dumbcountryboy

Hello all, this is my first post here and to some it may sound very beginner like but belive it or not I have rebuilt many engines through the course of my life, decades ago I even worked my way up to shop foreman in a 4 bay garage in Atlanta in my early 20's, but I have never rebuilt a sbc on this tight of a budget so when you ask"why do that" it all boils down to money and my pursuit of knowledge and my life long journey down the road less traveled, but if I had more money the crank would be turned and bla bla bla, the question is about the much debated Oil clearance, everyones theory is welcome, even a friend of a friends cousin said "bla bla bla" can be learned from so dont be afraid to express yourself, but what I'm really looking for is "OLD SCHOOL" first hand lessons learned experiance, I have a sbc 350 set up around .001 and most say thats to tight, but the fact is that totota and datsun became lengenday for long life engines, with rod and mains running as little as.0006 in late 60's early 70's long before todays modern high tech 00wt synthetic oils, I have torn old engines down (for reasons unrelated to crank) that the babit was gone with the copper showing on mains without any damage to the crank at all, like maybe they where a little tight but wore to fit on break in, really the crank should never touch the bearings just the oil, which has to wear the bearings just like water wore out the rock in Arizona, I think my crank or block may be less that perfect, the best I can figure is machined or bent about 1/4 of a thousand'th because when I toruqe my front main down, I get a tight spot in rotation, BUT I can still turn it by hand, but it's just tighter and not near as easy and free as before torqueing that last main down, will it loosen up in the first 30 seconds after start up? or will the bearing heat up and seize up? I know everything will move a little when it gets to operating tempeture as well. the darn'ed old plactic gauge says it has it has .001 of clearance but maybe the crush pressure of the plastic gauge is more that the pressure or the bent crank!!!???, It's just hard to keep these tight tolerances with a block machined by one man then a crank machined by another person and top it off with bearings made by another and I know if I where going.002 clearance no imperfections would ever be noticed, and am inclined to belive thats why .002 in the norm for most shops, however I have heard from guys dropping mega bucks on top fuel'er cranks claim as low as ,0007 all the way up to .004, with one guy saying he doesnt want his 5K crank anywhere near his bearing, then the 0007 gentlemen saying that he doesnt want his costly crankshaft sloshing around in a pool of oil.

HF_monster

if you want way old school what you can do is take some steel wool or a green scuff pad (more preforable) and take the top layer off the bearings to get the clearence you need I know plenty of people have done it. Alot of racers used to do it they said that it kept any debris from machining from getting imbeded in the bearing and causing damage. for a street motor that low of a clearence can be a problem also with the new oil's they dont have the anti wear additives that the old oil had (thank the EPA for that one) so if its a flat tappet cam youll need ZDDP additive.

Also platigage is inacurate mic the crank and the main with the bearing installed to get a better reading

sofakingdom

iTrader: (1)

Doesn't much matter what Datsun and Toyota called out for. Especially not if their blocks were aluminum. Keep in mind, aluminum grows more than iron when it gets hot; meaning, in such a block, the clearance OPENS UP as the block gets hot.

IMO about .0015" is about right for a SBC. Maybe a tweek more on the mains, like up to .002".

What racers "used to" do, doesn't apply to modern bearings. Best thing to do with current technology is to take them out of the box, drop them into CLEAN solvent such as lacquer thinner to wash them, take them out and let them air-dry, and put them into the block WITHOUT touching their working surface with a finger. Lube them with ATF or thin motor oil (0W-20 synthetic is good) out of a CLEAN Ples type oil can. Use an old V-belt and some 600 grit sandpaper and some ATF to size the crank journals down to get the right clearance. Leave the bearings alone.

Debris is SUPPOSED to embed into the bearing. That's what they're designed to do nowadays. Read ANY of the modern bearing mfrs' literature and see their claims about "superior embedability". Basically if the trash embeds deep enough, it won't tear up the crank. For the most part, once it gets in the clearance, it will NEVER get back out; might as well have it bury itself deep and harmlessly into the soft metal the bearing is made out of.

Personally, I prefer to build motors with no metal chips in them in the first place, though. I accomplish that by picking the finished block up from the machine shop without cam bearings or any of the plugs in it; then I take it to the quarter car wash and rod it out with diesel fuel and rifle brushes; then paint it, install the bearings and plugs, and build it. That way I can be sure that the debris left over from the last time a motor wiped out in that block is all gone. The vat isn't good enough by itself; solvent doesn't dissolve metal chips.

If the crank gets tighter when torquing the mains, then either something is out of round, or there's trash behind a bearing. They should LOOSEN up, as the bearing shells get crushed into the saddles and forced into a perfectly round shape (which they usually aren't when they come out of the box). STOP NOW and figure out what you did wrong. Otherwise you may be making an unhappy visit back to them later.

