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907s and oil pressure


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#1 Tony K

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Posted 06 June 2006 - 06:42 PM

This is a bit of a rehash of a post I just made in another thread. I thought I'd start a new topic on oil pressure in the 907.

As far as the longevity of the engine itself, this seems to be the key issue, at least in the S1 and S2 cars. I have seen dozens of S1s and S2s in person, and only a handful made it past 30k miles without needing the engine rebuilt. That's pathetic. Of the ones that got past the 30k mark, the one that went the longest was 100k miles, two cars were in the 60k range, and another went 45k miles on its original engine.

Let's start with a question for S1 and S2 owners:

1) How many miles does your car have?

2) Has the engine ever been rebuilt?

If you "don't know", here's the same question rephrased:

. . . 3) How many miles did it have when you bought it, and was that the original engine in it?

At this moment right now, I am not aware of anyone I know who has an S1 or S2 that has never had its engine rebuilt. And the vast majority of people I know, their cars' mileage is in the 30-thousands.

One guy had a head gasket failure. Another broke a piston or rod or something. The rest of them were all related to oil pressure. Here are some examples:

- starved going around a turn on the track
- "ladder rungs" in cam cover gaskets disintegrated and fell into sump, clogged screen
- engine sucked air through distributor o-ring failure
- engine sucked air through some hole behind or below the alternator mounting bracket on an A/C equipped car (I only read of this one and am not clear about it)
- oil pickup tube dropped into the sump
- oil pressure line to gauge (S2) broke.
- other debris partially blocking the oil pickup tube screen
- general accelerated wear for various/unknown reasons


It seems to me there are about a dozen ways the 907 can starve for oil or lose all oil pressure, and most of them are from causes that are minor and trivial (and can easily be prevented for little money) compared to the drastic results. Add the potential for fire from the carburetors sitting above the distributor, and it amazes me that so much catstrophe can result from such minor little things as o-rings, seals, etc.

But anyway, I see two main shortcomings in the 907 when it comes to oil pressure:

1) The half-a-dozen ways to lose pressure or starve it over something trivial, and

2) The amount of time the engine runs with zero oil pressure at startup before it finally registers on the gauge. On a cold engine, I have seen it take from 4-8 seconds (and that's just for it to reach the main bearings). When I change the oil on my 944, without priming the filter, it doesn't take more than 3 seconds to build oil pressure -- and that's with an oil change; with the 907, we're talking EVERY TIME YOU START THE CAR.


It seems to me that both of these shortcomings are related to the design and location of the pump. Whereas many cars have the pump down in the bottom of the engine, often immersed in oil, and it's job is to push it up through the engine, the 907's oil pump sits at the top of the engine, and has to suck it up like a straw before pushing it through anything. Ever try to drink through a straw with a tiny pinhole or crack in it? Every junction and seal along the way from the 907's sump to annulus/rotor is a potential air leak, and therefore a potential failure. Off the top of my head, this includes the "olive" and union bolt, the oil pump housing gasket, the distributor, the oil pump gasket (clear plastic thing), and the pressure relief valve. (Am I forgetting any?)

Some of you are probably aware that I lost my first 907 to cam cover gasket failure. The center "ladder bars" in the gasket disintegrated into a mulchy substance, travelled down into the sump, and then clogged the screen around the pickup tube, causing a loss of oil feed. The gaskets are "Permanite Ltd." or something to that effect, and are beige in colour. IF ANY OF YOU WITH SADDLE-SHAPED CAM COVERS HAVE BEIGE GASKETS, I SUGGEST YOU PROMPTLY DISPOSE OF THEM.

So anyway, this failure happened early in my ownership of the red car, and it has made me wary of (and keen to) oil pressure issues on the 907 ever since.

There is not much we can do regarding the design of the engine and oiling system, but just as we have little preventative things we do the the car in other areas (like replacing the carburetor mount o-rings every five years or so to prevent drippage), I am making a list of little preventative checks and measures to help keep 907s from suffering early deaths due to the causes listed above. Below are my suggestions so far; I welcome everyone's additions, criticisms, corrections, etc.:

1) Start with starting the car itself. When I first start the car, I do so with minmal revs until I see oil pressure on the gauge. The thinking here is that the difference in the number of revolutions it is going to take to build oil pressure is not as significant as the different amount of force/stress on the parts when it turns at higher rpms vs. lower rpms.

