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Bob Grimstead
Unregistered
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 Posted Friday, May 14, 2010 @ 09:29 PM
Hi Guys,
I need your help again.
You haven't heard from me for a few weeks, partly because I've been busy fitting a new 1750cc engine to HDO.
It was built for me four years ago, and we ran it for a couple of hours on the dynamometer, including full power runs, but it has been inhibited since then by completely filling it up to the spark plugs with new Aeroshell 15W50.
I've drained out all that oil and replaced it with 2¼ litres of straight running in oil.
I've removed the heads and checked inside -- no corrosion, so that's good.
I've fitted a brand-new oil cooler with the old adaptor.
It took a bit of starting (I've now got shoulder muscles like Arnold Schwarzenegger) and now it runs.
But...
As soon as it starts the oil pressure rises to around 2 bar (kg/sq cm or hPa - they're all the same, or I think 30-ish psi) but then it immediately (within five seconds) falls back down to about half a bar, fluctuating gently, but always less than 1 bar.
After 45 seconds I stop the engine.
If it was the old engine, and in flight, I would recognize from those symptoms that it was very low on oil, and the oil pick-up tube was becoming uncovered and sucking air, but I know it has 2¼ litres of good, fresh oil, because I only just put it in there.
I wondered if the pressure was fluctuating while the new oil cooler filled up, or whether the new oil pressure gauge and line was under-reading, or also slow in filling up. Well, I loosened the connection to the gauge while the engine was running, and not only is there plenty of both oil and pressure there, but now the whole cockpit is very nicely lubricated.
I've dropped the oil pressure relief valve -- the one at the front/distributor/dynamo/propeller end of the engine -- and that's clean and moving freely in its housing.
Today I'll go and check the oil pressure regulating valve at the back/flywheel/firewall end of the engine.
Does anybody else have any ideas?
Maybe I need to use a thinner oil?
I'm currently using 'straight 100' because it's all I can get in this normally hot climate.
I think that's supposed to be about a 40-weight oil, so it should not be too think, although it's not ideal.
If the regulator valve doesn't do the trick I'll swap to a 15-50 multigrade, but I don't think that's going to make any difference.
Obviously I don't want to smear my new bearing material all around my crankshaft journals, so I'm reluctant to run it any more than I have to before I solve this problem.
Can anybody help me?
Yours, Bob
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eugenio
Unregistered
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Posted Saturday, May 15, 2010 @ 02:55 PM
You probably have a problem of too soft or short spring in the regulating valves. Try to add one or two washer under each spring. The front valve is the bypass of the oil cooler and pressure relief valve, the rear one is the regulating valve. Try some different settings until you find the correct pressure under different conditions of temperature and RPM. 15w50 is fine, 10w40 too, I use 20w60 and works fine too.
2 bar just started is low, it would be better 3 to 4 bar , and while on temperature is should remain 2 bar up to 1800 RPM, than slow down until 1/1.5 at 1000 rpm and at idle it should be at least 0.5.
First try with the regulating valve (the rear one), than if not enough with the bypass valve (front one)
A slightly too high pressure with heavier oils (20w60) just started is not a concern, it will lower as soon as it warm up.
Eugenio
[Edit by eugenio on Saturday, May 15, 2010 @ 02:56 PM]
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Bob Grimstead
Unregistered
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Posted Sunday, May 16, 2010 @ 09:08 PM
Hi Eugenio,
Thank you very much for your advice.
Before I was able to read this, I tried starting the engine again. Previously the Fournier was on slightly sloping ground, with the nose a little higher than the tail. This time, I tried it the other way around, with the tail slightly high, so that the sump would be as near as possible to level.
Now the oil pressure was 2 bar, then after ten seconds gently dropping to 1.5 bar (all at 1,200 rpm).
Since there was clearly some oil pressure, I tried opening the throttle to 1,500 and then to 2,000 rpm.
The oil pressure suddenly jumped to 4 bar and stayed there.
When I reduced to idle 600 rpm the oil pressure stayed at 1.5 to 2 bar, but went back up to 4 bar at 1,000 rpm.
I can only think there must have been some small obstruction blocking the oil pressure gague line, which was cleared by the power and presure increase, or else the regulating valve might have been slightly stuck and then cleared. Either way, now all is well.
I will give everybody the full details of this engine change to 1,750cc as soon as I have enough spare time.
Yours with thanks, Bob
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Jorgen
Unregistered
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Posted Monday, May 17, 2010 @ 04:02 AM
Thanks Bob and Eugenio,
good news that it seems sorted out. I suspect the next gauge reading we'll have some discussion on is the temperature, right?
