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Old 06-28-2012, 04:44 AM   #81
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Quote:
Originally Posted by konrad View Post
I'm going to run the .0029 on rods and .0025-.0030 mains, should be a good compromise between.
being 22...i love threads like these...keep the conversation going gentlemen i need more knowledge!!!!
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Old 06-28-2012, 07:01 AM   #82
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Sorry to jump in, here. Can you please clarify?
What I'm reading is that the spec's for rods are 0.0013" - 0.0023" with a limit of 0.0028"
and jerry87 is advising 0.0035"
Is that what you're saying? (Not asking in a doubting way, I'm just asking for clarity.) In other words, this is exceeding the maximum clearance by 25%
I haven't checked this thread in a while but it's good to see some numbers come out of it because iirc, that's what the original intent was. On the other hand (and speaking as a guy without direct experience on this) wow, that sounds loose. If that's what works, believe me, I want to know! But, holy eff, that sounds loose! Without recommendations from those with more experience, I'd have aimed for the center of the spec at about 0.0018"
If you get a chance, can you please elaborate?
(I.ll check to see if I missed something earlier in the thread)
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Old 06-28-2012, 07:40 AM   #83
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Quote:
Originally Posted by DaveJackson View Post
Sorry to jump in, here. Can you please clarify?
What I'm reading is that the spec's for rods are 0.0013" - 0.0023" with a limit of 0.0028"
and jerry87 is advising 0.0035"
Is that what you're saying? (Not asking in a doubting way, I'm just asking for clarity.) In other words, this is exceeding the maximum clearance by 25%
I haven't checked this thread in a while but it's good to see some numbers come out of it because iirc, that's what the original intent was. On the other hand (and speaking as a guy without direct experience on this) wow, that sounds loose. If that's what works, believe me, I want to know! But, holy eff, that sounds loose! Without recommendations from those with more experience, I'd have aimed for the center of the spec at about 0.0018"
If you get a chance, can you please elaborate?
(I.ll check to see if I missed something earlier in the thread)
Yes Jerry is running .0035 clearances, but with thicker oil.
I don't feel comfortable with those clearances. The more I think about it the more I want to run .0025 rods.
Here is a vid of .0045 rod clearance. This is tourqued to spec. It's what I have with extra clearance bearibgs

https://www.youtube.com/watch?v=miIe...e_gdata_player
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Old 06-28-2012, 10:01 AM   #84
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exactly, the reason being is the stock engine is engineered for stock or mild power levels and stock thickness oil. once you start going with high power levels the oil breaks down alot quick or may offer little protection period theres numerous different examples of this across the web.

now with that said the bigger the clearance the thicker the oil you need. i wouldnt try to run anything below 10w30 with .0035 clearances, even then i would be kind of scared during warmup.

to be perfectly honest the clearances actually grow when the engine is warmed up, thats why your not supposed to drive until the engine is heated up, so the bearings can be loose enough to handle the power, ive never had a problem with that clearance and its pretty much the standard ive used on all my engine. something like a honda will need tighter clearances due to smaller diameter journals but the journal diameters on our engines are ****ing huge, nearly the size of a 572 chevy big block, so the clearances really arnt that loose. obviously too loose for oils like 0w30 and 5w30 but you just run the proper oil, which gives you more "cushion" between the bearing bore and journal anyway.

like i said the closest comparision we can make is a big block chevy, or a ls7 since they are the closest thing to our engines as far as journal diameter is concerned. said it in a previous message but ive seen .007 in a big block on meth, for normal gas that would be about a .0075-.008 clearane(since meth runs coolers.)

its all about the oil and proper warmup for clearances, for under 550 i would aim for bigger side of stock since that seems to hold up. above that(since thats where bearings seem to spin) definitly go beyond that with a thicker oil, preferably something with zinc. thicker oils naturally have better resistances to the extreme forces that are exerted on them in a race engine(i dont care what anyone says when your at 100 hp per cylinder or over 175 per liter thats a damn race engine and needs to be treated as such for longevity.) thats why we run thicker oil in transmissions, and even thicker then that in the rear end. the more force something sees the thicker the oil that is run to stop it from eating itself.

i believe my lower oil temps are partly due to my clearances but i dont have the list even glisten of anything in my oil and ive run that clearance on engines with smaller journal diameters on thinner oil(although lower power level) enough times im 100% confident in it. .0045 that konrad posted a video on should even still be ok, a little too loose for my taste and i wouldnt touch the motor with anything less then 25w50, but again with proper oil it shouldnt have any issues.

