Thread: 383 oil issues

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OK, first post!!
i dont usuallt have to ask questions about small blocks, but this one has me stumped!!!
First.. about me.. I built my first 350 in 1978 to replace a 250 6 cyl in a 1968 Camaro I bought for 300 dollars... was a CM (construction Mechanic) in the SeaBees.. NMCB 5.. and by 1988 was working for a chevy dealer as a truck mechanic during the day, and a performance shop building engines by night.. I am now retired.. having married a woman with college degrees that makes GOOD money.... I build engines and restore 4x4 chevys as a hobby income.

On to the issue...
Bought a 383... was told that they could not make it run right so they replaced it... Got the spec sheet with it.. not a bad build!! eagle crank and rods, Kieth black pistons, Canfield Aluminum heads etc etc...
A LOT of problems wit this engine as I pulled it apart...
First.. the chambers and exhaust ports had a thick layer of soot/carbon so they had WAY too much carb on it, or didnt know how to adjust it.. Cam was pretty hefty with approx 318 duration and 660 lift... didnt need that much cam.. pulled the main and rod caps, and they had installed standard Clevite bearings on the scat crank, that had radiused edges, so the bearings were ALL galled along the edges.. Oil pickup tube was an aftermarket bolt on tube in an M55HV pump.. ok... BUT, when I unbolted it.. it fell out of the pump.. as someone had GROUND the tube so it would easily slide into the pump.... Talk about buying someone elses screw up.... However, the price I payed for all couldnt have bought the heads alone...

I ordered the correct bearings, new rings etc etc... new oil pump pickup tube, new Lunati cam with a little less duration and lift than it had originally...
I put it all together, checking everything twice.. bolted it onto the stand and fired it up.. WOW, really sounds healthy.... except... as it begins to warm up.. temp hits about 120.. and the oil pressure suddenly starts to drop... I watch it go from 65 to 40.... 20.... 5... 0... I hit the throttle, Oil pressure jumped to about 25, then dropped again... in total, it probably took 30 seconds to go from 65 to 0...
I Pulled it apart, ordered new cam bearings, installed them, checked the plug under the rear main cap.. checked the rods and mains with plastigauge... Installed a NEW Melling M55HV, and put it all back together, bolted it to the stand and started it... same problem.. as it hits 110 to 120 on the temp gauge, the oil pressure suddenly starts to fall and does not stop...
I pulled the gauge, and hooked it to my 489... exactly matches the gauge in the cab... Pulled another gauge from the shelf and hooked it to the stand, and tried again... with the same results....

SO!!! I am befuddled, and looking for advice...
NO, i did not let it run with 0 oil pressure to check pushrods etc... I really dont want to toast the cam and bearings, so thats not going to happen. Just hoping someone has run into a similar issue... or asssit me to figure out what I am missing!!!!
ANY, input is welcome!!!! thanks!!!!

First - welcome aboard! Good to see you here..

You mentioned plastigauge, so what were the clearances? rods / mains... what oil pump? New one or used?

there more then one or two things it could be. but start at the basic.s.. post oil clearances

The rods averaged around .0015 and the mains were slightly wider at closer to .002 give or take .0001
The oil pump it had it in when i got it was a melling m55hv After I pulled it down the 2nd time I replaced it with another NEW Melling m55hv.

I have seen low oil pressure with excessive clearances, but normally the oil pressure drop is directly related to the temp. the warmer it gets the lower the oil pressure.. This thing seems to just suddenly decide to lose pressure, the gauge goes down like the second hand on a clock, going from pointing straight up to 0 in about the same time the second hand on a clock would go from 12 to 6. Bumping the throttle makes it jump about ten psi, but it continues to fall after. IE if the pressure has dropped to 40 it will jump to 50 when I hit the throttle.. if its at 30 it will jump to 40, then resume falling.

with such rapid loss I assumed there was a cam bearing problem, which is why they were replaced. I am going to start tearing this back down today. 80% chance of rain so good day to be in the shop.

If it has good pressure initially, and after running for a period of time the pressure drops to zero, its because the pump doesn't have any oil to pump---all your oil is probably upstairs-------------

A thing to try---time how long it takes for the pressure to fall and shut it off, wait 10 15 minutes and try again---same thing and time? now add 2 or 3 qts and see if it takes longer time---------If you want to be exact and truly scientific use 4 extra qts (1 in filter) and the time should double-----Quite possible the Canfield heads don't have the drainback holes drilled or they are in wrong place------------also look for casting flash/junk in the drains in the valley--------

If it's that fast a drop and timely too! I'd agree with Jerry and check the pan to pickup clearance first. Is the pickup welded to the pump?

Welcome to CHR, OldMech! It's strange that the "trigger" to the pressure loss seems to be related to temperature, around 120F on the coolant. I'll be interested in your thoughts on Jerry & Mike's ideas.

Thats a good thought.. I will check it!!! It has had two different pickup tubes on it, an aftermaket that was apparently screwed up.. and on finding it I thought I had found the problem... The pickup currently in it is a new OEM type that IS welded to the pickup(err.. PUMP) just over an inch from the bottom of the pan.. the pan is a 7 quart flare design standard depth with the "wings" to either side giving it the extra capacity. I had not thought of it running out of oil, and will address that issue to check on it. It runs several minutes fine, enough time to begin warming up... so this is a real possibility... Off to the shop to check on this... Thanks for the idea!!! Keep thinking outside the box! I need the brain power!

