We are building a B18...I noticed that the OEM lower timing gear has a key built in so to speak, with a taper that fits the end of the keyway on the crank. I was surprised at how short the key is. There is a little play in the key/keyway. The keyway on the crank looks good, no wallowing or anything.

We got a new lower gear for a B18C that has the built in back guide for the belt. This one came with a separate key...(not fused to the pulley and also not tapered at the end) This key is also short. And this new gear also has about the same amount of play in the keyway. Not a lot mind you, but you can rock it back and forth just enough to feel it move if that makes sense. The play is mostly the key in the keyway of the new gear...not the crank keyway.

I am an industrial mechanic by trade...I deal with keyways all the time...why on earth did Honda not use a near full length key for these? If you really want to split hairs, there is a rule for key length where you measure the length of the keyway, double it and use a fractional multiplier...the result is meant to be equivalent to the mass of the material taken out to make the keyway (for balance' sake) and that never comes up to quite a full length key, but if I did that calculation it would result in a much longer key the either of these pulleys have.

So is this key meant to be a weak point? So it would shear in some catastrophic event? When you build one of these for making 300 hp or so do you still use these tiny keys? This B18C lower timing gear--the key will be basically free to move up and down the keyway since there is no set screw and the length of the key is not sufficient for the rest of the assembly (front belt guide and engine pulley) to hold it still. Not that I would expect the key to exactly jump around in there for no reason other than it has the room to do so but still....can't figure out why they would have done it this way.

Also I should mention: The back and forth I can feel with this B18C pulley...its the clearance between the new key that came with it and the keyway in the new pulley. If this was a machine at work I would be shaking my head. Keys, by and large, should fit snugly. Especially in new equipment, it is sometimes necessary to tap them into place with a plastic or brass hammer. I have a Ford 302 on a stand next to the Honda...that lower timing gear was full length and fit tight. What gives here?




This is the B18C gear with its key shown

This the original pulley with it's built in key. It is short as well, and tapered.

 

You are looking for answers as to why "Honda designed this wrong" according to you... and yet, it essentially functions flawlessly. What changes would you institute to make an effective device better ?

 

I don't remember off the top of my head, but I think this is an M12 or M14 bolt that holds the pulley on right? Ballpark numbers: 15,000lb clamp load on that pulley when torqued to spec. If you measure the contact area on both sides you can work out the effective frictional force from that clamp load. How would that work into the results of your key size calculation?

The way I see it the key is there to make sure you can only put it on the right way. I suspect it only carries a small portion of the the power transfer load going up to turn the cams.

 

Agreed, keyway is just for installation alignment. Has nothing to do with transfer of torque. The clamp load does all the heavy lifting.

 

Never heard of anyone doing anything to their crank keys. Just seems like it's for locating to me. Why Honda did what they did? I don't know.