also remember that no matter the oil it will be thicker cold then hot. yes a 10w30 oil will act like 10w cold but it will be a cold 10w, and it will act like a 30w hot but a hot 30w not a cold 30w


Quote:
Originally Posted by DaveJackson View Post
Sorry to jump in, here. Can you please clarify?
What I'm reading is that the spec's for rods are 0.0013" - 0.0023" with a limit of 0.0028"
and jerry87 is advising 0.0035"
Is that what you're saying? (Not asking in a doubting way, I'm just asking for clarity.) In other words, this is exceeding the maximum clearance by 25%
I haven't checked this thread in a while but it's good to see some numbers come out of it because iirc, that's what the original intent was. On the other hand (and speaking as a guy without direct experience on this) wow, that sounds loose. If that's what works, believe me, I want to know! But, holy eff, that sounds loose! Without recommendations from those with more experience, I'd have aimed for the center of the spec at about 0.0018"
If you get a chance, can you please elaborate?
(I.ll check to see if I missed something earlier in the thread)

Last edited by jerryd87; 06-28-2012 at 10:07 AM.
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Old 06-28-2012, 07:52 PM   #85
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Jerry I feel like .0035 is too much clearance, I will go with +.0005 over the factory limit for both rods and mains. with 15w40 or 10w40 brad penn oil. I will still be over the rull of thumb .0010 for every inch of journal diameter
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Old 06-28-2012, 08:14 PM   #86
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yah, just be sure first 20-30 miles are like straight 30 weight, preferably a actual break in oil but break in additive will work in its absence. after that first oil change i would say start with 10w40 and see how your oil pressures look, if they arnt too high can try the 15w40 since i know your concerned about lower temps.
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Old 06-28-2012, 08:30 PM   #87
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Quote:
Originally Posted by jerryd87 View Post
yah, just be sure first 20-30 miles are like straight 30 weight, preferably a actual break in oil but break in additive will work in its absence. after that first oil change i would say start with 10w40 and see how your oil pressures look, if they arnt too high can try the 15w40 since i know your concerned about lower temps.
yeah planing to run brake in oil first 3 changes or so. on my first engine build my oil pressure would drop to 10-15psi on idle, and while running temps would go to 200-210* I was running 10w30 but I have no idea what clearances I had I did run STD bearings. I am so paranoid with having another spun bearing I feel like I want to go OEM block and low boost
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Old 02-26-2014, 10:22 PM   #88
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OIL CLEARANCE IS NOT A MYTH IT IS A CALCULATION
By: Carl Amundsen Date:2/8/2000

Over the years I have had many opportunities to discuss oil clearance with engine builders. Some are building for their own use, some are small shops while some are large. In any event when the question is posed "HOW DO YOU KNOW WHAT YOUR OIL CLEARANCE IS?" the responses vary. Some can give a good mathematical response, some don't have a clue. The common denominator here is that everyone knows they have oil clearance.
A common phenomenon that occurs when a motor fails is that no one looks in the mirror for answers. The vast majority of the time it is blamed on an engine part failure. The connecting rod too many times is the favorite fugitive.
A LESSON IN MEASUREMENTS
A very dangerous but commonly used method of measuring is a dial caliper. The average dial caliper is super for measuring the thickness, inside diameter, and outside of an empty toilet paper roll. A SHOCKING STATEMENT , NO DOUBT! If you look through some catalogs you will find a dial caliper for $40.00 that has an advertised accuracy of +/- .008 . That is an error factor of 16 thousandths. Pay $200.00 for a digital caliper with advertised accuracy of +/- .0015, the margin of error is now 3 thousandths. An error factor of 1 thousandths can cost you a motor. Calipers are great tools for some things but not for the task at hand. WE MUST BE ABLE TO READ IN TENTHS OF THOUSANDTHS(.0001)
ON WITH THE LESSON
If you were to take a good 0 to 1 inch micrometer and measure the thickness of a page in the ARC catalog, you will find it to be five thousandths (.005) thick. This is very important to remember as you read on. Now feel the paper with your fingers and imagine somehow splitting one of these pages 50 times. One single sheet would now be 1 tenth of 1 thousandth of an inch thick (.0001). I hope I have your attention, because this is getting down so that you can't even feel the thickness. Just incase I am going to be confusing you with decimals please remember the following:
1.0000 = 1 inch0.1000 = 100 thousandths 0.0100 = 10 thousandths0.0010 = 1 thousandth0.0001 = 1/10 thousandth

