HP-18 Push Rod Attachments
I would like to point out something that I have noted on a number of HP18ís( three that I have seen) regarding the attachments of the flat alu push rods as well as aileron attachment. The ones that I observed had just a bolt through the hole of the cranks and the flat push rod with a castel-nut secured. The steel bushing in some cases were pressed into the alu push rods or loose.
The correct way is as follows: The steel bushing is secured to the cranks between two steel washers and a nylon lock nut is used to tighten the assembly. The holes in the push rods are drilled appropriately and reamed. A tight assembly can be archived, with half to one thousands of inch of clearance, without a wiggle, also the flat sides of the push rod have to be milled or filed for sufficient clearance between the washers( just a little smaller then the length of the steel bushing. The rod end for the aileron is secured with a standard washer between the crank and rod end and a slightly larger washer (in case of rod end failure, so it can not fall off) on the out side and tightened with a nylon nut. The nut should be replaced every so often, when nylon starts to wear.
I have gone one little step further on the flat push rod, I used a thin wall brass bushing made from brass tube which is sold in Model air plane shops. I am sure that most long time successful HP18 flyers have been aware of the above.