jake corvette

I’m in agreement with a bjankuski that your main bearings are worn. As you open the throttle, there is additional downward load placed on the crankshaft, which in turn pushes it away from the upper main bearing shells. The resulting additional clearance will allow the oil to escape between the crankshaft main bearing journal and the bearing. Release the throttle and the downward load on the crankshaft will be reduced and the crankshaft will migrate upward a little towards the upper main bearing shell and upon it reaching it’s original position, the oil pressure will increase.

You can witness this very easily with a car equipped with a manual transmission by simply flooring the throttle in one of the upper gears at low or moderate engine speeds. If the oil pressure immediately drops under the increased throttle opening (load) with little or no increase in engine speed, (top gear, remember) then the main bearings have excessive clearance. Most of the time this is difficult to see with automatic transmissions because the torque converter slippage allows the engine speed to quickly increase and the increased rpm will mask the main bearing situation.

If an engine is in good shape – with normal oil clearances - high volume oil pumps in themselves will not result in additional oil being pumped though the engine at cruising speeds. However, they will increase oil flow at idle and off-idle speeds or any time the oil pressure is below the relief valve setting. On the production oil pumps that I’m familiar with, whenever the oil pressure exceeds the relief spring setting, the excess oil volume will then be routed back into the oil pump suction (inlet) side. Perhaps some relief valves do exhaust back into the oil sump but I’ve not seen any - then again I’ve not seen all pumps - LOL!. Disassemble your Melling pump and take a look at where the bypassed oil goes to and I am quite confident it will be routed back to the inlet side of the pump. But, I’ve certainly been wrong before!

High pressure pumps are different than high volume pumps in that HP units have relief valves with higher spring pressures. Compared to stock units, HP pumps will increase oil flow through the engine at higher speeds because of the higher pressures caused by the delayed opening of the relief valve.

A question of equal importance is why did the bearings fail under such light loads? If you weren’t really “thrashing” on the motor, the bearings should have held up just fine. If it were my engine, I would look very seriously at the oil pan baffles and make sure the baffles do in fact allow the oil to flow toward the pump inlet screen. Just a SWAG but I would look for air entering into the pump inlet – someway, some how - like the inlet screen becoming uncovered during your drive.

Valve train components clatter, rod bearings rattle yet main bearings can be relatively quiet even with some rather large clearances. Mains usually have a deeper thump kind of noise when they are really worn.

Melling high volume pumps are excellent pieces – have used them for decades with no problems whatsoever.

Just some thoughts – hope it helps a little.

Kubs

Thanks for your input. I have the 10552C Melling pump which is 10% more volume, but has the high pressure spring. I have not even looked in the garage since I found the bearing material in the oil. Too depressed. When I get back to it, I will be sure to check all these things.

Like cohocarl mentioned, I have the ARP stud for the oil pump which may be too long and could have wiped out the rear main bearing. That would at least offer a theory as to why it was OK when I first put the engine together, and why the bearings failed with such a light load.

Kubs

UPDATE:

Since finding the main bearings worn pretty bad I have been trying to think what might cause this. I was talking with a friend last night and he mentioned a bad harmonic damper has caused him to lose bearings in the past. I was just running the OEM one which is old, but looked OK but I never looked at it too closely. I will have to look it over again.

What are some good brands for harmonic balancers? I know ATI is considered top of the line, but my budget is no where close to the top of the line.

Sleazy Rider

KUBS, a little late getting to your party but here is my opinion on the balancer. with what you are doing with this engine, don't skimp on the balancer, get a quality piece that will handle the stress of a race envinronment. i am currently building a 383 lt1 motor and purchased an ati damper only because fluid damper does not make one for the lt1 vette. i used a fluid damper in my l-98 motor for drag/auto/road racing, freshened up the motor every year and never had an issue that could be traced back to the damper. not sure what we are going to do with the 89 at this point but still holding on to my fluid damper just in case this car and motor gets put back together. 2 cents please.

rklessdriver

I gave you some options on the balancer in Brians ST3 thread.

To be honest bearing problems like you seem to have are 99% of the time not releated to the harmonic balancer. I don't think it ran long enough for a problem like that to materalize.