It makes no difference who you buy your parts from, nor does it matter what brand they are, ARC included,they need to be checked and double checked. NOBODY IS PERFECT.
For example let's build a stock stroke Briggs racing engine. The following is the measurement specifications on the typical parts to be used:
Stock Briggs crank rod journal size......................... .998 +/- .0015Aftermarket Connecting Rod................................... 1.150 +/- .005Aftermarket Rod Bearing thickness........................ .075 +/- .003
ALL THE PARTS WE ARE USING ARE WITHIN THE MANUFACTURERS TOLERANCES.
You are going to use a medium weight oil and you are shooting for .0025
The Connecting Rod is on the small side................. 1.1495The Rod Bearing is on the big side.......................... .0753The Crankshaft is on the big side.............................. .9985
Let's put this motor together and go racing.
The Connecting Rod is small by .0005...................... 1.1495The Thickness of the Rod Bearingare big by .003(2 bearings) =.1506............................. - .1506Net Rod Bore size with Bearingsinstalled........................................... ........................ . 9989The Crank Rod Journal is big by .0005..................... - .9985The Calculated oil Clearance = ............................... .0004We were shooting for ............................................... .0025
With a little luck this motor will crank up and run, as long as the motor is running at no load and a low RPM it may be OK for a while. The minute you go racing the lack of oil flow between the bearing and the crank journal will cause heat build up. The bearing will seize on the crank journal, break the rod and just make a mess of everything. BAD PARTS RIGHT ? WRONG !
Now let's build another motor and go the opposite way, still trying to achieve an oil clearance of .0025
The Connecting Rod is on the big side........................ 1.1505The Rod Bearing is on the small side.......................... .0747The Crankshaft is on the small side.............................. .9965
The Connecting Rod is big by .0005............................ 1.1505The Thickness of the Rod Bearingare small by .003(2 bearings) =.1494............................. - .1494Net Rod Bore size with Bearingsinstalled........................................... ........................... 1.0011The Crank Rod Journal is small by .0015..................... - .9965The Calculated oil Clearance = .................................. .0046We were shooting for .................................................. .0025
This motor is going to run, but what is going to happen here is: The bearing is going to get pounded at the top and bottom of the rod bore, because there is an air gap between the two surfaces. The oil is not thick enough to prevent this from happening. This is going to convert the rod bore into the shape of an egg standing on end. The crankshaft will now start to loose it's round shape and wear.
EVERY MINUTE IT RUNS, THESE PARTS WILL INCREASE THE OIL CLEARANCE UNTIL IT EXPLODES. HOW LONG WILL IT LAST? I CAN'T SAY EXACTLY, BUT NOT TO LONG!
The crying shame here is that everyone will point their fingers at the connecting rod, bearings and/or crankshaft as the culprit.
THE MOST OVERLOOKED AREA IN ENGINE BUILDING IS AS FOLLOWS:You have a motor that has run for many months , but you notice you're getting a little blow-by and it could probably use a set of rings. It needs freshening up so we tear it down. Every thing looks great so we touch the bore with a hone and put a new set of rings in. Back to the races. If it ain't broke don't fix it. STOP! Under the most ideal conditions engine parts will change with use. Bearings can look good but will wear, connecting rod bores will change shapes and crank journals will wear and rod bolts will stretch and fatigue. It is just as important now as ever to check the dimensions of the parts. Don't go to sleep.
Some may think there is some deep mystery behind the term oil clearance. The reason is, everyone has a different opinion as to what it should be. As a rule of thumb, it can be anywhere between .0015 and .0035 and be in the ball park. If the clearance is on the low side, use thin oil, heavy oil will not work. If clearance is on the high side , use a heavier oil, thin oil will not work. How can you make a judgment on the oil to use unless you know what your oil clearance is? THERE IS NO MAGIC, YOU CANNOT KNOW WHAT YOUR OIL CLEARANCE IS UNLESS YOU MEASURE THE PARTS THAT AFFECT IT.
DEFINITION OF WHAT OIL CLEARANCE IS:
"The distance between two very smooth moving surfaces that will allow oil to be present at all times, coating both parts with a film of oil so that metal on metal contact never happens. It must be small enough to retain enough oil and large enough to allow a fresh cool supply to move through every microsecond."
If you do not check your parts and build 4 motors and 3 of them seem to have a pretty good life span you are lucky. If one fails out of the gate or shortly thereafter, shame on you. It takes less than 15 minutes to check and measure all the parts in a motor and the benefits are fantastic. It is possible to build an engine that will run until the cows come home, or something like that. There are many engine builders out there that do a fantastic job in this area, but on the other hand there are more that don't.
ASSUME NOTHING, BELIEVE NOTHING AND LAST BUT NOT LEAST, CHECK EVERYTHING.
I hope we have given you an insight to one reason for engine failures. If you need us, give us a call, it's all free. 1-800-521-3560
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Old 02-26-2014, 11:49 PM   #89
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i know i just posted in another thread about how i no longer come here, but this is exactly what ive been talking about since i joined and why ive said its all in the clearances and oil being used and willing to put money on most of the spun bearings being caused by not enough attention or simply not knowing proper clearances. ive built a couple of these engines now and measured other parts for them not going in and the clearance on these engines are TIGHT, 100k mile engines with cranks getting repolished and hx series bearings(.001 extra oil clearance) are STILL only showing .0030-.0035 oil clearance.

