tracking down an oil pressure problem

grumpyvette

Administrator
Staff member
I got this question posted to me

Thought you guys would like to hear the new motor. Got it done and it runs great.


Scat 900 crank, 6 inch scat I beams, kieth black forgings with 4 v relief, 11:1, 230 pro 1 heads, cam is 242/252 duration at .050, 565/540 lift, 112 LSA, RPM air gap intake, hooker super comp ceramic coated full lengths, holey 750 vac sec for street, pro form 750 for play, ls7 lifters, 4 bolt block, OE roller, fluid damper street damper, crower roller rockers...
Well, on the way to work today i had the oil presure fine till it gets into the RPMs, it will go up to 60 lbs and then start dropping to 40lbs while going up, and if i keep going it will drop to 20 lbs when i get closer to 6000. There is no noise from the motor so i hope it is a gauge problem. I bought another line kit in hopes it is from the small leak on the back of the motor where the tube goes in to the motor

thats FREQUENTLY a symtom of the oil pump pick-up being mounted too close to the oil pan floor or a restricted oil drain in the upper engine or too small of an oil pan capacity or no windage tray, ALL RESULT in restricted RETURN of oil flowing into the oil pump
THE OIL PUMP PICK-UP VIBRATING CLOSER TO THE OIL PAN FLOOR, OR LOOSE CRAP like bits of gaskets or sealants partly blocking the screen on that pick-up, COMES INSTANTLY TO MIND!
one of my friends had purchased a 1967 firebird 400 from a guy that had 120k on the orriginal engine it had good oil pressure at idle and up to about 3000rpm where it peaked then fell off if reved higher, the guy that sold the car said it had been that way for several YEARS, ever since he had the timing chain replaced? my buddy thought he was crazy, (thinking the timing chain had zero to do with oil pressure), but being more old school, I had a very good idea of the cause, and when I explained it too him he thought I was nuts, but I was correct, when we pulled the oil pan the oil pump pick-up was crammed full of plastic fragments from the orriginal aluminum and nylon timing set,and bits of gasket material clogged the oil pump pick-up screen
PICT0023.jpg
(similar to this)that had dropped into the sump as the old orriginal timing set had worn. replacing it with a cloyes true roller set and a baffled 8 qt oil pan, and a high voluum pump, instantly put the oil pressure curve back where it should have been[/b]

"It will idle at 45, when you rev it it will jump to 60-70"

ok the pump functions and the bearing clearances (SEEM) ok

"when you step into it and bring the RPM up slowly to 4000+ it starts dropping, in gear and without a load on it. I have a extra quart in her and it does nothing. "





then logically theres a restriction in the oil return flow too the sump,OR theres a restriction in the passages, in the block or oil filter, or pump feed/pick-up. if its a 4-5 qt oil pan your useing YOU could EASILY be having windage control issues where as the rpms increase the oil in the sumps beat to a froth, or a good percentage is being dragged around in the crankcase with the crank acting like a pump, impeller and you can,t get a solid supply into the pump stock pans seldom work on stroker combos above about 5000rpm, a decent pan/windage screen combo will cure that, and since I ASSUME youve checked or tested the other potential causes like your bearing clearances, oil pick-up clearance, and replaced the oil filter and verified the gauges, ETC.ETC, that seems like the most likey source & fix

http://www.moroso.com/catalog/categorydisplay.asp?catcode=11330

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thumbsup: Bearings and oil flow
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http://www.babcox.com/editorial/us/us90126.htm

http://www.thirskauto.net/BearingPics.html

http://www.micapeak.com/info/oiled.html

http://www.nordicgroup.us/oil.htm

http://www.carbibles.com/engineoil_bible.html

http://data.melling.com/Select/small_block_chevy.php

http://data.melling.com/Select/big_block_chevy.php

http://www.thirskauto.net/Engine_Thrust_Bearings.html

http://www.engineparts.com/motorhead/techstuff/crankinstall.html

http://www.babcox.com/editorial/ar/ar20128.htm

http://www.babcox.com/editorial/cm/cm99828.htm

http://www.thirskauto.net/Engine_Thrust_Bearings.html

http://www.diabolicalperformance.com/clearances.html

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

http://data.melling.com/TECH.php

http://www.babcox.com/editorial/ar/eb110127.htm

http://theoildrop.server101.com/forums/ubbthreads.php

http://minimopar.knizefamily.net/oilfilterstudy.html

you might want to read thru this

preventing cam & lifter break-in failures

viewtopic.php?f=62&t=1515

http://www.pbm-erson.com/uploads/cat%5B ... CEDURE.pdf

http://www.corvetteactioncenter.com/tech/oil/index.html

OPTIONS

it should be rather obvious that theres options, cam failures are usually the result of incorrect CLEARANCES or too much SPRING PRESSURE or LACK of ADEQUATE LUBRICATION,USE DECENT MOLY CAM LUBE, and decent quality oil, adding MAGNETS to trap metallic CRUD HELPS, be sure to change your oil filter and oil after the first 3-4 hours or 100 miles as theres bound to be crud and assembly lube trapped in the oil and filter
 
