Most allowed main bearing clearance on 440

[minnesota guy]

Survey what you guys allow as the most allowable tolerances you allow on 440 main bearing clearances and also the rod bearnings. 500Hp motor.
Thanks.

 

[lewtot184]

depends on if your driving or racing.

 

[Kern Dog]

My understanding is that there is a tolerance range that you'd aim for in a street engine that is expected to last approx 100,000 miles. The spec I aim for is .0015-.003 on the main bearings and .002 to .003 on the rods. A race mill can run slightly looser, say .0025 to .0035. The oil pressure will drop a bit but it frees up a slight bit of restriction.
My 440/493 runs great oil pressure. The rods were all in the .002 range. My mains spec'd out weird though. They got tighter from the rear to the front. My rear bearing was at the end of spec, .003. The front was at the other end, .0015. Not sure if this was related to the crank or the block. No biggie either way. It runs hard!

 

[Dibbons]

I use maximum factory tolerances, usually .003, can't go wrong.

 

[dieseldazzle]

.0017 -.003 I wouldnt go any tighter or looser....

 

[lewtot184]

i use the old .001" per 1" of journal diameter. a racer can go a little looser. the streeter/driver i'm putting together now will have between .0022"-.0024" on the rods. and .0027" on the mains. i use mics and dial bore gauges to measure.

 

[69Bee]

My understanding is that there is a tolerance range that you'd aim for in a street engine that is expected to last approx 100,000 miles. The spec I aim for is .0015-.003 on the main bearings and .002 to .003 on the rods. A race mill can run slightly looser, say .0025 to .0035. The oil pressure will drop a bit but it frees up a slight bit of restriction.
My 440/493 runs great oil pressure. The rods were all in the .002 range. My mains spec'd out weird though. They got tighter from the rear to the front. My rear bearing was at the end of spec, .003. The front was at the other end, .0015. Not sure if this was related to the crank or the block. No biggie either way. It runs hard!

If you did not align hone the mains, I can see this happening because green iron moves when it relaxes (seasoning, stress relieved, etc). Normal stress relieving is accomplished during the heat/cold cycles of operation. This is why I always recommend customers align hone/bore their block first, because everything else is based off of the crank centerline. Chevys like a little more clearance for the rear cap as the oil pump is bolted to it, and you would be amazed at how much the cap moves just by bolting it in. I use a pump jig attached to the cap when I align hone to ensure it is round when the pump is attached.

A little (0.0005" or so) additional clearance on the #1 main helps so as to not burn up the bearing by over tightening the belts. I like to see 0.002" to 0.003" (0.0025" is better) on the mains, and 0.0015" to 0.0025" on the rods. Just remember, the larger the rod clearance, the larger internal oil leak you have, so ALL clearances should be commensurate with the intended use of the engine (stock/street/race).

 

[bm02tj]

Use proper gauges for clearance not plastigage as it is not accurate enough

 

[dvw]

I would absolutely not run less than .0025". Min spec is usually .001/inch of journal diameter. I've personally run .004" with no issue. Current race motor (572") runs 0W30 Royal Purple , 60psi@7100. Bearings have been checked 3 times, every 100 passes. They look like they came out of the box. My two street cars that have been together for over 10 years, both shifted at 7000 rpm (blown 340 and 360 with stock cranks and rods) with .0025+ clearance. A wise man said, "if you have extra bearing clearance you will know, if you don't have enough everyone will know". The more inaccurate the machining the more likely you are to have issues with tight clearance. A side note. On the recommendation of several top engine builders I didn't worry that my race motor had .004" clearance. When it ran there was low oil pressure, I panicked. Not paying attention to the professionals I pulled the pan and tightened the clearance up to .003". Guess what it did for oil pressure? NOTHING. Turned out the pushrod holes were to large sending to much volume up top (pushrod oil).
Doug

 

[dieseldazzle]

I always use plasti gauge and my mics it's a way of double checking myself. I'll be honest here when I first started building motors years ago I wasn't very good at reading the mics or placing them in the main saddled or rod journals took awhile so I always used plasti gauge to help teach me. It worked as I can read as far down as my mics can accurately measure which has worked for 20 years now

 

[bm02tj]

Yes plastigage is a good back up if it flattens out it is to tight