Crank Bearing question

[LJSB]

I'm having work done on a 3.0 NSX engine.
The service manual on 7-8 seems to indicate that the crank bearings are different from the top and bottom. The illustration shows the top half of the bearing having a groove and the bottom half not. Are the tops different from the bottom or are the top and bottom bearings both grooved?
I understand what color combos I need for my application but all the bearings I got from my dealer were grooved. I ordered by color and did not ask if there were upper and lowers.
The engine I'm taking apart has had someone there before and it had all grooved bearings, top and bottom halfs but I want to make sure this was right.
The illustrations and some information in this section of the manual were not completely correct ie., the number stamp was on both the bearing cap and the rod NOT half of the number on one and half on the other as the picture illustrates in this section.
Is this pic of the upper and lower bearings as it is supposed to appear or are they both grooved and the picture is inaccurate?

 

[sjs]

Top vs bottom. By "top" do you mean block side? I just checked some bearing caps and the bearings on that side have the grooves (and holes), which they should given the oil passages. Unfortunately I can't lay my hands on the block or those bearings at this time, but I would be surprised if they are different. I'm sure someone will come along soon and confirm this, but I think that what you have is correct.

 

[Gerry Johnson]

They are both the same for top and bottom as are the rod bearings.

 

[LJSB]

Thanks gentlemen.
I thought the picture might be goofy and it seemed to make sense that there would be a oil groove all around the crank but wanted to be sure. Didn't want to be thinking about this AFTER the assembly.

 

[RP-Motorsports]

Also you don't want to just re-order individual tops or bottoms based on the originals. You need to plastic-guage each and every one to see if the OEM size will still work. You could have a diff size (color) on each and every main and rod and different on the top vs- the bot. If you pick a color that is too tight, you run the risk of spinning a bearing. Too loose, and you will have crank walk etc. Make sure you know what you are doing! Honda's 2-piece bearings may be a small part, but can cost a ton if NOT respected.

 

[LJSB]

Also you don't want to just re-order individual tops or bottoms based on the originals. You need to plastic-guage each and every one to see if the OEM size will still work. You could have a diff size (color) on each and every main and rod and different on the top vs- the bot. If you pick a color that is too tight, you run the risk of spinning a bearing. Too loose, and you will have crank walk etc. Make sure you know what you are doing! Honda's 2-piece bearings may be a small part, but can cost a ton if NOT respected.

Absolutely.

 

[hlweyl]

Pbassjo, I'm curious, what happened that you are doing a complete teardown? If you spun a bearing, it's probably a good idea to get a competent machine shop to mic everything and have them magniflux all of the parts while they are out.

And as T Bell said, at minimum plasti-gauge the clearances between the main caps and crank.

 

[sjs]

I'm having a little trouble with a couple of the ideas above. First off I'm not sure I see an otherwise unmolested crank needing a different bearing shell size than it had previously. If a hardened journal on a forged crank changes diameter then there are other problems. If the block and/or main caps have deformed then they need to be re-bored to specifications. Similarly, if measurements indicate different bearing shells top vs bottom then either your measurements are bad, or the crank is bent (after all, it rotates so it doesn't have "sides"), or the block/cap need to be re-bored. In any case I can’t see using an unmatched bearing pair. I’m not trying to state either of the above as absolutes. Perhaps there are things I’m not considering here, but a combination of personal experience building other engines and straightforward logic lead to me these conclusions.

As for plasti-gauge, I've used it for years but many people will say it just isn't accurate enough for high precision assembly. I always try to combine it with using a micrometer as well as a dial indicator and comparing results.

 

[RP-Motorsports]

Honda themselves reccomends guaging whenever a tear down occurs (service manual). Just plain simple wear could cause a color change. The name brand of rods used can differ in tolerances including OEM. I have torn a Honda motor down, and believe me the most frustrating part in the whole process, was getting the correct color tops and bottoms right for the rod and mains. Hell just because you have one color on the top of a rod/main, you could have a different color on the bottom of the same rod/main. At first I was pissed @ Honda for getting too accurate in their tolerances, when you could just go down to NAPA, and buy a universal bearing kit where all the bearings are the same color for all pieces, but why NOT be more accurate? This motor was used mostly for track use, so accuracy was a must! I never regretted all the headaches and time it took us to get all of the color combinations sorted for a perfect fit of the crank to the block. Even with FI added, the motor was reliable.

