When rebuilding my last engine I came across a question of oil bearing clearences. Of course the book calls for their to be a clearence of .0013-.0035 between the crank bearing and the connecting rod. They also call for a Main bearing clearence of .0010-.0035 depending on the main.

When I checked the crank it came out fine, when I checked the journal diameters with the bearings it came out fine. When I put them together (subtracted the two) I got values that were OK and a few that were off a little.

For instance, for the connecting rod oil clearences I got a max number of 0.00457 and .0045.
For main oil clearences I got a max number of .0029 and .0227.
I got these numbers after swaping a few of the bearings out also.

Would those numbers be too excessive? Is that two much clearence? Would torqueing it down another foot pound or two (one of the large ones) be OK? Am I putting too much thought into this?

 

They way I was taught growing up was, run mains and rods a little loose, and run a high volume pump. Factory motors like tight clearance, drag motors like fat almost knocking clearance. Street/strip can be loose.

I shoot for around .003 for mains, .005 or more for rods.

Just make sure only one shell is grooved, and run a high volume pump (and propper pan)

-- Joe

 

Or, you can follow the recommended specs and run a normal volume pump. My mains and rods are at .0015, and my oil pressure is around 25-30 at idle warmed up.

 

If the crank was in good condition and did not need to be ground and you are using new rod and main bearings ( I PRAY) than you don't need to worry about the clearances. just put them in right and tork to spec. no worries I just did my motor and no problems. if you had to turn the crank than yo wil have to check clearances to find out what bearings to get .10 , 020. 30 over and so forth. hope I anwered your question

 

Or you can run them loose like the pro's recommend, vs the haynes manual.

Tight clearances are not for street / strip cars. If he's looking to build a 10 year daily driver, sure. If he's building a 500hp street / strip car, then run them a little on the loose side.

Whats your oil pressure at 6500rpm?

-- Joe

 

So your guaranteeing his mains are bored and honed 100% to spec with the crank journals?

-- Joe

 

I actually think that is the reason my 355 gave up so soon. After 6,000 miles the rod and main bearings were worn down to the bronze, they were Clevite 77s.

At 6,500 RPM I was always around 60 psi oil pressure.

 

Is there any advantage to running them looser?
Could I torque them down another ft lb or two and then remeasure and run them that way?

 

You could always get slightly undersized bearings. Companies offer .001" or even .002" undersize to help reduce the clearance. I would say only torque to spec. I don't think you're going to make up a lot of distance just by overtightening. You should definitely do something about the rod clearances, those are way too much.

 

Sounds fishy... first I have never been a fan of Clevite bearings and second it sounds like to tight caps if it happened in both the rod and main... did you have your crank checked for clearances?

 

I had not measured the crank after I got it back from the machine shop after having it polished. Live and learn. Not checking clearences that one time really, hurt. The first engine that I don't check clearences on goes bad, who would have thunk it.

Why is it that there seems to be a good amount of people who do not like Clevite 77 bearings?

 

My oil pressure is 60 psi up top. Bearing clearances are more of a personal preference. The newer cars run tighter clearances with thinner oils. Running big clearances means running 20-50 oil to keep the pressure up and a high volume pump. I'm not planning on pulling this motor every season and checking bearings, so I put them in tighter than the 'pro's'. The 'pro's' probably take their motors out each winter and check clearances.

 

I will answer this question:

Why is it that there seems to be a good amount of people who do not like Clevite 77 bearings?

With this:

[QUOTE]Originally posted by Tibo

Enough said

 

clevite has no quality control on the parts they ship. i quit using their parts in any engine i put together several years ago.

 

I too have heard this rumor on TGO over the last year or so. However, I've called a few different pro engine builders and they all said it was horse crap.

I'm sure one or two parts left wrong, as with any mfg. But I'm guessing its about .009% of the overall bearings they've shipped to the WORLD.

-- Joe

 

i've got a new set of clevites for a BBC that look like they have 200,000 miles on them. big pit in a few shells, black looking crap on them, partly coated with the silver outer layer. your pofessional engine builders might be right be there's at least one dumbass that builds a couple of engines every year that won't use them.

 

Black looking crap? Are they H bearings? I know the H bearings look black and sooty.

Like I'm said, I'm sure a few make it out the door with problems. But clevite sells a *LOT* of bearings every year.

-- Joe

 

So what bearings would everyone recomend using?

 

Myself and a few friends have had pretty good luck with Federal-Mogul bearings...

 

I swear by them and so do my friends who race.

Clevites I swear at them