S14 rod bearing question.

[BlackbirdM3]

I just pulled my #1 rod bearing to see what size I was going to need to order. The thing is, the part number doesn't match anything. On the side with the retainer it says BMW then a part # 1310515. With cross reference to RealOEM its a "red" sized bearing that should measure up at 48mm, however as close as I can tell its larger, more like 48.66mm by my digital calipers, measured at the top of the bearing shell at what should be its widest point. Am I correct that I need the "red" 48mm shells?

On the other side of the same shell, it has the numbers
0269
06-86

Stamped in that way. Is the 06-86 a production date? The car was built 10-87.

Thoughts?

Will

[BlackbirdM3]

Original measurement was done out of the cap, in the cap the bearing measured in at 48mm on the nose.

Will

[spdracrm3]

you cannot measure rod bearings with them out of the con-rod they naturally spring open at flange ends (you'll never get an accurate enough reading with calipers),there are two ways to measure correctly ,first mic the crank rod journal with and outside micrometer 90 deg apart and then measure inside bore of con-rod with shells installed and torqued to specs(measure vertical (in line with rod arm ,then at 45deg each way of vertical)) a special soft touch inside bore gauge is need so as not to mark soft shell surface, subtract the journal from bore to get clearance .

second and cheaper method is to use plasti-gauge on con-rod torqued to spec on respective crank journal with shells installed (dry,no lube). do not move once torqued , remove con-rod cap and check clearance using plasti-gauge.

as you've cross referenced to "red shells " i would purchase those and measure them for clearance, if in spec run em

[BlackbirdM3]

you cannot measure rod bearings with them out of the con-rod they naturally spring open at flange ends (you'll never get an accurate enough reading with calipers),there are two ways to measure correctly ,first mic the crank rod journal with and outside micrometer 90 deg apart and then measure inside bore of con-rod with shells installed and torqued to specs(measure vertical (in line with rod arm ,then at 45deg each way of vertical)) a special soft touch inside bore gauge is need so as not to mark soft shell surface, subtract the journal from bore to get clearance .

second and cheaper method is to use plasti-gauge on con-rod torqued to spec on respective crank journal with shells installed (dry,no lube). do not move once torqued , remove con-rod cap and check clearance using plasti-gauge.

as you've cross referenced to "red shells " i would purchase those and measure them for clearance, if in spec run em

Thanks. Since the motor is still in the car, plastigauge is the way I was going to go. That said, I'm having trouble finding the correct clearance required for them. I found them once, but now I can't seem to find them again. I found one site that states 0.03-0.07mm but its not from the site that looked to be a BMW shop manual that was in PDF form. I can't remember, but is that the green plastigauge?

One last question, am I going to have to drop the power steering rack to get to the #3 and 4 cylinder bearings? There was a whole thread on this on S14s, but the site is down

Thanks,
Will

[spdracrm3]

this is the spec on Alldata here at work "Note: Exc. double class, .0012-.0028 inch; double class, .0008-.0022inch.", i think both red or green will check those tolerances we mostly used green in our machine shop if i remember right
i have the factory manual at home and will try to remember to check that for specs tonight

ive never done rods in the car so cant help with second question

[BlackbirdM3]

this is the spec on Alldata here at work "Note: Exc. double class, .0012-.0028 inch; double class, .0008-.0022inch.", i think both red or green will check those tolerances we mostly used green in our machine shop if i remember right
i have the factory manual at home and will try to remember to check that for specs tonight

ive never done rods in the car so cant help with second question

What is "double class" I've never heard of that. I ordered the stock red 48mm bearings. I also never found anything that was colored red on the back side of either half.

Thanks,
Will

[spdracrm3]

BMW at the factory used a double or triple bearing classification to set clearances "double" used just paint dots/codes on the crankshaft journals to determine which shells to use , "triple " uses both the paint dots on the crank and the paint dots on the rods (or block/console for main bearing) to determine correct shells to use ." triple "combining both the rod journal outside dimension and its color coded paint dot and the connecting rods inside big end dimension with its paint dot to set tolerances very precisely. in the factory they had two shell choices for "double " classification (red and blue) and three for triple classification (yellow green white) for standard, first second and third undersize.... thats a lot of different shells......but this also allowed them to use parts that werent to exact tolerance range and still get clearance in spec.

unfortunately the paint dots get very faint,change color or disappear over time ,fortunately only two shells are available for rebuilds (red or blue double classification) which limits the choices so try matched colors or one of each to get the tolerance you need (color codes on old shells are on side of shell if still there)

crankshaft radial play spec is 0.020-0.046(0.0008-0.0018 )
rod radial clearance spec 0.020-0.055(0.0008-0.0022)
right out of Big Blue factory manual

factory replacement crankshafts are only supplied with "double" classification bearings due to the fact that they dont know exact dimension of block mainline bore or rod big ends

[BlackbirdM3]

So in other words, there is a chance that I might have a single or more 1st undersized bearing(s) out of the 8 possible.
I knew they did that with the main bearings, but I wasn't sure on the rod bearings. I assumed they were running a constant size on the rods.

That said, from a thread I started on S14power, it sounds like there is a tendency to run on the wide side of the clearances, 0.06- 0.07 rather than on the tight side. resulting in less heat build up. (which makes sense). I don't know what the clearance is on my current bearings, I haven't measured yet.

Will

[spdracrm3]

So in other words, there is a chance that I might have a single or more 1st undersized bearing(s) out of the 8 possible.
I knew they did that with the main bearings, but I wasn't sure on the rod bearings. I assumed they were running a constant size on the rods.

you should not have 1st undersize unless your crank has been ground in which case all journals will be that undersize, (they dont just grind one journal undersize)

you might have any combination of the two available bearings (red or blue ) though in most cases the same shells can be used and will be in spec.

That said, from a thread I started on S14power, it sounds like there is a tendency to run on the wide side of the clearances, 0.06- 0.07 rather than on the tight side. resulting in less heat build up. (which makes sense). I don't know what the clearance is on my current bearings, I haven't measured yet.

yes for racing they run on the loose end of tolerances

Will