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F 750 GS Engine nature

S

saladd

New member
Good day,
I just purchased a 2021 F 750 GS low mileage bike from a gentleman in NH. The motor's feel is that of a 1 cylinder (a thumper). I did a lot of research before this purchase and no one mentioned this attribute. Please let me know your impression of this motor.

Thanks, Scott
 
40+ yrs since owning a thumper soo, I just went from a boxer (RT) to a very mildly used '21 750 (age, weight, no longer trips, etc) . A whole different animal, but I'm really getting to like it with a few changes ( windscreen,sengine guards,seat,bar risers, etc) BUT I do find this motor is loud. Hear it over the exhaust. I just turn up the tunes in my helmet lol.
 
check the settings for rain, road or off-road settings on the TFT. I know when my daughter 2019 750 Gs was in the rain setting it felt way under power. Changed the setting to road mode the pep came back.
 
Loncin engines in general are considered to be good value for the money, but even when exact copies of others designs they tend to be a little rougher or noisier than the original they were copied from.
I wouldn’t be too worried about it. Many manufacturers are using Loncin engines these days and they seem to hold up just fine.
 
When BMW switched from a 700/800 to 750/850, they also changed the firing order to give the engine a more "V-Twin" feel. I had a 700 years ago and the 750 I had definitely was not as smooth.
 
F-750 engine mods

Is there any way to get a little more horsepower/torque from the 750? If it is the same engine setup as the 850, can it be re-mapped? A different fuel manager perhaps; different exhaust, etc?
 
rmcfadd2 said:
Is there any way to get a little more horsepower/torque from the 750? If it is the same engine setup as the 850, can it be re-mapped? A different fuel manager perhaps; different exhaust, etc?
Click to expand...

Yes, but you'll need to add a Power Commander. You can't "reflash" the ECU like most sport bikes. I had a tuner put one on mine and got a modest gain. I was looking mainly for smooth throttle control down low because I used it in my motorcycle classes for slow speed maneuvers.
 
OldCamper said:
Loncin engines in general are considered to be good value for the money, but even when exact copies of others designs they tend to be a little rougher or noisier than the original they were copied from.
I wouldn’t be too worried about it. Many manufacturers are using Loncin engines these days and they seem to hold up just fine.
Click to expand...

Except in this case I'd assume that BMW designed the engine/parts and Loncin is just putting it together...
 
followup to re-mapping

to re-mapping
crna59 said:
Yes, but you'll need to add a Power Commander. You can't "reflash" the ECU like most sport bikes. I had a tuner put one on mine and got a modest gain. I was looking mainly for smooth throttle control down low because I used it in my motorcycle classes for slow speed maneuvers.
Click to expand...

Exactly the problem I had during slow speed maneuvering training with "Ride Like A Pro", here in Arizona. Took the mode out of dynamic, and into enduro, and it helped. But more low-end torque would be nice. I wonder if putting a power commander on would void warranty, or cause other issues?

Dealer service manager told me to buy an 850, but 750 fits me better. I do miss my africa twin horsepower/torque, but bike was too tall.
 
drneo66 said:
Except in this case I'd assume that BMW designed the engine/parts and Loncin is just putting it together...
Click to expand...

Which I suppose is exactly what BMW would want buyers to assume.
In fact many BMW motorcycle drivelines have had significant design influence from outside engineering sources over the years. Peugeot, Rotax, Ricardo, Getrag, Bosch and Kymco come to mind. It’s probably not in BMW’s best marketing interest for potential buyers to think their “premium” priced products have significant non-German content. But, it’s a global economy and good designs do come from other parts of the world.
 
OldCamper said:
Which I suppose is exactly what BMW would want buyers to assume.
In fact many BMW motorcycle drivelines have had significant design influence from outside engineering sources over the years. It’s probably not in BMW’s best marketing interest for potential buyers to think their “premium” priced products have significant non-German content. But, it’s a global economy and good designs do come from other parts of the world.
Click to expand...

Don't forget the "G 310" bikes made in India!
 
Re: Loncin

drneo66 said:
Except in this case I'd assume that BMW designed the engine/parts and Loncin is just putting it together...
Click to expand...




Then F bike engines were developed by Rotax with some modifications specified by BMW. The early single 650s had 4 valve heads where same engine used in BRP (parent co. of Rotax) used 3 valve heads in their powersports products. When the twins came out the 650 single was rebadged a "g" model and assembly of the single engine moved to China but apparently with Rotax components. Up through the 700 and 800 twin models it was a Rotax but again when they became 750 and 850 assembly moved to Loncin in China. There were significant changes to the engine (from right side chain drive to left, different crankshaft configuration and others) Not sure if it is still a Rotax design or not. Maybe someone else knows.
 
The original “Rotax 655” 650 single was an Aprilia/Rotax 5 valve design used in the Aprilia Pegaso cube.
The “Rotax 654” design variant built for BMW by Rotax and then later Loncin had a 4 valve head. That engine design lives on in the world market Loncin/VOGE “650DSX” and in an earlier Loncin model that was likely restricted to China sales only to avoid directly competing with BMW.

The “Rotax 804” design was used in BMW 650, 700, and 800 twins. They were all 800’s and varied in tuning and final gearing. I believe they were all built by Rotax.

There is nothing to indicate Rotax assisted in the design of the Loncin twins currently being built for BMW.

I suspect BMW realized significant cost savings by sourcing engines from Loncin rather than Rotax. Some Rotax engines are certified for aircraft, after all. Still, the Loncin twins do seem to be holding up well. The Chinese ARE building some decent motorcycles these days. We will probably see the Loncin VOGE brand here in the US soon and that may be a game changer for certain BMW models.
 
Last edited:
OldCamper said:
The “Rotax 804” design was used in BMW 650, 700, and 800 twins. They were all 800’s and varied in tuning and final gearing. I believe they were all built by Rotax.

There is nothing to indicate Rotax assisted in the design of the Loncin twins currently being built for BMW.
Click to expand...

Correct on both counts. Removing a side cover on the 800s reveals a "Made in Austria" stamp in the casting.
 
It has always been my understanding that the Rotax engines, like the F800 and F800st and GT motors had a 360 crank, where both pistons rose and fell together, like an old Triumph. Lots of potential for vibration with that design. The new China-supplied 750/850 has a 90 degree crank offset, which should make for a smoother engine than the earlier designs.
 
motormike said:
It has always been my understanding that the Rotax engines, like the F800 and F800st and GT motors had a 360 crank, where both pistons rose and fell together, like an old Triumph. Lots of potential for vibration with that design. The new China-supplied 750/850 has a 90 degree crank offset, which should make for a smoother engine than the earlier designs.
Click to expand...

You have overlooked something important. The F800s are in fact smooth running because of a Rotax innovation - an ingenious counterbalancing pivoting connecting rod mounted on the crankshaft between the two piston rod journals. The connecting rod moves in the opposite direction of the two pistons. The first order forces are 100% compensated for and the secondary forces are 70% compensated for. The Rotax motors are in fact smoother that the Loncin engines.

Conterbalance.jpgEngine cross section.jpg
 
The 1993 Ducati Supermono incorporated a similar dummy rod counterbalancer system, which predates the Rotax design. Still pretty clever, though.
 
The principle of counter balancing rod/piston assemblies goes all the way back to steam engines at the turn of the 20th century.
 
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