Originally Posted by Chris99
Surely the BMW coupling has some torsional compliance otherwise what's the point of using it?

Also, I may be mistaken, but I understood the KH coupling to be from the current 2019 M4 so heavier duty than would ha e been available before this year


Andy,

I have one of the BMW/Mercedes couplings from one of the original Harley M3W compensators in my shop. It does not have any rotational or torsion flexing. It does allow for a very little bit of flexing angle wise between the two couplings though.

From what I found when researching them, they have like a carbon fiber disc molded inside that is aligned with the six holes, three for shaft and three for flange. And it's probably not as "solid" as a metal to metal, but you're not going to get any wind up accel or decel with engine torque with the KH setup.

Over the years there have been several Harley adapters for VW transaxles and from the pictures I've seen, there's not room for any type of a compensator; so much be direct coupling through the clutch. These were not production, as in M3W production, but have seemed to last.

So just maybe there's enough damping in the BMW coupling to absorb the crank torque spikes.

If I were to start from scratch, I would use the Lovejoy type coupling that would allow for 5 to 14 degrees for rotational wind up and still handle the rated torque of the motors. I would not be worried about the extremely high torque spikes that some here have indicated, upwards to 1500#/ft. I would just go with the dyno torque reading and feel comfortable with that. I'm sure they would be the worst at idle, but no load then anyway. Under power and at rpms, my gut tells me that it would not have time to react to them anyway, but to just smooth them out like an average so to speak.

Rob is going to be putting his KH through very tough testing and time will tell. On the Miata forums, the part that's not a problem ever is the transmission. These Miata 5 speeds are very tough and almost indestructible. So M3W has that going for them.

The KH or any other coupling type connection is greatly simplified over the Centa or earlier Harley compensator setups. Fewer parts is always a good thing!

Dan