Why don't I have any oil pressure

[534BC]

Originally Posted by j cAT

so if you just paid to rebuild an engine, 12 psi of oil pressure at idle or any other operating rpm , would be what you would expect ?

Only at idle if I didn't spec the sizes. Rebuilders are notorious for building in twice as much clearance as ideal , then using a hi-vol pump to make up for the mistake if necessary.

[big dwag]

So what scars the crankshaft Jcat when the bearings & crankshaft gets hot?

[534BC]

Crank wears when oil is sparce or non-existant between it and the bearings. Metal to metal contact causes fast wear over very little time.

[j cAT]

Originally Posted by big dwag

So what scars the crankshaft Jcat when the bearings & crankshaft gets hot?

only the crank shaft bearing surface is hardened steel . this is a surface treatment that is very thin but very hard when compared to the original hardness of the non treated metal.

I many years ago work at a lab that come up with this method. using lasers to do this with no distortions on the machined parts.

any way once the surface has a groove or not mirror like surface the crankshaft is junk .. with worn bearings because of low oil no oil it is condemmed !

run some 40wt oil in it might help.

[534BC]

SBC cast cranks are around 30-35 rockwell (if memory serves me)and not surface heat treated. (unless you are talking about a "thin" 1/8 inch.)

[j cAT]

Originally Posted by 534BC

SBC cast cranks are around 30-35 rockwell (if memory serves me)and not surface heat treated. (unless you are talking about a "thin" 1/8 inch.)

the typical gm crankshaft is surface treated only. this is about .005 inches ..that is thin .with engine heat damage this is now scrap metal value .

I guess you could get something from china or india that has a different spec.

[j cAT]

Originally Posted by 534BC

SBC cast cranks are around 30-35 rockwell (if memory serves me)and not surface heat treated. (unless you are talking about a "thin" 1/8 inch.)

this is from a crankshaft manufacturer:
Nitriding
Surface hardness and fatigue strength can be significantly enhanced by the process of nitriding. Performed after final machining of the piece, this process involves diffusing nitrogen into the surface of the steel at high temperatures (500 deg F or higher), This is done by bathing the hot piece in ammonia gas (NH3) for a period of time . The ammonia splits into hydrogen and nitrogen and the nitrogen reacts with the steel penetrating the surface (to a depth of .010" or so) to form nitrides.
By this process a much higher surface hardness (you can't touch it with a hacksaw) is obtainable when compared with case hardening. The piece becomes extremely resistant to abrasion and the fatigue strength is enhanced.

now you get that bearing surface too hot because of low oil .you can very easily get up to 500deg f area ..then you got a soft surface and then its all down hill ...

[534BC]

I don't think any sbc cranks are nitrided , especially the grocery getters like this one above. One grind and this would be gone anyways.

[j cAT]

Originally Posted by 534BC

I don't think any sbc cranks are nitrided , especially the grocery getters like this one above. One grind and this would be gone anyways.

it really don't matter who or how it was made . once the metal has been overheated it is scrap metal.

I just threw the hardness thickness spec in, to show it is truely a surface only hardness..A VERY THIN HARDNESS...

[Scrapper]

Originally Posted by j cAT

If the oil pressure is 80psi cold then drifts down to 12psi I would say the crankshaft is worn....did you measure this for excessive wear /clearances.


as stated this could be many things. you will need the spec's and re-open the engine and start measuring the tolerances..


I never liked the CHEVY 307....not very good back in the old days..

i seconed that on the 307.........

[MrPbody]

"Cast" crankshafts, "as produced" are NOT nitrided OR "hardened". Cast parts have a much higher "surface tension" than a forged part. We HAVE sent castings off for nitriding with good results. A casting is more "dimensionally stable" than a forged part, until it reaches it's "limit" of stress. For lower-level performance, castings are fine. Steel "forgives", iron does not... Thus the desire for a forged crank in most performance engines.

Many modern engines (particularly diesels) have "induction hardened" journals, not unlike the valve seats from mid '70s iron heads. It's clearly visible where the "bluing" shows.

The old 3" stroke forgings for the DZ engines, and some of the early LT-1 cranks were "Tuftrided" (a form of nitriding no longer available due to chemical restrictions). It's a "medium gray" in color. Nitriding borders on "black".

FWIW

Jim