Camshafts, broken cam tips, cam sprockets, alternator & cam
seals, crank nose bearing, etc, as on BMW Airhead Motorcycles
© copyright, 2011, R. Fleischer
Article 60
sub-section 7
cams.htm
****>>>>This article is meant to be used with the timing chain article. timingchain.htm
Broken tip on pre-1979 Airhead camshaft:
This relatively serious problem is seen now and then, and the
cause is typically from someone overtorquing the M6 nut holding the automatic
advance unit to the camshaft tip. It could have been abused
long before you got the bike, and weakened, and it was YOUR
unlucky day to snap off the tip even using proper torque. Officially the nut
torque, at least in one BMW manual, is .6-.7 Mkp. 0.7 Mkp is 6.86 Nm or
5.1 ftlbs. I would not go that high. 4 footpounds is, I think,
plenty good enough. MOST torque wrenches that read,
perhaps, to a maximum of 75 footpounds are VERY INaccurate at low settings of 4
or 5, even if they can be set that low at all. If you must use a
torque wrench, use an INCH-pound wrench at maximum 52...or some other lower
torque type of wrench, with appropriate conversion of values...there is a chart
on this website. I
personally tighten these nuts by feel, and I use the original
type of washer or a waverly locking washer. I do NOT use a
split-type of washer. Nuts need NOT be overly snug, but
must be snug enough so the nut does not back off! I suggest
that folks use less torque, more like maybe 40-44 inch-pounds,
which I THINK is enough. I do NOT use Loctite on these nuts.
What to do if the tip does snap off, is a decent question!
A Boyer ignition will likely fit, but you can PROBABLY fix the tip, if you do the following very carefully:
1. File the cam nose smooth and flat. Do NOT
remove any of the D shaped boss area.
2. Center punch the EXACT center of the cam tip,
with a SHARP centerpunch. You need to make up
something or use the proper
centering
tool, to ENSURE that it is
dead-centered. I cannot emphasize this enough.
A machinist can do that for you, or, contact one of the Airheads
LIST guru's. You also need a drilling guide and tap guide
made up.
3. Using your drilling guide, drill the cam tip, very slowly, very carefully,
to a depth of 7/8", using small sized increments of drills,
and ending with a diameter of
11/64". Clean out the chips often. Use
tapping oil and tap for 5 x 0.8 thread, to a depth of
3/4"....carefully!
Do NOT break the tap! Use
a GUIDE for the TAP too!
HINTS: USE a brand-new tap of the taper tip 'starting
tap' type, do a thread or two, then back out and repeat. BE
ABSOLUTELY SURE that you select a thread pitch that you can
purchase screws for at the same time! 5 x .7 and 5 x
.8, etc., are metric sizes, but you may find that the .7 is not
common for tap and screw. Yes, I know that many
of you will use American size taps and screws and not
Metric. Do it right, use metric.
HOLD the advance unit counter-clockwise while
snugging the screw you install;...against the D-flat, to remove any slop and
prevent shifting movement.
BMW
Airhead motorcycle camshafts:
This is a VERY confusing subject for many
folks. Besides the confusion on camshafts, there are
sprocket complications. There are several stock camshafts, and
some available camshafts. For the stock cams, at
.080" valve lift, the timings are as follows, keep in
mind that TWO types of these are available, the 3° advanced one
and the NOT advanced one. There are a number of stock
camshafts, 284°, 308°, and also a 336 degree. The 336 camshaft was
NEVER installed as stock.
Please note!.....some of this camshaft information may be difficult at first glance to understand. This is especially so on some details such as the change in 1977 and 1978. Please see the timingchain.htm article on this website!
R50/5, R60/5, and R60/6 to 1975: INtake
opens 40 ATDC; closes 40° ABDC. EXhaust opens 40° BBDC;
closes 40° BTDC.
R60/6 1976 and R60/7 1977: INtake opens TDC; closes 40
ABDC. EXhaust opens 40 BBDC; closes TDC.
