I recently rebuilt my 2 bolt 350 sbc. By rebuilt I mean crank honed, new bearings, new cam, new bearings, new pistons/rings, new heads, new oil pump, new lifters, and new gaskets all around. My gauge is only indicating 4-7 psi at idle though, and only going up a couple psi per thousand rpm's. It's only been ran for ~4-5 minutes. The gauge was displaying 80psi before the swap, but I think it wasn't connected or something weird like that. Any ideas? This is with 5w-30 oil and a standard pressure pump.

 

Rule of thumb, 10PSI per 1 thousand rpm's. Drive the car at 3500-4K rpms and see if the gauge shows 35-40PSI. If it is lower the bearing clearances might be high or the oil pump screen is clogged. Did you run the engine for about 20 minutes at 2K rpms? After you do that you have to drain the oil and refill with fresh oil then run it for about 1500 miles and then change it again.

 

I haven't done the 20 minutes yet because I was afraid I was going to hurt something. Oil is definitely flowing as I pre lubed the engine and saw oil coming out cleanly and steadily at a good rate.

 

Get a mechanical gauge to double check your pressure reading.

 

On a fresh rebuild you will have all the assembly lube; which in itself is very thick; metal from parts breaking in, e.t.c When you 1st fire it up you should run it at about 15-2K RPM's to start the initial breakin then follow the other steps.

 

Possibly break in lube jammed up in the sending unit of the oil pressure gauge.

 

Surely you dont want to break in an engine with low oil pressure? Did the block have anywork done? If so someone could of taken the plugs out on the front of the motor that are behind the cam gear.

 

I was running it at ~2500 then shut off when I noticed the pressure.

Good thought, will check with a mechanical gauge when I get the chance (putting in t56 right now).

It was bored and cleaned. I got the one under the rear main cap and forgot the 1/4npt plugs when I prelubed and oil shot across my garage but I put those in before it went in the actual car.

 

By the way, I did use a LOT of assembly lube. All journals were lubed, 2 packets of cam break in lube for cam+lifters, bottle of zddp additive, piston walls, etc.

 

Which oil pump did you use??. Standard,high volume,high pressure??. Oil pressure is normally a derivative of the bearings,oil pump,pressure relief valve. Did you check the clearances during assembly??. You said the mains are line honed??. Not line bored??. Where the main caps cut to restore them??. Why where the mains machined in the first place??. Where they out of round??. If so,was the crank turned also??. Did you step torque the mains and did they seat correctly on the parting line??. Did you do the same for the rods??. What was the torque value you used for the mains and rods??. What brand name bearings did you buy??. Did you rife brush clean the passages??. A important fact during oil priming a engine is you want to prime it so the drill motor bogs down only twice then stop right after. Once to fill the oil pump and once to pressurize the oil passages to prevent a "dry start". Otherwise you could wash out the assembly lube. The 2500 rpm break-in at 20 minutes is mainly for a cam break-in on flat tappet cams. If it is a roller it isn't as important. Varying the speeds you drive at over time helps set the rings. Don't run it at a consent speed for a long time. If those rings are chrome rings it can take a long time for them to break-in. Did you check the ring end gap??. On a standard rebuild you wouldn't normally check each one,but aleast spot check randomly. The same for piston skirt to wall clearances. How did the walls measure??. Out of round??. Honed??.

Yes,I know it is a long bucket check list. But all important things to consider.

 

None of that will affect oil pressure. Did you get the oil pickup tube pressed in all the way? If so then tou have a bad oil pump or your bearings are wrong. Recheck oil pressure with a mechanical gauge.

 

So I finally got around to pulling the pan after I double checked the low reading. Oil sump is on firmly, and the pump is brand new. The rods, however seem to move horizontally on the crank until it hits the counter-weight or the other rod. Is this normal? The machine shop who turned the crank turned it 10/10, so I bought 10/10 bearings. The crank was already 10/10, the shop didn't mean to say it was an additional .010, do you think?

 

This is where id put a sad face.... ya thats not good, yes its very possible they ment an additional 10 under. So u would need 20 under bearings.

 

Dannnggggiiitt. Yeah that's what I figured. Well, I know what i'm doing tomorrow Would the engine run with the oversized bearings though? And how can I check tolerances so this doesn't happen again? I've read mixed things everywhere ranging from plastigauge blows to jesus checks my bearing tolerances for me.

 

Plastigauge, ya it sucks cause its time consuming. If youre not too considered with absolute accuracy is get digital dial caliper measure outside crank journals and then measure inside of bearings.

 

Dont hit yourself too hard, it could of been worse.

 

Yeah I guess. I just hope one of my local stores will have the bearings in stock, I just put a 6 speed in and am pumped to drive it.

 

If I was running the machine shop I would of handed you the 20 over bearings when you where picking up your crank IMO.

 

Right, they could have been .010 too tight. That would have been much worse, don't you think? ;-)

 

Heh...it's not so bad. Got all the rod bearings done, and end caps off, just need to put the main cap bearings on. I'll let you guys know how it turns out tomorrow...

 

The world doesnt work that way anymore. Most no longer care bout the customer, do the job get paid move on.

 

Sonofabitch...this is starting to really suck. Long story summarized, ended up breaking the harmonic balancer bolt turning over the engine and ended up pulling it. Measured and re-measured .010 and .020 bearing clearance. Got .0015 for both on the rods. .020 split the plastigage giving it that reading (expanded, reshrunk?). Crank seized with .020 bearings. The .010 bearings seem to have been correct. Now what caused the oil pressure do you guys think? There was some oil behind the distributer and dripping down the back...but where could that come from and or cause 40psi oil pressure drop? I know the cam bearings were installed correctly (centered upon the oil groove) with the hole in the correct position, etc. Any thoughts?

 

Well, there is a vertical oil galley hole on the rear rail just behind the intake. Most of the time GM put a sending unit right there. These cars don't always follow that, but the hole is there anyway. What do you have in your hole? That could make for 0 oil pressure if it were open, but there would be oil everywhere. Are you sure about your pressure gauge? A leaking sending unit is often a bad sending unit.

 

Yup... definitely a sender unit there. I'm fairly confident about the oil, as the engine would stall when the oil got to 0 and the lifters would click as well

 

The rods will slide back and forth on the crank. Thats called side clearance. to much and the oil psi can be low. to little and itll be higher with hotter oil.
The crank will slide back an forth in the mains also, thats called end play and its measured at the thrust bearing.
10/10 means 10 under on the rods and 10 under on the mains.

Always always check your clearances and write them all down in your engine assembly note book while building.

 

Something goes in these holes...doesn't it?

 

Um, yes, 1/2" cup plugs, 3 locations. Be sure to stake them, and NO sealant on them. You can also drill small 0.040" holes in the two side ones to additionally lube the timing chain.

I hate to say this, but this is the first I read your thread and they are the first item that came to mind. Wish I had read it sooner. But you'll be up and running in no time.

RBob.

 

I think they usually come with the soft plugs set. Did you or the machine shop install soft plugs?

 

Wow... If your careful you can tap them for pipe plugs..