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So, Matt, from your research can you conclude that the keyways on the cams were unchanged when the timing advancement took place? If this is the case, one could use an early sprocket and install a 336 cam straight up. This may be something usefull when building a race only motor.

mattcfish wrote:Are you saying that the key position on the cam did not change place, only the slot on the sprocket?

Yes...ignore the R65/45 and the R50/60 that had different configurations. All of the "standard" 308 camshafts...small seal, big seal, no seal...have the keyway in the exact same location. The valve timing change was done by moving the keyway in the sprocket (in 1978)...this change was kept until the end of the run.

I tried the same method you tried to prove/disprove my position. I put a few sprockets in a row on a square shafted screwdriver...the shaft fit the keyway pretty well. WAY too much variation...I could wiggle them all around and make the teeth line up or not...not a good method. My method of indexing with a dual row timing chain very securely located the sprockets relative to each other...it is the only method that gave very repeatable and consistent results.

Now...the 336 cam. First, you should read this page that links to the page you reference: http://moragafalconers.org/BMW_336_cam/

Note the fact that this document is from an unknown source. I'm not convinced that it's a factory document (I'm not convinced it's NOT a factory document, either). The arguments FOR it being a factory sheet include: the assumption of experience and ability (although, honestly, they don't usually come out and say it in factory documents like they do in this one). The comlete lack of information regarding the sprocket change might be an argument FOR...because that information would have been covered in another factory document...you have to understand BMW's way of doing it, but very few factory bulletins stand by themselves...it is assumed that the reader of one bulletin will be familiar with all current/recent bulletins...going back to the assumption of experience and ability.

Now...reasons why I think it's NOT a factory sheet: it has one glaring mistake...if a "3*" 336 camshaft really exists, when installed in the 1978+ bikes which have the 3* sprocket, the displayed timing charts would be wrong (it would HAVE to be 12 degrees difference at the crank positions). If, on the other hand, the exact same camshaft were installed using the two different sprocket configurations, the chart would be correct. So...my GUESS is that the author of the document didn't really have a firm grip on what was and was not going on. My GUESS is that there never were two versions...BUT...a guess is a guess...assumptions can be expensive.

Matt, you made an assumption, but you also did the critical step of checking it along the way...you took the long way, but fortunately, you ended up where you needed to be. Some of your data doesn't quite add up in my mind...using a slotted camshaft with a 1970-77 style sprocket to get the asymmetrical valve timing. That doesn't fit with any of the above information...but that's fine. It just proves the point that there are too many questions...in my mind, a degree wheel and dial indicator are the only path to answering the questions.

the quinner wrote: Now...reasons why I think it's NOT a factory sheet: it has one glaring mistake...if a "3*" 336 camshaft really exists, when installed in the 1978+ bikes which have the 3* sprocket, the displayed timing charts would be wrong (it would HAVE to be 12 degrees difference at the crank positions). If, on the other hand, the exact same camshaft were installed using the two different sprocket configurations, the chart would be correct. So...my GUESS is that the author of the document didn't really have a firm grip on what was and was not going on. My GUESS is that there never were two versions...BUT...a guess is a guess...assumptions can be expensive.

Matt, you made an assumption, but you also did the critical step of checking it along the way...you took the long way, but fortunately, you ended up where you needed to be. Some of your data doesn't quite add up in my mind...using a slotted camshaft with a 1970-77 style sprocket to get the asymmetrical valve timing. That doesn't fit with any of the above information...but that's fine. It just proves the point that there are too many questions...in my mind, a degree wheel and dial indicator are the only path to answering the questions.

I've never thought to question the authentisity of the famous Falconer ducument. It's been refered to by so many over the years that it's authenticity was not in question. I'll try your double row test tonight and see if I come up with other results.
One fact going on my side is that I followed the directions from the sheet to deepen the intake pocket (not exhaust on a "advanced" cam). When I did the clay test I came up with over 2.7mm clearance on both intake and exhaust (infact the clearances were now equal) after the mod. If my cam were at O degrees (because I used an earlier sprocket), my exhaust clearance should have been smaller because I did not alter the pockets. Of course you could argue that Siebenrock's valve pocket depths are unknown, but it seems an odd coincidence that my valve clearance results match the predicted results on the bulletin.
I didn't retain the old sprocket to change timing, I wanted to keep the mechanical tach.
Good to have you back on the phorum, we need more discussion about this stuff.

mattcfish wrote:I've never thought to question the authentisity of the famous Falconer ducument. It's been refered to by so many over the years that it's authenticity was not in question. I'll try your double row test tonight and see if I come up with other results.
One fact going on my side is that I followed the directions from the sheet to deepen the intake pocket (not exhaust on a "advanced" cam). When I did the clay test I came up with over 2.7mm clearance on both intake and exhaust after the mod. If my cam were at O degrees (because I used an earlier sprocket), my exhaust clearance should have been smaller because I did not alter the pockets.

That's exactly what I'm saying...your results jibe with the data when they shouldn't...raising even more questions...making the degree wheel and dial indicator the only thing I can put all of my faith into. That document has GOOD info...but not ACCURATE info.

I really just wanted to contribute some information that I knew to be true. In the process, I got so confused by the data that I began to question that which I had been so certain was true...so, I had to "re-prove" it to myself...which I did (not easy...I'm my own biggest skeptic. AND I even took pictures for all of you folks). I have (re)convinced the person I need to convince (me) and don't really have the energy to take further steps to try to convince anybody else. The world is flat...or it's not...it doesn't really matter.

the quinner wrote:

mattcfish wrote:I've never thought to question the authentisity of the famous Falconer ducument. It's been refered to by so many over the years that it's authenticity was not in question. I'll try your double row test tonight and see if I come up with other results.
One fact going on my side is that I followed the directions from the sheet to deepen the intake pocket (not exhaust on a "advanced" cam). When I did the clay test I came up with over 2.7mm clearance on both intake and exhaust after the mod. If my cam were at O degrees (because I used an earlier sprocket), my exhaust clearance should have been smaller because I did not alter the pockets.

That's exactly what I'm saying...your results jibe with the data when they shouldn't...raising even more questions...making the degree wheel and dial indicator the only thing I can put all of my faith into. That document has GOOD info...but not ACCURATE info.

I really just wanted to contribute some information that I knew to be true. In the process, I got so confused by the data that I began to question that which I had been so certain was true...so, I had to "re-prove" it to myself...which I did (not easy...I'm my own biggest skeptic. AND I even took pictures for all of you folks). I have (re)convinced the person I need to convince (me) and don't really have the energy to take further steps to try to convince anybody else. The world is flat...or it's not...it doesn't really matter.

You're confused....how do think I feel? I'm just glad the bike is runing and meeting my expectation without valve and piston union. . Perhaps one day I will do the degree test, but I think I'd rather ride it for awhile. I