1250 Shift Cam

[runnerhiker]

  Shift Cam.pdf (Size: 326.92 KB / Downloads: 9)
I traded my 1200RS for the 1250RS six months ago, from the very beginning I thought the Shift Cam engine was smoother and rev'ed more willingly. I took it as a good thing and didn't think about it more until a few days ago.

While taking some long rides recently I started wondering what criteria the Shift Cam system used to shift from one cam to the other. I thought it shifted at a particular RPM, sot I told myself let me just find at what RPM that happens. That's not what I found.

I went to my Owner's Manual and to videos on the internet. BMW calls them "partial load cam" and "full load cam". My first finding was that it shifts based on engine load, not RPM. The second finding was that the "partial load cam" has a different cam profile for the "left" and "right" intake valve. The two inlet valves in each cylinder do not open and close together nor do they have the same lift. The Owner's Manual claims this makes the engine run smoother. I guess that's the explanation for my seat of the pants feeling that this engine is smoother than the 1200.

I don't know how to embed a YouTube video here, maybe GG can help. The 2.5 minute video of Shift Cam clearly shows that the two intake valves in the one cylinder have very different cam profiles. You can clearly see that in the video, if you know to look for it.



I finally get the ultimate magic of Shift Cam: BMW is doing what no one else has done, at partial load, the two intake valves have different valve cam profiles, and at full load they have the same profile. That's 3 different inlet cam profiles!

Shift Cam - my engine with it feels better than my old engine without it.

[Lee]

Interesting

[Grumpy Goat]

I traded my 1200RS for the 1250RS six months ago, from the very beginning I thought the Shift Cam engine was smoother and rev'ed more willingly. I took it as a good thing and didn't think about it more until a few days ago.
....
Shift Cam - my engine with it feels better than my old engine without it.

Excellent post Ron. Thanks for the explainer! I'll work with you to get the Youtube video in the post.

UPDATE: Link to video included in Ron's post above.

[Lee]

from the very beginning I thought the Shift Cam engine was smoother and rev'ed more willingly.

This and the quieter idle is what has my interest in the shift cam.
Better mid range is always a plus.

[SIOP]

I traded my 2016 R1200RS in on a 2021 R1250RS about a month ago. To me, the engine feels smoother and seems to rev quicker. Also, it feels like it has more grunt in the low end. Besides that, the TFT dash is a vast improvement over the R1200’s dash. It’s everything I hoped my R1200 RS would be, but it’s still no replacement for my K1300S!

[Lee]

I traded my 2016 R1200RS in on a 2021 R1250RS about a month ago. To me, the engine feels smoother and seems to rev quicker. Also, it feels like it has more grunt in the low end. Besides that, the TFT dash is a vast improvement over the R1200’s dash. It’s everything I hoped my R1200 RS would be, but it’s still no replacement for my K1300S!

When it comes to power it's hard to beat the K1300S engine.

[runnerhiker]

I traded my 2016 R1200RS in on a 2021 R1250RS about a month ago. To me, the engine feels smoother and seems to rev quicker. Also, it feels like it has more grunt in the low end. Besides that, the TFT dash is a vast improvement over the R1200’s dash. It’s everything I hoped my R1200 RS would be, but it’s still no replacement for my K1300S!

I am completely pleased with my 1250 shift cam, and I am amazed at what BMW has been able to do with this boxer engine.