and with suitable testing I might be able to find one that fits, but i still would not trust the metalurgy of the spring in the first place. The supplied springs do work, its that they are not secured properly to the piston, that seems to cause this problem, IMHO. Thanks for the hint !!

Anyone interesteed in pictures, please PM me and I will email them!

Joe

[n502pd]

UPDATE! recently I tested different rear piston regulator spring strengths, using a spring manufacturers program to identify their closest spring inventory. I calculated, and thru ground testing, a spring length that allows for slightly shortening the standard spring by one turn. Initial testing on standard spring, cold OP was over 80, hot was something near 65 at 2000 rpm, using 20w-50 oil. with modified length spring, cold OP was close to 70, hot was 62-65 psi, hot idle about 40. I have about 2.5 hours flying time sinse installing short spring, along with spring to piston centering item inside piston, as mentioned earlier, and WOT climb to 5500 feet showed pressures very steady at 65, cruise at 62+, temp at 180 F, 2900-3000 rpm, and no hint of any upward movement. Also, and this may be the actual fix, I installed a very strong dc motor magnet on the drain plug externally, because there is not room inside for a store bought magnetic plug and those have a very weak magnet anyway. Further, I installed another very strong magnet to the oil filter can. These will remove any magnetic particals from the oil, and appear to have elliminated those particles from jambing the pressure regulator piston.

With that, I recommend anyone with worries of very high OP fine stron nyobium(sp?) magnets and safty wire them to the drain plug and filter can if there is a filter installed. My concerns so far have been greatly reduced about blowing an oil cooler at a very inappropriate time. Let me know what you all think!

Thanks! fly safe, greasy side down when landing!