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biglar
Joined: 14 Jan 2006
Posts: 457
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 Posted: Fri Feb 03, 2006 9:42 pm Post subject: Bearing Wash-out |
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A while back I posted that Vamoose' oil pressure was over 80 psi, and someone made a remark about "bearing wash out," I think. Never heard that expression before, and haven't been able to find anyone around here who has. Could you explain what you mean by that ?? What causes it, what are the effects, etc. I, and people I've talked to, seem to feel that the more oil flow the better. Educate me, please. Lar.
Larry Bourne
Palm Springs, CA
Building Kolb Mk III
N78LB Vamoose
www.gogittum.com
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Larry Bourne
Palm Springs, CA
Building Kolb Mk IIIC
"Vamoose" |
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Don G
Joined: 10 Jan 2006
Posts: 156
Location: Central Illinois
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| Posted: Sat Feb 04, 2006 11:42 am Post subject: Re: Bearing Wash-out |
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Larry
I cannot specifically comment on the subject of washout at 80 psi on that VW engine you have, but as it is cold as a welldiggers (at)#$ here and I am not able to paint , I thought I would respond in theory here.
Remember that your oil pressure comes from resistance not flow. and you are generally correct in thinking that more oil flow is usually better.
However oil pressure is not a function of flow but of the resistance to flow generated by the oil passages and bearing clearances in an engine.
Some engines are designed to have proper flow at higher pressures like 80 psi...but not many. I do not know about yours. From what I remember from the past, you have a Vw conversion or some kind right? I also remember that you have had stuff happening like lines blowing off or seals ruptureing and oil leaks of somekind. This could certainly be a warning that you have too much oil pressure in certain parts of the engine.
Let me create a make-believe scenario that you might consider.
Somewhere in the engine there is a restriction to flow so the volume of oil the pump is pushing cannot pass. Maybe a plugged passage..maybe a misaligned fitting or maybe even tight bearing tolerances somewhere. The resultant decrease in flow is causeing the pressure to increase in all oil paths elsewhere in the engine, resulting in a higher oil pressure that a certain bearing seal cannot handle..and the seal blows. The blown seal may not be anywhere near the restriction,,but blows anyway because it is the component upstream from the resistance least capable of handleing the higher pressure.
What you need to do is find out what the oil pressure is supposed to be in that engine from the builder.
Don
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Don G.
Central Illinois
Kitfox IV Speedster
Luscombe 8A
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edchmiel(at)mindspring.co
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| Posted: Sat Feb 04, 2006 3:49 pm Post subject: Bearing Wash-out |
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Hi Lar,
I never heard the term before, but in the case of oil pressure "too
much of a good thing" can indeed be bad. A fluid under great pressure will
find the path of least resistance, and indeed with high oil pressure the
bearings may be exposed to less-optimum lubrication due to the oil going to
places it's not meant to, or in the wrong proportion. Your oil cooler and
thermostat will both be operating at the edge (or beyond) of their design
limits also. I saw more than a couple VW oil coolers rupture after a HP
aftermarket oil pump was fitted, and had a filter rupture on a bus I owned
after I dialed the pressure up a bit too high. 60 psi (IIRC) seemed like a
good upper limit. We used to grind the pressure springs down, before they
came up with the adjustable pressure limiters.
With GA aircraft after an engine change or other major work, it's
important to have the A&P adjust the pressure (usually down) on the high
limit to keep it in the green arc.
Ed in JXN
MkII/503
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biglar
Joined: 14 Jan 2006
Posts: 457
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| Posted: Sat Feb 04, 2006 4:29 pm Post subject: Re: Bearing Wash-out |
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Thanks to you, too, Don. Right now I'm grabbing at straws, trying to avoid pulling the thing apart again. If this doesn't work.........OK, tear'm to pieces. We'll see. It's getting to be daylight late enuf now to where I'll soon be able to do a little on it after work. Lar. Do not Archive.
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Larry Bourne
Palm Springs, CA
Building Kolb Mk IIIC
"Vamoose" |
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biglar
Joined: 14 Jan 2006
Posts: 457
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| Posted: Sat Feb 04, 2006 4:47 pm Post subject: Bearing Wash-out |
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Thanks, Ed. With the stock spring, the pressure should be down around 40
psi when warmed up. Running out of time today, but may get to it tomorrow.
Lar. Do not Archive.
Larry Bourne
Palm Springs, CA
Building Kolb Mk III
N78LB Vamoose
www.gogittum.com
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Larry Bourne
Palm Springs, CA
Building Kolb Mk IIIC
"Vamoose" |
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JetPilot
Joined: 10 Jan 2006
Posts: 1246
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| Posted: Sun Feb 05, 2006 10:32 am Post subject: Re: Bearing Wash-out |
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That sounds like a pressure releif valve problem. On most engines... The oil pump pumps more oil than the engine can possibly use, and the extra volume of oil is let out the pressure releif valve, and returned to the engine tank. If that valve sticks, or the return is blocked, you oil pressure will go way high and something will blow and you will lose all your oil 
New bearings, etc should not even have much of effect on the pressure, because if the releif valve is working properly it just returns more oil to the tank and the pressure is keept it at a proper level. Even a blocked passage would not normally result in a higher pressure because the extra oil is just returned to the tank and normal pressure is maintained. A blocked passage is very bad, but the symptom is usually not a high oil pressure. So I would look in other areas before I would tear the engine apart looking for blocked passages.
I have never been into a VW engine, the Germans do some wild and crazy engineering that is sometimes very "different", but this is what I have seen with other engines....
Michael A. Bigelow
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