Seems like every company has their own way to describe a bearing. Here is where I find the confusion and need some direction.
This involves a '86 G63B with some modifications like Carb, Header, Schneider Cam, tweaked dizzy. I had a lower end rebuild and spun a #1 rod bearing when the bearing coating gathered and clogged the oiler hole and closed off oil pressure, all while doing 25mph. Anyway I decided to do the job right, and do it myself. I pulled the motor again and started pulling rod bearings and they were in rough shape. Main bearings looked decent, but I figured if I'm going to do this, do it all.
The recent rebuild on the lower end had the following size bearings. .025 Rod bearings and 010 main bearings. I pull the original crank and decided to replace the crank with a doner that was in extremely great condition. The crank looked good enough to drop in without any work but, I had it polished anyway. Now it is perfect and has been checked for an install. The machinist marked it with a #10 on it which told me they removed material and now the crank is .010 smaller on the journals. I brought the crank home and bagged it, then started measuring the motor for clearances. The original crank was marked with a 10 also and the rod bearings that were removed were .025. So I purchased a set of King .025 X series bearings for the rod ends. I will be checking these for clearance after the Main bearings are clearance and fitted. Well here is where I start finding the confusion and it has to do with bearing sizes to achieve the correct oil clearances.
Bearing companies have their own information they give when checking the details on a set of bearings. I see STD for standard size or stock size to fit the OEM measurements on rods and mains. Then I start seeing 010, 0.25, .25 and most do not say inches or mm when displaying their bearing details. Then companies start throwing the word undersized and oversized into the game. Now it would nice if they stuck to one way of saying something, but they don't. I take the word Oversized as an oversized bearing to compensate for the removed material off the crank, so oversized fits the wording correctly in my mind. Then while checking for bearings I see the undersized bearing. This tells me the bearing is undersize you would think, but noooo! I am told that it means it is to fit an undersized crank that has material removed and now is undersized. See where I am going here, it's like WTF!. Anyway, I hope I have the right explanation for bearings so far. They mean the same thing depending how you look at it sort of, so I'm ignoring those words and zero in on the size of the bearing I need.
Ok, when a bearing says 010, does this mean .010 or 0.10 and is it mm or inches? Oh crap here we go again. The .25 bearing, is it the same as the .025 or just a typo when placing the decimal point, I'm not sure yet, but that is why I ask you folks for some experience in this BS.
My calculations on my crank told me I needed to compensate for the material removed and that number came to that I needed a .025 oversized main bearing set to fit an undersized crank. Still with me? Ok, this is not that difficult, so I ordered them. The stupid company sends me the STD size by mistake. I knew they were wrong before I open the box. Well, for sending me the wrong ones, I decided to use them to check my clearance on their dime or their bearings in other words. So I fitted the STD size bearings and knowing they were too small I then plastic gauged them and sure enough they were short and gave me too much clearance.
Here is what the test looked like and as you can see I have an excess of oil clearance.
The maximum clearance should be .0020in and the minimum should be .0008in, so I am not in the ballpark with the STD size bearing which I knew I wouldn't be. But, it told me what I need to do sort of. The gauge is showing close to .076mm size on the measurement, I need to get this down below the .051mm or aka .0020in correct? Now tell me if I'm wrong...if I installed a .025mm oversized bearing this would bring my clearance to .076mm - .025mm= .051mm? This would meet my maximum size allowable for oil clearance exactly at .051 or aka .0020in . But I would like to get this to maybe .040mm so I am in the middle range of my required oil clearance of .0008in to .0020in / 0.02mm to 0.05mm.
So what do you suggest on this and what about these bearing sizes .025 and .25 are these the same but just misread? Would a 010 bearing get me closer to the midrange of my recommended oil clearance? I have done so much research on this it had finally broken me, lol. Though my test (the photo) does say I need a thicker bearing obviously, so that fact gives me that information. What size main bearing would you suggest I get to correct that problem in the picture and have my clearance in a safe range.
.025, .010 etc. is imperial (inches)
.25, .50, .75 etc. is metric (mm)
You need to call the machine shop and ask which measurement they used when machining your crank. Can't mix and match the two with proper results. I'd suggest not using the plastigauge, it's more of a 'close enough' type of measuring. Get your self a quality set of digital calipers, or if you want extreme precision, ID and OD micrometers. Mitutoyo or Starret are a couple of the best. Harbor Freight will not do here. Measure your crank and write it down. Install the bearings into block and cap, install cap and torque it proper without crank installed, measure and write down. Subtract and you have a more precise direct measurement of clearance. Same goes with rods, measure crank, install bearings into rods and assemble to proper torque then measure, and subtract. This is also known as "blueprinting" since you have all measurements and clearances documented. If you really want to get picky buy a bunch of bearings, all of them will have slightly different tolerances and you mix and match sets until all are the exact clearance you want.
That is exactly what I have been doing is measuring and using micrometers.
I admit though, I need an inside bore micrometer and the 3 way type at that. I am trying to get the feel for my Telescoping Gages.
Double action, self-centering gages for taking inside measurements without leaving scratches.
I first measure the #1 journal, then zero the bore gauge inside the micrometer, then use the bore gauge to measure the bearing. The actual measurement doesn't matter, you end up seeing only the difference in the measurements, which is the clearance measurement you wanted to check in the first place. I also am trying to use only one measuring device for the final clearance since mixing tools will create more room for error.
I am hesitant about mixing and matching because there will be different wear tendency between one bearing and another of different size. Though I do get your idea on that suggestion but the measurements should fall within certain limits and if 2 are so far that different size bearings need to be used, then the part needs to be corrected so that the substituting can be eliminated.
I think your correct and I will chat with the machine shop, though they only had the crank on this and don't know the bore sizes for the rods and mains. I would luv to try different bearings also, but doesn't that get a little pricey when you end up only using one set?
Harbor Freight isn't all bad. You do need to be careful about a purchase as I am. I purchased these micrometers for an unbelievable price and I had them calibrated at a machine shop and they are within 1% of total accuracy.
It depends what you buy and if they are handled aggressively I will agree. If I dropped one, I'm sure it would be garbage.
Thank you very much for this information on the inch and mm size description. it helps a lot..
(images in my post will be removed from my server when my thread is satisfied)
.010 is bearing measurements in inches, .25 is bearing measurements in mm. They are very, very close to the same measurement and will appear the same on the plastigage tape, hence my "close enough" statement. The biggest difference in the two is how they sell them. Most manufacturers label their over/under size depending on where the vehicle was manufactured or what is detailed in factory repair manuals/technical papers. If the OEM lists pertinent engine tolerances/measurements in mm the aftermarket manufacturer will list them that way as well.
Example 1: Honda, Mitsu, Toyota will all be mm as that is the standard in the country of manufacture.
Example 2: Your good ol' small block chevy or ford will be in inches since they were made in the US.
That is the industry standard but not always followed by all aftermarket manufacturers. Some of your older rebranded vehicles (Mitsu/Dodge) you will find parts listed both ways.
Think about it this way, how much material would be taken out on .010 of a mm? How much grinding for .25 of an inch. Very large difference!
It all depends on how close you want your tolerances to be. Measure in one or the other, buy parts in that measurement, and assemble. With your mods, I'd say close enough should get you where you want to be. If you were going turbo and pounding down hundreds of HP, measure, measure, measure.
I'm at work and unfortunately can't see your pics.
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