"Two trick pony "

[GrinningGSer]

Or "Bimodal power curve"
I highly rate Ryan FortNine and his productions are a graphical excellence
Here he dissects the 1250. Published March 25th 2009
Variable Valves are Bad for the BMW R1250 GS-Review:
<iframe width="560" height="315" src="https://www.youtube.com/embed/cG8Z6RAaHb8" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>
You must admit, he is correct ?

 

[beaver]

Already on... https://www.ukgser.com/forums/showthread.php/528039-This-will-upset-a-few-tossers-on-here

 

[GrinningGSer]

Understood

 

[Delboy777]

So because this guy says it, it must be true

 

[beaver]

So because this guy says it, it must be true

100%... He's on TV so must be right ??

 

[rovert57]

So the variable valve effect only works after 7000 revs don’t know about other people but I don’t ride a bike at those revs very often.

 

[RallyeGS]

So the variable valve effect only works after 7000 revs don’t know about other people but I don’t ride a bike at those revs very often.

I wouldn’t have thought that many riding in ‘real world’ conditions would.

 

[malcopopolo]

I was led to believe shitcam technology was introduced for euro 5 ?

The 1250 was an interim tweak to give the PCP brigade something to upgrade to?

The standard 1200gs lc is fast enough for me so much so I am on my 2nd. At least its potential problems are well known

 

[IrishGaucho]

GS in all it's variants are extremely polarizing bikes, seems like you either love them or hate them.

F9 pulls amazing videos and pretty good Technical information on them, I do get the point presented on the video but I could also see his clear bias towards the GS and his obvious personal choice of the 800 instead.

So yeah, good video, nice info but it must be taken with a grain of salt due to heavy personal opinion.

 

[knutk]

So the variable valve effect only works after 7000 revs don’t know about other people but I don’t ride a bike at those revs very often.

Not quite.
The timing of the shift depends on engine load, and may happen at rpms from 2500 (not 100% sure about lower limit) to 5000. But if not before it will always shift at 5000 rpm.

The challenge for engine designers is to achieve both low end torque and a spirited high rpm characteristic. What it takes to make the low end strong restricts the high rpm part. By introducing two sets of lobes for the intake cams, this range may be broaden.
Using the system BMW uses in their car engines (VVT) would of course be evne better, but it is a rather complex mechanical system, and needs more space in the head. Thus, a wider engine.

The shift cam is a compromise indeed, but it offers a good chunk of improvement and at the same time it does not require much extra space in the head and is technically dead simple.

So, yes, the shift cam also benefits the regular rider.

 

[RallyeGS]

What amazes me is that at say 5000rpm the engine is spinning round circa 83 times a second, the precise timing needed to ensure that lobe slides across at the right point in time is bind blowing!

https://youtu.be/C8IqAjSWGPE

 

[Deleted account 250319001]

So because this guy says it, it must be true

If you've bought one = Not true
If you haven't = True

Probably

 

[knutk]

What amazes me is that at say 5000rpm the engine is spinning round circa 83 times a second, the precise timing needed to ensure that lobe slides across at the right point in time is bind blowing!

https://youtu.be/C8IqAjSWGPE

That is true.
But again. quite simple.
There is machined tracks into the end of the camshaft, so the proper plunger just needs to be in position when ECU wants to change, then the plunger will slide past and be caught by the track when the shaft is at the correct position. So the plunger may pop up at anytime with respect to the faze of rotation. The thing that must not happen is for both plungers to be up at the same time.

 

[RallyeGS]

That is true.
But again. quite simple.
There is machined tracks into the end of the camshaft, so the proper plunger just needs to be in position when ECU wants to change, then the plunger will slide past and be caught by the track when the shaft is at the correct position. So the plunger may pop up at anytime with respect to the faze of rotation. The thing that must not happen is for both plungers to be up at the same time.

A few things need to be working in perfect harmony then!

 

[Micko123]

Does the camshaft not spin at half the speed of the crankshaft ? If so, that would be 41.5 times per second ? . Shirley....
and stop calling me Shirley .


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[RallyeGS]

Does the camshaft not spin at half the speed of the crankshaft ? If so, that would be 41.5 times per second ? . Shirley....
and stop calling me Shirley .


Sent from my SM-G950F using Tapatalk

It would make sense for it to yes, still bloody quick though!

 

[Micko123]

That's faster than I can move my hand

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[GrinningGSer]

&quot;Two trick pony &quot;

So the variable valve effect only works after 7000 revs don’t know about other people but I don’t ride a bike at those revs very often.

I once fancied a Honda S2000 , highly respected by track guys, but it’s vtec also only cuts in at the sort of rpm which normal drivers do not use . Pointless in the real world .

 

[Belco100]

So the variable valve effect only works after 7000 revs don’t know about other people but I don’t ride a bike at those revs very often.

Not really sure what that is supposed to mean? There is no mention of 7,000 rpm anywhere in BMWs literature, only part load and full load?

The motor is pretty damn smooth throughout the range.