Incidently, this May I've certainly not had any overheating problems in XST. Coldest May I remember, must be that Icelandic volcanic ashcloud....
May the 4's be with you/ Jörgen
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jb92563
Unregistered
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Posted Tuesday, May 18, 2010 @ 11:40 AM
From everything I have read about VW aeroconversions it sure sounds like a stuck oil regulating valve.
Glad that got sorted out for you.
However the 100 weight oil is a little alarming.
I have read that you should never exceed 50 weight oil since the oil passages to the bearings in the VW are too small to allow sufficient oil flow rate to the bearings if too heavy an oil is used.
The viscosity is too thick when cold and the clearances too tight in a new engine especially.
A thinner oil also has a greater flow rate through the system (lower viscosity = lower resistance in the oil passageways), doing a better job of carrying away heat and keeps parts well lubed.
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Bob Grimstead
Unregistered
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Posted Tuesday, May 18, 2010 @ 09:23 PM
Hi Ray,
Thanks for the advice, but beware, herein lies a continual source of confusion.
There are two ways of determining and categorising oil viscosity.
One is basically for airplanes, and the other is for automobiles (SAE -- Society of Automotive Engineers, I think).
The numbers come out differently.
Automotive oils get SAE numbers from around 5 to around 60.
In monogrades, 30SAE is appropriate to temperate climates.
The RF4D handbook suggests using Esso multigrade automotive oils: 20W / 30W or 40 in summer and 10W / 20W or 30 in winter. Those are presumably European seasons, so I guess you would use the lower viscosities in freezing-type temperatures.
Aviation oil mostly comes as 80 weight or 100 weight, except for the multigrades, which for some reason use SAE designations like 20/50.
I don't have an aviation oil container here in my office, but if you look closely at the small print on the bottle or can, you will see that 100 weight aviation oil is approximately equivalent to 30-40W SAE and 80 weight aviation oil is similar to 20W SAE.
I am breaking-in this new engine, so I need to use oil without any additives ('straight' oil).
I cannot get hold of any automotive oil without additives, so I'm using aviation oil.
No problem, it's just mineral oil, as sucked up from the ground and refined, with no additives, so there will be no difference between 'straight' 'aviation' oil and 'straight' 'automotive' oil.
Perth has a hot climate (officially on the borderline between 'Mediterranean' and 'semi-arid'.)
It is early winter here, and the night-time temperatures drop down to around 5°C, while in daytime it's generally 25°C (thats about 40°F to 75°F for our dinosaurs out there). That equates to a European summer (and a good one, at that) so aviation oil stockists here only carry 100-weight aviation oil. Since that's similar to a 35W SAE oil, there's no problem with its viscosity in a VW.
When I have finished breaking-in this new engine, I shall switch to a 20-50SAE multigrade.
In England, I use a 15-50 SAE multigrade.
I hope that clarifies, rather than muddies the viscosity thing.
Yours, Bob
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jb92563
Unregistered
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Posted Thursday, May 20, 2010 @ 03:16 PM
I just knew there had to be a good explanation for all that....I learned something new today.
Better to mention things in any case as it ussually provides knowledge for one or the other party
and perhaps all the readers as well.
Thanks for the clarification.
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Bob Grimstead
Unregistered
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Posted Thursday, May 20, 2010 @ 08:12 PM
Yes Ray, you're right.
Thank you very much for your input.
I'll make a whole post about this engine change when I've finished, so folks can learn from my mistakes.
Yours, Bob
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Jorgen
Unregistered
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Posted Thursday, July 7, 2011 @ 05:06 AM
Bumping an old thread here,
but I had a change in oilpressure that I wanted to discuss. When I bought G-AVNX I got some great advice from former owner James Hallam, among them a comment about oilpressure: "-Anything below 40, you're in trouble!" (That's 40 Lb/O (=PSI? = bars?) if I read my Smith's gauge correctly).
G-AVNX now SE-XST has always stayed at 40 Lb/O regardless of rpm, except perhaps when I've allowed oil level to become low. Yesterday suddenly I had fluctuations, down to 20-30 Lb/O that came back to 40 with increased RPMs. Went home and landed, oil level was fine. I should add that last 20 hours or so has been mostly on low rpm, around 2200.
What say you Fournieteers- stuck regulating valve? Gauge issue? Oil pump starting to faulter? Normal oil pressure fluctuations?
May the 4's be with you/ Jörgen
Edit: changed the units to the one appearing on the gauge, sorry for the confusion.
