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oil pressure drop  Rating:  Rating
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 Posted: 02-26-2006 01:15 pm
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greenthing
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Hi guys!

This is my first time posting, so hopefully I'll do it correctly. My father's 1973 JH is having oil pressure problems. The funny :-(  thing is that he has an old Ferrari (1965 330 GT 2+2) that is displaying exactly the same symptoms.

When driving at a steady speed, the oil pressure stays stable.

When the accelerator is touched even lightly, the oil pressure goes DOWN


When letting up on the accelerator, the oil pressure goes UP
.

Both engines are running Chevron oil instead of Castrol which we have run for years.

I have not found anything on the board which describes this particular situation.

Please help....

Greg Parris

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 Posted: 02-26-2006 05:40 pm
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Jensen Healey
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I would say the situation you discribe should be impossible. The oil will make no difference but the filter could. Did you use the same brand filter on the ferrari and the Jensen?

 

Change the filters.

Kurt

Last edited on 02-26-2006 05:42 pm by Jensen Healey

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 Posted: 02-26-2006 08:38 pm
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Judson Manning
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I have witnessed this correlation between oil pressure and throttle position that you are describing in several JHs.  However, the difference I've seen is only around 5psi, and the oil/filter won't make any difference.

Chalk it up to a well used engine with worn bearings and/or worn oil pump rotors. 

Between the aluminum block and 360^ grooved bearings, this isn't uncommon and nothing to worry about.  The only 'fix' would be to use a x-drilled crank, 180^ bearings and a 'beefier' set of main bearing caps.

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 Posted: 02-27-2006 06:06 pm
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Jim Sohl
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I'm going to make a guess here, but I've seen similar things in the past in engines with mechanical oil pressure gauges, or some other gauge that responds quickly to slight changes in pressure.  The culprit as Judson suggests, is simply wear.  Possibly, end-play in the crankshaft.  Try to sight from above the engine while it is idling, across the crankshaft pulley to a mark or reference point on the floor.  Without moving your head – line of sight – run the throttle up and down.  It won't take much change in RPM.  At the point where the RPM changes from up to down or vice versa, in a worn engine, the crankshaft will move in or out of the block by roughly the end-play clearance.  In a new or fresh engine, end-play will be quite low, 5 thousandths  or less, and that much movement is difficult to see by just sighting across the crankshaft pulley.  However, worn engines will show more end-play, sometimes 15 – 20 thousandths or even more.  This much movement is relatively easy to see, at least with some practice.  This much movement, if indeed you have excessive end-play, can effect oil pressure, especially at the time of change to or from run-up to over-run.  There is no cure other than a general rebuild that includes use of appropriate thickness thrust bearings on the crankshaft to bring end-play back into spec.  If the pressure change is slight, something like 5 - 10 percent of the highest reading (hot) or less, don't worry, just be informed and warned that track-day racing is not advised on an engine showing end-play that can actually be seen. Good Luck!

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 Posted: 03-03-2006 03:17 am
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greenthing
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Thank You so very much for your replies evrybody. I think that the correlation between the JH and the ferrari is that I added an oil stabilizer to both. Upon looking at this(?) month's or last month's letter about additives, I think that this is causing the problem with both the cars. Sorry it took me so long to come to that conclusion. Wow talk about the newsletter being worth it! I will try a Motor Flush as recommended in another post by Judson and hopefully I will be able to get both of these cars up and running.

Thanks,

Greg Parris

Last edited on 03-03-2006 03:19 am by greenthing

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 Posted: 03-03-2006 04:33 pm
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Jensen Healey
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What is oil stabilizer? I have never heard of it. Is it like Slick 50 or Dura Lube? It shouldn't cause the symptoms you describe.

I quit using oil additives after Dura Lube corroded the drain plug in my SAAB. Modern oils are really good and if I want better oil I use synthetic.

Kurt

 

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 Posted: 03-03-2006 05:36 pm
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Greg Fletcher
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Judson mentioned wear on the oil pump rotor. Excessive end float can cause that problem. The way to check this is to remove or loosen the timing belt and pull the ignition sprocket front to back to check end play and measure with some dial indicator calipers. The gap on this end is exactly the same gap as the rotor to housing gap inside. If it's not too bad, you can shim the housing with a special, thinner plastic Lotus gasket (there used to be 4-5 sizes available). The manual calls for the end float to be 0.0015 inch plus or minus 0.0005 inch which I have always found wildly optimistic. You can also measure this directly at the rotor with Plastigauge. Plastigauge has the advantage of measuring any uneven wear across the rotor as well. BTW, use only the correct plastic Lotus gasket here- the wrong one (if you make your own for example) can ruin your engine if the pump becomes seized. It's happened and it's not pretty. Service Bulletin 73-26 covers some of this I think.

http://www.plastigaugeusa.com/

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 Posted: 03-12-2006 10:37 pm
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greenthing
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Lucas. Oil Stabilizer. I don't know if I should say anything more as I don't want to get sued. Still problem with oil pressure but only shows below about 3500 rpm.

