small blocks and low oil pressure?

[max]

well, i must be doing something wrong. i have built (3) small blocks in the past 4 years and all are doing the same thing.

oil pressure 85-90 psi cold and as soon as they warm up they drop to around 20 psi with 10W30 oil 

2) are 360 bored .040 over and are built the same. the bearing clearances are .0015 and the lifter bores are stock and i have checked the lifters to be sure they were the right ones.

all of the oil plugs in the galleries are in the right places i have ran different oil filters and oil with the same problem.

on this last 360 i even put a Milling oil pump with a spring kit in it trying to get the oil pressure up and it is still around 20 psi.

1) is a 340 bored .030 and it is doing the same as above and it is running Rotalla 15/40 engine oil.

these engines had the machine work done at the same shop so i kinda have a small theroy that "maybe" they put some weird clearanced cam bearings in these engines but other then that i don't know what is going on.

btw i checked the plug under the rear main which leads up to the oil sending unit on these engines and it is there so i know that isn't the problem.

i must be over looking something but i'm just at a loss as what it could be.

[JimShine]

My 318 currently runs around 25 hot. I changed the oil pump last fall as I was running Rotella and my pressure was suffering anyway. I am on the same oil (10-30), but am going to try Rotella next just to see what happens.

[deathcharger71]

my 360 was at 80 cold in the first few thousand miles of its life and has been at 65 cold and 40 warm for a couple months now, maaybe drops down to 30 if the rpms get low enough....in gear, badly tuned.

[max]

i'm starting to get the idea that it may have been the machine shop that did the work to them

all 3 engines had the machine work and cam bearings installed at the same shop.

the only thing i have been able to come up with so far is to much cam bearing clearances. which i guess they could have gotten into alot of seconds or bad bearings from the factory

i just started this last 360 on the garage floor with a radiator in front of it to see what it was going to do before it went in the car and when it is first started it is hold 95 psi with 10w30 oil and then when it gets to around 180 degrees of water temp it drops like a rock to around 20-25 psi.

[Chryco Psycho]

I suspect it is the machine shop

[deathcharger71]

just curious, have you dyno tested any of the engines to see how strong they are? if they all have a common problem it seems they would all have lower power then expected...

[max]

I suspect it is the machine shop

unfortunatly i believe you are correct and i was thinking everything over for the last 4 years running everything i did on each engine and there is one thing i remember and that was the first engine i built (360) which i went through that engine twice thinking i did something wrong in it.

but i went to the shop and was talking with the owner about the low oil pressure and was told all sb mopars run low pressure and i was told to disconnect the sending unit to keep it from flickering at idle, that is what they told the owners to do after they rebuilt engines for customers

i should have gotten the picture from that but i didn't so that ones on me

i believe it is time to find a new shop.

[max]

just curious, have you dyno tested any of the engines to see how strong they are? if they all have a common problem it seems they would all have lower power then expected...

unfortanatly they are street engines and i never had the extra money to put them on a dyno but i will say this much.

on the first 360 i put togeather it ran like a scolded dog but after it got about 30 miles on it the power level fell off and was very noticable.

so when i took it apart the second time the crank was eat up and needed turned and i found a ring that was broken and was still in the piston so it didn't hurt the cylinder bore.

after i got it back togeather it ran like a scolded dog again but as before the power fell off and then i decided to build the 340 short block that i bought from a late friend that worked at that same machine shop.

by this time the 360 was at 2 psi hot idle when i took it out and the engine might have had 100 miles on it from 2 rebuilds. i haven't opened it up to see the damage yet but i know the crank must be ate up again.

the 340 is holding 20 psi hot with rotellia 15w40 so i wonder how long it will last?

[deathcharger71]

thats a shame that a shop is continuously putting out bad engines, i hope you figure out a way to make it better.

[max]

thats a shame that a shop is continuously putting out bad engines, i hope you figure out a way to make it better.

well, to be honest i will not be using that shop again for anything. there are too many in my area that do better work for the same amount of money.

i have pretty much narrowed it down to those cam bearings but i'm not 100% sure, but everything else is right at the factory specs so unless i'm really doing something wrong or i haven't run across the right information that is all that is left.

[69chargeryeehaa]

just a fyi and my 2 cents but my 440 runs 80 when cold, and 20-30 when hot, in gear, at idle of about 650rpm.  cruise at about 65-75 psi all the time.  i remember reading some where where u should have roughly 10 psi per 1000rpm?  the guy who built my engine said it was allways like this, but for the first 100mi or so it dropped from 40-50psi at idle hot in gear.  by the way this is 10W30 regular castrol GTX oil.  i'm not so sure light weight oil or synthetics should be used in the break-in.  i've allways broken SB and BB engines on straight 10W30 and never had any problems ever.  i still run straight 10W30 oil and change it often, for the 10 mins it takes to drain, change the $3 filter and fill with $13 of oil, it's good insurance.  so i really don't think that 20psi at idle is a "bad" engine, if i bump my rpm up at idle to 700rpm hot in gear then i have 40psi at idle.  but on the other hand if your eating cranks then i'd definetly suspect the machine shop and not use them anymore.   

[max]

just a fyi and my 2 cents but my 440 runs 80 when cold, and 20-30 when hot, in gear, at idle of about 650rpm.  cruise at about 65-75 psi all the time.  i remember reading some where where u should have roughly 10 psi per 1000rpm?  the guy who built my engine said it was allways like this, but for the first 100mi or so it dropped from 40-50psi at idle hot in gear.  by the way this is 10W30 regular castrol GTX oil.  i'm not so sure light weight oil or synthetics should be used in the break-in.  i've allways broken SB and BB engines on straight 10W30 and never had any problems ever.  i still run straight 10W30 oil and change it often, for the 10 mins it takes to drain, change the $3 filter and fill with $13 of oil, it's good insurance.  so i really don't think that 20psi at idle is a "bad" engine, if i bump my rpm up at idle to 700rpm hot in gear then i have 40psi at idle.  but on the other hand if your eating cranks then i'd definetly suspect the machine shop and not use them anymore.   

i have never had any trouble with a big block holding less the 50 psi hot idle with 10w30 (knocks on wood) coarse it is really easy to adjust the relief spring if you do have any troubles but most of the time i have never had to do any adjusting except on my 426 and it was too high. it was running around 90 psi hot or cold so i changed the relief spring in favor of a weaker one and it holds 55-60 psi hot or cold with 10w30.

that is what i am used to seeing and when these SB's are in the 20-25 psi range i get alittle nervious and i also heard of the 10 psi for every 1k rpm as well and that first 360 was in that range but it really ate that crank up and i'm sure it has eaten it up again because right before i swapped the 340 in, the 360 was sitting at 2 psi hot in gear

maybe i'm just old school but i like seeing that oil pressure and i will take a lose of a few hp to see that difference.