What is the diff in hexhead and Oilhead?

[johnhunter44]

Can anyone explain the difference between the hexhead and the oil head? Which models are under each and what makes the engines different? Just curious.....

[T__]

John, there are many small differences & a few more major differences..

 

It will probably take a full multi person thread here to come up with ALL the differences..

 

To start the thing rolling here I will state both the hex head & oil head are the same design engine,, that is a boxer engine design,, opposed twin,, internal combustion engine..

 

The oil head basically got it’s name from the oil cooling of the cylinder heads & valve area.. The hex head is still basically an oil cooled design but the cyl heads & valve covers now have a hexagonal shape (that is why they are called a hex head)..

 

Probably the biggest mechanical difference between the hex head & the older oil head is that the hex head has a single balance shaft added where the oil head didn’t..

 

The hex head has slightly larger pistons as the displacement is now 1200cc (actually 1170cc).. The older oil head came in many versions from 850cc to 1150cc & even came in a 1200 version on the 1200C..

 

The 1200 (hex head) has a better electronic fuel control system,, higher compression,, knock sensors,, automatic cold fuel enrichment,, idle control stepper motors,, balance shaft,, 2 spark plugs per cylinder (but so did the late oil heads),, twin 02 sensors,, more..

 

I will let someone else list the models that fall under oil head vs hex head & add more engine differences between the hex head & oil head..

 

If everybody adds a little more you will soon have a good idea of the differences between the hex & oil head..

 

Twisty

 

[motoguy128]

Actually, on the Hexhead, they increased the stroke only to increase the displaceemnt by 40cc's (1130-1170). The stroke went frmo (70.5 to 73mm). But the compression was increased from 10.3:1 to 12:1 and the valve convers made a little thinner using stronger magnesium alloy so the overall engine width wasn't increased significantly. The cylinder bore was not changed... still 101mm.

 

As mentioned, the balanceshaft is the most significant mechanical change.

 

Few other changes just comparing spec sheets:

 

1) Valve size increased from 34mm/29mm to 36mm/31mm intake/exhaust respectively.

2) oil capacity increased from 4.0L to 4.2L

3) Alternator output increased 20 Watts.

4) BMW went with a more typical 180mm rear tire

5) Large clutch diameter (165mm to 180mm)

6) 1st gear lowered on most models.

7) 6th gear made same as previous non-overdrive transmissions.

 

The biggest change in performance occurs above about 5000 RPM. Before that, the engines are very similar, with the Oilhead possible having a little more low end grunt from lower compression and smaller valves, but again, since 6th gear is shorter and the motor runs smooter, it seems much more responsive.

 

Also note that the GS models, have slightly lower compression and revised cam profiles for better low RPM performance. The S model is the opposite and has increase compression and revised profiles for better high RPM performance.

[swilson]

In case you were looking for a less technical answer. In 2005 they started using the new hexhead motor, so the models prior to that were oilheads. Most oilheads are 1150cc, all hexheads are 1200cc. (by name, not by actual displacement)

 

So for an R1150RT... the R tells us its an opposed twin motor, 1150 is the displacment, RT is the model.

 

A R1200GS.. R (opposed twin), 1200 (displacment), GS (model)

 

Bikes that start with 'K' have the 4cyl inline motor. K1200GT, K1300GT, etc.

 

 

[Penforhire]

The balance shaft makes my hexhead FAR smoother than my old oilhead. I never had the common surging complaint in my single-plug oilhead.

[dduelin]

Bikes that start with 'K' have the 4cyl inline motor. K1200GT, K1300GT, etc.

 

Unless they are a K75 variant with 3 cylinders.

[AviP]

A hexhead is a hexagonal oilhead.

[keithb]

"Bikes that start with 'K' have the 4cyl inline motor. K1200GT, K1300GT, etc."

 

2004 and earlier K bikes is an inline 4 cylinder engine with the engine laid on its side. The new generation K engine (2005 and later ie. K1200S, K1200GT, K1300GT) is an upright inline 4 cylinder engine.

[James Clark]

... the R tells us its an opposed twin motor, . . .

 

Not exactly.

 

[cali_beemer]

The biggest change in performance occurs above about 5000 RPM. Before that, the engines are very similar, with the Oilhead possible having a little more low end grunt from lower compression and smaller valves

 

I cant speak about what the engines may doing by themselves on a dyno, but my 1100 and 1150 motors were gutless under 4k rpm. However my 1200 is alot more potent in the lower RPM range. Maybe this has more to do with a weight loss and gearing but I can run lower RPM's better on my 1200. My 1100/1150 bikes I always had to run in the high RPM's for them to have any balls. Granted the 1200 still likes to be revved around 4k and up but it takes off the line way better than any oilhead I have ridden. I cant imagine that this big of a difference is weight and gearing alone. I think a large part is the 20hp increase taking affect. It would be cool to see an 1150 dyno chart with 1200 numbers as well, maybe even throw the 1100 numbers in just for fun. Also, is it just my imagination or does the hexhead rev faster? I may just be smoking the crackpipe again but it seems alot better at fast revving and has more of a formula race car feel to it. Okay, I will go back in the corner now.