Last edited on 03-12-2006 10:39 pm by greenthing

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 Posted: 03-12-2006 10:43 pm
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greenthing
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Greg Fletcher wrote: Judson mentioned wear on the oil pump rotor. Excessive end float can cause that problem. The way to check this is to remove or loosen the timing belt and pull the ignition sprocket front to back to check end play and measure with some dial indicator calipers. The gap on this end is exactly the same gap as the rotor to housing gap inside. If it's not too bad, you can shim the housing with a special, thinner plastic Lotus gasket (there used to be 4-5 sizes available). The manual calls for the end float to be 0.0015 inch plus or minus 0.0005 inch which I have always found wildly optimistic. You can also measure this directly at the rotor with Plastigauge. Plastigauge has the advantage of measuring any uneven wear across the rotor as well. BTW, use only the correct plastic Lotus gasket here- the wrong one (if you make your own for example) can ruin your engine if the pump becomes seized. It's happened and it's not pretty. Service Bulletin 73-26 covers some of this I think.

http://www.plastigaugeusa.com/

Thank You for your help. I will see what happens.

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 Posted: 03-13-2006 12:00 pm
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Judson Manning
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Actually...

While the rotor-to-housing clearance is VERY important, what I found to be often overlooked is the rotor-to-rotor clearance.  The max clearance between lobes is .006".

I've installed rotor w/ as much as .012" clearance between lobes that WILL pump oil.  However, it does take much longer to build pressure at start-up, and max pressure at temperature is limited.

 

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 Posted: 03-15-2006 03:50 am
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Joel
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Does anyone have a link to some photos - or a copy of the Service bulletin that covers the oil pump clearances, etc? 

I took off my carbs and manifold today.  And since (I'm sure  you all remember) the last time I drove the car the oil pressure started plummeting at temperature - I figured I should just take a look at the oil pump as well.  I didn't take off the entire pump - just the end where the distributor fits in.  To my untrained eye it doesn't look so bad. . .I haven't gotten out the feeler guage yet but the lobes seem quite tight together. . .

Everyone (including Bean Engineering) thinks I've got a problem w/ my front carb (Strombergs).  Everyone things this is probably why I'm firing intermittetly on the from 2 cylinders.  Instead of dinking around w/ the strombergs - I have a freshly rebuilt pair of Dellorto 40E's that I'm going to put on them.  Even more variables!!!

Only one more problem then I'll let everyone alone for a bit :-) .  When I took off the Carbs and manifold - i didn't drain the radiator - so unfortunately, I got some h20 in some of the valves and of course a little bit of water in the cylinder that the valves were open on.  I sopped it all out and sprayed everything down real well w/ WD40.  Then I turned the engine over by hand a couple of times and sprayed it down again.  Does everyone figure that's good enough?  I took out the plugs and sprayed everything w/ WD40 to try to make sure that I dissipated all the h2O. 

Who knows, I might even have it running again in a coupla weeks. 

Cheers,

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 Posted: 03-15-2006 03:40 pm
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Jensen Healey
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Where did that water go? It's either sitting in the cylinders or in the oil pan I would put a few squirts of oil in each cyl and turn the engine again. Then drain the oil and change the filter. The sooner you get it running, the less chance of having rusty rings.

WD-40 displaces water which is still somewhere in your engine.

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 Posted: 03-15-2006 03:44 pm
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Mark Rosenbaum
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Your coolant removal procedures sound adequate.

The oil pump clearance specs are all in the shop manual, and I've repeated them below, with comments.

Inner and outer rotor clearance: 0.006" max.
This is the lobe to gulley clearance between the two rotors.  In my car it's about 0.007" with no apparent ill effect.  As Judson notes, this clearance helps determine the maximum pressure available when the oil is hot.

Inner and outer rotor float: 0.000,5" min, 0.001,5" max.
This is the total gap between the flat faces of either rotor and the flat floor/roof of the cavity where the rotors sit.  This is the most critical clearance in the oil pump, as the pump loses the ability to prime itself when the clearance exceeds 0.004" or so.  The thickness of the gasket between oil pump casting and aux. housing casting affects this clearance.

Outer rotor to housing clearance: 0.001" min, 0.003" max.
This is the clearance between the outer edge of the outer rotor, and the side wall of the cavity in the oil pump casting.  In my car it's about 0.006" with no apparent ill effect.

 

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 Posted: 03-16-2006 12:16 am
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Joel
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Thanks for the replies.

I measured the clearances (as I understand them) and it looks fine to me.  I may have someone corroberate my findings but it doesn't look bad to me.  I think I'll put it all back together.  If I have problems again - at least this time I'll know how to tear it apart more quickly. . .

Also, I'm a little confused how one would measure the 'inner and outer rotor float).  The lobes don't sink below the casing so I would 'assume' this measurement is fine.  The gap between the lobes (measured at the tightest space when the lobes are 'closed' seems to be in spec.  And the measurement to the outer casing seems right on (measured on one side) the outer limit.   Ergo - my little brain thinks it's fine. 

Since I have the carbs off this was the time to check it so no foul. 


