Oil pressure problem 15

[patprimmer]

This is not work related, but is really getting me down. If anyone feels it should be red flagged, then fair enough.

I just built a 409 CI SBC for my very good friends social ski boat, being the boat I regularly ski behind. It has been nothing but trouble in many areas and with several changes of plan mid stream.

I will stick to the bottom end and oil system at this stage.

Crank. Brand new Eagle 4340 non twist forging std 400 CI SBC configuration.

Rods. Eagle "I" beam 5.7" stroker rods with 3/8 ARP 2000 Cap Screws.

Oil pump, Brand new (well never used, but 15 years old) Mellings 55 oil pump.

It is a so called centre mount configuration, with the motor in back to front so it drives of the timing cover end of the crank, and is close to the bottom of the boat with the flywheel and the bottom of the timing cover only about 1.5 to 2" off the bottom.

This calls for a flat wide shallow pan, that has journal #1 running into the oil, but the oil pump clear of the oil.

It has a roller cam and the lifters restrict oil flow to top end. It has 240 deg at 0.050 and 0.600 lift.

It has new Clevite cam bearings installed by a reputable machine shop.

It has new King main and big ends. These are Std +0.001" bearings.

The pick up is an OEM flat pan shaped thing that is about 4" dia, has a bottom side half cover that stands 1/4" below a fill circle screen, so it keeps the screened pick up area about 1/4" clear of the bottom of the pan.

It has a tray of sorts that presses this pick up down below oil level.

With the engine turned off and plenty of time for drain back the oil is about 3" deep and well over the top of the pick up.

The inlet port of the pump has been tapped to 3/8" BSP thread and a -8 nipple inserted with originally Loctite 515 and later with Teflon thread seal tape.

The pick up has a -8 nipple welded to it.

The pick up is connected to the pump via a 1/2 steel reinforced high pressure rubber hydraulic hose over press in -8 fittings.

The oil pump was assembled with Clevite assembly lube, and the cover was sealed down with Locktite 515. Remember this pump is well above normal oil level due to 14 deg incination of the motor.

Filter is in stock location.

Main galleries and lifter galleries had plugs removed and tapped to 1/4 BSP as required to properly clean and reseal. Plugs were checked for length so as not to cover galleries and were installed with Locktite 515.

No plugs leak oil.

Sump Gasket. Felpro one piece.

Tray is a simple hoop with rear facing louvres. It clears the crank by a country mile and really does nothing but hold the pick up down.

The sump, tray and pick up are all from the previous engine.

It has good oil pressure when started, but it falls away fairly quickly after a minute or two running. If we stop, and restart 15 sec later, it has 75 psi pressure again, but falls to 10 psi at 2000 rpm and develops a knock.

We have had it in and out 5 times now, replaced the hose, checked the pick up position in the sump, re tightened the fittings, checked cap and pump are down square etc.

It uses Penzoil 20W50 GT or something or other oil.

On original assembly, many shortcuts were taken, to the point of the owner snatching parts and tools out of my hands and doing it himself as I was "wasting time checking things". These things were ring end gap, cam timing, piston to valve, and bearing clearances for instance.

It is carby/petrol with no apparent dilution of oil. There is a little water in the oil from a previous head gasket problem due to a dowel pin holding the head off just enough so the compression sealed, but the water did not and came up one stud into the rocker box, but only very slight discolouration due to emulsification.

Every time I question the system, I get abruptly told it worked OK for 25 years.

It has about 7 litres of oil. The old engine (an old school bog stock 350 CI SBC) with the same oil system except it had a BBC pump, previously ran OK with as little as 5 litres of oil.

Bottom line.

How can an engine have good oil pressure, loose it quickly after a few minutes, then have it again 15 or 20 seconds later, then loose it again after a few minutes running on a repeating basis in a stationary position resembling attitude of normal operation. The temperature rise of the oil was minimal and had no impact on the results.

It is the quick decline while running at a fast idle, then the instant recovery after stopping and restarting that has me puzzled as it seems it is not sucking air, at least not where we can determine.

