oil pressure probs

I have a 540 Chev Merlin block with moroso single stage external oil pump with moroso two piece pan with single pan outlet (-12) feeding the pump and pump outlet feeding the block with oil filter adaptor. Pump is over 10 years old and never been checked or rebuilt. I bought new.

Had a oil pressure problem for a while now and figured I need to figure it out. I have had only one bearing issue in four years. spun rear main after breaking 4 inputs shafts so I attribute that bearing to overrev and not pressure. Never any rod bearing issues.

For the below graph pink line (sorry for the print ballon) you can see it has about 70psi at idle and when get on 2 step it goes to 75 psi. Then when trans releases it immediately starts dropping and gets down to 30/40 by end of run.

Obviously I figured it was pumping all oil to top, so I added 2 more quarts for a total of 10, no change. I recently noticed that when the trans brake releases the pressure immediately starts dropping. It doesn't rise with the RPMs then fall like you might expect and like it does from idle to 2 step RPM.

The sensor is at the back of the gauge in the cockpit, so could the acceleration be giving me inaccurate reading? While car is slowing down after pulling chutes and getting stoped the pressure on the gauge is usually in the 20 psi range and falling. So I kill motor at end of track.

Thanks for help and suggestions.

 

oil pressure

I'll take a stab at it just so someone else can explain why I am wrong.
It looks to me like your oil pressure is somewhat inversely proportional to your RPM. It even seems to level off a little after the gear change and then drop more as RPMs go up.
My guess would be that your pump is cavitating a little. A fix, if I'm right, would be a larger feed line on the suction side.
A test for this would be to use a lower viscosity oil to see if that made a difference. It's easier than changing all of your plumbing, and you would know in a single pass whether or not it was the right direction to go.
No, I don't know if that is a SAFE thing to do, but I would be surprised if it wasn't.
You are still below 30 lbs. of boost aren't you?
A friend of mine said his oil pressure went down due to oil foaming or frothing, and his solution was to use less oil and keep it away from the slinging crankshaft under acceleration. That seems like a bit more risky test, but it could be tried at small bites, like a half qt at a time and 60' or 330' runs to see.
See you at the races...eventually.

Kendrick

 

responses

Will - Thanks, I had these thoughts to and added 2 more quarts of oil which didn't make any difference.

I am thinking that if it were to be pumping it all up it would not be losing pressure exactly at the hit as the graph is showing. Graph looks same everytime.

Kendrick - Thanks, when I added more oil I am almost certain that the crank is running in the oil now, but afraid not to use that much as I don't know where it is going.

Traditional thinking says that your are pumping it to the top which I can believe only that as I pointed out above to Will that it seems unlikely that it is running out exactly as the hit, regardless of time on 2 step.

I run 20W50 Lucas now, what would be thinner, like 5W30 valvoline?

 

g force

Also notice that when the red g meter shows the chutes hit, the pressure spikes.

 

Is it possible that you have a crack in the rear main sadle area that when the trans brake is released and there is a load applied to the thrust area of the block it seperates the crack a little and you start looseing pressure? We just cracked a merlin block in that area but never ran it after the crack so I do not know if that is a possibility or not but it is a theory I would be looking in to if it were my problem since that added oil did not seem to fix it. Also on our block issue it was due to clutch heat and input shaft issues. We had no other main or rod bearing issues either.

 

Casey, pull your pan and fill it one quart at a time with oil or mineral spirits untill the oil is at your windage tray. Then add more until you figure it is where the bottom of the crank is. Alot of time the advertized cap. of a pan is alot less than what will actually fit. Then add two or three more quarts to this number to account for the oil trapped in the block, filter and heads. Don't worry about "frothing" as soon as it fires it will pump it back down to the tray. I'd stay away for anything lighter than 50 weight in a blower motor. As a side note I run 60 weight valvoline (13 qts with 2 qt's of Lucas Heavy Duty Oil Stabilizer) Could run 16 total but oil pressure is fine at 15 qts. MBR 526 with an Olson short pan. Hope this helps. However if it dosent call me and I'll see if Mike at RAGE Fuel Systems can do some of his fuel pump magic on your oil pump.

 

nail on the head

this is probably exactly what is happening. when it spun the rear main it did crack it from oil hole toward back. budget forces us to run as is taking the chance. checked it over winter and didn't see any change so continued to run this season. I did look at data from before spinning and it did fall off but only to about 50 psi by end of run and started to trend down while on chip so pumping oil up does make since in that case.

I will hopefully make it through as is for remaining three races and then we'll see what santa leaves under the tree.

Thanks for everyone's help. I think this is probably the culprit.

 

Ours cracked from the oil hole to the front. I am going to fix ours this winter and probably use it next season.

 

mr. fix it

What are the procedures for fixing something like that?

 

After we have ours done I will let you know if it works if you are interested in having it done.

 

Some places can bronze in the crack to fill it to keep oil psi.

If it gets welded (as in high nickel arc welded) the weld is a different hardness and its extrememly hard to line cut that bore round again as the cutter cuts different in that weld material.

 

Have you guys heard of Lock N Stitch process ?? This can be fixed without welding. Welding is a last resort.

http://www.locknstitch.com/

The guy that invented this did so because of similar issues in Cat blocks back in the 80's , it is the only way to repair cast iron , IMO.

There are dealers all over the US, the main shop is in Central Calif, the can recommend you to the closest dealer or you can buy the kit and do it yourself.

 

I seen a large lathe stitched back together after it had an incident and was broke in half, it worked and we used and even moved the machine afterwords. The lock n stitch impressed me.

 

The guy that started it all , Gary Reed has what I think is the most impressive wall of poloraid pictures of before and after repairs of simply huge castings as big as 14 foot tall and 30 foot long which literally broke in half and were repaired-----lots of on site repairs too, they have a crew that will travel the world to repair things, large ships with a broken jug and block on the engine , they will spend a few days and fix it right there. Simply amazing.

 

Crack fix

I am all for fixing the crack, but I don't buy that it is what is causing your problem.
I'll tell you why.
The thrust on the crankshaft that is created by the transmission is directly related to the line pressure and the area of the torque converter neck. Think of it as a hydraulic piston trying to push out of the trans pump. While you are on the trans brake, and on the chip, the load is infinite, like you are parked against the wall at WOT.
As your RPM goes up and you multiply torque, there are increasing loads inside the torque converter, but they are internal to the torque converter itself. If they were translated to the back of the crank, you would loose the thrust surface of your thrust bearing very quickly.
If this problem were related to thrust from the trans you also probably wouldn't see the spike when the chute hits.
I agree with Jody on how to figure what you need for oil, both in amount and viscosity. I wouldn't go lighter since you are already fairly light, I was just trying to think of a way to test my theory.
Just my opinion, feel free to dissect it.