Just as I said before, you do NOT have to use Honda custom colored bearing configurations, you can go to say NAPA and buy a standard set, being equally sized for all pieces, but in a sports car especially an NSX, isn't the extra time/money/headaches worth it?

 

[LJSB]

Refer to page 7-8 of the NSX Service manual and it explains how to choose the correct bearings using the codes on the crank.
It works well if you can't read the original colors. As it shows in the chart and later notes below there can be different color bearings mated together.
The pic of the bearings made me ask the original question. Just didn't make sense to look at and wanted to be sure the pic was wrong.
I appreciate your concerns and your suggestions but really I'm ok from here. Thank you all.

 

[sjs]

I know of the colors representing sizes of course, but I am still surprised/confused about the different halves for the same journal. Obviously I need to refer back to the manual before spreading more falsehoods. But I only recall that the crank itself is stamped with codes for the main bearing, one per journal, not two. But that makes sense for the crank which can have only one diameter per journal. Since those translate to colors/sizes, where is the information indicating any miss-match caused by the block/cap bore (which if the only other variable). Rods would seem to follow the same logic. Hmmm... back to the book.

 

[sjs]

OK, that didn't take long. Apparently I had forgotten or never known that besides the letter & number stamps on the crank, the block has a bar-code stamped into it for the crank bore size per journal, and of course the rods are stamped with a number. And now I understand how/why you can have different ones top & bottom. The point is that if no color is exactly right you can effectively split the difference by using two adjacent sizes to achieve an overall diameter midway between the two. (obvious now that I think about it) Technically that would mean the crank (or rod for rod bearings) is slightly offset at that point, but the amount is so miniscule as to be irrelevant. They do state clearly that when doing this it does not matter on which side each half is used (top vs. bottom), but logically I think I’d at least be consistent with the mains or it seems that some of the benefits of all the precision would be wasted. I wish they published the bearing shell thickness by color.

I’ve often wondered why the crank couldn’t be exact but figured it must be more difficult than it sounds even these days, but I must say that I’m a bit surprised that the crank bore is not more precise. Oh well, whatever works.

Well I’ve learned something new today, so once again my time on Prime has been worthwhile!

 

[Eddy]

reason for gauging

One of the reason for gauging the bearing is that the bearings have tolerances as well. Take a sample batch of 3-4 bearings of the same color (say green) and mic them with a micrometer that can measure down to a micron (0.001mm or 0.00001") and you will see that they vary within 3 microns.

In fact, if you ever get a chance to take a look at the Japanese service manuals, it states the tolerance range for the bearings, journals and bores and each color covers a 3 microns range. This means given 2 bearings, crank size and block main bore size you have a total of +/- 12 micron tolerance.

Now since the oil clearance only has a 24 microns tolerance, it is possible to get all the colors/codes right and still fall slightly out of tolerance. And that's precisely the reason the manual tells you to try a different bearing of the same color before changing the color.

As for making parts more precisely. Well, they are getting better but it all comes down to economics. Your hair is about 70-80 microns thick but your bearings, crankshaft and block are made to be 2-3 microns in tolerance. You can tighten down the tolerance even more (say down to 0.5 micron) but you would drive up the cost of the parts significantly. It's because you will need better CNC machining centers to make the parts, throw out more parts that fall out of tolerance and make servicing nearly impossible for mechanics including us since we can't afford the tools to do that kind of measurement.

Do an experiment at home if you have a micometer. Even different room temperature changes the jounal size of the crank. You can see a 1-3 micron change in size in steel parts and even more in aluminum parts like pistons. So if you are really picky and anal, you should spec all your jounals, bores, bearings in a temperature controlled room. So can you imagine making these parts, we are talking about carbide cutting forged steel, while maintaining the right temperature and getting it the right size everytime?

Eddy

 

[LJSB]

Here's a update. Followed the procedure in the manual, including plastic -gauge check and all is perfect. Should be all back together soon.
The proceudure works but the illustrations are not always righht on.

 

[RP-Motorsports]

I wish you luck!
What rods/pistons did you go with??

Compression ratio?

Make sure you break it in slow after the re-build. Do a mix of city AND some highway driving. Do a few medium trips, as well as a few short and longer trims, and try to not enguage vtec or redline until properly broken in.

