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Old 01-12-2013, 08:52 PM   #33
Beastly Adventurer
Joined: Mar 2002
Location: North Coast (Lake Erie)
Oddometer: 1,056
While looking at Snowbum's site for something else, I ran across this section and thought it might hold some information of interest for this thread. And by the way, I'm just the messenger.

7. BMW 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 clearance, 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.

R50/5, R60/5, and R60/6 (to 1975): INtake opens 40 ATDC; closes 40 ABDC. EXhaust opens 40 BBC; 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 and R90; R100/7; R100S; R100RS 1977: INtake opens 10 BTDC; closes 50 ABDC. EXaust opens 50 BBDC; closes 10 BTDC. (This is the symmetrical cam talked about a bit farther down in this section #7)
R80/7, R100/7, R100S, R100RS (1978): INtake opens 16 BTDC; closes 44 ABDC. EXhaust opens 56 BBDC; closes 4 BTDC. (This is the advanced cam talked about a bit farther down in this section #7)
From 1978, the U.S. models (R80/7 and larger) had INtake opening 10 BTDC; closing 44 ABDC; EXhaust opening 56 BBDC; closing 4 ATDC.

note that sometimes cams are spoken about as the total degrees, and the 1978 would be 308

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 come with the oil pump parts.

NOTE #1: The 336 cam has about a .424" lift, soft ramps, and runs strongly between 5700-7700 rpm, with roughly 8000 max rpm.

NOTE #2: BMW uses .080" of valve setting clearance ( 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 all 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. The 284 camshaft has 8.62mm lift; the 308 camshaft has 9.40 mm lift, for some reference points here.

11-31-1-258-053 has small cam seal, used on /5 to R90S (to 1976 model year); and was replaced by the -337-848 cam per book, in error, says K.
11-31-1-263-412 has 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.

NOTE further confuse the issue, there were TWO versions of the -053 and -412 camshafts. The difference is the KEYWAY for the gear. The later versions 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.

NOTE #4: 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.

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:
That is a link 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 fibre, and insulates the spring from heat, when the engine is suddenly stopped.

NOTE #5: 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 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.
Here is a sneaky way of determining things, 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 gear 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.
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