R60/7 1978: INtake opens 6 BTDC; closes 34 ABDC.
EXhaust opens 46 BBDC; closes 6 BTDC.
R75 (all) and R90; R100/7; R100S; 1977 R100RS: INtake opens
10 BTDC; closes 50 ABDC. EXaust opens 50 BBDC; closes 10
BTDC.
R80/7, R100/7, R100S, R100RS (1978): INtake opens 16 BTDC;
closes 44 ABDC. EXhaust opens 56 BBDC; closes 4
ATDC.
After 1978, the U.S. models (R80/7 and larger) had INtake opening 10 BTDC; closing 44 ABDC; EXhaust opening 56 BBDC;
closing 4 ATDC. I am NOT sure about the R45/R65.
Note that sometimes cams are spoken about as the total degrees,
and the 1978 would be 308°
see: http://W6rec.com/duane/bmw/engine.htm
also see Clymers, Haynes, the BMW books, etc.
336 degree camshafts, the so-called sport cams, are the ones ending in part number -053, -412, and -393, see below and note that the last batch of the 336 cams was for the square drive oil pump, and the cams came with the oil pump parts. The 336 cam has about a .424" lift, rather mild soft rise ramps, and runs strongly between 5700-7700 rpm, with roughly 8000 max rpm.
BMW uses .080" of valve setting lift (
2.0 mm) as the reference point for cam timing, and the tolerance
on timing is + or - 2.5°. Also note that if you are
measuring at the CAM lobe itself, that the R60/7 had a
0.2417" lift; and the later larger bore engines had
0.2634" lift. NOTE however that the rocker arm ratio
on the engines is 1.39, so for valve lift you multiply the cam
lobe lift by that 1.39 factor.
Another way of saying all this is that the valve pockets in the
pistons might have to be modified if you change camshafts.
The 284° camshaft
has 8.62mm lift (0.339"); the 308° camshaft has 9.40 mm lift
(0.370"), for some
reference points here. Yes, you multiply by the rocker arm
ratio, to get actual valve lift. Yes, these figures may
disagree by a FEW thousandths.
11-31-1-258-053: has a
small cam seal,
used on /5 to R90S (to 1976 model year); and was replaced by the
-337-848 cam per book, probably this is an error.
11-31-1-263-412: has a large
cam seal, used on
R60/6-R100/7 (to 1979 model year); replaced by the 337-843 for
both /5 and /6.
11-31-1-336-393: used on canister ignition models,
from 1979, including the R65 (?). This cam has a slot on the
front face (flat nose). This cam is only available in
the advanced timing version.
NOTE!! BMW presently sells a 336° cam to fit early models; but it is for the large seal, see above. If you have an early bike, with the engine cover that has a small seal, you need to get a later large seal cover...and you can get them with or without the tach cable hole area. If you order that 336 cam, it comes with a oil pump rotor. This is because the cam end that drives the pump has two flats, while the original rotor was keyed.
NOTE!! Do NOT use the BMW Airhead one-piece pushrods with non-stock camshafts!!
To further confuse the
issue, there were TWO versions of the -053 and -412 camshafts.
The difference is the KEYWAY for the gear. The later
version is advanced 3°, so the valve timing versus the
crankshaft is changed 6°. The -393 flat nose cam is
available ONLY in the advanced version.
The cams are not easily
identified by appearance, and must be measured. If
an old cam is installed in a 1979+ engine, the slot is retarded 3
degrees.
Here is the timing for these sport cams:
ZERO degree cam: INtake opens 32 BTDC; closes 52
ABDC. EXhaust opens 52 BBDC; closes 32
ATDC.
THREE degree cam: INtake opens 38 BTDC; closes 46
ABDC. EXhaust opens 58 BBDC; closes 26 ATDC.
UNconfirmed data for the sport cams, where
P=(inches):
4000 rpm, 3° cam, P= 46. For 6000 rpm
P=30. For 7000 rpm, P= 25.
for the zero degree cam, add about 2 to the P figures above.