In other words, it is going to take the same number of revolutions of the engine (and hence oil pump) to push oil all the way through the engine regardless of how fast it is turning, save for a little bit of more time for oil to "flow out" at lower rpms; on the other hand, you are putting more physical force on the engine when you rev it, both in terms of the speed of the parts turning and the force of the ignition stroke (think of the fact that rod bearings wear on the top side, not the cap). So if it going to take nearly the same number of turns to push oil through the whole system whether you rev it or just let it fluff at idle, doesn't it make more sense to, while the engine has to spin with no oil pressure, let the engine spin at low rpms, when the force on the moving parts is less? (This makes total sense to me, but I welcome counterpoint)


2) The oil filter. As per my post in the oil filter thread, I am going to eliminate all of the other variables I can between my two cars, so I can see if and how much different oil filters affect the amount of time the engine runs without oil pressure.

Just as with all cars we are told to prime the filter when we do an oil change, my assumption here is that a filter that lets oil drain back out of it is similar to an unprimed filter, and will therefore add to the time the engine runs without oil pressure. As I mentioned in the other thread, so far my favorite is Mann. It looks to be a winner, but of course that doesn't mean others aren't too. Beyond just "does the filter have the correct anti-drain valve," I am also concerned about quality of construction and materials, as well as quality in terms of consistency, as in "are the standards to which these filters are made precise enough that every one is going to work as well as the one I am holding, or might the anti-drain seals on some fit/work better than on others?"


3) Cam cover gaskets. This pertains to the early engines with the saddle-style cam covers. First, again, if you have the beige ("Permanite") ones, get rid of them ASAP. If you have the neoprene ones, they don't seem to pose any problems. If you use the fiber ones, like me, here is my suggestion: Cut the three "ladder bars" out of the middle of the gasket. Use a sufficient but sparing amount of the proper sealant so as to not squish too much to the inside, and whatever does get squished in will not harden, break off, and land in the sump.

The thinking here is simple: Maybe the black/grey and blue fiber style gaskets don't have a chronic problem of crumbling like the beige ones, but let's not give them a chance--cut the middle part out. Again, this is for the fiber gaskets, not the neoprene. I have been doing this for a while now, and have not had a problem with trying to keep the cam cover from squeezing the sides out. The ladder bars appear to only be there to hold the long sides in from squeezing out; they are not necessary, and all you need to do is be a little attentive as you tighten the six cam cover bolts, to make sure they are not starting to creep (if they are, just push them back in, no big deal).

As for the sealant, I suppose the original stuff recommended (Silastic) works fine; I have been using some stuff for Mercedes-Benz that works very well: It is designed for cam covers and other oil-soaked areas, it withstands intense heat (important especially for the exhaust cam gasket, as it takes a lot of heat from the manifold), it stays flexible (so it won't crumble in there), and it is nearly impossible to tear (it will stretch and strech instead) -- again, a good prevention for not crumbling. Oh, and it's black. I can't think of what it is called, but I can ask my buddy who owns a M-B repair shop, whom I get it from. You can buy it at the dealer, but I assume every manufacturer has an equivalent high performance sealer for this kind of application.


4) Oil sump. As a preventative measure, if the condition of the inside of your engine is unknown to you, at some point it might be a good idea to remove the sump and check things out. There are a few things to do here:

- see what kind of crap may be partially clogging the screen around the pickup tube. Even on the perfectly healthy (bottom end, at least), low-mile Eclat engine I put into my red car, there was some crap partially blocking the screen. It could be gasket material, it could be sealant, who knows. Keep that screen clear.

- see what kind of silt is lying in the bottom of the sump. This stuff will never drain out from regular oil changes, even when you run the engine to operating temperature. Hold it in the sunlight so you can see the glint of the particles in there -- are they gold-colored or silver/gray? (gold color comes from the thrust washers, and may indicate that your main and rod bearings are worn to the bronze.) Swoosh a magnet around in there, and then swoosh it in a cup of degreaser -- if you are left with little particles on the magnet, that is probably top end wear or other steel parts. Sure you will have some of both; be alarmed if there is a lot of either for the mileage of the engine. Just do this to get to know your car, as well as to "start over" with cleaner oil going forward.

- check that the baffles on the sump are intact!


Be careful and patient and systematic when reinstalling the sump -- make sure to tighten the nearly two-dozen little nuts and bolts in order like you were doing a cylinder head, and if you don't have a suitable torque-measuring device, be conscientious to tighten them consistently in a similar manner to when you do the cam covers.


