Crankshaft; front main bearing & cover; rod bearings; MISCL.
crank.htm
Article 60, sub-section 10
©
Copyright, 2012, R. Fleischer
Front
main bearing and its holder/carrier:
Pay attention to the information in the books about properly
positioning things, and the oil holes being vertical and about
the drilling needed on the two holes through the
bearing...0.124"...right through the existing front bearing
carrier, and then the bearing area. A new locating pin
hole....taper hole, partial at 0.156", and full at
0.148"....there is a special ream...etc. all
this is being mentioned for you, and not put in exacting
detail.... to be extra cautious in not just willy-nilly changing
things.
***NOTE that things can get rather complicated in setting up a lower end, particularly if it is a NEW crankshaft. BMW has specifications for the matching of the crank color code; main bearing bushing, and the bearing cap.....generally, it is a matter of matching color codes on these things...but the Factory Manual has the various specifications. MOST of you will never have a crankshaft out, let alone changing one. A very few of you may have the crank out for re-shimming...and I have the information later in this article on that. BMW lower ends are very long-lived, providing they get clean oil all the time.
To remove the front holder you need to use a puller, either BMW's, or a steering wheel type for a car. Use a good hardened bolt with a countersunk depression you put in it on a lathe, in the crank nose, for protection. YOU MUST HEAT THE AREA QUITE HOT, WITH A LARGE FLAME TORCH.
Timing chest seals:
Grinding crankshafts:
Do NOT regrind crankshafts, even though undersize bearings are available from BMW, unless you are prepared to re-heat treat the area that was ground, and to radius the sharp corners, etc. This is VERY tricky to do. BMW offered the undersize bearings because of RARE production use of undersized crank journals. NOTE that the hardening of the stock crankshaft is not very deep!
Crankshaft
end play, spacers, ETC:
Fairly rarely and after huge mileages usually, one sees an Airhead that has
two or more of the following symptoms: Shifts hard
(BUT
isn't lack of input shaft lubricant or bad clutch); most probably
has a lurching, grabby clutch action; idle rpm is unstable and
varies with clutch pull-in; engine vibration.
If you have an airhead with those symptoms, you may want to check
the end-float (end play) of the crankshaft. This is a serious
subject. You are advised to see an expert, or to get the BMW official
information, but here are some things that may clear things up a bit. You
will have some color(s) of thrust washers on both sides of the engine
housing. It is these that set the end-float of the crankshaft.
SOME BMW Manuals have the sizes of these WRONG (in converting the mm to inches).
A lot of work is involved in setting up a crank from scratch, so if your crank
just had excessive end play, you may want to just change the thickness of the
OUTSIDE (rearward) spacer. BMW has specifications on end play, or
end-float as they call it, and
you need to understand that it varies if oily or
dry, and BMW does not tell you about that. The end-float specification is
0.08 to 0.15 mm (which is 0.003" to 0.006"). This is for DRY. If
oily, the minimum is 0.15mm (0.006"). If starting from crank
out, you may want to lower your labor by installing the thinner RED spacer
inside. Thusly you likely will not have to remove the crank again, just
select the appropriate rearward spacer. Note that BMW has a limit for
wear, and it is 0.20 mm (0.008")
Here is the real values of the thrust spacers:
RED: 2.483 mm to 2.530 mm (0.0978" to 0.0996").
BLUE: 2.530 mm to 2.578 mm (0.0996" to 0.1015").
GREEN: 2.578 mm to 2.626 mm (0.1015" to 0.1034").
YELLOW: 2.626 mm to 2.673 mm (0.1034" to 0.1052").
Regarding
rod bearings and caps and bolts:
I will not reuse the rod
bolts!.....
NOTE that the conrod bolt is a
special type, although it looks like a Torx. You can
get the tool from NAPA as part 2305, which is the same as K-D
tools part 2305.
Be sure to oil these parts well as you assemble
them and also put the tab into the cap slot; and the rod on
correctly....that is, the located pins will be facing forward!
Tighten the rod bolts slowly, don't use too much torque at first,
so you can check for smooth operation of the rod on the
journal....BEFORE you tighten to the final value of 35-38
footpounds; NOTE that the R80GS, R80R, R100GS, and R100R are to
have the rod bolts tightened in stages, by degrees.
Initial preload on them is 15 footpounds, then you go to 40-45
degrees more.
rev:
01/26/2008: new, released
03/03/2009: Update and clarify details on crank end float and spacers
01/23/2010: update, clarify front holder information
© Copyright, 2012, R. Fleischer