10 years ago I installed a Subaru EA-81 in my experimental catagory aircraft, a Rans S-7 Courier. This engine was professionally converted for aircraft use by Stratus Inc., the fleet hours number in the tens of thousands, with many units in the field (or over it, as the case may be) with well over 1,000 hours of trouble free operation. My own is one of them, at 1215 hrs TT I have had zero problems, compression is as good as new, oil consumption is nil, and power is also as good as new. BUT, I recently cut a filter open for inspection and the engine appears to be "making metal", non-ferrous metal flakes were readily apparent in the folds of the filter.
The engine, due to its out -in-the -slipstream installation, cools very well, too well in fact perhaps. My oil temps are often only 140 degrees, sometimes as high as 165, but rarely. I have been using Castrol 20-50 and change it and the filter every 50 hours.
Question: Have I been using too thick an oil in the tight little Subaru, perhaps impairing proper crank lubrication? What viscosity oil would be suitable for this situation? I will soon (later today) be dropping the pan to inspect the crank bearings and hope to find out where the metal is coming from. I will also be getting the results of an oil analysis within a couple days.
Tom
Subaru in a airplane
- Thread starter TOM SIMKO
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Tom, sounds like you might be onto the problem. 20W-50 would be really thick at those temps and that maybe your problem.
Why not make a partial cover for your crankcase so that your oil runs in the 180 to 200 range? That would put the 20W-50 at more reasonable viscosity.
Even at 180-200F oil temps it sounds like 15W-40 HDEO would be more than thick enough, or you could run a good synthetic.
[ March 24, 2004, 06:36 PM: Message edited by: XS650 ]
The usual reasons, weight and drag, are why I would like to keep it as is. BTW the installation can be seen at www.skylinesolar.com, click on the "about us" page, and then they'll be an aviation link at the bottom of that. I was also told by a local gearhead who's opinion I respect that a synthetic may be my best option.
Tom
I would try a thiner oil and then do another UOA. Did you send out a sample? Are you running automotive lubricants or aerospace lubes? I doubt that 20W50 is the root cause of any problem but it is worth trying a lighter weight! 140F-165F really is not that warm and 20W50 definately is not needed under those conditions.
If you have multiple UOA as well as this most recent one send them Terry and let him take a look at it! It is money well spent if he spots a problem or if he says to continue use!
[ March 24, 2004, 10:11 PM: Message edited by: TheLoneRanger ]
The difference bad UOA results from an aircraft and from a car.
Bad UOA from a car: That's interesting.
Bad UOA from an aircraft engine: WTF!!!
I burn unleaded auto fuel, in an extremem emergency I may buy just enough 100 LL to get me to the next mogas outlet, maybe 15 gallons av gas in 1200 hours. Thats good to know however if I ever change my fueling practice.
quote:Tom, I'm posting a direct link to your homebuilt page because people -have- to see the part about your runway! http://www.skylinesolar.com/seewhatifly.htm You da man!
Originally posted by TOM SIMKO: The usual reasons, weight and drag, are why I would like to keep it as is. BTW the installation can be seen at www.skylinesolar.com,
The usual reasons, weight and drag, are why I would like to keep it as is. BTW the installation can be seen at www.skylinesolar.com, click on the "about us" page, and then they'll be an aviation link at the bottom of that. I was also told by a local gearhead who's opinion I respect that a synthetic may be my best option.
Tom
Tom, did you pull the sump pan off and inspect it? I doubt if this is oil related, considering the aluminum flakes are large enough to see. I would look to see if either the cam or crank gear is rubbing on the case....? You might try pulling and pushing on the prop (mag off of course
), and see if there's excessive endplay in the crank. My thoughts are that the Subaru engine wouldn't have the thrust bearing area that an aircraft engine would, and maybe wear out sooner (because of the prop "pull" on the crankshaft).....
), and see if there's excessive endplay in the crank. My thoughts are that the Subaru engine wouldn't have the thrust bearing area that an aircraft engine would, and maybe wear out sooner (because of the prop "pull" on the crankshaft).....I did pull the pan last night, and saw what what be best described as flakes. Due to the fact that it is a taildragger (of course) when the oil is changed a small amount remains in the pan, maybe a 1/2 cup or so, (The Soob engineers no doubt had no idea it would end up in a conventional geared airplane,) thus these flakes may have been there a while. Future oil changes will take place only after I raise the tail!