 

Staying on track to the differnce in the oilhead and 1200 motors, I thought I read that the 1200 has oil jets for the piston skirts. Is this true? I know someone hasnt mentioned it yet but the hex head weighs alot less. I believe my dealer said it was around 40lbs less in weight. Someone on here may be able to confirm that better than me. The hex head also revs out much higher than the oilhead, and there is no manual fast idel adjuster. The 1200 just starts up and ides perfect from the start even in cold weather. I think the hexhead is bit rougher at idle but once you give it throttle it becomes night and day over the oilhead. I think they also relocated the slave cylinder so it cant piss on the clutch anymore. Is this true or just a myth? I hope some with more techinical knowledge of the hexhead can confirm this so I dont get flamed for starting untrue roomers. My 1200RT is the only bike I have bought with almost no research done beforehand. I just bought it and started riding.

[Ken H.]

[i thought I read that the 1200 has oil jets for the piston skirts. Is this true?

No

 

[i know someone hasnt mentioned it yet but the hex head weighs alot less. I believe my dealer said it was around 40lbs less in weight. Someone on here may be able to confirm that better than me.

The engine itself? No. The bike as a whole? Yes in some versions even more.

 

I think they also relocated the slave cylinder so it cant piss on the clutch anymore. Is this true

Not really. It’s still located at the rear of the transmission and still operates the clutch via a push rod up through the center of the hollow transmission input shaft.

 

[cali_beemer]

 

[i know someone hasnt mentioned it yet but the hex head weighs alot less. I believe my dealer said it was around 40lbs less in weight. Someone on here may be able to confirm that better than me.

The engine itself? No. The bike as a whole? Yes in some versions even more.

 

 

 

Does anyone know the actual weight differences? I looked through searches but I cant find anything. I have only come across articles talking about the 1200 dropping the weight with things like the pistons being lighter from lighter materials. Just curious. It was guy from a dealer that told me the engine alone made up a great amount of the weight reductions on the hexhead bikes.

[T__]

 

[i know someone hasnt mentioned it yet but the hex head weighs alot less. I believe my dealer said it was around 40lbs less in weight. Someone on here may be able to confirm that better than me.

The engine itself? No. The bike as a whole? Yes in some versions even more.

 

 

 

Does anyone know the actual weight differences? I looked through searches but I cant find anything. I have only come across articles talking about the 1200 dropping the weight with things like the pistons being lighter from lighter materials. Just curious. It was guy from a dealer that told me the engine alone made up a great amount of the weight reductions on the hexhead bikes.

 

 

 

cali_beemer, I haven’t ever seen anything posted on the actual engine weight difference between the 1150 oil head & the 1200 hex head but with the hex head having a balance shaft & related weighting & drive gear as well as a bigger clutch I really can’t see how it could weigh less,, even if it did it couldn’t be very much.. The 1200 hex also has two 02 sensors, 2 cam sensors,, 2 knock sensors,, stepper motors on the TBI’s,, etc so that all adds a little weight over the 1150 engine..

 

Part of the bike weight savings is the lack of tool kit (well other than a screwdriver) in the 1200RT so by the time you add a decent tool kit to the 1200RT,, include the electronic suspension ,, cruise control,, add a decent sounding 2nd horn I’ll bet you are pretty close to the what the 1150RT weighed..

 

Might be a little weight savings in the later 1200RT’s due to the brakes not having servo motors..

 

Having owned both an 1150RT & a 1200RT the 1200 sure rides & handles like the weight is lower on the chassis but not sure the total weight is much different with all the extras on the 1200 over the 1150..

 

 

Twisty

 

[cali_beemer]

 

[i know someone hasnt mentioned it yet but the hex head weighs alot less. I believe my dealer said it was around 40lbs less in weight. Someone on here may be able to confirm that better than me.

The engine itself? No. The bike as a whole? Yes in some versions even more.

 

 

 

Does anyone know the actual weight differences? I looked through searches but I cant find anything. I have only come across articles talking about the 1200 dropping the weight with things like the pistons being lighter from lighter materials. Just curious. It was guy from a dealer that told me the engine alone made up a great amount of the weight reductions on the hexhead bikes.

 

 

 

cali_beemer, I haven’t ever seen anything posted on the actual engine weight difference between the 1150 oil head & the 1200 hex head but with the hex head having a balance shaft & related weighting & drive gear as well as a bigger clutch I really can’t see how it could weigh less,, even if it did it couldn’t be very much.. The 1200 hex also has two 02 sensors, 2 cam sensors,, 2 knock sensors,, stepper motors on the TBI’s,, etc so that all adds a little weight over the 1150 engine..

 

Part of the bike weight savings is the lack of tool kit (well other than a screwdriver) in the 1200RT so by the time you add a decent tool kit to the 1200RT,, include the electronic suspension ,, cruise control,, add a decent sounding 2nd horn I’ll bet you are pretty close to the what the 1150RT weighed..

 

Might be a little weight savings in the later 1200RT’s due to the brakes not having servo motors..

 

Having owned both an 1150RT & a 1200RT the 1200 sure rides & handles like the weight is lower on the chassis but not sure the total weight is much different with all the extras on the 1200 over the 1150..

 

 

Twisty

 

The big improvement I find on my 1200 is slow speed manuevers over my 1100RT, even compared to my 1150GS. I agree on weight feeling lower. I dont want to hijack this thread but a dealer I had my bike serviced explained that even the 07 and up have servo brakes, but they were redesigned so they are speed sensitive and dont kick in at a stop. The design was changed to make bleeding easier. I see alot of peopel saying the 07's dont have servos but the mechanic was starting to explain how they really still do but dont have the drawbacks of the previous design. Can anyone elaborate? This was stricty regergitation as I remember hearing it.

[Boffin]

The latest brakes do not have a servo inthe way the older design did - each lever operates its own caliper in the normal way. The front to rear linkage however, is effected with a servo motor to apply the rear brake when the front is applied.

 

Andy