Bearing clearance- how much is too much?

Trying to assemble a 500" RB and I have two different sets of main bearings, King HP's & Speed pro 's. The King MB5116HP's (STD) are at .0025" and the Speed Pro M119 are at .0040". I would like to be at .0030"-.0035" The most logical solution would be a a set of King STD X's, but I can't find anyone that has them. Any suggestions?

Thanks, Brian

Given the choice of too tight and too loose, i will go loose every time. That being said i would stick the M119's in it and not give it a second thought.
There is a old saying " if your clearances are too loose, only you will know it, if they are too tight, everybody will know it".

Joe

We mocked up our 540 using Clevite 2324P and had .0029 but wanted more so we ordered 119M and that gave us .0033 which is great for our application. Maybe the 2324P would give you the clearance you are looking for (.0004 tighter in our block) The 119M was much tighter on the thrust and we had to work on that to get thrust clearance we needed.

Is this street or strip set up for you?

Drag race only, 5.80's eight mile.

Brian

I've run .004"before. Bearings looked the same as they did close to .003" No real difference in oil pressure either. Better a little lose than too tight.
Doug

Me Too

.004 here a couple times too.

You can always run gear oil in it to get the pressure up!

Almost all the engines I have built(small and big blocks)have been between .0029 and .0036 ans one at
.0022 and it cooked a bearing.. went back and opened it upon all to.0032... not much but it worked on all
of my engines.. I did run a old alum rod engine at .0046

back in the days they put aluminum foil back side of bearing to tighten up

The gauge shows what the relief valve says.
It's not the local pressure at each bearing, or an average.
Loose clearance insures that the pressure drop between the first and last bearings in a gallery is higher than a small clearance.
My conclusion: .004" is safer than too small, but stay away from the 0W20 stuff.

BTW: .001" clearance per inch of journal diameter was industry standard 100 years ago.

When I was a kid I watched my dad working on a Chevy 6 cyl .. he had spun a rod bearing(pretty sure
it was a rod).. he pulled the bearing and lowered the crank ... he got some emery paper at a hardware
and smoothed out the crank(as good as you can by hand.. cut a chunk of his belt off.. enough for a
upper and lower bearing and put it back together using the old oil.. had to add a couple of qts of oil
but we made it back home .. this was on our Deer hunting trip about 140 miles from home... he got another
junk yard engine when we got home.. I pretty much said I was gonna become a mech at that point

Soviet "repair" of needle bearings in Harley-Davidson WW2 military bikes, when no needles are available?
Cut pieces of coat hangar to length, pack with heavy grease.
Sell the bike.

Love the last line... SELL THE BIKE

Chevy 6's had babbit rod bearings into the early 50's. That was a very common roadside repair in the days of babbit bearings. Insert bearing made it more difficult because the insert was a lot thinner so the leather that thin wouldn't last long. But, if your choice is make the repair or walk home...

Wouldn't it be nice to be able to make roadside repairs like that today? But today's car are usually much more reliable.

Interesting responses. I'm absolutely not disagreeing with anyone here as everyone seems experienced and knowledgeable. In all the B and RB builds I've put together I've shot for .0025" on the mains, but would have been comfortable up to .003". Being that I've never ran an engine as loose as .004 I have no experience to say it's a bad idea, but my concern would be oil pressure.

I'm currently assembling a 289 Ford. My mains are just shy of .0015" and it feels a bit tight to me although it's within factory spec. I'd be more comfortable with .002 on the smaller 289 journal.

Point being, old factory specs are much tighter than many of us like to run, even at a time when oil technology was inferior to what we have today.

To the topic starter, I would have recommended the .0025 bearing without hesitation, but it seems like you might be okay a little looser. Happy Racing!

When we were searching for a bit less clearance on a set of bearings we had them coated and it worked like a charm.