Likewise, if the crank doesn't turn smoothly, then IT'S not round, either. The "high spot" on the crank is dragging on the "high spot" on the bearing.

Sounds to me like this motor is just generally not ready to be built yet.

I agree, Plastigage is inaccurate; but it makes a decent enough guide for people who don't have a good bore gauge. It's pretty tough to inside-mic a main or a rod bearing with a caliper any more accurately than what Plastigage will do if used properly.

dumbcountryboy

Thanks so much gentlemen,
Now Sofakingdom your correct that alluminum block expands more than A cast iron block or A steel crank shaft but you really think that when an alluminum block heats up and expands that it moves away from the from the main caps, it grows in every direction, if you take a peice of alluminum round bar stock and heat it up, it gets longer and bigger around, like I said in my original post it's either the crankshaft or block is out 1/4th of 1 thousandth, there is no trash under a bearing and the crank is not egg shaped, it's out .00025 (1/4 of one thousanth in a couple of feet) the length of the crank shaft, far better and behond any spec on any internal combustion engine ever installed in any automobile, the tolerances of most where surpassed .001 ago, and nowhere in my post did I ask anyone what was wrong or what caused it, and whats with this stuff dont touch the bearing with your fingers, I think your thinking of a halogen light bulb. this is not a quantum phase pulse inducer on a warp drive, its just a 350 chevrolet.
Monster I have already worked on the bearing as you suggested W/600 grt paper before posting this, the GM factory steel crank has not been turned, the bearings in it now are .002 oversize, with the front main having been done with the 600grt. which allows it to be turned over by hand with one tight spot, I also have a set of.001 oversize bearings which dont give me the tolerances I want, now I know I can stick a standard bearing in the front main and spinn as free as a bird, or sand on the .001+ bearing with the 600grt as monster said, It's very common among the truly presision engine builders too the mix .0005 and .001 and .002 over and under sized bearings to get custom oil clearance's that no machine shop can give, just as long as you do it on the same side of the crank, either the block side or cap side, cant plus size one cap and negitive size another cap, I can mix and match them like Smokey yunick , what I'm trying to do is get that kind of persision with out mixing my bearing sizes, or spinning one for that matter, but of course if I do spinn the front main on start up, it may have been caused by finger prints,LOL

sofakingdom

iTrader: (1)

When you tear one down that YOU built YOURSELF, and you see a fingerprint (YOUR OWN) all corroded into it, then you'll know what's with that stuff.

Excuse me for trying to be helpful. I'll try to avoid that in the future.

dumbcountryboy

I may remember seeing a finger print in a couple engines before, I cant say for certain because I may have dreamed it last night, but dreamed or not, if a finger print is in and egine its probly because the guy had just wiped sweat from his forehead or some other part of his where salt builds up,
I have nevr stoped to help a stranded motorist on the side of the road and hear, "she went down on me, damned old finger print got too her,
and by all means please dont stop trying to help, I was cooking biscuits this morning and stuck my finger through the middle of one and made a hole in it, I watched through the glass oven door as it heated up and expanded and the hole became smaller just as the biscuits all appeared closer together on the cooking sheet as expanding, however not a single one of them actually siezed to the adjoining busicuit because I used a mic to set the tolerances between them, and just to play it safe I hit all the inside edges with shot of pam cookin spray, I got by on that one,

mlynch001

Sorry guys, early (1965 -1990) Datsun, Toyota, Mazda and Hondas almost ALL had Iron blocks! Aluminum did not become common until much later later 90's and beyond. I bored hundreds of them, so that is some kind of "urban legend". What the Japanese engines had was extremely high strength iron, well designed rigid blocks, rigid forged cranks and very precise manufacturing! They could run tight clearance because their stuff was built right! Like it or not, the JAPS taught US manufacturers how to get out of the stone age and into modern engine building practices. What American Hot Rodders were doing in their race shops, by hand is what the Japanese manufacturers were doing on the production floor!

FYI HONDA motorcycles hand fit EVERY Rod and every Main bearing selectively! And that is PRODUCTION, not just the prototype, one off "dyno" engine or every 100 or 1000 engines! EVERY engine is built like that! That must be part of the reason that a CBR 600 HONDA makes damn near 4 horsepower per cubic inch, without nitrous, on pump gas and carried a 12 month unlimited mileage warranty!

A typical Honda Motorcycle engine has at least 5 and up to 7 different rod bearings alone and these are fit up based on a size code on the 5 different selective fit rods and the 3 - 5 different crank journal codes. And, NO, they do not touch the bearings with bare hands.

Sofakingdom is EXACTLY correct, build it clean and you do not need to worry about anything embedding in the bearings. Even though the bearings are CAPABLE of this and it is desirable to be able to accomplish this on occasion, having the bearings "Catch" the trash floating around because you were too darn lazy to wash the crap out of the block is stupid!

