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I have a 90 5.7chevy hyd roller engine in my truck. I got the engine with a deal where i bought a bunch of parts off of a guy. He told me it had like 50k on it but i would think it was closer to 80/90 k. So the motor in my truck (88tbi 4x4 chevy)goes south and i decide to install this one and see how it runs. I put a new chain and oil pump on it before i installed it. Upon starting the engine i discovered it had very low oil pressure when warmed up. It was winter time and i really needed the truck so i just put 20/50 in it and ran it that way..( This was 4 years and about 50 k ago) Well you guess it i never did any thing about it because it worked fine with the 20/50 and i never had 1 problem with it ever...... Flash foward to 3 weeks ago. I notice the oil pressure driving is not going over 30 lbs. (it would run around 45 or so before) And when i would come to a stop with the a/c on it would drop to zero and turn the ligh on in the dash. No rattles or noises, the engine is very quiet.....

So i do the normal things, switch the senders ( i have never had this ever fix a low pressure problem but i had to try it) change oil and filter, check with another gauge.. Same thing. I am thinking the pick up fell off but it does not make sence that when the engine is cool the pressure is fine..... The other thing that is kinda stupid if i run the engine at idle and let it come up to temp the pressure is fine. Even on short drives where the temp it up to normal the pressure stays good. It only happens when i drive for like 15 minutes or more with the engine up to temp. The engine is still quiet and even when it drops to zero there are no sounds.. If you raise the rpms slighty it will come up to 10 lbs or so but never over 30 even driving up the road...

I am pulling the pan this weekend and replacing the pump and inspecting a bearing or two. I think it's a pump problem since it had low pressure from day one, plus i put almost 50k on it since the first low pressure problem and if it was a internal problem the enging would have been trashed by now.

Agree, dis-agree and opinions??????

Sorry it was long i was trying to give all the info i could

thanks keith
 

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IMO, you probably will find loose brg clearances, cam and crank, allowing for the press loss, as well as side clearance on the rods possibly, it doesn't take much press. 3-5 @ idle to keep it quiet, I doubt it's the pump? A hp pump may keep up with it?
 

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I would agree that it is in the pump. Plus, the whole engine is tired. I would bet a donut that the pressure relief spring is broken. (I've seen about 5 or 6 do that in SBCs and 4.3s)

tom
 

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Discussion Starter #4
up date

I got the pump off tonight. The spring wasn't broken ( I'll be out to collect the donut tom L.O.L.) but it was really weak. When i took the retaining pin out the end of the spring just stayed where it was at. I know they will usually pop out past the end of the pump. I am going to install a new pump with the high pressure spring. I really have nothing to loose. it was only a 1 and 1/2 hour job getting it out so i am going to try this....

Don't get me wrong i know it's only time untill the engine is done for, but i don't have the next one built yet......

I found something interesting. On the bottom of the oil pump gears there is a number stamped on them. The old pump was a 6 and a 4 the new pump were both 3's the old pump had .010 clearence between the gears at the pitch diameter, and the new one had .006 between the gears at the pitch diameter. Do those numbers represent the clearence or was it just a fluke that it worked out like that????

I also set the end play on the new pump to .002 the old one was .006



Keith
 

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low oil pressure

I once had a 426" Plymouth with a stage 3 max wedge, that was clearenced and at an idle, warm, it would run near 0-5 or so pounds pressure. I worried about it but never had any problems...
 

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Most every SB Chevy engine that I have had, the oil pressure has not been high. Even on a fresh rebuild, if I got 50# when warm, I would be lucky........Seems to be the nature of the beast. Have never blown one up.
 

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I have had a number of old stock sbc that acted similar. Change the broken or weak relief spring and they have a whole new life. Probably with the heavy oil and if you drove at higher speeds it pushes the relief further than it usually goes and with a broken or weak spring they can get stuck. I have an old pick up that did that and I would just stop the engine, with the pressure gone the relief would come back and the rest of the day would be normal. I finally put a new spring in it and have run it that way for the last 8 years.
 

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Discussion Starter #8
oil pump

Wow....this came back from the grave!!!! look at the orginal date...


Nothing i did fixed the oil pressure problem... I just built another engine for the truck... I think the new engine has about 20k on it all ready....

When i took the the engine in question out of the truck and tore it down,I carefully inspected all the main,rod,cam clearances and believe it or not found nothing wrong...I am still not sure where the low oil pressure problem was... maybe in the hyd roller lifters???


I am using the block for a R&D engine i am building for my shop beater car...So we will see if the problem follows the block or goes away... I am using a different crank/rod combo in it....


Keith
 
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