Wrenn Class 20 Bo-Bo coupling screw issue

[97xx]

Just been servicing my one of the above.

 

Looking to convert it to HD couplings - it has the Tri-ang tension lock, held to the bogies with a large-ish self-tapper with a plastic washer and the coupling sits on a plastic plate on the die-cast rectangular protrusion on the bogie.

 

The 'conversion' appears simple - use a cranked H-D coupling and the plastic plate has a 'stop' to control (badly I might add) the movement of the H-D coupling and a very slight shoulder to locate it. It's almost clever in that it will work with tension lock or H-D couplings.

 

What I've noticed is that the self-tapper sits so high that its head rubs on the buffer beam, irrespective of the coupling used.

 

Anyone come across this?

 

A solution would be to use a shouldered screw which would have less height. However, seems odd as this is as it left the factory with the by then standard tension lock couplings.

Edited April 28, 2021 by 97xx
adjusted title to be more specific