low oil pressure

[Guest vince d]

I work for a major engine rebuilder and a group of us have been tasked with addressing a warranty issue of low oil pressure on 350 engines. Compared to the # of engines we sell the fallout % is pretty low but could be better. Most of the claims the customer states "going up hill under a load" sometimes a new oil pump fixes the problem and sometimes it doesn`t I know there are a lot of variables involved in this problem like pick up tube,relief valve spring, and other variables we have no control over like proper break-in and oil and filter change. Is there any hope for us. Any help would be appreciated.

[dr_hunt]

So, what are you calling Low? Sounds like your using "used" oil pumps when you say a new one will cure the problem. Is that true?

[Guest vince d]

No we get our oil pumps from melling. They are new but resently there have been a change in the relief valve spring specks. Before this change we noticed a fluctuation of oil pressure on the test stand. The change seemed to currect this problem.

[grumpyvette]

and? are you setting the bearing clearances to the stock dimensions? are you useing standard or high volume oil pumps? are you setting the oil pump pick-up to between 3/8" and 1/2" from the pan floor and BRAZING the oil pump pick-up to the pump,so it stays in that clearance range?

what else can you tell us? and keep in mind ,naturally a 4-5 qt oil pan is going to have more potential for problems than a 6-7 qt oil pan

 

ideally you want about 20-25 psi at idle but Ive seen no damage as long as the idle psi stays at 15 psi or higher, now PRESSURE is a MEASURE of RESISTANCE to flow so if you want to increase that resistance in a larger clearance application , swapping to a thicker/higher viscosity will boost the pressure reading....but it may not be a good idea as the oil flow reaching the parts may be delayed. now the other approach is to install a high volume oil pump, since it pumps abouy 10%-25% more oil (depends on part# used) that will accomplish exactly the same result,(higher readings on the gauge) and faster oil flow, but generally you want to run a deep or wide baffled high capacity oil pan and a windage scrteen when a high volume pump is used.

face facts, larger clearances require more oil volume/flow

why not talk to these guys

 

Melling Engine Parts

2620 Saradan Dr

PO Box 1188

Jackson, MI 49204

USA

 

Customer Service: 517-787-8172 ext: 125

Fax: 517-787-5304

 

technical@melling.com

[Guest vince d]

what is a windage screen. Is it necessary in a stock application. Is the milodium wrap around type the standard. Thanks for the info on proper pick-up tube placement. I just had a warranty return for the same scenerio I had described and sure enough the pick up tube was noticably bent up to close to the crank

[lbhsbZ]

As grumpy stated earlier, pressure is a direct result of resistance to volumn pumped. There are only 2 reasons why low oil pressure would occur. Either not enough is being pumped, or there is not enough resistance. If not enough is being pumped, you need to check the pickup location, check the pump gear clearance, and check for the appropriate amount of oil in the engine. If there is not enough resistance in the system, you need to check all for all the proper clearances in all the oil fed bearings. If the clearances are good and the pump and pickup tube location are good, the oil pressure gauge is bad.

 

On a side note: Are these problem engines being used with external oil coolers? I switched to an external cooler on my VW race car, with a fresh motor, and noticed about a 20 psi drop in measured oil pressure. Also, where are they measureing oil pressure. If you measure it at the back of block you will get a considerably higher reading than if you measure it at the fitting above the timing cover.

[Forces]

As grumpy stated earlier, pressure is a direct result of resistance to volumn pumped. There are only 2 reasons why low oil pressure would occur. Either not enough is being pumped, or there is not enough resistance. If not enough is being pumped, you need to check the pickup location, check the pump gear clearance, and check for the appropriate amount of oil in the engine. If there is not enough resistance in the system, you need to check all for all the proper clearances in all the oil fed bearings. If the clearances are good and the pump and pickup tube location are good, the oil pressure gauge is bad.

 

quote]

 

Or start by bench testing the gauge before checking all of your clearances....might be easier. But if it is a recurrent problem among many engines built the same way, it is unlikely that all of their gauges are bad.