If you don't know what P is, well, too bad, and I am going to
leave you UNinformed.
The entire camshaft story is very complex, and I
am not going to put it all in this article, but, refer you to
someone else's article:
http://moragafalconers.org/BMW_336_cam/
You can also try this: http://moragafalconers.org/BMW_336_cam/Sport%20Cam%20Installation%20Draft.pdf
Those are links to an article that was translated and edited
by David Paulus.
I think that on the first page there is an
error in the part number for the item 2 cam, which should be, I
think, 11-31-1-263-412, and, that it is questionable that the
cams won't fit the R45 and R65. One additional note:
under figure @1, at C., it describes a 'suitable
washer'. Try 11-34-0-026-186, as originally used on
the R69S. NOT cheap! The washer is tough, made of fiber,
and insulates the spring from heat, when the engine is suddenly
stopped.
Explaining
the 3° and 6°:
In 1977-78 BMW made changes, that amounted to a
6° difference in timing. This was done by changing the
keyway in the camshaft sprocket. Because of this, if one
uses the 1978 camshaft, and then uses a 1970-1977 sprocket
(11-31-1-250-253), then the timing is retarded.
Engines/bikes imported to the U.S. from roughly January 1st of
1978 HAD to have the advanced
timing, to meet the 1978 emissions rules. Many just before
this date did NOT. Thus some
"1978" might not have the emissions
camshaft. If you are interested in another way
of describing all this, see the timingchain.htm
article. The 1978 duplex camshaft sprocket had the 3° offset, but no
mechanical tach gear on it.
With the simplex sprocket, as used with the flat nose camshaft that also had the
ignition canister, the number was 11-31-1-335-588.
Here is a NEAT way of determining
which type of camshaft, symmetrical or not, an edited version of
something passed on by Tom Cutter:
Remove the spark plugs and valve covers.
Put bike in 5th gear and rotate the rear wheel in the forward
direction until the EXHAUST valve rocker arm pushes the valve
inwards and then JUST returns ALMOST all the way outwards.
As you rotate the wheel (jerks work fine on the system backlash for
that purpose) and the exhaust valve starts to come back out, the
intake will start to go in. This is the overlap
phase. Lay a straight edge across the adjustment LOCKnuts,
from the exhaust to intake rockers. Looking straight down
on the rockers, and on the straight edge from above, the straight
edge will change angle relative to the valve cover gasket, as you
turn the rear wheel. STOP when it is parallel. At
this point, if OT mark is lining up in the window, the cam is
symmetrical. If it is about 3/8" below the window, it
is the advanced timing cam.
MISCL:
There is sometimes confusion over the alternator and camshaft
seals used in the the inner cover. All models use
11-14-1-255-011 alternator seals, probably 28 x 47 x 7 mm...have
not measured to confirm that size.
The camshaft seal up to models built in 9/1975 was
11-14-1-261-193. It must not be use in later models,
or there will be leaks.
The later cam seal is 11-14-1-262-977, is 20 x 32 x 7 mm.
For the curious, the chain size is 3/8 x 7/32, both SIMPLEX, and, DUPLEX.
Crankshaft bearing: For many years, this was number 07-11-9-981-722, and is 35 x 62 x 9 mm. The bearing number has been changed to 07-10-1-468-882. It is a common bearing, but you must get the correct GRADE. The bearing is FAG16007-C3
Changing the front main bearing?...and confused about its holder/carrier??: Pay attention to the information in the BMW factory literature 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.
rev.:
NEW. Released 01/26/2008
4/26/2010: remove bad hyperlink
05/03/2010: fix two errors where valve clearance should
have been valve lift.
05/21/2011: Minor cleanup
11/06/2011: explain cam sprockets and cam numbers here and there, a bit
better. Add note about timingchain.htm article.
©
Copyright, 2011, R. Fleischer