Regards

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[ivymike]

excessive aeration of the oil due to crank dipping?

Do you have an external filter mount kit? You could try to rig up a viewing glass inline with the oil hose, and see what the oil looks like as it goes by.

 

[patprimmer]

Thanks ivymike.

That thought crossed my mind, but it improved somewhat when we increase oil level or lift the nose of the boat. The improvement is in the form of extra time to loose pressure. Also recovery on stopping is virtually instant, when I would expect it to take some time for the air to escape. Maybe a layer of froth is laying over a layer of good oil.

This engine has 1/4" more stroke, but more compact rods, so I can't imagine that is increasing aeration enough to make that much difference. In the old system it aerated the oil or left more upstairs and dropped level at sustained speed over 5000 rpm, like after 5 min running.

I have gone from a BBC oil pump to a high performance SBC oil pump to reduce oil flow and get less upstairs. It also has oil flow limiting lifters to put more to the bearings and less to the push rods and valve train. I expected this to help the sustained high speed situation.

Thinking on it overnight, I intend making a good windage tray and scraper and about 3/16" deeper sump. At that depth I estimate it will occasionally have light contact with the bottom of the boat, but not hard enough to cause a problem. It will have a full steel pick up bolted to a main cap via an extended stud. It will extend further back toward the back of the boat and will have some gates to trap oil at the low end. It will still have the crank running in oil at #1&2, but not so deep.

If I can improve return and windage, I can run a lower static oil level and reduce aeration.

The real answer is a simple dry sump system.



Regards

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[patprimmer]

The filter is in the stock location.

Regards

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[Peter7307]

pat, my thoughts...

If the "friend" pulled the tools from my hands because I "was wasting time checking things" then my obligation ends right there.

My response would be along the lines of
"You built it ; you fix it".

"Friends" like that I don't need.

The fluctuating oil readings may be either entrained air or a sticking relief valve from the 15 year old oil pump.

Cheers , Pete.

 

[MikeHalloran]

I'd feel better about that steel reinforced high pressure hose on the pump suction if it had a gun spring trapped inside so the liner couldn't collapse.

.. or if it were replaced by steel tubing.



Mike Halloran
Pembroke Pines, FL, USA

 

[patprimmer]

He has been a friend for over 50 years and is more like a brother. He is to good a friend to let this become a real problem at a personal level.

Regards

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[cheapcharlie]

Pat you are right about friends being more important than mechanical problems.Your also rt about the dry sump sys.The thing I can,t get past is the angle of the eng. The design requires the bulk of the oil to drain at the rear of the lifter valley so it misses the crank.One thing you might wanna ck before you pull it again is the bypass valve. If you still have the old eng just remove it and swap em. Its in the thing the filter screws on, but you knew that.
good luck, hope you get it figured out

 

[patprimmer]

I used the bypass valve off the old engine.

It bypasses the filter but still feeds the main gallery, so no real change in pressure.

Regards

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[RossABQ]

I tend to agree wit MikeH, I would be concerned with that suction hose section. How long is it? Was it replaced during the rebuild? If not, it could be too old, if it were, it may not be equal to the old. It is designed for internal pressure, not negative pressure.

I don't know why you mentioned the use of TFE tape on oil system fittings, but that is not a good idea.

The other thing is (not clear if these are new to the engine), you have a lot of fittings on the oil inlet system that necessarily reduce flow area. That should not be an issue at idle, tho.

 

[MikeHalloran]

One other thing: Most of these engines are installed in a car with the nose a few degrees up. If I'm understanding what you're doing here, the engine is installed nose down, maybe more than ten degrees.

... which brings up the question of whether there's an adequate oil drain channel from the lifter valley, at what is normally the high end.



Mike Halloran
Pembroke Pines, FL, USA

 

[Tmoose]

Melling 55 is a stock replacement pump.
55A is a high volume pump.