This Soob conversion uses a reduction system (cogged belt) so there are no prop loads on the crank, no thrust loads that is, regardless, no end play is discernible in the drive pulley.
I just got my oil analysis results (Aviation Labs of Louisiana. ) Summary is "SAMPLE APPEARS NORMAL". Then the specifics which I really don't know how to interpet, but I can sure post it here in order to get some feedback: IRON 20.4 COPPER 13.6 NICKEL0.0 CHROMIUM 0.2 SILVER 7.3 MAGNESIUM 14.2 ALUMINUM 12.5 LEAD 504 (MUST A BURNED A SMALL AMOUNT OF 100 LL) SILICONE 5.6 TITANIUM 0.0 TIN 0.0
MOLY 42.8
quote:The belt drive would put side loads on the crank that it wasn't designed for. I have seen bad main bearing wear on a couple of engines that had big side loads applied to the end of the crank. That probably isn't what's happening since your type installation has a lot of air hours behind it by a lot of people. How's your belt tension?
Originally posted by TOM SIMKO: This Soob conversion uses a reduction system (cogged belt) so there are no prop loads on the crank, no thrust loads that is, regardless, no end play is discernible in the drive pulley.
The belt tension is good, meaning not too tight. This type of reduction is pretty proven though I suspect anything is possible.
Tom, others here can interpret the oil analysis better than me, but I would agree it looks OK. The lead has to be from the LL fuel, because abnormal bearing wear would show up as having more copper and tin in the mix along with the lead.
As you alluded to, maybe the (aluminum?) particles have been there all along, maybe since the conversion. One thing you might try, and I'm shooting in the dark here, is to examine the particles with a magnifying glass (or microscope) to see how fresh they are. If they're shiny, something is wrong. If they look dull and oxidized, maybe they've been there awhile.....
Are you running 100LL or Mogas? The reason I ask is that you do not want to try synthetic oil with leaded fuel. Rotax recommends 15W-40 conventional or synthetic blend for all fuel types in the four-stroke 912 series. Ashless aviation oils are not recommended. Synthetics are prohibited for use with 100LL fuel.
Just an observation-140 degrees is WAY too low for your oil temp, needs to be a minimum of 175, way better 185 to 190. Under 175, your cylinder wear will increase dramatically, and the cam may show abnormal wear as well, but the wear likely won't produce visible particles. Hope you track down the source of this. It isn't normal.
My oil temps MAY not be as low as 140, the sender for the temp gauge is a fitting on the side of the oil pan, not actually a well immersed in the oil. As the engine came set up like that I have always figured it was accurate enough. As it is, since it exposed to the airflow also (85 MPH) perhaps it is reading on the low side. As a test I plan to temporarily install a test probe, duct taped to the rear of the pan out of the airflow, with a little insulation over it, and then run the leads to the digita readout in the cockpit. My guess is it'll show its hotter then the main gauge display. I agree a bit warmer would be better, I may have to insulate the pan, easier said then done though with out creating more drag on an already draggy plane. Thanks for the input
Tom, after giving this some thought, here's another idea........Camshaft lobes have a very thin layer of hardened iron where the lobe surface meets the follower or lifter. (The entire cam is not hardened, only the lobe surface). When this hard, brittle layer wears through, the lobe starts to disintegrate very fast, and flakes of iron are produced. This might be one possible source of your flakes. It also would coincide with the 20.4 ppm of iron in your oil analysis (although this is still fairly low in my opinion).
The only fault with this theory is that the flakes would be ferrous (iron), not non-ferrous....???
I use that same engine in gyrocopters. Presently using Mobil 1 5-30 and a high-hour teardown shows no wear to speak of.
I have put another 60 hours on the S-7 so far this season, another oil sample showed no change. It sounds great, uses no oil, has as new power....screw it, I'm flying it until the problem is obvious.!I have changed to Castrol 10-30. Maybe this winter I'll do a teardown.
Tom S.
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