well the 355 is in and running but as soon as it reaches 190 degrees for a bit the oil pressure drops to nill unless i hold rpm around 1500. I know i put this engine together without plastigage and prob screwed myself, but the block and crank was fresh from machine shop with matching bearings. i doubt it is the sending unit since the motor has some bottom end noise when the oil pressure gets very low. motor sounds tight and great until it warms up then pressure slowly drops till nada.

I am still on the breakin oil and its about 1qt low from rocker adjustments, it has a greyish color to it mixed in with the clear new oil look. should i go ahead and change the oil? maybe it just got thin from breakin?? motor did get hot (240) on first run because the fan didnt kick in.

cold engine start up pressure is over 60 for 5-10 secs then stabilizes around 50, goes up with rpm.

warm engine pressure is around 25 and goes up with rpm.

engine at operating temp (190) for 5 minutes or so pressure is 1 notch above the red or in the red, will go up to about 30 at 1500 rpm but falls right back down to nada at idle. with bottom end noise (not a knock yet, but close enough you can tell its not oiling properly)

engine idles at 750 right now in park. I have moved the timing around some but doesnt make any noticeable change in pressure.


any ideas?

 

Expand more on the grayish color? Does it look sort of like a milkshake?

 

Does it have a 'graphite' look to it or milkshake like Stekman said? If graphite looking could be the assembly lube and moly lube from assembly...

 

Usinga factory guage? Would be worth your while to get an aftermarket gauge to test before you start pulling the motor. Graphite color sounds normal far as moly lube goes and all the fresh metal on metal getting seated with a brand new motor. Best thing to do is drain your oil and get a oild filter cutter so you can actually see what's in the filter element and this is the best way to know if tear down is necessary since copper will not stick to a manget when your doing your filter investigation.

Losing oil pressure when at operating temp is normal. I run 10w-30 fully synthetic with a qt. of lucas. Cold psi is 75, warm idle is 50-60 psi, and hot operating temp is 25psi at idle and goes up with rpm.

I assume your prelubed the engine before firing, and had the filter full of oil?

 

just drained the oil and inspected filter, got the graphite color and no pieces of metal, so it sounds like all is good inside the engine. i put fresh oil in and fired up the engine it went pretty much down to 20 psi (engine was at 120 degrees already, cold oil) so i am going to change the oil pump i guess unless anyone has other ideas.


was a brand new m-55 melling pump the way it fell from 30 to near zero the first time acts like the pump was bad but this is the first pump i have had to go bad this fast (not even an hour of use)

and yes the engine was fully lubed with moly based lube, then just before we set it into the car we ran the oil pump primer and turned the engine by hand 4 full revolutions to let all the oil get into the engine.

it ran great and held good pressure for first 45 minutes or so, i was tuning on the carb when the pressure hit zero and beeped.
and for the guage concerns, i am using a factory guage but when the pressure drops to zero i can audibly hear the bottom end a little bit so i trust its really losing pressure.

 

Thats interesting... I am running the M55-A on my new motor, and it has performed great so far. I cruise at about 45psi of pressure, and then at idle the lowest I have seen it is 25 psi and that is in traffic w/ the motor running 200+ degrees...

Could be the pump... you make sure the pickup was at the right distance from the pan?

 

see thats sounds about right it was holding 30 psi hot the first 30 minutes or so the car ran (after 15 min warm up) then it just dropped , I am going to start it up in a couple hours to move it into garage but i have a feeling i will be hard pressed to get pressure from it with a cold engine now.

I have never seen a pump go out this fast..they always work, or rarely dont work at all, but to work great for about an hour then die has never happened to me ever.


i used stock pan for engine and stock pickup tube from the engine so i didnt do any measurements. i made sure the pickup tube was aligned right for the pan and then tossed a couple tac welds on it so it wouldnt drop off etc etc.

 

Pumps don't "go bad" like that. You'll be wasting your time.

Sounds to me like the cam bearings aren't indexed properly; I bet if you pull the cam, you'll see all their oil holes at 12:00, or something stupid like that.

I've built more motors than I can remember with M55 pumps, or the equivalent for whatever motor it wqas (M77 etc.) and never had one fail. The onliest failure I've ever had was the dumb plastic sleeve broke (it was on a M77 BTW, exactly like a M55 except different), and the rod ate the top of the pump, so I always use the metal sleeve version of the rod (IS-55E et al) now.

 

well RB we agree 100% , i too have built quite a few engines and used melling pumps, i have never seen one go bad like this either.
considering these things are mass produced i guess there has to be a first time for a weak/bad pump to slip by QC at Melling.

i have 2 choices avail to me right now, change the pump and see or pull the lg4 out of my 85 prix and drop it in while i tear the 355 down to see what the hell went wrong.

so i am going to dress the lg4 in my prix back up and get it running (so i have a car that moves) then i am gonna try the oil pump, if that dont work the engine is coming back out for a thorough inspection.

And the cam bearings will be my first area of inspection, would be the first time i had a machine shop slip on the cam bearing install. hell this is the first time i have built an engine and had any internal problems, my way of working is to do the job once then double check it later before a pan covers it etc etc.