ok heres the deal, i had a cranked turned, put it all together, no oil pressure, took it apart, changed the bearings and oil pump, still bad oil pressure when hot and at idle. so i took it all apart, found out the crank was never turned, and had .020 over bearings, so i bought a NEW std crank and NEW std bearings, i just plasti-gauged it the first on had .001" clearnce, and the 2nd and 3rd didnt even smash the plasti-gauge?? i dont understand, any suggestions, what could be wrong with it? thanks oh and what is the clearance suppost to be? thanks

 

i take it you're doing this without a manual, that'd be first thing i bought before i went any farther. i wouldn't worry about plasti gauge, i'd measure it and be sure. i'd also suspect soemthing other than the mains or the oil pump. did you check it woth a mechanical gauge. i would, and i'd look for a missing oil plug somewhere ,also check the cam bearing oil feed holes. as for the clearances i'd say .0015 to .0025 is about right.

 

i have a mechanicle gauge, it reads about 10 in gear, while hot, so i put a NEW CRANK AND NEW BEARINGS, both std, so theres nothing to measure, but before i ran it i wanted to make sure that i have the right clearance, so i dont hurt the new crank, but since it isnt plastigaugeing right do you have any tips to plastigauge, or y it could be off, i already know it isnt a plug or a oil feed, because when we pulled it out 2 years ago it buried 80 hot at idle, so it cant be that, considering the cranks the only thing we messed with, it has to be it. but since the crank is new and the bearings match it, shouldnt it plastigauge??? y isnt it??? thanks

 

any other suggestions, can this be the block?

 

ede is right on. My motor has main bearing clearances no greater than .0023. You might want to overlook his post again. he mentioned the cam bearings, or oil plug. Engines build oil pressure thorugh resistance to flow...so you've got a loose end in there somewhere

 

That’s not right, did you spin any mains before you had the crank turned. I would check the clearance on the 2nd and 3rd ones and find out what is going on with them.

 

Is it possible you put some of the bearings in backwards.I was reading some brands they have to go in a certain way.

 

anyone that thinks a new crank and new bearing to match don't need measuered is a fool or a careless engine builder.

 

exactly if the engine is not building pressure either something was overlooked or you have excessive oil clearances. The oil pump does not build pressure in an engine as stated earlier. The clearances are what builds it. Make sure all your oil passages are clear and that all your bearings are installed correctly with the oil passage holes lined up. When starting an engine up for the first time check the pressure with a mechanical guage hooked up to an oil passage in the block, don't rely on the vehicles guage. And check the pressure before running the engine.

 

This is actually impossible. If the crank was standard, and you put .020 bearings in the motor, you wouldnt even be able to set the crank in the block, or get the rods to fit. A .020 bearing is thicker than stock, to account for the material removed when grinding the crank, so with .020 bearings, and a std shaft, you would have about .018 interference. Did you take the block to a shop and have them clean it???if so, there is a small plug, under the rear main cap that plugs 2 intersecting drillings on a small block. Most shops will remove this plug for cleaning, and alot of people do not know it should be there. The engine will have very low oil pressure if its not there. If you had the block cleaned, ill bet a six pack that plug isnt there. Get a 1/2 plug, and install it, and your on the road again. You still should mic every piece, whether new or not. We get $5000 cranks that are out of tolerance occasionally, so do yourself a favor and mic the crank, and find someone who can dialbore gauge the mains and rods to find the actual clearance.

 

you say that it wasnt posiible, but thats what happened, i had a friend, whos a engine builder, his car is in the 9's with a 350, and he said it was standard, and the bearings said .020 on them, as for the new crank the first main had .001 clearence, the second had about .0035 the third had about .0035 and thats all i had time to do last night, no it never spun a main, oh and the plug your talking about, isnt it recessed about 1-2" in the hole? thanks

 

yes, the plug is about 1" up from the rear cap mating surface. And if your crank was standard, and you really had .020 bearings in it, the crank would not turn, it would have about .018 smaller bore diameter in the main bearings than the outside dia of the crank would be. If standard size is 2.500, then .020 bearings would be for a shaft that measures 2.480, which would be a .020 interference fit. Those may not be the right sizes, but you get the idea. BTW, .001 is too tight to run, i would try to keep it at least .0025 or so. good luck
Bob

 

i talked to a buddy thats a ford guy, hes tore apart alot of motors, he says it needs aligned bored, when i found out it was standard a gauy that was new to michs miched it, so the old might be right. i am getting some snap gauges and michs from my best friends dad, hes a tool a die maker, what measurements can i take to tell what the problem is and what should they be? my dad said that he has built 20 + motors that had great oil pressure, buried 80 psi at idle, and he never miched them or anything, thanks again guys oh yeah ede, where can i get a manual, and how much

 

Unless it spun a bearing, it probably doesn't need line bored. Snap gauge the inside of the main bores, and check to see they are the right size, I believe it should be 2.6406-2.6417 is g.m.'s tolerance. If thats ok, put the bearings in, and measure the dia of the inside of them with the caps torqued on. Then measure the od of the crank, and subtract off the difference. The best way is to use a dial bore gauge, but if careful, snap gauges will work, just takes longer. You can probably check out a motors manual from the library, or autozone also sells manuals on specific cars.Just make sure the plug is installed under the main cap, ive seen alot of people not put it in, and it did exactly what you describe.
Bob

 

you can get a manual at any parts store for 20 dollars or so. lot of people slap engines together with parts straight out of the box and never have problems, but they can't say it's blueprinted, measured, or what the clearances are. there's always a chance someone somewhere screwed up too and you get wrong parts and trash an engine because you were too lazy to check.

 

I'm guessing these snap guages your refering to are the same as telescoping guages.

Check Main bore alingment if not done already with a straight edge and feeler guage. Also check mains for out of round and taper with caps torqed to specs.

 

it's good to check the clearances but i tihnk your problem lies elsewhere. i still think you're missing a oil plug in one of the oil passages or maybe the feed holes aren't right in the cam bores.