5) Distributor O-ring. Replace it if it is old and flat. Easy, cheap, no-brainer. Don't overtighten that clamp nut!

6) Oil pressure gauge tube. Check the condition, check for potential sources kinks, cuts, burns, other damage, and replace/protect/reroute as necessary.

On S1s it is short and goes to the sending unit on the right side of the frame, and on S2s it is long and goes through the center console and connects to the back of the gauge. I have heard of one breaking (brittle from age and heat) on an S1, and on an S2, I know someone whose tube had a hole burned in it from an electrical short under the center arm rest. Sure, if there is any problem with it, you will see no oil pressure on the gauge; but we're trying to avoid it getting even that far (before it pumps oil out all over the engine or under your carpeting and into your footwell. With Murphy's Law, that one time you feel so confident in your S1 or S2 as to not check the gauges every few minutes will be the time when this thing fails. I am not sure whether a failure in this thing may starve the bearings after it on the line, or if you have until it pumps a quart or two of oil out and your whole engine is starved . . . ??? Let's not wait to find out!

By the way, in the case of the S2 with the line that got burned (actually melted), it was the wire going to the temperature sensor or fan (I forget which) on the federal S2 that extracts heat from the engine compartment -- that wire shorted (and the extractor fan quit running), but that wire happened to lay across the oil pressure tube going to the gauge, and the heat from the shorting wire melted the tube. The engine ran for a good five minutes like that: I noted the oil pressure gauge on the dash, how it was just flicking a little bit above zero, and told the owner to shut the car off. He said, no, the gauge was just sticking, the engine is fine. I was adamant, but he persisted. Five minutes later, the carpet started turing black. The black spots were growing and growing. I touched one, and it was oil -- put two and two together, and "SHUT THE CAR OFF, NOW!" Original shag wool carpet ruined, engine probably still okay, lots of cleanup afterward . . .


7) Oil Pressure test -- Attach a calibrated gauge when your engine is cold and take a reading of what it is at a specified idle speed when cold. Reattach the line to the gauge, go for a long hard drive, and when you come back, quickly reattach the gauge (the oil will cool quickly) and take readings at idle and at 3500 rpm. I would like to gather data from everyone on how many miles their engine has, type of oil in it, oil and operating temperature, and oil pressure, to see what really is the "norm" for a healthy engine; that way we can all have a reliable basis for comparison.

Whereas the service manual says "not below" 5 psi at idle when hot for the oil pressure, I found 5 psi to be the minimum borderline, about 1000 miles before an engine is so worn that it starts to get a knock at startup. For a true healthy engine, I have seen as high as 22-25 psi at hot idle using Mobil 1 15w50 synthetic on a freshly rebuilt 907, with 18-21 psi being the "norm" for a healthy hot engine at idle using a something-w-50 oil. Sometimes down to 15psi. I think it is a good idea to, every year or so, check up on the oil pressure with a calibrated gauge to 1) make sure the dashboard gauge is not lying to you (mine did), and 2) generally monitor the engine to catch any accelerated wear before it becomes a catastrophy.


Okay, that's it for now. These are my suggestions. My suggestions for safeguarding against oil-related catastrophe in the S1 and S2. I think that, at the very minimum, the cam cover gasket thing should be added to any checklist as a "must do" for S1 owners, as the intense heat under that engine cover will shorten the life/reduce the flexibility of any cam cover gasket.

Please, add your thoughts, suggestions, and corrections!


Best regards,

Tony
Tony K. :)

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#2 DanR

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Posted 06 June 2006 - 11:43 PM

Thanks Tony. Lot there to think about. I'm now inclined to install a permanent mechanical oil guage in the engine bay to monitor the oil pressure like you suggest.

Note that if the anti-drain valve is working properly the filter, being horizontal, should retain about half its oil. Also the pump has to push the oil through the coolers and back to the engine before it gets to the galleries.
DanR

#3 USAndretti42

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Posted 07 June 2006 - 05:35 AM

Sounds like if an engine that's a bad starter whould last longer as all that cranking will get the oil circulating before it fires up.

Does the oil from the cooler drain back into the sump or does is stay full?

#4 Tony K

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Posted 07 June 2006 - 01:53 PM

Sounds like if an engine that's a bad starter whould last longer as all that cranking will get the oil circulating before it fires up.

Does the oil from the cooler drain back into the sump or does is stay full?