[Edit by Jorgen on Friday, July 8, 2011 @ 05:23 AM]
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Bob Grimstead
Unregistered
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Posted Thursday, July 7, 2011 @ 06:45 AM
Hi Jorgen,
My immediate reaction was that this is a clear symptom of low oil elvel, but then you say it isn't, so I will have to think a little harder.
But I would not worry too much.
It might be a gauge problem, Red WGN's gauge turned out to be seriously under-reading, and it cost me a new engine to discover that. I thought the engine was stuffed because the pressure was low, but the new engine exhibited precisely the same pressures. Changed the gauge and all was well, so there was clearly nothing whatever wrong with that original engine!
You might like to take a look at the filter, just to reassure yourself that there are no tiny flakes of metal or other debris floating around the system.
My old 1,300-hour Rectimo in blue HDO now always runs with a fairly low oil pressure, after eight years and 300 hours of hard aerobatics.
The original American VW manuals had some recommended minimum pressures.
I cannot remember them right off the top of my head, by they're something like a minimum of 20psi at 2,500 rpm with an oil temperature of 70°F, and an absolute minimum of 8psi at a 600rpm idle in the same temperature.
As you will probably remember, I run both my engines with molybdenum disulphide additive ('Molyslip', 'Liquimoly' and other trade names apply). This will continue lubricating the engine even with extended periods of low or no oil pressure. Molyslip demonstrated it at various venues (including full-length races) by running automotive engines for many hours after draining out all the oil, with no apparent ill effects.
If you have any concerns, I would pour in a quarter litre of one of those products, and then you need not worry about fluctuating or low oil pressure. I could not do that in my new engine, simply because it would have extended the break-in period to infinity!
Good luck.
Yours, Bob
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milnerd
Unregistered
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Posted Thursday, July 7, 2011 @ 10:11 AM
Hi Jorgen,
1 bar is 14.5 psi so 40 psi is 2.75 Bar so your 2~3 Bar reading is close to being okay. It does sound like a bit of carbon in the oil pressure regulating valve though. Anything in the seat of the valve would hold the valve further open than it should and will therefore bypass more oil back to the crankcase resulting in lower oil pressure in the pressure circuit.
Perhaps Collin has some ideas on what to do to check it. Seeing as though you can adjustteh oil pressure from outside the engine I would think that the valve assembly can be removed, inspected and cleaned without pulling anything off the engine - but I don't know that for a fact.
Best regards,
Dave
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Jorgen
Unregistered
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Posted Thursday, July 7, 2011 @ 01:09 PM
Thanks,
that's reassuring and sound advice that dropped my cortisol levels noticeably. It's time for an oil change anyway so I'll go ahead and check the filter and this time I'll try to find that Molybdeniumdisulfid-slip and pour some of that in. It appears Liqui-Moly has a Swedish distributor now.
Collin, do you know if it's possible to check the valve without draining the oil or should I do that while I have an empty engine?
May the 4's be with you/ Jörgen
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Collin
Unregistered
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Posted Thursday, July 7, 2011 @ 05:25 PM
Hi Jordan,
Yes you can pull the relief valve with the oil in. Some oil will come out. The hole that goes from the relief to the sump is about 45mm above the sump plate.
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Jorgen
Unregistered
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Posted Friday, July 8, 2011 @ 05:19 AM
Thanks Collin,
I'll look into checking the oil pressure release valve as I do my oil change. The Swedish Liqui-Moly distributor pointed me to a shop in Lund that sells Liqui-Moly additive so I will add that too.
May the 4's be with you/ Jörgen
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Jorgen
Unregistered
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Posted Saturday, July 9, 2011 @ 03:36 PM
Dave,
thanks a lot for the pointer and sorry to confuse you all with different units. My gauge is graded in "lb/O" ( the "O" has some circumscript I can't find on the computer) so I guess my "normal" reading of 40 equals (40/14.5)= 2,75 bar. That means my "low" reading of 20 equals 1,4 bar assuming my gauge reads true. I'll keep you guys posted.
May the 4's be with you/ Jörgen
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Jorgen
Unregistered
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Posted Sunday, July 10, 2011 @ 12:33 PM
Hi again,
it's actually smart to reply to your own posts, that way you always win the arguments 
Had an hour Fournierflight today, oil temps rock solid on 40 lb/O on start up and after, when warm no less than 30 lb/O on 2200 rpm. It took 15 min to establish that, then the thermals were so strong I didn't need the engine anymore today so I shut it off. I like doing engine off landings to hone my soaring skills.
For now the hypothesis is that it's hot here at the moment and that might have thinned the oil some more, causing more oilpressure fluctuations than I'm used to.
May the 4's be with you/ Jörgen
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