Connecting Rod Offset

[Highway41]

What is the amount of offset between the left and right bore centers on R1200RTs? Searched but had no luck. Thanks. Bill

[dirtrider]

 

Morning Highway41

 

I have no idea where you will find that data. I’m sure BMW doesn’t list it anywhere.

 

Here is a picture of a 1200 hexhead crankshaft, you might be able to extrapolate the info you need by blowing the picture up a bit then using the main bearing diameter as a reference than comparing that to the connecting rod center to center offset.

 

Or maybe try calling a bike breaker like Beemer Boneyard and asking them if they have a rouge crankshaft that they can measure the crank pin center to center offset.

 

 

[BerndM]

My eyes must be playing tricks on me but the rod pointing toward us sure looks bent to me.

Probably just an optical illusion (I hope)

I'm thinking the only way that could happen is to rip off a jug.......

 

[Ponch]

Looks like it.

[Don_Eilenberger]

Hydrolock could do this also..

[Troy]

Only time I've seen something time that was when the motor had been submerged in water.

[notacop]

I've thought about this for a couple days now and I'm convinced if you can change the off set by a bit it would be possible to make the exhaust note sound like a Hardley. That would be the desired effect, no?

It may be easier to put a governor on one of the exhausts and have it sound like a stationary engine.

[dirtrider]

I've thought about this for a couple days now and I'm convinced if you can change the off set by a bit it would be possible to make the exhaust note sound like a Hardley. That would be the desired effect, no?

It may be easier to put a governor on one of the exhausts and have it sound like a stationary engine.

 

Afternoon notacop

 

The crankshaft connecting rod offset has no effect on exhaust note. An offset change could effect the rocking couple shake but not the exhaust sound as there would be no change in the crank pin phasing or cylinder angle. (the firing sequence and crank pin/cylinder phasing would remain the same)

 

To change the exhaust note you would either need to change the firing sequence from 360° to180° (this is easily doable on a boxer engine)

Or change the cylinder angle from a pancake opposed boxer to a V or L configuration of some defined degrees then match that with a similar crank pin phasing to match, then configure a camshaft to work and time the ignition to fire correctly.

 

 

 

[Paul Mihalka]

After all this we still don't know why Highway41, the OP, is interested in the offset distance between crank pins. As a side note, if I remember well BMW significantly reduced the crank offset from the airheads to the oilheads, making them run smoother.

[ShovelStrokeEd]

Properly used, the term offset would only apply to two rods sharing a common crank pin. HD's have zero offset with their forked rods. Chevy V8's have about 5/8" or so, depending on the width of the rods. BMW boxer motors have cylinder offset, not crankpin offset.

[dirtrider]

Properly used, the term offset would only apply to two rods sharing a common crank pin. HD's have zero offset with their forked rods. Chevy V8's have about 5/8" or so, depending on the width of the rods. BMW boxer motors have cylinder offset, not crankpin offset.

 

Afternoon Ed

 

Technically you are correct as on a 360° crankshaft it should be called connecting rod journal (or crank-pin) spacing but the term off-set has been used in the BMW world as a catch all phrase for a long time now. (rod journal spacing should match cylinder off-set)

At least BMW doesn’t use splayed crank pins like the old 90° even fire G.M V-6 (common crank-pin off-set rod clocking).

 

[notacop]

I know about that offset stuff now, that's why the carburetor used to hit my boot all the time on the 80/7 and all the other airheads I had.

I suppose the factory makes it just enough to work, eh?

I thought the cylinders were diametrically opposed to attain primary balance. I do know that unless timing and fuel supply, carbs or injection are right it will rock and vibrate.

I couldn't take it anymore and got the vertical twin with the 3rd member as a vibration damper.

[NewBlue]

Just asking, do you think hydrolock would cause that?

I would think the piston would have to of gone off half cocked to cause that. With all things being equal when trying to compress that liquid, not sure it would look like that.

 

dirtrider, your pic, do you know what happened?

[dirtrider]

Nothing bent there (just looks that way), if you look closely the crank also has a slight curve to it. That is just the camera lens distorting the view.

That crank is in a new block and has over 30K on it since that picture was taken.