Loose as a Goose! Are Bearing Clearances Absolute?  

Some bearing manufacturers have two, special part number bearings that will give you either .001 more, or .001 less than "standard" factory clearance when mated with a "standard," OEM original journal size. When you are a 1/2 thousandth (0.0005") either too tight or too loose, you can combine 1/2 of a bearing shell from the standard set with 1/2 of a bearing shell from the tighter or looser set to get exactly the clearance you desire. Standard, factory-recommended clearances ensure plenty of oil pressure throughout the life of the engine, especially to the rearmost bearings. Slightly looser clearances increase the depth of the oil film which may be beneficial for heavy loads or high rpm. However, there are downsides to wider clearances. Oil pressure with a standard pump will likely decrease due to increased "leakage" at the bearings; the rearmost bearings are more likely to see starvation. Switching to a high volume oil pump will "keep up" with the bearing "leakage" and ensure pressure to the rear; however all the additional oil being shed through the bearings creates additional windage/drag, and the higher volume of oil thrown onto the lower cylinder walls may overcome the oil rings' ability to control it and lead to increased oil consumption, combustion chamber deposits, preignition, etc. With a standard volume, factory oil pan and a high volume pump there can also be a risk of pumping the pan dry at high rpm or uncovering the oil pickup during hard acceleration or cornering, leading to engine damage due to complete loss of oil pressure. Bottom line: bearing clearances are a balancing act. Either too tight or too loose creates significant problems.

I use a machined staight edge to check straightness of mains by seeing if a .001 thou. Feeler gage will slide under it, then i torque all mains and dial bore gage them, then release all caps and install just front and rear bearings and lube them then i lay the crank in them and use a dial gage to check crank straightness by rotating the crank and check runout on 2. ,3. And 4 ,if all is well then i plastigage

One time a shop I worked at the engine builder having trouble with his girlfriend did check the bearings on the mains what number they were, ended up putting standard bearings on a 10/10 crank. The engine ran well suffer one problem oil pressure light so you can tell the oil pressure, but it had a vibration at a certain RPM show the new I was a good troubleshooter after many mechanics looked at it! So I asked him did you disconnect the torque converter yes they did that, so ask him to take the fan belts off; then I grabbed the front of the harmonic bouncer and moved it up and down I said to them somebody put in the wrong main bearings.

Looks like crank polish is too rough ! ? Make sure you always mike the crank to be sure the grinder did it right, because.... there is a lot of shody work being done out there, i have my own shop and encounter it all the time !

You could send some of your bearing shells to Callie or Calico and get them coated . You might be able to tighten up the clearance by .0005" . Also it would probably be better to measure the crank journals and bearings with a micrometer and a dial bore Gauge , to get a more accurate measurement . Swapping bearing shells to different locations is a great idea , possibly buy another set of bearings so you have more of a chance of getting the clearance you want .

im sorry but i do not understand what you are saying about oil flow the further you go back on the crank. Pressure is pressure, if you have 30 PSI at one main, it is 30 PSI at all the others. the #7 failure is usually doe to not having a 4/7 swap for balancing the load on the crank.

When bearings are on the tight side, run a lower viscosity oil.

Seeing bearing clearances all over the place tells me the block probably needs to be align honed. The #1 cam bearing going out tells me the cam had runout between #1 and #3 cam journals.

My hubby says, on Ford engines he runs off the shelf vandervels and has the cranks ground .ooo5 equals half a tho. Under the bottom toletance for .oo3 on mains, .oo2 on the rods, with the rods re sized on tight side. For the truck pulling engines

Clearances determine viscosity...

Thats some interesting stuff your trying there. Thanks Mr. Rodder!

Dial Bore Gauge .0025 mains and .002 rods. Running it too tight will cause all kinds of issues.

Flow takes the path of least resistance. Send it.

I have grooved the block and dilled extra holes in the lower bearings to feed oil in a larger circumference. But have never tried to use two tops like that. Could be interesting. I have also grooved the crank journals themselves to feed oil all the way around. And if i remember right some of the stage 2 cranks were cross drilled for the same reason.

Those main bearings are 3.25 on that Buick. I wouldn't run any less than 2.75 - 3 thou clearance on those... This ain't a stock sbc. That's why those rods can't take much rpm before they kiss the crank....I appreciate what you did to even it out, but as far as I'm concerned, only one of the clearances was correct. #4 the one you changed...

Usually, I don’t want to try, ti

Torque mains down with bearings installed check it with a dial bore Guage then mic your crank journals remember to let your measuring tools sit out with what you intend to measure don't just stick the mic in your back pocket and think that's fine and keep your finger off the business end or your gonna get a bad reading

Loose is our friend unless we're talkin' 'bout women!! On a more serious note... it would seem to me you would want the tighter clearances forward, and the looser as you go back. Otherwise you're just shooting your load all up front and not leaving anything for the back holes!! You want to try and share all of that slippery liquid goodness with all of them holes, right? But don't take anything I say seriously, I rarely get anything right!!

