Author Topic: Hick Crank Overhead engine  (Read 8774 times)

Offline ettingtonliam

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Re: Hick Crank Overhead engine
« Reply #60 on: December 23, 2021, 02:22:57 AM »
Yes, split bearings were commonly called 'brasses, and your 'cotter pads' were 'gibs', the whole being known as a gib and cotter joint.

Having gone through the process 16 times for the coupling rods and connecting rods for my 7 1/4" gauge Locomotion model, I wish I'd seen your system first!

Offline AVTUR

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Re: Hick Crank Overhead engine
« Reply #61 on: December 23, 2021, 12:09:42 PM »
The major problem I had with the cotters was collecting them after the final cut with the slitting saw. Sometimes they just sat in the gap or on the cross slide. Other times I had to search the tray under the lathe. It is always wise to clean out the tray before doing such work!

AVTUR
There is no such thing as a stupid question.

Offline AVTUR

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Re: Hick Crank Overhead engine
« Reply #62 on: December 23, 2021, 04:06:02 PM »
I am going to try to get this on to the forum site before Christmas!

The connecting rod bushes, brasses, although very much smaller, were be produced in the same way as I had planned to make the crankshaft bushes two years ago. And I had similar problems. They were made from COLPHOS 90 bar. For the halves that sit against connecting rod the bar was milled to a rectangle twice the height of the half, hole drilled under size and the sides slotted to take the strap and connecting rod. The result was the halved by milling away the surplus on the strap sides. The halves that were held by the strap were just turned, the centre with a parting off tool, drilled with same size drill and halved as above. So far so good.

Fixtures were made to hold the mating bushes so that they could be reamed to size (which would have been a mistake) and faced to length. The thickness of the metal at the end faces is small. On the two smaller bushes it is 1/64” and the fixture did not give adequate support. Another set of bushes were made and this time they would by faced to length and bored to size when assembled on the connecting rod.

Getting the lot to fit took time. A lot of small fine filing work was done on the end of the connecting rod, the straps and to the cotters. I guess it would have been easier to work to looser tolerances but... In the end the pads would fit the straps if the straps were just squeezed slightly by finger pressure. The bushes, assembled, were then filed to length and the bores opened up to suit the trunnions on the crosshead and crank pin using a clockmaker’s broach. This allowed the small end bushes to be line “reamed” (sort of).

Obvious there is no interchangeability of parts so all the bits had to be matched. I generally used small centre punch marks to match parts but this is out of the question with the bushes so each bit of the assembly is painted with different coloured permanent marker (hence the blood on the assembly). Trouble with this is that the dried ink easily rubs off so the marking is repeated after every assembly. All this work was done in a large document box lid since I would never find anything that fell off the bench.

The crank web and pin were made without difficulty. Once again the pin’s bearing surface had to be produced used a parting off tool. The broaching of the web keyway was easy and the web fits snugly on the shaft with its key.

At this point problems return. More should follow before the New Year.

Happy Christmas

AVTUR
There is no such thing as a stupid question.