 

Not to highjack, but what does it mean if you oil pressure doesn't change and stays constant at 15psi when the engine is rev'd up to 4,000 from idlewith no load on the engine? normal?

[Guest vince d]

This is not a big problem, less than 1% of our total warranty. Will a windage screen help on our stock rebuild applications.

[grumpyvette]

"but what does it mean if you oil pressure doesn't change and stays constant at 15psi when the engine is rev'd up to 4,000 from idlewith no load on the engine? normal?"

 

NO!....THAT would indicate a PROBLEM!!!!

http://www.babcox.com/editorial/ar/ar10180.htm

 

the general rule would be a MINIMUM of 10PSI per 1000rpm and that should hold true untill the bye-pass circuit in the pump activates at between 60psi-70psi, but oil pressure higher is no real concern up untill the 90psi range.

in most cases its the oil pump pick up that moves that causes many problems, IT MUST stay in the 3/8"-1/2" range and BRAZENING the oil pump pick up to the pump body after carefully verifying the correct clearance with clay between the pick-up and oil pan floor is strongly advised, but be aware that the bye-pass spring needs to be removed durring the brazeing to prevent anealing

 

 

NOW I POSTED THIS BEFORE BUT IT NEEDs REPEATING

ok look at it this way,what your trying to do here is keep an pressureized oil film on the surface of all the bearings to lube and cool them and have enough oil spraying from the rod and main bearing clearances to lube the cam and cylinder walls/rings. now a standard pump does a good job up to 5000rpm and 400 hp but above 6000rpm and 400hp the bearings are under more stress and need more oilflow to cool and because the pressure on the bearings is greater you need higher pressures to maintain that oilfilm.lets look at the flow verus pressure curve. keep this in mind, good oil flow volume across the bearing surfaces to cool and luberacate them and to provide a boundry layer between the metal surfaces is more important than the pressure reached at all rpms. since oil is a liquid its non-compressable and flow will increase with rpm up to the point where the bypass circuit starts to re-route the excess flow at the point were the pressure exceeds the bypass spring pressure. but the voluum will be equal to the pumps sweep voluum times the rpm of the pump, since the high voluum pump has a sweep voluum 1.3-1.5 times the standard pump voluum it will push 1.3-1.5 times the voluum of oil up to the bypass cicuit cut in point,that means that since the engine bearings leakage rate increases faster as the rpms increase because the clearances don,t change but the bleed off rate does that the amount of oil and the pressure that it is under will increase faster and reach the bypass circuit pressure faster with the high voluum pump. the advantage here is that the metal parts MUST be floated on that oil film to keep the metal parts from touching/wearing and the more leakage points the oil flows by the less the voluum of oil thats available for each leakage point beyond it and as the oil heats up it becomes easier to push through the clearences.now as the rpms and cylinder preasures increase in your goal to add power the loads trying to squeeze that oil out of those clearances also increase. ALL mods that increase power either increase rpms,cylinder preasures or reduce friction or mechanical losses. there are many oil leakage points(100) in a standard chevy engine.

16 lifter to push rod points

16 pushrod to rocker arm points

32 lifter bores 16 x 2 ends

10 main bearing edges

9 cam bearing edges

16 rod bearing edges

2 distributor shaft leaks

1 distributor shaft to shim above the cam gear(some engines that have an oil pressure feed distributor shaft bearing.)

so the more oil voluum the better.chevy did an excelent job in the design but as the stresses increase the cooling voluum of the extra oil available from the larger pump helps to prevent lubracation delivery failure, do you need a better pump below 5000rpm or 400hp (hell no! at that level the stock pump works fine) above that level the extra oil will definitely helppossiable deficient oil flow and bearing cooling and a simple increase in pressure does not provide a big increase in voluum that may be necessary to keep that oil film in the correct places at the correct voluum at all times.the stock system was designed for a 265cid engine in a passenger car turning a max of about 6000 rpm but only haveing the stress of under 300hp transmitted to the bearings, Im sure the orriginal designers never thought that the sbc or bbc would someday be asked to on occasion hold up to 450-800hp and 6000-8000 rpm.nore did they forsee valvesprings that placed sometimes as much as 500lbs and up loads on the lifters and the use of over 9 to 1 compression ratios in the original design so the oil voluums and pressures necessary to cool those valve springs and bearings at those stress levels were never taken into account for that either , the stock pump works but was never designed for the loads and rpms that a modern engine hotrodded to over 450hp sees

