Bearing clearances: Tight vs. Loose??

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n2omike
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Re: Bearing clearances: Tight vs. Loose??

Post by n2omike »

A little loose, nobody will know.
A little tight... EVERYBODY will know. lol

0.0010" clearance is only 0.0005" on each side. Most basic automotive machinists shoot for half a thou precision. Once you account for taper, out of round, etc... and do so for the block, crank, rods, etc... things stack up. Not all shops are have 9001 standards. Plus, parts FLEX under power, throwing everything out the window. Newer stuff flexes less. When it comes to bearing clearance with typical small/big blocks ALWAYS err on the side of loose. It will help cover minor variances in machining, etc.

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Re: Bearing clearances: Tight vs. Loose??

Post by Bigchief632 »

PackardV8 wrote: Wed Oct 05, 2022 10:48 pm The bad old days, loose was fast.

Today, a F1 engine is built so tight, it won't turn over at room temp. It has to have an hour of preheat of the oil and coolant to get all the assembly up to a pre-determined safe temperature to fire up.
Why do you guys always bring up F1 engines in these threads? Seriously, stop it, they have nothing to do with these boat anchors we're working with here. Is it to argue? A 632 needs .003 minimum on the mains, and .0025 minimum on the rods. Period. ESPECIALLY if the crank doesn't have a center counter weight.
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Re: Bearing clearances: Tight vs. Loose??

Post by Tom Walker »

Personally, I find it ironic and somewhat amusing, a guy that has been on the site for 2 months commands a senior member with almost 7000 posts and decades of experience to stop doing something.
Certainly good to have new members, and I welcome you to this fantastic place, just a little surprised and disappointed with the attitude taken.
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Re: Bearing clearances: Tight vs. Loose??

Post by mt-engines »

Tom Walker wrote: Thu Oct 06, 2022 3:54 pm Personally, I find it ironic and somewhat amusing, a guy that has been on the site for 2 months commands a senior member with almost 7000 posts and decades of experience to stop doing something.
Certainly good to have new members, and I welcome you to this fantastic place, just a little surprised and disappointed with the attitude taken.
Build a 632 using F1 clearances and see how long it runs before it seizes yourself.
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Re: Bearing clearances: Tight vs. Loose??

Post by Tom Walker »

My comments had nothing to do with the mechanics of the situation, only with the attitude of the situation.
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Re: Bearing clearances: Tight vs. Loose??

Post by Bigchief632 »

Tom Walker wrote: Thu Oct 06, 2022 3:54 pm Personally, I find it ironic and somewhat amusing, a guy that has been on the site for 2 months commands a senior member with almost 7000 posts and decades of experience to stop doing something.
Certainly good to have new members, and I welcome you to this fantastic place, just a little surprised and disappointed with the attitude taken.
Who says I haven't been here longer? I've been on here since 2004 or so. 2 different screen names. Lost my password, and didn't bother with it. My attitude? What about your attitude? Seriously. I'm trying to save the op from a disaster waiting to happen if he ran the clearances he was suggesting. My comment to the F1 comment, is 100% correct. Please explain to me how an F1 engine has ANYTHING in common with a 632 BBC? I'll wait

I'm not sure if Packard knows why they set them up as tight as they do? I'll tell you. They run at 16,000+ rpm for hours. How much heat do you think they generate during that time? They use oil heaters to pre heat the oil before the race, and are easy on it until it comes up to full operating temperature. In other words, it's necessary for the engine to survive the harsh environment it runs in. Follow? Otherwise, the engine would have waaaaay to much clearance at "their" normal" operating temperatures. I'm just tired of this retarded argumentitive attitude because someone doesn't bow down to someone's ignorance. And that's what it is, I'm right, you're wrong. I'm usually right. And in this case, .003 minimum on the mains, and .0025 on the rods, Period. And yes, I'm blunt. Because I'm sick of misinformation.
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Re: Bearing clearances: Tight vs. Loose??

Post by Tom Walker »

I totally agree with you on the bearing clearances.

I totally disagree with you on the “bluntness” approach, but it is not the end of the world.

All in all, I hope you have a good day and we can discuss speed talk type of conversations in future threads.
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Re: Bearing clearances: Tight vs. Loose??

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Re: Bearing clearances: Tight vs. Loose??

Post by 1972ho »

LOL good one🤣🤣🤣👍🏿👍🏿😎😎
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mt-engines
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Re: Bearing clearances: Tight vs. Loose??

Post by mt-engines »

How about this.. .0032m .0032 r
Callies CC crank
Callies Ultra rods
Dart big M billet caps

Mind you these are coated bearings.
16650979259627242995970942409421.jpg
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Re: Bearing clearances: Tight vs. Loose??

Post by 1972ho »

I wonder why ford was all over the place with there passenger car engine clearances back in the sixties/seventies
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Re: Bearing clearances: Tight vs. Loose??

Post by bob460 »

Must be a reason why NASCAR run tight bearing clearances :-k
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Re: Bearing clearances: Tight vs. Loose??

Post by mt-engines »

bob460 wrote: Thu Oct 06, 2022 8:02 pm Must be a reason why NASCAR run tight bearing clearances :-k
What does a 3.3" stroke billet crank and a 4.75 inch stroke have in common?

He's not building a NASCAR engine..

Does a nascar worry about cold start?
Does a nascar make a full throttle pass with 60 degree coolant temps?
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Re: Bearing clearances: Tight vs. Loose??

Post by modok »

It also depends on the bearing material.
Bearings with a thick lead/tin layer can run very tight and the material will......... flow? , to allow create clearance if needed. But a tri-metal bearing with a thin babbit layer, or a high silicon aluminum alloy bi-metal bearing has far less of an ability to CONFORM, nor should it need to.
Dura-bond cam bearings for instance, is a modern example of a very complaint bearing material. Very commonly used and you hear ZERO complaints.
Cam bearings often run half as accurate as main bearings, so for example .001-.004 is acceptable clearance. Housing bores are all over the place, looks like ford preferred to bore the cam tunnel with a dull drill half the time. #-o but it works.
But because modern oil is better, gas is better, filters are better, machining is better, there isn't much need to do it like that anymore besides cam bearings. the expectation that it will get looser as it wears was obsolite 50 years ago. Go ahead and measure some one bearings. did they get thinner? or did they get thicker? Sometimes they just didn't change at all.
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Re: Bearing clearances: Tight vs. Loose??

Post by Tom68 »

1972ho wrote: Thu Oct 06, 2022 7:46 pm I wonder why ford was all over the place with there passenger car engine clearances back in the sixties/seventies
All over the place yet 1.3 thou clearance would be OK for every main bearing there.
Last edited by Tom68 on Thu Oct 06, 2022 9:43 pm, edited 2 times in total.
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