Engines > Restoration of Model Engines

Stuart Beam Restoration

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smfr:
Now for some new radius link bearings. The hole was off on the originals. I cut up some bronze bar stock using a slitting saw, and discovered that bronze sure does like to squirm around in the vise when being cut! See the messy cuts on the upper right piece. Some paper between the bronze and the jaws fixed that though.



The originals are the two on the left; my new ones on the right. They started out oddly shaped because I got two out of one slice by placing them diagonally. The lower right one shows another boo-boo; I was a bit eager with the rough milling. Oh well, time to use the extra piece of bronze!

Getting closer now, just need some filing:



I turned some filing buttons, and used them to shape the radius:



My first use of filing buttons!

smfr:
The next adventure was to make a new crankshaft. I had some 7/16 drill rod, reduced one end to fit the crank (actually this took two tries :) ), and then wondered how to fit the pin (which was used on the old crank). I knew there was no way I could drill the pin hold with the crank in place; the drill would just wander toward the crank. So I turned a sacrificial collar, lower left.



With the collar in place, fitting tightly, I started to drill:



Darn, broken bit >:( The collar rotated while being drilled, catching the drill. Let's try again:



Much better! Another option would have been to Loctite the collar on, I guess.

Now with the crank in place, I drilled a slightly larger hole to clean up the mess from the broken drill:



Turned a pin to fit the hole, and knocked it in:



After some cleanup, not too bad!

smfr:
I got the radial link bearings done today (other than the final polishing). Here I'm taking them down to the final 3/8" thickness:



For drilling the attachment holes, I taped them to the arms:



The tape both kept them in the right place, and took up any difference between the bearing and arm thicknesses so that they'd both be secure in the vise.

Some careful hole drilling:



and after a bit of clearance drilling, and tapping the arms, we're done. I did make one minor error, which was to choose too large a drill for the clearance holes in one bearing. I was reading the drill size table upside-down :D



I'm not sure if those are the right screws, but it's what was in place before.

smfr:
Now it's time for the piston rod. I debated whether to make a new one, but the old crosshead had an ugly hole in the top:



and there was no way I was going to be able to unscrew that crosshead from the piston rod without damaging it. The old rod is also slightly undersize, and is not stainless steel. Here's what the whole rod, piston and cylinder cover look like:



So, I started with some 3/16" drill rod, and made a collet out of aluminum so that I could hold it in the chuck without marking the rod.. I turned the piston end, and threaded. Here's my handy home-made tailstock die holder:



The top end gets a 2BA thread, to fit into the crosshead:



I decided to attach the crosshead to the piston rod before drilling the other hole and bringing it to size so that I could ensure that things were square to the piston rod. The chunk of CRS for the crosshead was drilled and tapped, with a bit of messing around with the depths, since it felt loose even when screwed in. However, once I screwed it on tight it was fine, and Loctite helped ;D

I made a little fixture to keep the piston rod horizontal in the vice while I machined the sides of the crosshead:



then drilled and reamed for the linkage hole:



You can see that I'm too lazy to remove the layout dye from my vise clamps :)

Here's my ghetto DRI when I need to move the carriage accurately:



It's a micrometer that I knocked on to the floor, and bent the tips. It's still good for this purpose though 8)

OK, now we're here:



Time to chuck it up again (in the collet, centered in the 4-jaw) to turn the shoulder, and bring to length:



And this is when disaster struck. I had done the shoulder with a nice bevel, and then thought that it would be smart to use the parting tool to cut off the top. Big mistake! As the tool broke through, it bent the top of the piston rod; not a huge amount, but enough to write off the part
 :'(



Oh well, now I have an excuse to re-make it using precision-ground SS rod, which is what I should have used for the piston rod in the first place :)

smfr:
I had a couple of hours this evening, and after yesterday's piston rod disaster, decided to do a dry run fitting the new parts together. Here's the parallel linkage, with newly machined parts:





It's a real jigsaw puzzle to put together. But once assembled, I was very pleased to find very little play in the mechanism: it's a bit stiff, but I think that's good. It should run in nicely. There's a bit of play in the piston rod, but I'm pretty sure that's play from the piston rings moving in their groove (I plan to make a new piston).

There are more serious problems at the crank end. As the crank rotates around it's forcing the crankshaft to wiggle, and I can't insert the spindle through the little end of the connection rod and the beam because of misalignment. I'm guessing that something is out of whack with the crank or the connecting rod. I can make a new conrod, and maybe drill out the crank pin hole in the crank, fit a bushing, and drill it straight.

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