Good video Dallas, we were just doing the same thing

Tighter is better

Industrial engine specialist..einsteins..sean astins..audie murphys gilda..here.. Um..many designs in production FAIL...but are Patentable....and Buyable. First most fail with power oil coolers more than enough for Oversizing and competition or longevity plans...because of planned obsolescence or....or other CORRECT designs are already patented...in other Countrys or Corporations. SECOND....the primary feed should be split from middle to outside...WHY....heat is CENTERED. THIRD...is Viscocity Perfection....changes from Journal sizing. Professionally...higher speed viscocity works on Rods at operating temps or load temps. However start up requires less viscocity or ... Or higher pressure aka speed or flow. Mains need higher viscocity than rods because of WEIGHT or VIBRATIONAL TORQUE TRANSFER which requires....EQUAL or SAME power values or TOLERANCES.......and specifically..emission engines require TIGHT tolerances...1.5..maybee 1.8 at INSTALL... Where COMPETITION appears to favor 2.0up to 3.0...approx. FOUR.... NOBODY can design the peeeerfect ENGINE..because of PANTENTS. For public use. However Engines that are MODIFIED NOT FOR RESALE.....can be...Designed PROPERLY. Now as far as CAMS..VANOS/Valvetronic...really this is a Hydraulic system favors....VISCOCITIES that of....very tight tolerances.....and requires oil coolers aswell. That leaved....Piston JETS..CAM follower jets......BUT with....emission recirculation with direct injections....should be recirculated in POOL with a SECONDARY EASY access OIL FILTER SYSTEM........before...vanos or oil pressure solenoids.......PERFECT design is...NO filter on solenoids...but around soleniids....that these filters should be EASY access aswell......WHY.....many Engines are MODIFIED...for CHANGE in VISCOCITY....requiring fine screens to be removed or FILTERs designed. MANY engines are designed for Planned obsolescence racket....or Pantent restricted designs or Greed or Stupidity. THE best engines ARE MODIFIED..TESTED.TRUED.Professional Applied Competition Motors.....however..WE USERS demand OUR AMERICAN QUALITY RETURNED.

this is painfull to watch

Great solve. Never dealt with anything like this myself so cool to see. Thanks Dallas.

Is why you put in squirters on the far holes.. rather than the drip youl get a directed drip aimed right on the money shot.. take a little shitty toyota 2az motor.. they’re known for burning oil which winds up overheating or melting a bearing. Its because the piston design is crap with 4 small holes in the oil ring that get clogged up solid along with the rod holes. That causes gum to clog different passages with that hot burnt oil.. the fix is installing squirters to directly lube everything if the pistons get clogged up and doesnt allow oil to return like it should, the squirters put the oil right on the spots..

Great video,thanks

Yes I us KB pressure plate and have 100 lbs at 5000 launch and try to keep .002 on all mains and run 5W30 mobil synthetic. Line hone a must on Buick and a known good Buick machinist is a must. I shaved the main caps down to get .002 after a bad crankshaft grind. You tell a machine shop one thing and get something different. hate machine shops unless they do what you tell them. I never swap caps.

I'd imagine those that rebuild engines all the time want to see as much closeness as possible between bearing clearances. Are bolts making the difference? Some engine builders use a specific type of treatment on the bolts.

Seems like the bearing surface with the largest bearing gap looks rough with micro scratches. I'm guessing they grinded/polished it and started running out of material and stopped.

I Think using mics to measure clearances of the crankshaft is the best idea . High Volume oil pump makes enough pressure to over come half thousands of a inch .And yes they make crank bears in 1-2-3 thousands from stock to correct incorrect tolerances . I would only worry if you hit 2.5 to 3.0 thousand out of spec ,from normal 2 thousand ,for a normal rebuild . Late to the show.

You do not have to Think about it, just take the Clevite Bearing Class,

Good video. Thought this was common knowledge

Thanks for clear explanation..!

very interesting info about the buick 455. Since that number 4 bearing is 2.5 wide, would installing a volume oil pump to assure oil to all the bearings make a difference ? anyway thanks for this video.

If the tops have grooves and the bottoms don’t. I would not use a top for the bottom. Main load is to the bottom shell. This. You want full bearing surface for that wedge of oil to live on. Top shell has groove to ensure oil supply is constant.

Pump up the volume dance , dance .

Interesting concept.

I'd like to see a follow up on this (or autopsy) whichever was the result.

Loose? Lol

tell me when do you know that the crankshaft needs to be polished? if you can't feel unevenness with your fingers and nails, is it ok even if the best shine is gone?

Rrr. Iv worked out the problem. That main journal has different clock timing, iv noticed its oil hole is in a differant spot to the ather main journals. All you have to do is use fully grooved main bearings. Also Allways keep you clearances epual or you might crack the crankshaft. Mad mick

Run a no 6 bypass line to the back of the block

All of them need fully grooved bearing so the bigends gett the sam pressure.

They used to call that “Blueprinting”.

1.5 and 1.7 are too tight, I'd hit those with a scotchbrite to get some clearance, or just find another set. Matter of fact, I'd go for 2.5 to 3 thou on all of them. I'm running 0.003 on the mains on my cleveland. Bigger mains can handle more clearance and like it, especially with rpms. 2 thou is good for rods. The larger clearance will also allow for more oil cushion. Don't sweat the "spillover" that won't be your biggest leak. One thing to do is make sure all of the bearings in the block are the same thickness and that if you mod any bearing halves to only do the cap halves. This will help with keeping the crank straight in the mains. I highly recommend you reconsider not using a high volume oil pump as they put a lot of stress on the pump drive system and often aren't necessary. Especially on engines like buicks and clevelands.

Oh Mr Rodders is a person in your neighbourhood....

i have noticed the difference in new main bearings a stock set i fitted caused a crank to be tight so i swapped them round and all was well that was over 30yrs ago on a austin sprite (maybe the cheap bearings i used)but i had never thought to do this to correct tolerences as you have just shown

2.5 is 2 inch 500

As long as the pump can keep up and the pan stays full enough .It should be way better .