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 Posted: 03-16-2006 01:58 am
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Mark Rosenbaum
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Re the rotor end clearance, or end float: I will emphasize that one should not rely on an eyeball estimate, as a significant failure in either direction wll have dire results.  To determine this clearance, there are two practical methods:

1.  You can reassemble the pump with a length of Plastigauge in place, then disassemble and check the Plastigauge.  This is difficult to do unless the aux. housing has been unbolted from the engine, and does require a minimal expenditure.

2.  You can measure the protrusion of the rotors above the oil pump casting using a feeler gauge in conjunction with a straight edge placed atop the rotors, and compare this to the thickness of the oil pump casting to aux. housing casting gasket.  The difference between the two is the clearance.  This method is much quicker and non-costly, but in theory is marginally less accurate.

In either case, clearance is adjusted by either (a) installing a gasket of a suitable thickness, (Lotus used to provide gaskets in a variety of thicknesses but apparently no longer does so), or (b) removing material from the oil pump casting.

Only the proper Lotus gasket should be used as it is made of a special plastic with very good dimensional stability.  It is normally sealed with Loctite 515 or 518 (which is also an excellent adhesive and may glue the rotors to the castings if too much is used).  This means that one rebuilds the pump with minimum end play, and relies upon the thickness of the Loctite to increase the clearance by half a mil or so.

Attachment: Rotor end float.jpg (Downloaded 245 times)

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 Posted: 03-17-2006 02:04 pm
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Judson Manning
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Mark points out the 'correct' way of determining which gasket to use via plastigage.  If your plastigage skills are limited, I've had luck with another 'low-tech' method.

Delta, et. al. sells the gaskets in a number of different sizes, I have a box with about a dozen or so in thicknesses ranging from .002"-.007".  Don't ever assume the .005" gasket supplied with the gasket set is correct, get several.

My 'method' is basically to assemble the pump with the smallest gasket I have and see if I can turn it easily by hand.  If it won't rotate, I install the next thicker gasket until the assembly rotates by hand.  As the gaskets come in .001" incriments, the experienced hand can find that sweet-spot between .0005"-.0015" fairly easily.

I do disagree a little with Mark about which dimension is 'most critical' as I spent years concentrating on the rotor-to-housing clearance (while overlooking the rotor-to-rotor clearance) and had chronic oil pressure problems.  Safe to say all three dimension are critical, and none should be overlooked.

You think I've been bitten by the rotor-to-rotor clearance thing a few too many times???

 

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 Posted: 03-17-2006 04:32 pm
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Greg Fletcher
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Interesting thread guys! A very important topic. Unfortunately, too many owners spend bags of money on rebuilding a 907, but completely gloss over the whole rotor clearance thing. Getting a new rotor set, if needed, and taking extra time to check clearances is something that will pay you back down the road on the 907.

While I don't recommend that anyone make their own plastic gasket for rotor clearance, since a mistake will result in a ruined engine, I have done it and it does work. You need to be sure you are using dimensionally stable plastic (I used some commercial negative film material) and you must check the thickness accurately with a micrometer.

Judson mentioned "plastigauge skills"- Plastigauge is really very easy to use. For a novice, it's much easier than using vernier calipers. Plastigauge is no more "low tech" than any other mechanical measurment and has the distinct advantage of being a direct contact measurement. Genuine Plastigauge® is fundementaly accurate to 100 to 600 micro inches or 0.00001 to 0.00006 inch.

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 Posted: 03-17-2006 08:55 pm
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Joel
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Ok, I just got off the phone w/ a really pleasant fellow who does restoration work (B&A in San Marcos, CA).  i told him I thought the oil pump was ok.

So, when he heard the oil pressure had dropped thru the floor - he thought that it might be the main bearings.  He believes that even if the oil pump was shot - the pressure would only drop 10 psi or so - not all the way down TO 10psi or less.

Damn, I don't want to tear this engine all the way apart!  I was just looking to see if he could help me get some of the stuff back together since I'm traveling so damn much on business in the next 2 months. 

Comments?

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 Posted: 09-22-2006 07:02 pm
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jonseeley
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I had the same problem with a 907 engine. It was time to freshen up the engine so after dissassembley I miked the main bores with a one ten thousands bore gague and found that the main bores were eliptical.

I worked part time at an auto machine shop so I had access to the tools. I decked the main girdle about .005", then bolted it up and put the block and girdle in a align boring machine. I trued up the bores and the problem went away.

It is an expensive fix but since then I have found two other 907 engines with similar problems. I do not know if the fault is in poor machine work at the factory or whether the soft girdle gets pounded out of round.

 

Jon Seeley

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 Posted: 09-25-2006 01:58 am
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Sylva
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Here's somting you may be interested in. Last year at the Moto GP event in Sepang I ws introduced to a few 'old hands" from Lotus, (Lotus are owned by a Malaysian Company and people are ofton here). Some of these went back to the days when the 900 was being developed, and worked on the 2.2 development and as mechanics when the S4's raced in the US. Any way they knew their stuff.

Their advice was tha that the only oil to us in a 900 was Castrol RS synthetic, this protected the engine for 10 Degree C mre than any othel, and that oil surge caused by braking did less damage.

 

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