<{POST_SNAPBACK}>


I would think that since both of the lines lead up to the filter attachment and the cooler sits lower than the attachment, that the cooler would stay full. (Going from memory) . . ???
Tony K. :)

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#5 peteyg

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Posted 07 June 2006 - 02:29 PM

1)  Start with starting the car itself.  When I first start the car, I do so with minmal revs until I see oil pressure on the gauge.  The thinking here is that the difference in the number of revolutions it is going to take to build oil pressure is not as significant as the different amount of force/stress on the parts when it turns at higher rpms vs. lower rpms. 

<{POST_SNAPBACK}>


Doesn't the manual say something like 'do not allow the engine to exceed 2000rpm until pressure has registerd on the guage'?

Great info Tony, thanks for the effort.

Bought my car with 56k on the clock, though I'm pretty sure this was much less than it actually had done! The whole engine needed a rebuild, actually the whole car did in the end. Done nealry 50k since in 8 years of ownership (six on the road) and the pressure has been perfect.

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#6 JRTurbo909

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Posted 07 June 2006 - 03:01 PM

that is a lot of information but first i will answer ur questions about my car...

1) 57,600 miles

2) rebuild at around 50,000. Not sure if there was one earlier. I know the car had its motor out during the rebuild and a jensen motor put on place for a lil bit.

3) it is the original engine, just overhauled quite a bit with better parts in it...


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#7 molemot

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Posted 07 June 2006 - 03:07 PM

It's a long way from engine to gauge, and - especially in cold weather - it can take a long time to get pressure registering on the gauge, even if the engine is fine. Used to get this with the aeroplane; even shut the engine down on one occasion, only to find the true explanation later. Then, aircraft oil is notoriously viscous stuff, as well as being hopelessly "old tech."

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#8 Tony K

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Posted 07 June 2006 - 06:05 PM

It's a long way from engine to gauge, and - especially in cold weather - it can take a long time to get pressure registering on the gauge, even if the engine is fine. Used to get this with the aeroplane; even shut the engine down on one occasion, only to find the true explanation later. Then, aircraft oil is notoriously viscous stuff, as well as being hopelessly "old tech."

<{POST_SNAPBACK}>


Speaking only for the S1, some of them have a translucent clear tube and some have a black tube. On the couple I have seen with the clear tube, it stays filled with oil after you turn the engine off. Granted, I don't for how long, or how consistently. Does not hold much volume. The tube is probably 10" long. (yes, I know on S2s it is a mile long! no clue there about how much is held in on S2s..)


Pete -- I don't have my owner's manual around, but I will check!


Thanks for comments, everyone. Please don't hold back any of your well-thought opinions. :lol:

Edited by Tony K, 07 June 2006 - 06:08 PM.

Tony K. :)

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#9 dglotusltd

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Posted 07 June 2006 - 06:56 PM

Great info as usual Tony.

Bought my S1 a year ago. Has about 87,000 on the clock with a rebuild by the PO at around 81k for a failed liner. Total milage is an estimate as the PO also pulled the veglia gauges and replaced the whole lot with VDO at about 60k.

Pressure rarely goes below 15 is ever since I cure a cronic overheat with a recored rad and new fans. Pressure is over 40 at startup. I use Castrol 20-W50.

Pressure seems good at startup but I have one of those hard to start S1s. Slowly playing with the mixture to find just the right amount for an easier cold startup without adversely impacting hot start and backfires on shutdown.

Engine is running dual 45 Dellortos with a Euro Spec non-vacumm advance distributor and Lumination ignition. All care of the PO.

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#10 yeller77

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Posted 08 June 2006 - 04:35 AM

Wow, Tony, great post! How's that journalism career going? :lol:

Also begs the question, anyone out there with an Accusump?

As to the poll, rebuild in progress/long term project with about 35k on the clock with the reason being partly my fault. However, after losing compression in one hole, I found the other 3 to have puny compression as well. Moreover, on teardown the "bearing" surfaces on the cams as well as the cam bearing bores were significantly scored. It's been a while, I don't recall the rod and main bearing condition. An additional data point, I subsequently acquired an S4S parts motor which was also reportedly in the 30k range, #4 rod and #1 main bearings were in to bronze.