BTW if you go to pre prime the oil passages,..in the block before starting the engine, ID advise prefilling the oil filter if you can,and point out that the lower distrib housing forms one side of a main oil passage wall in the block, and without it youll never get full pressure,

sum-901011.jpg

this type above is nearly WORTHLESS

this type bellow works just fine


pro-66896_w.jpg


http://store.summitracing.com/partdetail.asp?part=PRO-66896&autoview=sku

they are dirt cheap or you can make one from and old distributor
SBCprimer.jpg


be sure you turn the engine over at least two full turns while applying pressure to and lubing the oil passages to get full access to all the lifters,rockers,bearings etc.

OK first lets clear one factor up

"I Did not put in a HV oil pump but engine builder said “ we did put in high pressure pump”. Isn’t this the same thing? "

NO! its not the same, all standard design chevy oil pumps use a BYE-PASS circuit to limit MAX oil pressure, a HIGH PRESSURE pump is a standard pump with the heavier spring to delay the opening of the bye-pass circuit from the standard 60-65 psi to a higher 70-75 psi, thus it has zero effect on the voluum of oil only the pressure level the bye-pass circuit opens at that limits the MAX oil pressure.

pump02.jpg

this spring keeps that piston in place UNTIL the pressure on the high pressure side of the pump overcomes the resistance and opens a return passage to the low pressure side of the pump, thus limiting the max pressure the pump can achieve.

pressure is the way we read the resistance to flow, oil is a liquid and can,t be readily compressed, adding a bit of extra pressure from 65-75 psi has very little effect on the amount of oil flow but it does increase the effort necessary to pump that oil and the wear on the cam gear and distrib gear contact area, a high voluum pumps have 10%-30% LONGER gears and thus sweep a larger voluum of oil at any given pressure, so it reaches any flow voluum about 10%-30% faster or at a lower in the rpm range.
adding a high pressure spring generally won,t hurt a thing, but it won,t normally help much either, if you want more oil, go with a high voluum pump.
the mod to the lower band on the distributor is not mandatory, but it does tend to add to the life span of the cam/distrib gears

BTW
look at the spring in the picture, notice one ends LARGER , this end goes against the retaining pin, get it reversted and the piston in the bye-pass circuit tends to bind and won,t work correctly, some guys slide a small washer/shim :WTF between the pin and the spring, on most pumps that won,t do a thing but add slight resistance and delay the bye-pass circuit opening a lb or so, BUT on SOME pumps IT WILL cause the bye-pass circuit to not fully open or open at all, if you want higher pressure USE THE CORRECT SPRING,DON,T SHIM the factory spring, it tends to cause far more problems that it could ever cure.


the larger the oil capacity in a CORRECTLY DESIGNED baffled oil pan with a windage screen, the less likely youll have problems, thats why I built a custom 10 qt baffled oil pan and run with a crank scraper and windage screen ON MY 383 vette.
BUT,6 qts is fine in a good pan, 7-8 qts is better, if you have the room, yet, its not the capacity as much as how well the flow and scavaging is that the system has as it circulates the oil quickly back to the sump, like your timing chain the oil circulates from the lower to upper part of the engine and as long as the amount is adequate and the temp is reasonable and it continues to CIRCULATE and cool/lube the bearings ETC. the amount is not as critical as the constant flow and transfer of heat away from the parts that are suspended on that pressurized oil film:thumbsup:

BTW


A windage screen BOLTS to your MAIN CAPS holding the crank in the block, or its part of the oil pan, its NOT the oil gallery sheet metal cover that keeps hot oil off the under side of the intake

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21318_inside.jpg

710-20403.jpg


a crank scraper

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removes oil forcing it into the sump as the crank rotates by it, both ideally need to be fitted with in about an 1/8" clearance to the rotating assembly, naturally the crank scraper DOESN,T CONTACT the crank assembly and mounts on the side of the oil pan where the rotation is UPWARD from the sump, so it tends to restrict oil flow from the oil pan that might otherwise get dragged around with the rotating assembly in the lower engine acting as an impeller at high rpms, you WANT the crank assembly to throw oil into, but not too drag oil out of, the sump, the windage screen or tray helps oil flow back to the pump and reduces drag from liquid and mist oil in the lower engine from oil that would otherwise be rotating with the crank assembly if it was blown around in the sump due to the spinning crank, the windage screen tends to isolate the sumps contents and speed the return of oil draining back from the upper engine
 
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