 

the standard volume pump gears are about 1.2" long the high volume pump gears are about 1.5 inches long (depends on manufacturer)

heres the discriptions right from chevy

 

12555884

SBC Oil Pump, High Pressure Z28/LT1. Production high-pressure oil pump with 1.20" gears.Will produce 60-70 psi oil pressure. Does not include screen. The pickup tube dia. is 5/8" for this pump.

62.17

 

14044872

SBC Oil Pump, High-Volume. This high-volume pump has1.50" long gears.It has approximately 25% more capacity than a production pump at standard pressure. Does not include screen.

 

and yes I comonly build small blocks useing bbc oil pumps like the ls7 pump, it has 1.3" gears but they are bigger in dia. and have 12 not 7 teethlike the small block pumps (many standard sbc pickups use 5/8" dia. pickups) (the ls7 pump is best used on 8qt-9qt road racing oilpans as the larger 3/4" pickup flows lots of oil for extreme high rpm engines with a multi baffled pan useing windage screens, scrappers and cut outs for extreme (G) loads where a dry sump can,t be used or cost makes you stick to a wet sump pan. these LS7 pumps dont fit most sbc oil pans so your stuck using the high volume sbc oil pump if your not using a true racing 8-9 qt style oil pan in some cases

 

I have done that for years whenever the oil pan clearances would allow the use of a standard voluum big block oil pump, the advantages of 12 tooth gears (over the standard 7 tooth gears in a sbc pump) for smoother running and the 3/4" inlet pickup size (over the common 5/8" sbc size)the slightly higher voluum of oil that builds pressure faster and the stronger pump design are benefits. (not huge but I use every thing I can get that returns a resonable return in performance for the money spent)

#21-210 SBC with BBC (5 bolt) oil pump

conversion oil pump Drive Shaft.

http://www.cantonracingproducts.com/oil_pumps/acc.html

don,t forget to braze the pickup onto the oil pump or use the bolt on style pickup

AND THE USE OF A WINDAGE SCREEN AND A BAFFLED OIL PAN to control oil flow THAT HAS A 6QT MINIMUM voluum is a great IDEA

 

 

once its correctly possitioned ,remove the bye pass spring and gears from the oil pump,and have the pick-up brazeD or welded to the pump body, then after it SLOWLY AIR cools (DON,T DROP IT IN WATER LET IT AIR COOL)replace the byepass spring and gears, lube the pump,with assembly lube on the gears, check the clearances, check clearances again! and install! just be damn sure its brazed or welded in the correct location as that 3/8"-1/2" is critical to good oil voluum feeding the pick-up

 

http://users.erols.com/jyavins/solder.htm

http://www.tinmantech.com/html/faq_brazing_versus_soldering.html

 

http://www.epemag.wimborne.co.uk/solderfaq.htm

 

silver soldering is basically lower temp brazeing , the soldering metal flows over the surface and into micro cracks in the surace of the other metal forming a almost unremoveable bond to the other metals surface it allows you to stick iron to steel or brass to steel, it works more or less like normal solder does on copper but at higher temps and has a much stronger grip in addition too working on iron and steel

I vastly prefer the 5 BOLT BBC style pumps with the 12 tooth gears and thier larger 3/4" pick-up VS the small 4 bolt pumps with thier 5/8" pick-ups and 7 tooth gears. the oil flow is both higher pressure at low rpms and smoother in pulse presure spread,no! you don,t need it on a non-race combo, or even on some race combos but its nice to have and I willingly will loose a few hp pumping oil for better engine lubracation