as far as tools i like digital calipers but its not the only thing i use, caliper, micrometers and dial bore guage are all used(admittedly not much on the caliper) and tool steel calibrated lengths are required. my stuff gets checked every time it gets pulled out of the box to verify that they are reading properly.
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Old 02-27-2014, 06:22 AM   #90
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Whats sucks is that unless you build engines yourself you never REALLY know what you have...and when the original builder tears down their failed engines they are never gonna admit (or probably even know) they slacked on the clearances. So much easier to say VQ's just suck. I've seen builds on here where engines had such tight clearances they were hard to turn over (e.g. one of Cass's builds). Needless to say it blew up on the dyno and the verdict was always 'oil starvation'. Anything but the clearances LOL....anyone think for a second clearances that tight might not let oil thru??

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Old 02-27-2014, 07:12 AM   #91
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true on that.

for example this is what i found om clearance and oil. (correct me if iam wrong)

Rod clearance-----------Vis cst----------Oil manufacture castrol/ Mobile 1

0.0018 - 0.0020-------10-15--------------5w30 / 0w40
0.0020 - 0.0025-------15-20--------------5w50
0.0025 - 0.0027-------25-30--------------10w60
0.0027 - 0.0032-------35-40--------------.....
0.0032 - 0.0040-------40-up--------------......

on smal clearance see if the oil has Zink ppm thats better.
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Old 02-27-2014, 08:51 AM   #92
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Anyone that builds a Hi Performance Motor should BluePrint it.

That is how it's done in the Real World of Hi Performance and Racing.
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Old 02-27-2014, 09:47 AM   #93
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i think 10w60 is pretty thick for only a 25-30 ten thousandths i run 15w40 in my 35 ten thousandths engine and i know alot of methanol motors run 60-70 ten thousandths and use 75 weight. i would use the 15w40 up to prob about 38 to 40 ten thousandths then switch to 25w50 rotella. something with high zddp's

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Old 02-28-2014, 06:30 PM   #94
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Quote:
Originally Posted by DaveJackson View Post
Sorry to jump in, here. Can you please clarify?
What I'm reading is that the spec's for rods are 0.0013" - 0.0023" with a limit of 0.0028"
and jerry87 is advising 0.0035"
Is that what you're saying? (Not asking in a doubting way, I'm just asking for clarity.) In other words, this is exceeding the maximum clearance by 25%
I haven't checked this thread in a while but it's good to see some numbers come out of it because iirc, that's what the original intent was. On the other hand (and speaking as a guy without direct experience on this) wow, that sounds loose. If that's what works, believe me, I want to know! But, holy eff, that sounds loose! Without recommendations from those with more experience, I'd have aimed for the center of the spec at about 0.0018"
If you get a chance, can you please elaborate?
(I.ll check to see if I missed something earlier in the thread)
You need loose.

