doctor_ratz

I need some suggestions on what to look for when I tear this engine down. Please bear with me, as I think the history may have some relevance.
A year ago I put a pair of completely new custom built 540's in my boat. For whatever reason one of the engines melted three pistons and blew all the oil out the dipstick before I could shut it down. The engine had about 10 hours on it at the time of it's melt down.
Last winter, I replaced the block, pistons, rods, roller lifters and had the crank turned 0.010". I re-used the cam, oil pump, sheet metal, heads and intake.
This spring after sufficient break in, the oil pressure just off idle runs at 60PSI, and stays there up to about 4000 RPM. At 4000 - 4500 the pressure will drop to about 20 PSI and stay there through wide open which is about 5200 RPM. During the same run, you can throttle back to about 3500 or so, and the pressure will start to buld back up, and after a few minutes it will be back to the 50PSI mark.
I thought it may be electric gages, so I put in a pair of mech gages to compare. The mechanical gages follow the electric gages perfectly. The oil temps on both engines run pretty low, and are the same, but only one engine shows this symptom.
I will be tearing it down this winter, any suggestions on where to look ???

TxHawk

iTrader: (2)

Lifter bore clearance is one place to look.

Does it carry better PSI with fresh oil?

If its not jumping around you could rule out a drain back issue where it is cavitating.

What oil filter are you running?

MikeyFIN

+1

TooTall

what oil filters are you using ? Do they have an anti-drain back valve on them?

kvogt

1. Make sure you don't have the oil level too high.

2. What is the oil pump pickup to pan clearance?

MILD THUNDER

iTrader: (3)

Burning 3 pistons sounds like you leaned it out or a timing issue.

Is it possible your oil pump was damaged from pushing aluminum piston shavings thru it?

Do you have oil temp gauges? If your pistons are glowing red from heat maybe your cooking your oil so hot its thin as water?

I had a buddy who insisted 10:1 compression, iron heads, tiny blower making 5 psi, turning 6000rpm wot was ok. It detonated itself to death, and right before the carnage, his oil temps were pegged over 300*

PatriYacht

Burning holes in the pistons usually means bad gas, lean carburation or too much ignition timing. But detonation usually shows up as high oil temps. You say that your oil temps are low, does that mean below 240 and where do you measure the temp? Do you use a windage tray in your oil pans. Long stroke cranks tend to blow holes in the oil unless separated by a windage tray. Also check the rod and main clearence. Centrifical force will tend to throw a lot of oil if the clearences are too large.

Griff

It could be aerating the oil in the pan at higher rpms. Try running it a quart lower on oil.

doctor_ratz

Great feed back, here are some more details. The pick up is about 1/2 " off the bottom of the pan. The pan is a 12 qt Dooley with a bolted in windage tray. Bearing clearance is 0.028" - 0.030" on rods and mains using H type bearings. Oil pump is a melling high volume standard pressure unit (re-used from damaged engine). Oil filters are standard Fram big block 1 qt truck filters, running SAE 30 oil. Oil temps are 220 - 240 with the temp sender screwed into the same spot as the factory sender along the oil pan rail in front of the filter boss on the block. I did not check the lifter bore clearance, but it is a brand new Scoggin Dickey GM block, and the lifters seemed to fit properly.
This only happens above 4000 RPM. It will run at 50 - 60 PSI all day if I keep it below 4000.
Yes, the old engine managed to get into detonation. Could very well have been a clogged water pick up.

Thanks again for the input.

mike tkach

iTrader: (3)

i dont like the fram filters,use either wix or moroso filter,also,30 w oil is to thin in my opinion,i use brad penn 20w50,it has zink&phosperous additives that help lubrication.also,useing the oil pump from the expired engine could be the problem,posibly shavings in the pressure relief valve.also,as allready stated,lifter bores might be oversized,i have seen this before.