Hackworth valve gear - self-build question

M

MickBlow

Registered
Hi
I'm assembling a Roundhouse Hackworth valve gear. Unlike other Roundhouse valve gear I've built, the return crank isn't pinned to the plain crank, only gripped with screws and nuts. Despite by best efforts at ensuring alignment, the vibrating lever shoots out of the slide block because the return and plain cranks don't stay aligned. Any thoughts on how to stop this?

Many thanks
Mick Blowfield
 
Mick, I could have done with seeing some pixxies of the bits in place. Hackworth is the most simple of valve gears, but like any of them, if not assembled correctly will not do it's job. First the crank pin needs to be firmly fixed in the wheel, there is a surprising amount of stain applied from time to time (Locktite 601 if you're desparate). Next, the return crank obviously needs to be secure on the crank pin, this is quite usually just a clamp fit and should be set so the pivot is 180degs from the crankpin position in relation to the axle. This can be a little difficult to viisualise. I'll look for a pic of a bigger scale one and PM. That position should ensure that the die-block does not exit the slideway. Come back with your results whichever way.
 
I just completed a Round House chassis kit and it did include pins to lock in the return crank not sure how old my kit was but if your having trouble they were 1/16 pins and it was easy to drill and pin them.
It was not easy to get the valve gear running correctly in both directions but several attempts and adjustments then it was fine. Several attempts and a cooling off period for the assembler was part of the process.

Steve
 
Bob and Steve
Thanks to you both for getting back. I'll try to post some pics, but the alignment is as you say, and the vibrating lever is at 90degs as per your picture. But after a couple of rotations, the crank slips. The nut and bolt fixing don't move without force when stationary and any tighter I think I'd shear the thread. On the Walschaerts, the fixing pins seem to stop that, but that doesn't seem an option here.

Thanks
 
You must log in or register to reply here.
Back
Top