Think of it this way. The more hp/torque you have, the more load the oil patch between the crank and rod will see. And the faster your engine revs (more power) the quicker oil pressure needs to be made. The more oil between the rod and the crank, the more force/quicker things can spin. If the clearance is too low, you can 'squeeze' too much oil out/over compress the oil. Both of those conditions can cause a spun bearing. And when you get into detonation situations, you can see even more issues with a tight bearing clearance.
I'll be running 10w40. California has it's benefits.
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Old 03-01-2014, 11:54 AM   #95
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Stock clearance is designed for stock horsepower... don't forget that.
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Old 03-01-2014, 12:35 PM   #96
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Tight bearing clearances and relatively thin synthetic multi-viscosity motor oils work well in many performance applications from NASCAR and circle track racing to drag racing.


Keep in mind, however, that most of these engines are purpose-built engines that are machined with exacting tolerances. Crankshaft journals are precision ground to be as round, flat and true as possible, the journals are micropolished to a mirror-like finish of a couple microinches Ra or less, the bearings are precision fit to exact tolerances using a bore gauge and micrometer (not deformable plastic gauge), and the engines are run on high quality synthetic racing oil, not ordinary motor oil.


The oil clearance is the gap between the inside diameter of an installed bearing and the outside diameter of the crankshaft or camshaft journal. The clearance is measured 90 degrees to the bearing parting line, which is the thickest part of the bearing (bearing thickness tapers slightly toward the parting line).


Reducing the oil clearance between the rod and main bearings and the crankshaft has a number of advantages. A smaller gap spreads the load over a wider area of the bearing surface and distributes pressure more uniformly across the bearing. Thatís good, provided the bearing is strong enough to handle it. A smaller gap also decreases the volume of oil that has to flow into the bearing to maintain the oil film between the bearing and shaft.


Thatís also good, provided the oil is thin enough (low viscosity) to flow well into the bearing. This also reduces the amount of oil pressure the engine needs, so some extra horsepower is gained by reducing the load on the oil pump.


In a NASCAR engine, rules limit the minimum diameters of the rod and main journals on the crankshaft. The rods are 1.850? in diameter while the mains are 1.999?. Most of these engines are running rod and main bearing clearances of .001? or less, and they are doing it with low viscosity racing oils such as 0W5, 0W30 and 0W50. These racing oils are as thin as water and are highly friction modified.


They also contain extra anti-wear additives such as ZDDP (phosphorus levels up to 1,850 ppm or higher) to protect the cam lobes and flat tappet lifters. These are race-only oils and are not recommended for street use because they do not contain the same detergents, dispersants and corrosion inhibitors as ordinary motor oils. Ordinary motors have to handle extended oil drain intervals while racing oils do not. Also, the level of ZDDP is too high for late model vehicles equipped with catalytic converters.


With fuel injection, many NASCAR engines are now making close to 900 horsepower without a restrictor plate, and are turning 9,500 rpms for 500 miles. The bearings take quite a pounding but hold up extremely well (when was the last time you heard of a NASCAR engine blowing because of a bearing failure?). But what works great for NASCAR may not work in other forms or racing or on the street.


One of the disadvantages of closer bearing clearances is that it can increase both bearing and oil temperatures. Thatís no problem as long as the bearings and oil can handle the heat, but if they canít it increases the risk of lubrication breakdown and bearing failure. Thatís why high quality synthetic motor oil is absolutely essential if you are building an engine with tighter than normal clearances.


The old rule of thumb is to provide .0007? to .001? of bearing clearance for every inch of shaft diameter in a stock engine. Consequently, if the crankshaft has two-inch diameter journals, the rod and main bearings should be assembled with about .0015? to .002? of clearance.



For performance applications, some bearing manufacturers recommend adding an extra half a thousandth of clearance. Why? Because the rod bores donít stay round in a performance engine at high rpm. When the piston reaches top dead center on the exhaust stroke, inertia stretches the rod and elongates the bore on the big end of the rod. This, in turn, deforms the bearings and reduces bearing clearances on the lower rod bearing while increasing it on the upper rod bearing.


For high revving performance engines, some bearing manufacturers recommend rod bearing clearances of .002? to .003?, with an absolute minimum clearance of no less than .0015?. The tighter the clearances, the tighter the geometry requirements are for the crank journals (as round, straight and smooth as possible with little or no taper).