About 35 years ago I put a TRW hi volume pump (not sure if it was std or high pressure) in an old Chevy truck with a high mileage 283 that had slightly low hot pressure. When driving much over 40 mph with the HV pump the Stewart Warner mechanical oil pressure gauge would start to swing wildly, dropping real low and recovering every few seconds. My theory (which I now consider imperfect) was the oil drain passages in the heads and valley were too sludged up to let the oil return properly, and the high volume pump was pushing more oil everywhere, including up into the heads and valley than ever before, so in time the pan level dropped too far. At any rate, a new stock pump cured the problem.

I understand the sump, pickup and tray are the original items. Is that hydraulic hose new both times? How stiff is the new hose compared to the original?

Milodon says something like 1/4 " minimum to 3/8” maximum clearance between pickup and pan.

How long has the engine run at each re-assembly?

Is that long front to back pump pickup line path continuously up hill as mounted in the boat, or is there an up and down hill run with a possible high spot before the pump? Centrifugal pump manufacturers make a big deal about not allowing pockets on the top of suction piping that can trap air.

Before I took the engine out again I might change the oil for something real thin, then pull the distributor and valve covers, and use an electric drill to run the pump like I was priming it, while I watched the oil pressure and the oil caught in the heads, and checked the pan oil level. That would be an attempt to get crank whipped oil froth out of the picture, and gauge how much oil is making it upstairs.

If that test could re-create the low pressure condition, but the oil level in the pan stayed pretty good even with low pressure it would at least kind of shoot down the too much oil upstairs theory.

 

[patprimmer]

Ross

The hose was replaced twice, first time with a softer hose that was canvas reinforced and rated to 300 psi internal oil pressure, It could be squeezed down with very hard thumb pressure, but that was replaced with new steel reinforced industrial grade 3000 psi internal pressure hose. The second hose is identical to the hose on the original engine.

It is about 12" long (maybe 14" max). It is very hard and hardly deflects with thumb pressure till your thumb really hurts. It will not collapse with 15 psi outside and vacuum inside. I think you could probably drive a fork lift truck over it.

I never use Teflon tape. I use Loctite 515. It has never ever leaked before on threads sealing petrol, oil or water, or on metal to metal joints like VW crankcase halves. The owner insisted on using Teflon "just to make sure" because that is what he did last time. At least it was good "skived" Teflon tape or gas grade.

The new engine has a slightly longer tube and a 90 deg instead of straight fitting going into the pump as the SBC pump is smaller in outside dimensions, is shorter (so mounts higher in the sump, and has the inlet in the side rather than in the end closest to the timing cover like the BBC pump in the old engine. I have run a 3/8" drill through all fittings. I did that at home before I delivered them so as not to be seen as wasting time.

Mike

It is 12 to 14 deg nose down as installed. I enlarged the drain back holes into the timing cover, grinding the bottom of them down to level with the floor of the valley and adding a radius to the turn into the timing cover to assist drain back and I polished drain back channels in the valley floor with the inclination in mind. I checked the gap between the front main cap, timing cover and sump and while not a lot of room for drain back, it is at least as good as previous and I polished and enlarged any areas that did not impact on seal integrity or strength. In fact I ground a little off the edge of the pan gasket rail on the block in the area inside the gasket contact area, but I was not convinced it improved the most restricted area between the cap and timing cover. I did not tough the cap for obvious reasons.

As 400s have a bigger cap and wider spread main cap bolts, and as I type this, I now wonder if this area is more restrictive and restricting drain back. The timing cover/dog clutch housing/thrust bearing housing is very bulky around the front sump to timing cover seal area vs a std timing cover. The 400 main cap might be further restricting that area.

Tmoose

From old memory, I bought the pump as a Mellings high performance small block pump, as allegedly fitted to genuine OEM Z28 an LT1 engines.

The engine has been run 5 or 6 minutes average total each instal, so say 15 to 20 minutes with good pressure and 5 minutes max at low pressure. The second last time, the boat was driven and I only have the owners word. He claims it was OK for a few minutes then dropped off suddenly in a turn at about 4500 rpm.

