What do you guys use for bearing clearance on a stock 396 build?

[L78fanatic]

My "new to me" nitrided, std/std, 3856223 crankshaft checks out on the journals (although my engine builder will be more accurate measuring the journals, I have no doubt). So, assuming stock journals, I am assuming .003" on the mains, with about .0025 on the rods. Does that sound about right? The spec on the mains for a 396/375hp engine is .004" max. so I may go a bit looser there. I can easily be within the rule of thumb of .001" clearance per each inch of journal size.

I will be running a standard Melling M-77 oil pump with a med/high pressure spring.

Thanks for any input,

John

 

[cheveslakr]

IIRC, the forged crank can get away with a big more clearance?? 3 is at the loose end. I talked myself into a good set of mics, inside and outside. Sterite on the inside and Mitotoyo outside. Both used, for I believe no more than $300. Now I won't have so many one sided conversations with my machinist. lol.

Edit add, forgot about your rods....002 is a good number. As it was explained to me, your oil and diameter determine clearance. Oil globuals measure .0006 ish, you want 3 at least to reside between the surfaces, 4 on the mains. That's minimum, you can push more globuals in and around the others, but they'll loose the stability the more that exist in that void.

 

[68Chevele]

I use .002 to .0025 on 1-4 and almost .003 on the rear main. Never had any trouble with that. Remember once you warm up the engine you can lose .0005 clearance just in heating up the bearings alone.

 

[bikeron]

I use plastigauge to measure clearance and also is useful to check for out of round. Rods no more than 3 mils ( I was told rods run hotter as they are closer to the combustion chamber, so a little more clearance) mains a little less at 2.5 on a 350.

5-40 oil, synthetic, get a spring that allows 45 psi oil pressure after warm up and 800 rpm.

Where did I get this info? From and old engine builder I worked with in High School.

Is it accurate? Not sure. Following these "rules of thumb" and measurement techniques have not let me down.

 

[Nashville Cat]

I was told 2.5 on both with a minimum of 2.
3 is too much IMHO unless you are going to use thicker oil like 20W-50, and that costs power.
I use plastigage.
The standard oil pump with blue high-pressure spring is what I'm running (Wolfplace recommended).

 

[68Chevele]

I was told 2.5 on both with a minimum of 2.
3 is too much IMHO unless you are going to use thicker oil like 20W-50, and that costs power.
I use plastigage.
The standard oil pump with blue high-pressure spring is what I'm running (Wolfplace recommended).

I have run a test back to back with 10W30 vs 20W50 at the track the same day, car ran the same times.

 

[L78fanatic]

I have run a test back to back with 10W30 vs 20W50 at the track the same day, car ran the same times.

Back in the day, living up North (in Illinois) when my car was new, I remember using 10W-30 in the winter and 20W-50 in the summer on my factory built '67 L78...I never had an issue. That engine was so sweet, that's why I am building another one. I used Kendall GT & Castrol oil as I recall.

 

[KwikSS]

Clearances are something you want to determine based on your intended performance. If you don't intend for high rpm useage use factory recommended spec's. If you are going to lean on the thing with some passion you might want to loosen up your spec's a bit.
Be honest with your intended use.

Checking Engine Bearing Clearances Without Breaking The Bank

Plastigage is a handy tool for the weekend engine builder to check engine bearing clearances. Find out more about this handy home-shop tool.

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