Street engines can benefit from tighter tolerances and thinner oils for everyday driving. But when power adders such as nitrous oxide, turbocharging or supercharging are used, or the engineís power output gets up in the 450 to 500 plus horsepower range, looser bearing clearances are probably safer to accommodate crankshaft flexing, main bore and rod bore distortion.


The same reasoning applies to drag motors, truck pull engines and other performance engines that produce serious horsepower. Many of these engines are built with rod and main bearing clearances in the .0025? to .003? range.


For the Saturday night dirt track racer, clearance is your friend because of the contaminants that often get into the crankcase. Looser is usually safer.


Rod and main bores should be as round as possible with no more than plus or minus .0005? of variation for a performance engine (.001? is close enough for stock). You also have to take into account the fact that the bearings themselves may not be perfect. Manufacturing tolerances of up to plus or minus .00025? are not unusual in some bearings, while others may vary only .00015? or less.


Main bore alignment is also critical. Some bearing manufacturers say adjacent main bores should have no more than .0005 inch of misalignment (.001? overall) if you are using tri-metal bearings, and no more than .002? of misalignment between adjacent bores (.002? overall) with aluminum bi-metal bearings.


One of the advantages of looser bearing clearances is that it allows more room for ďslop,Ē which is important if the crankshaft isnít machined to near perfection or there is some misalignment in the main bores. Wider bearing clearances do require a heavier viscosity oil (such as a 20W50 multi-viscosity oil or a straight 30, 40 or 50 oil). The heavier viscosity oil is absolutely necessary with wider clearances to maintain the oil film between the bearing and shaft so the bearing isnít starved for lubrication. This also requires more oil pressure from the oil pump and/or more oil volume.


The amount of oil that is actually between the bearing and shaft surface at the point of highest load isnít much. Though the installed gap between the bearing and shaft may be .001? to .0015? or more, the oil is displaced when the bearing is loaded. At its thinnest point, the oil film may only be .00002? thick (1/100th the diameter of a human hair!). Thatís not much oil between the metal surfaces, but it doesnít take much to maintain hydrostatic lubrication. When the shaft starts to turn, an oil wedge forms between the shaft and bearing that lifts the shaft up and away from the bearing surface. The shaft then glides on the oil with minimal friction.

If a crankshaft grinder wobbles while a crankshaft is being ground, it can leave lobes around the circumference of the journal. These may be invisible to the naked eye and very difficult to detect with a micrometer. But if thereís any distortion on the surface, it may interfere with the formation of the oil wedge under the shaft if the bearing clearances in the engine are too tight. Polishing the crank can reduce surface roughness on the journal but it wonít get rid of the lobes or ribbing.


Another factor to consider is that the upper Babbitt layer on a tri-metal bearing is very thin, typically .0005? to .0008? thick. The top layer of Babbitt acts as a dry film lubricant when there is no oil between the shaft and bearing. Thatís fine for a dry start that may only last a couple revolutions of the crankshaft, but it is quickly wiped away if the engine starves for oil when it is running under heavy load or at high rpm.


And once the protective upper layer of Babbitt has been destroyed, the intermediate layer of copper/lead alloy will quickly seize if thereís no oil film to keep it separated from the shaft.


One of the reasons why many performance engine builders use tri-metal bearings is because they want bearings that have good seizure resistance in high rpm applications. Tri-metal bearings also handle high engine loads well and have good fatigue resistance. The Babbitt surface layer also provides embedability if dirt or debris gets past the oil filter. Tri-metal bearings are typically recommended for use with forged steel crankshafts.


Aluminum bi-metal bearings, by comparison, have high wear and corrosion resistance. With harder aluminum/silicon alloys, they can also handle higher loads while providing good anti-seize properties. Aluminum bearings are often recommended for cast iron cranks because they have a polishing effect on the journal surface. Whatís more, according to some bearing manufacturers, a high silicon alloy aluminum bi-metal bearing will actually resist seizure longer than a tri-metal bearing if the protective oil film goes away.


That brings us back to the oil and bearing clearances. The oil doesnít care what kind of bearing and shaft it is lubricating. It only needs to maintain enough oil film between the two surfaces to provide hydrodynamic lubrication and prevent metal-to-metal contact. There has to be enough oil pressure and flow to keep the bearings lubricated and cooled, and the oil itself has to have enough shear strength so it isnít pushed out of the gap between the bearing and shaft at the point where the load is greatest.