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#11 Esprit Aviation

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Posted 27 June 2006 - 01:15 PM

Good article to begin the thought process. All of the points you mentioned should be rigorously adhered to!!! When disassembling my turbo engine, two things occurred involving oil pressure. First, the filter screen was almost completely blocked by the factory sealant used on all the mating surfaces, which had turned brittle and broke off where it squeezed out. Pull that sump immediately if you are still running w/ a factry orig. engine!!! You may find that you can clean the screen and continue driving for a much longer period prior to a 'necessary'rebuild.Second, I eliminated my distributor by using an electromotive crank triggered system. I tried to bring up oil pressure after my rebuild by spinning the pump w/ the timing belt off, to no avail. There is a vacuum drawn by the distributor hole, which needs to be plugged in order to pull oil from the sump. Bottom line is, that o-ring is VERY important!!

Also I had designed a motor driven gear pump that will pre-oil the engine prior to start-up. No more worries about length of time! As a bonus, this thing will pump 100+ psi so in the event the internals conspired to lose pressure the external pump could be made to turn on and provide full pressure(unless all the oil has blown out of the engine). Cheers, Lee

#12 Guest_Troy Halliday_*

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Posted 27 June 2006 - 04:06 PM

I think the biggest problem with engine longgevity is that everyone seems to be in such a rush. I let the car warm up and cool down allmost all the time. I would say all the time but occasionaly you have little choice but to turn the engine of abruptly. Must admit on the two 912 engines that I have stripped down neither had blocked oil pick up pipes. Both did however have main bearings that were either worn or so close it wasn't even worth thinking about. The sumps did have a certain amount of sludge in them but then again I have yet to work on a car that is any different. Fuel lines were a disgrace as were the O rings. My oil presure climbs very quickly I will have to time it now you mentioned it but then again I have just fully rebuilt the engine.

#13 scotty

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Posted 27 June 2006 - 09:14 PM

On my S3 the pressure stays very high for the first 5-10 mins, up at about 75-80psi. As the engine gets fully warm (about 80c) then the pressure drops to about 30-35psi for normal driving and down to about 5psi at idle. I always get a bit worried at the start that I might blow a gasket when the engine's cold.

The warm figures seem fairly textbook so I've never worried. Is the high pressure initially normal? and if so why is that? what is the mechanical explanation - my small brain hasn't worked it out.

#14 Dodgy

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Posted 27 June 2006 - 11:11 PM

my dry sump turbo, when running (currently off the road again due to a attempted easy change of the rear brake pads - handbrake lug on 1 of the calipers snapped off :) ) was rebuilt at 40k by the PPO, its now done 64k and has 70psi on cold start, 45 to 60psi on warm driving and 25psi on tickover.
i recently changed from mobil1 15/50 to valvoline racing 20/50 with made no difference on the pressures.
I did however, find that the anti-drain valve on the new style lotus filter, was not working and it was taking at least 10 seconds to register pressure, for a quick temporary fix i brought a coopers equivelent filter which cured it - oil pressure within 3 seconds, much better.
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#15 Esprit Aviation

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Posted 28 June 2006 - 12:29 AM

dodgy, do you have the P/N for that coopers filter? Thanks, Lee

#16 Dodgy

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Posted 28 June 2006 - 09:15 PM

Lee, its Z27A ( at least thats whats on the box)
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#17 USAndretti42

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Posted 29 June 2006 - 03:58 AM

On my S3 the pressure stays very high for the first 5-10 mins, up at about 75-80psi.  As the engine gets fully warm (about 80c) then the pressure drops to about 30-35psi for normal driving and down to about 5psi at idle.  I always get a bit worried at the start that I might blow a gasket when the engine's cold.

The warm figures seem fairly textbook so I've never worried.  Is the high pressure initially normal?  and if so why is that?  what is the mechanical explanation - my small brain hasn't worked it out.

<{POST_SNAPBACK}>


When the engine is cold all the main and big end clearances are smaller so the oil can't get through the gaps. The pump is pretty much a constant volume per rev device so, as the oil does not have so many places to go, pressure is high. As the engine warms up, the aluminium of the block and cam carriers expands more quickly than the iron crank and camshafts opening up the gaps between the bearings and their housings so pressure drops.

The oil pump has a pressure relef valve to dump excess oil, but they normally cannot cope with cold flow.

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#18 david

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Posted 10 August 2006 - 05:54 PM

Oil pressures in my Excel are very similar to Dodgy Dave's Esprit. Almost 80k miles on the original engine.
Oil pressure picks up in 1 to 2 seconds with a Mann filter.
Have used a variety of oils over my 20 year ownership - no noticeable difference between them.




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