As far as seeing "copper" in bearings after a tear down, that is an engine headed for failure, sooner or later. If it was built with the right clearance, turned free and properly lubricated, there would be no contact to "rub" the top bearing layer off the bearings. Tri-metal bearings with copper showing have experienced a failure of assembly, the lubrication system or lack of lubrication at some point. The plain bearing engine MUST have an oil film and oil pressure to keep the oil on the bearing to cool and provide the hydrodynamic wedge that the crank floats on. EVERY crank from $5.00 to $50,000 that runs on plain bearings "sloshes around in a pool of oil"! I have built engines and PERSONALLY run them HARD for 100K miles, torn them down and the bearings looked like new! With proper maintenance and assembly, there is no reason that you should see that much wear on the bearings!

I use .0015 on rods and .002 on mains as a target. I clean and deburr EVERY surface in the engine, paying particular attention to the main bearing caps and saddles in the block. I wash everything at least twice in clean lacquer thinner and air dry. keep cotton shop rags away from the block as much as possible since the lint can get behind the bearings and cause trouble (just like Automatic transmissions). I also use CLEAN, DRY shop air to blow everything off just to make sure that dust is removed. Bare crank MUST spin free and smooth, by hand and without tight spots when the mains are fully torqued! Rotating torque should be checked while adding piston and rod assemblies to assure a linear increase in rotating torque. Each additional rod assembly that is added, should add a predictable amount of resistance. A big jump immediately after adding one rod means that there is something wrong with that assembly. Stop and fix it.

The bottom line . . . If you do not want to make it clean, build it clean and keep it clean, do not worry about clearance, the crank will make its own clearance!

dumbcountryboy

I dont remember anything about keeping it clean in my original post, I swear people just go to the key board without reading the original question, it was tight for aproximately 45 degrees of 360, I had left it in the tight spot several weeks ago, when I unbagged it yesterday it was as smooth as silk, maybe sitting in the tight spot alloweed the crank to give? maybe a bearing was not seated? I had removed and cleaned bearings and caps several times hoping it was trash or a burr or something, like I said it was the block or crank, allign boreing the block or turning the crank may have or may not have helped, I just belive that the .002 is to allow for the rest of sloppy specs allowed in the combined steps, blocks,bearings and cranks all have a .0005 size window, I wonder what the oil clearance of those honda motorcycle engines are? regaurdless it now spins easy,and I dont belive it was the tempature change of the last month, the crank was never stored laying down, I have transported it laying in the back seat for short distances, andit has beed sitting in block tourqed down setting on the tight spot for a few weeks, which I would not be able to find now if it where not for me marking it, Thanks for the replys and suggestions,

mlynch001

Sorry that I mentioned dirt! You are the one who mentioned copper showing through bearings! That is usually caused by Dirt or no oil pressure!

The fact is, that regardless of how you store a crankshaft, it will distort slightly. The least damaging way is on the end, but that will still cause problems if it was stored standing on end for a long time. The BEST way to keep a crank straight is to support each main bearing journal as if it was in the block and on its side. The worst way is on the side and resting on the counterweights. Your crank could have been slightly distorted when you put it in and YES, it could have straightened its self out after resting supported properly in the block. I have ground hundreds of cranks, and until you have seen how flexible that a crankshaft is, you will find it hard to believe that this can happen. You can actually "flex" a crank simply by pushing on the center of the crank while in the grinder! Glad to hear that your problem has "solved" its self.

ASE doc

Oil clearance goes hand in hand with oil viscosity and both vary by the engine's intended application. For instance, a new OE engine will be machined for .0001 -.0015 oil clearance and will run on 5W20 engine oil. The tight clearance is necessary to create oil pressure with such light oil. And the light oil is intended to reduce frictional loss and thus increase efficiency. A NASCAR small block is machined for .0025 oil clearance on rod bearings and .0035 on mains, and runs on either 40 weight or 20W50. The larger clearances are intended to allow more oil flow throught the bearings to help cool them. The heavier oil is intended to create high oil pressure within the large clearances. The high pressure and heavy oil prevent metal contact under the extreme forces generated in a small block engine producing 750hp.

From reading this thread, I gather you are not talking about oil clearances as much as tolerances. Tolerances in an OE engine are .001- .0015. Tolerances are the amount of total runout or out of round allowed in a bearing. Tolerances on a NASCAR motor are typically .0001. While these engines run larger oil clearances, they are machined to much stricter tolerances because of the high revs they will see. A bearing that runs thight is a bearing that will get hot and seize or spin. A spun bearing destroys the block as well as the crank.

ASE doc

Oops! I finished my last post in a hurry and made some errors. First, OE tolerances are .0025. Second, tolerance is the total amount of out of round and/or taper allowed in a bearing.