Multi-viscosity synthetic motor oils flow more easily than conventional straight weight oils at both low and high temperatures. So they can handle cold starts as well as elevated operating temperatures (which is really important with turbochargers). To reduce friction and improve fuel economy, most late model stock engines are factory-filled with 5W20 or even 0W20 oil. Combined with tighter engine assembly tolerances, these oil and bearing combinations work relatively well for everyday driving and even mild performance use. For racing applications, though, the oil needs to be formulated specifically for racing Ė especially if the engine has a flat tappet cam that requires plenty of ZDDP in the additive package.


You can get oil viscosities ranging from 0W5 to 120W60, with 15W40 being a popular viscosity for stock car racing, road racing and spring cars. For wider bearing clearances, some prefer to use a heavier 15W50 or 20W50 oil. In drag racing Top Alcohol and Pro Mod classes, AHDRA Nitro Bikes and blown alcohol tractor pulling, 20W60 may be the lubricant of choice. For NHRA Top Fuel dragsters and Funny Cars, a 70WT oil might be used. So the type of oil thatís used will depend on the application and the bearing clearances inside the motor.


An additional layer of protection can be achieved by installing coated bearings. Various types of proprietary coatings are available that provide scuff resistance where there is no oil between the bearing and shaft. Such coatings cost extra, but are good insurance against dry starts and may save a crank if the engine loses oil pressure in a race.


Finally, regardless of what type of bearings you put in an engine or how close you set the bearing clearances, always use plenty of assembly lube to coat the bearings. Also, use the proper break-in oil when the engine is run for the first time. Break-in oils are typically a straight 30W oil without friction modifiers for fast ring seating. But they also contain extra ZDDP anti-wear additives to protect the cam and lifters. The break-in oil can then be drained and replaced with the type of oil (conventional or synthetic) that will be used from that point on. Be sure to tell your engine customer how important it is to use a high quality oil and that it has the correct viscosity to match the bearing clearances and lubrication requirements of the engine and application.
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Old 03-01-2014, 04:59 PM   #97
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ive never seen a high power drag engine run tight clearances, .0060-.0070 is normal for 2000+ hp methanol or nitro meth engines, and thats using tiny honda bearings i cant imagine what they would use if they used standard sized bearings and they run 75 weight oil. not to start a argument but if you tryed to tell a even a outlaw 10.5 guy to run a .0025 or .0030 clearance he would laugh at you. hell the GM ecotec drag program even runs .0050-.0070 clearances depending what class they are running and what power since they go anywhere from 1200-2000whp on the fwd chassis.

even 500-700 whp gen 1 sbc's spin bearings all day long under .0025 clearances.
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Old 03-01-2014, 05:07 PM   #98
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plus as i said previously on this site, the bearings in the vq are ****ing giant and the number of spun bearings that have plagued the platform have shown that tight clearances are a bad idea and asking for trouble even company's with multi million dollar machine shops cant get tight bearings to work. more power means more heat, which means faster oil degeneration, and more expansion of the metal not even figuring the fact that the greater force means exponentially more force being placed on the bearings pushing oil out and allowing metal on metal contact that the thicker oil resists hence why the big power drag racers use such a thick oil and its not that it allows it to last longer since they change the oil every pass due to so much blow by that some of those engines make. never met a single engine builder or racer who has knowledge on building engines who supports tight clearances.
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Old 03-01-2014, 06:37 PM   #99
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Here's one for you! But there Hundreds and Hundreds out there.

http://www.enginelabs.com/engine-tec...us-horsepower/

[QUOTE=jerryd87;10339046]plus as i said previously on this site, the bearings in the vq are ****ing giant and the number of spun bearings that have plagued the platform have shown that tight clearances are a bad idea and asking for trouble even company's with multi million dollar machine shops cant get tight bearings to work. more power means more heat, which means faster oil degeneration, and more expansion of the metal not even figuring the fact that the greater force means exponentially more force being placed on the bearings pushing oil out and allowing metal on metal contact that the thicker oil resists hence why the big power drag racers use such a thick oil and its not that it allows it to last longer since they change the oil every pass due to so much blow by that some of those engines make. never met a single engine builder or racer who has knowledge on building engines who supports tight clearances.[/QUOTE]
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Old 03-01-2014, 06:52 PM   #100
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Here's another one…..

SBC 1500HP

http://www.hotrod.com/projectbuild/h..._engine_build/
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