Originally Posted by OldMech

..... just over an inch from the bottom of the pan.. the pan is a 7 quart flare design standard depth with the "wings" to either side giving it the extra capacity.

Sounds to me like your pickup is too far off the bottom of the pan, too. I'd have thought not closer than 5/16" to 3/8", but not more than 1/2" from the bottom. More space will tend to limit the volume available to the pump.

I would shoot for 1/4" I don't think you'll suck the bottom of that pan up

In my opinion, Jerry nailed it. The motor is running itself out of oil.
Sling the HV pump over the fence and install a standard M55 pump. It's all the pump the motor will need. Set the pickup at 3/8" to 1/2" off the floor of the pan, using modeling clay to find the clearance. Make an ice-cream-shaped lump of clay and smush it onto the bottom of the pickup, then trial fit the pan, observing the length of the clay. Any closer than 3/8" to 1/2" may allow the pump pickup to suck down against the bottom of the pan and shut off supply to the pump. Any farther away than that will leave oil in the bottom of the pan that should be moving around the motor.

Some fellows will use Play-Dough for finding the clearance. I like to use oil-based modeling clay from the crafts store.

Has plenty of oil in the pan... I pulled the dist and put my primer and electric drill on it,and a different gauge mounted directly beside the dist hole. I can pull the trigger on the drill and the oil pressure jumps up instantly, and just as instantly starts to go down. if I keep the drill running it does eventually drop to 0.. I put a gauge on it that reads from 0 to 100 so i would have a more accurate reading than the cheap one on the stand...
Drill running, Oil at 0.. let off the trigger, hit the trigger, oil pressure jumps up to over 40 psi, and starts to go down again... ran drill to 0 oil pressure and checked oil.. reads full on stick, no oil pooling in the heads, drain back ports are open and clear.
If this was not the second oil pump to do the same thing I would think the pressure relief was bad in the pump.. possible? Yes, probable? no... to date, I have never had one, much less two (new) pumps with bad reliefs.. Have had the older melling pumps CRACK at the neck on hp motors causing a VERY similar problem, but have not had any issues with them since they redesigned the necks to beef them up.
Please... Keep the ideas coming!!!

Originally Posted by techinspector1

In my opinion, Jerry nailed it. The motor is running itself out of oil.

"I do agree, that is exactly what it acts like."

Sling the HV pump over the fence and install a standard M55 pump. It's all the pump the motor will need. Set the pickup at 3/8" to 1/2" off the floor of the pan, using modeling clay to find the clearance. Make an ice-cream-shaped lump of clay and smush it onto the bottom of the pickup, then trial fit the pan, observing the length of the clay. Any closer than 3/8" to 1/2" may allow the pump pickup to suck down against the bottom of the pan and shut off supply to the pump. Any farther away than that will leave oil in the bottom of the pan that should be moving around the motor.

Some fellows will use Play-Dough for finding the clearance. I like to use oil-based modeling clay from the crafts store.

Yes.. have clay I keep in the fridge for that purpose. On an OEM pump pickup the shaped bottom of the pickup precludes it from "totally" being blocked off.. onlike the flat pickup it did have in it. It can still cause a problem if there is gunk in the bottom of the pan...
From taking pumps apart, the only main difference I can see between the m55hv and the m55 is the pressure spring. You can take a set of stock vanes from a GM pump and slide them right into either Melling pump. I have often wondered HOW they can call it a HV pump if it has the same amount of vanes in the impeller.. I use the HV because of the higher pressure it delivers. this engine will run 8k rpm on a regular basis, but blocking a stock GM pump, grinding a groove for cavitation and putting a white spring in it would serve the same purpose, but the price of the melling pumps makes the labor or modifying a pump like we used to do not worthwhile.
Going to go drop off another block to have it bored Monday. When i get it back I'll transfer this rotating assembly, heads etc to it, and then have this block checked. If I, or one of you guys dont come up with a brainstorm before then. Reaching the end of my rope... Wife always did say my rope was short...

My first thought was cam bearings, but you already took care of that.... I did hear of a similar problem, though not as severe, on an engine that someone had drilled some too big holes in the front galley plugs to keep the (noisy and worthless) gear drive oiled up????? As the oil warmed up and thinned out the engine lost some oil pressure, not near as bad as yours is doing, though!

It did come with a gear drive, and had a 1/8 hole in the front plug, but it was replaced and the gear drive is now in the scrap bin...

I have a 400 on another stand.. Came out of a pickup because it was smoking badly and had about 5 lbs oil pressure at idle.. To satisfy my curiosity when i pull this down, I am going to bolt the pump on it and see what happens. We all know anything is possible when it comes to mechanical contrivances, but I am having a hard time thinking its the oil pump/pickup/pan.. The pickup is tilted down slightly and I dont feel it needs to go deeper with 7 quarts of oil around it and the baffles in the pan keeping it there.. but... I will take a look at that as well.. because, as mentioned.. it DOES act like its running out of oil....