We pulled #7 big end after this and it looked OK

Last time out we used a pump priming shaft and electric drill and removed the pressure sender to see what came out. with the flywheel end low, it pumped a bit of oil then froth and even pumped a reasonable supply of air. When we rocked the engine over to it's as installed angle, it instantly sprayed oil everywhere as it blew out little PVC hose off the temporary adapter. By the spray pattern it was at least 50 psi on the drill. On reconnecting the line we ran for say 15 or 20 seconds but stopped as the drill was getting hot. To do more we need a heaver duty lower speed drill.

The hose is new and is parallel to the crank and runs consistently uphill at about 12 to 14 deg.

We run it with no tappet covers and there is only a dribble of oil in the heads as is normal with Competition Cams roller followers which deliberately restrict oil to the top end. This is desirable as it has roller rockers and only needs minimal lubrication.

I need to fit a sight glass to the sump and I need to install a remote filter adapter so I can temporarily intal some clear tube to see the oil flowing.





Regards

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[dicer]

Pat, I think I remember something about oil leakage around the distributor body, especially if it is an after market distributor assembly. I just quick glanced the posts here, what about bearing clearances? What viscosity oil?
How about lifter bores to tappet clearances? Just some extra input here maybe it will help.

 

[patprimmer]

dicer

Thanks for the thoughts.

I was going to check the dissy annular grove.

This still does not explain why it comes back almost as soon as you shut down.

I think it has to be one or more of the following five, in order of probability considering attempted rectification already done.

Sticking pressure relief valve.

Sucking air into pump or pick up.

Aerated oil due to increased stroke and poor tray design.

Poor drain back between front main cap and timing cover.

Sucking pick up tube flat due to lack of coil spring liner.





Regards

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[RossABQ]

Pat, I would replace as much hose as possible with SS pipe. Even my old flathead has a solid 3/4"-ID suction pipe. It's the only theory that immediately explains the quick recovery.

 

[cheapcharlie]

I run 2 .060 restrictors scewed into the rear cam galleys with a 4 quart pan. oil pump is stock. z-28s used stock pump with a stiffer relief spring.This is now the same spring supplied in all gm small block replacement pumps I believe.You may want to check with comp cams on this but i think the lifters restrict the upper oiling by edge orfices at the top of travel which is going to put it in the lifter valley and its still gonna get wound up in the spinning crank on the way back down.

 

[NormPeterson]

Any chance that the pickup itself is collapsing or being drawn down such that the open area in the bottom is being restricted? Given that the pump suction is a through a flex hose, how is the pickup restrained against moving downward and/or rotating?


Norm

 

[JOHNDOE333]

I am curious as to what the rod and main bearing clearance is? Based on the components you listed and the intended use I would expect to see between .0025 and .003 on the rods and .003 and .0035 on the mains. If you are significantly looser than this then I could see the pressure falling off because of that.

My other thought was regarding the pick-up screen becoming uncovered based on the pan you have and the angle of the engine making proper drain-back an issue. However, I have seen pick-up screens become uncovered in the past (high volume pump with stock pan - for instance). But when this ussually happens the pressure will drop to zero and that does not sound like it is happening based on what you are saying. Best of Luck

-Good Day

 

[Thecardoc]

It sure sounds like you are collapsing the hose inbetween the pick-up and the pump. No matter how much pressure it's supposed to hold from bursting, avoiding collapsing from vacuum is a totally different ball game, especially when we are talking about a fairly heavy oil. I could see this tolerating some very small connecting hoses, with the oil pickup replaced with pipes. Cut the pipes so the ends of them almost touch if you want to change the pick-up assembly to something you can guarantee won't be the cause..

One thing occured to me, but I don't have a solid answer for all of the arguments against this. What about the discharge from the pressure regulator "fire-hosing" the oil away from the pick-up? It's possible the reversed mounting on the engine would have the normally positioned regulator flow blowing right at the pick-up. Engine RPM would play a major role in this because the higher the RPM, the more discharge there will be from the pressure relief.

If I had to pull this out one more time, I'd be rigging this to be run out on an engine stand in order to solve this problem.

The majority of engine oil flow in a running engine is pick-up, pump, and then pressure relief valve. By your description the failure has to be occuring before the filter, and then the rest of the engine.