Boxerworks.com

Not that it takes much, but I'm realy confused now.

For me it would be degree wheel time.

Garnet wrote:Not that it takes much, but I'm realy confused now.

For me it would be degree wheel time.

I've got several old double row sprockets from various years and the single row sprocket that came with the 336. I can stack them up and see if the timing mark is different. It doesn't make since that it would be though, because the key slot change was made to the cam (3 degrees retarded on the cam according to the 336 bulletin= 6 degrees advance valve timing ). I'm betting the sprocket marks are the same in relation to the notch.
When I checked the valve to piston clearances (after deepening the intake pockets .7mm) I came up with equal 3mm clearance for both intake and exhaust.

the quinner wrote:It really depends on what one calls "performance."

Exactly.

vanzen wrote: Improvement is a pretty nebulous term that may be defined to any individual's preferences.

A common misconception will be that HP = something better, the holy grail for any machine.
True on the track, but bullshit otherwise – ignore the advertising / racing hype.
If you are riding on the street – TORQUE RULES.

+1 Area under the torque curve is what you want for street riding!

vanzen@rockerboxer.com wrote:If you are riding on the street – TORQUE RULES.

+! Right on Vanzen.

I seem to remember that quite a few people found the 336 cam to be somewhat too peaky for road riding, one of the really good things today is that there are such a variety of cams available for our bikes from 320s to asymmetrical cams from Motoren Israel and seibenrock, and they seem to be available for the earlier bikes as well.

I can only comment on the asymmetrical cam on my 1070, that delivers a kick from about 5500 rpm as well as improving torque under those rpms.

As always the bike engine is a system and to get the best of a cam change, you need to consider compression ratios, pinging issues, gas flow etc etc.

mattcfish wrote:I've got several old double row sprockets from various years and the single row sprocket that came with the 336. I can stack them up and see if the timing mark is different. It doesn't make since that it would be though, because the key slot change was made to the cam (3 degrees retarded on the cam according to the 336 bulletin= 6 degrees advance valve timing ). I'm betting the sprocket marks are the same in relation to the notch.
When I checked the valve to piston clearances (after deepening the intake pockets .7mm) I came up with equal 3mm clearance for both intake and exhaust.

After stacking up the cam sprockets from an early /6, late /6, and a late single row sprocket I can tell you that the timing mark and key slot are all the same.

After taking the bike for a vigorous ride, I can tell you that the late cam and this early bike is are a very good combination.

mattcfish wrote:After stacking up the cam sprockets from an early /6, late /6, and a late single row sprocket I can tell you that the timing mark and key slot are all the same.

Matt, I'm really not trying to be argumentative or abrasive...but I'm absolutely positive about this one...

I spent twenty minutes yesterday holding sprockets against each other...I flip flopped from being thoroughly convinced that I was right...to convincing myself that I was completely full of it. The bottom line is that trying to compare sprockets by stacking or holding them up to the light is NOT a good way to prove/disprove this issue. I was on the verge of actually machining a piece of brass to the ID of the sprockets to make the comparison...then it hit me: index them to each other with a dual row timing chain...

So I took the three different examples of camshaft sprockets...indexed them front-to-back with a dual row timing chain...and now I'm back to being absolutely positive that the keyway in the 1970-77 dual row sprockets is different than BOTH the 1978 dual row sprocket and the 1979+ single row sprocket.

Here are the three sprockets...L to R: 1) 1970-77 2) 1978 only 3) 1979+



How to ID 1970-77 vs. 1978 sprocket. The 1970-77 (L) sprocket has the stepped shoulder near the hub to accept the tachometer drive gear...the 1978 (R) sprocket has a square shoulder.



This shows the 1970-77 sprocket placed against the 1978 sprocket (front-to-back...they're both facing the "same" direction). They are indexed with a dual row timing chain...which holds them quite tightly with almost no slop. The keyways do NOT line up...they are (if I had to guess ) about 3 degrees different. Sorry about the picture quality...



This is the 1978 dual row sprocket indexed with the single row sprocket. The keyways DO line up.



Summary: In 1978, BMW changed the valve timing. They did this by changing the keyway location in the camshaft sprocket. The "revised" keyway location remained throughout the remainder of airhead production.

Thank you very much for the clarifaction.

the quinner wrote:Summary: In 1978, BMW changed the valve timing. They did this by changing the keyway location in the camshaft sprocket. The "revised" keyway location remained throughout the remainder of airhead production.

I don't mind in the least if you push this issue. Are you saying that the key position on the cam did not change place, only the slot on the sprocket?
The famous 336 bulletin http://moragafalconers.org/BMW_336_Cam/ ... 0Draft.pdf the slot is retarded 3 degrees on the cam and that you can't tell the cams apart by looking at them.
"The following are the different versions of the 336° camshaft:
BMW Part Number Model
1. 11 31 1 258 053
(small seal)
R50/5…R90S up to 1976
2. 11 31 1 336 393
(large seal)
R60/6…R100/7 up to 1979
3. 11 31 1 336 393
slot on the front face for the ignition
canister
R80/7…R100RS after 1979
For R45/R65 motors there no sport camshaft is deliverable.
For the camshafts listed under number 1 and 2 there are two versions, which differ in the
location of the slot for the woodruff key. In the older version the slot is at 0° camshaft angle.
For those to be installed in versions later than 1978, this slot is retarded 3°. Because these
camshafts cannot be differentiated by appearance, they can only be identified through
measurement of the timing. "
If the change was made to the cam why move the location on the sprocket?
When I stacked the sprockets I ran a straight edge through the slots and all the teeth lined up.
If you are correct I wonder what the valve timing is on my bike? It's running extrmely well..