Without seeing the parts first hand, I can't tell for sure you what cause this but I can tell you how to prevent it a second time.....

Just my opinion, but re check the size of your crank journals... re check the bearing housing bore sizes in block (mains) and rods. Make sure of your bearing clearance on the rods and mains.

Before assembly and even before the cam bearings get installed this time.

Remove every oil galley plug and blow thru it with carb or brake cleaner and then again with compressed air. Do it several times. The crankshaft, lifters, rockers and pushrods as well.

Of course you'll want to soak the lifters and rockers in a tub of new oil once they flushed out clean.

Once you know the oil passages are 100% clean - Then put the cam brgs in the block, then put the galley plugs in the block and then you can start assembly.

I'm sorry if you already know to do this but I have seen many bearing problems come back to metal and grit left in the block or crank from machining....

After it ate up a set of bearings this time you can bet it's got brg material everywhere now. I don't want to see you do this a second time.
Will

Kubs

Thanks Will!

Here is what the main cap under the pump looked like:



Two of the middle mains had no coating left on them. I have not checked a rod bearing yet.

rklessdriver

Wow. Thats flat out lack of vertical oil clearance.

The crank journal was actually contacting the brg shell....
Will

Kubs

The crank was actually turned 0.020" under so all the brlearings are 0.020" oversized. I don't have a bore gauge but can borrow some inside mics to measure clearance when I take it apart. It sounds like moving to a 0.019" bearing would be better?

Churchkey

Hard to tell from the shadows in the pic but the bearing shell looks like it has seen a lot of heat = lack of oil.

Kubs

The bearings are Engine Pro brand and they kinda looked dark/brown when they were new, but it would make sense that if there was not enough clearance it would be hot.

rklessdriver

There is no way to know what brg to buy until you know what you have....

Borrow the inside mics and outside mics and see what everything measures...

At .020 under the crank should measure:

MAINS 2.4280

RODS 2.0800

I will break down what I see on the brg shell.

The contact marks on that upper rear main brg shell show the heaviest contact at 10 and 2 (oclock). Thats lack of clearance.... Now it's not that heavy of contact because its just wear and not flaking or scoring.... This indicates to me lack of clearance not lack of oil.... lack of oil would be way worse.

Then you can see the shadow at the parting line where no contact occured, which just indicates the housing bore is not perfectly round.... typical in a factory block that has not had the mains blue printed with a line hone.

You can also see there is some taper ground in the crank journal since it only shows contact marks on the back/crank flange side if the the brg shell.

Now I assumed the brgs were an "H style Racing brg" which typically does not have the silver flash coating. race brgs when new they appear a balck or dark brown color.

Otherwise black is an indicator of heat on s tock stlye bearing.. which could be an indicator of oil starvation. But IMO if it were starved for oil the brg would look way worse than it does... best palce to tell that is to look at the backside of the brg shell and the saddle of the main cap and main register in the block... See if it is burned black.

Will

Kubs

Thank you for that detailed analysis. The block was line honed too, but perhaps the crank was not machined straight like you mention (it was done before I got it, not done with this build).

They are not black on the back, and yes they are Engine Pro brand race bearings which did not have a coating on them from the beginning.

Black89Z51

In addition, have your crank checked for trueness. The machinist I used on my last engine said he's seen a decent amount of cranks that are not 100% straight and have a tiny bit of wobble. Essentially bent cranks.

Kubs

It was supposed to have been checked this past time, but I will have him check it again.

jake corvette

Some very good advice here but I'll stick my neck out and say that for some unknown reason, there was a momentary lack of oil getting to this main. The bearing shell in the pic is a lower shell since there is no oil feed hole. My guess is that when you "roll out" the corresponding upper main shell that it will be almost like new.

Couple of thoughts: Did you plastigage the bearings for oil clearance as the engine was being assembled? Reground cranks always warrant measuring. I have seen a couple of cranks with different undersized journals, ie; .020 on one surface and .030 on another.

Here is a link for some pretty indepth stuff regarding bearings. Make sure you take a look at the second page too.

http://www.precisionenginetech.com/t...g-tech-part-1/


Best of luck.

Jake - -