 

[NSXTCY]

Tom,
If you remember when I built your Integra motor the bearings you supplied were all lower (cap) side and no top side, I noticed this because they were all smooth with no groove. Upper (block) side in most motors have this groove to allow a larger oil path to the journal, and not on the bottom as it needs film area to support the crank aginst firilg pulses. The colors were the same top and bottom for the same journal.


P.S. Please do not use pictures of my shop in your profile


Kevin
The Shop

 

[Jimbo]

and mic them with a micrometer that can measure down to a micron (0.001mm or 0.00001") and you will see that they vary within 3 microns.

Eddy,

Are you sure about this? I don't think you really mean microns do you?

-Jim

 

[satan_srv]

like eddy said it's best to buy several bearings of the same colour and plastigauge them until you get the perfect clearance.

You can buy the bearings from honda you just pay a 10-15% restocking fee when you return the ones you dont need.

Since we usually build motors to have a specific clearance, we will go through the same colour until we find the perfect size.

 

[Eddy]

microns!

Yup.. 100% sure.. Japanese engines are in general very precise.. Tolerances are usually in the microns. That's not just the bearings alone.. For example, NSX piston to wall clearance is specified to be from 0.007-0.030mm (or 7 to 30 microns) with a limit at 0.0785mm (78.5 microns) . Imagine that! The S2000 piston start at 0.004mm. That's why our NSX engines lasts over 150k miles without a rebuild. When I build engines for my team, it is not uncommon to get a batch of new Honda OEM pistons that are $30 a piece from the dealer and find several to have the exact skirt diameters down to a micron and the weight difference to be within 0.5 gram. It's pretty amazing to have a machining center that can do that kind of quality with that kind of volume.

Most of these tolerances are hard to achieve with typical machine shops in the states since their minimum tolerance is at 0.0001" (or 0.0025mm/2.5 microns) and most machine shop don't have the capability to do anything smaller than 0.001" consistently (unless you have access to aircraft co./research center/big race team's machine shops).

And your question may be, "how do you measure a micron?" Well, it's not that bad.. Mitutoyo for example has micrometers (under $500; about $200) that will easily do a micron consistently.. For more money, you can measure submicron too. But when it comes down to measuring microns, your technique matters as much as your tool. Difference in temperature and stress in the part or tool due to handling will show up in your measurements being inconsistent.

Eddy

 

[Jimbo]

Eddy,

The max NSX piston to block clearance is 0.00032 inches. That is 3 ten-thousandths of an inch. A micron is another order of magnitude smaller yet (1 micron = 0.00003937 inch).

The tolerance on a new NSX "A size" piston can be anywhere from 3.5427 to 3.5434 that's 7 ten-thousandths of an inch.

The tolerance on the bore on a new block is 3.543 to 3.544 or 1 thousandths of an inch.

I would agree that these tolerances are fairly close but it's certainly nothing that would require the measurement of micron sized features - is it?

-Jim

 

[Eddy]

You don't absolutely have to be able to measure a micron since a 10 micron resolution will be able to put you in the ball park of the tolerance but it only puts you in the ball park.

Let's say you measure a piston clearance of 0.01mm (or 0.0004in) which falls perfectly in the spec. Well, your instrumention always has one digit of uncertainty (it's a fact that's always stated in the micrometer's instruction and taught in high school science classes), that means your clearance can be anywhere betewen 0.005 to 0.014mm. Well, if you are lucky, it's 0.014mm and everything is fine. If you are unlucky, it's 0.005 and it's out of tolerance and guess what, your piston would stick to the wall because of it. This may not seem to matter so much but when you are reving at 8000rpm, it matters.

Now, take another example that we measure the same piston clearance at 0.010mm (note the extra digit of precision). Now we know the clearance falls between 0.0095mm and 0.0104mm. And we are sure we have it in tolerance regardless of the uncertainty of the last 0.

Technically, it would be nice to able to measure down to 0.0001 (or 1/10 of a micron) so when we are near the very edge we are sure it's on the edge and not off of it, but those are different kind of beasts.

Like you said, it's not absolutely necessary but it does matter when you are near the end of the range. It all depends on how precise you like to have your engine and how much money and effort you are going to put in.

Eddy