Stuart No 4 Steam Engine

[f350ca]

Had just made some bushings for a small backhoe from 660 bronze, seamed like piston ring material. Turned the ID and Od the parted off 1/8th wide by .05 thick rings. When I went to split them didn't they close, don't think I've ever cut a ring where it didn't spring open. Managed to use the vice jaws to gently spring them out.


Need to mount the bearing that holds the valve linkage but a clamp and some playing with the valve timing has it purring away. 




Need lots of scale nuts now and flanges and valves.

[TomG]

Getting close Greg.

The method I use for rings is to make them oversize, split them, and compress them on a two piece stepped mandrel for a final cut on the diameter. That way they are perfectly round when compressed in the bore.

Tom

[f350ca]

(12-22-2018, 10:04 AM)TomG Wrote: Getting close Greg.

The method I use for rings is to make them oversize, split them, and compress them on a two piece stepped mandrel for a final cut on the diameter. That way they are perfectly round when compressed in the bore.

Tom

I was wrong to assume these would spring out, had cut them to size. I ran them dry for a few seconds with a drill, can see the wear pattern isn't perfect.How did you make the stepped mandrel? That sounds like a much beter way to do it.

[TomG]

(12-22-2018, 12:48 PM)f350ca Wrote:

(12-22-2018, 10:04 AM)TomG Wrote: Getting close Greg.

The method I use for rings is to make them oversize, split them, and compress them on a two piece stepped mandrel for a final cut on the diameter. That way they are perfectly round when compressed in the bore.

Tom

I was wrong to assume these would spring out, had cut them to size. I ran them dry for a few seconds with a drill, can see the wear pattern isn't perfect.How did you make the stepped mandrel? That sounds like a much beter way to do it.

Just a piece of stock with a step on one end (longer than the width of the ring) and cap that slips over the step with a center screw for clamping. A hose clamp works well to compress the ring before tightening the screw.

Tom

[Dr Stan]

(12-10-2018, 09:51 AM)f350ca Wrote: The kit came with castings for the valve rods but they look bulky, almost as heavy as the piston rod, so thought I'd try making a lighter looking set.
Still need to fashion the offset clevises for the ends.

Those look great, but what about the balance of the engine?

[f350ca]

Horrible Stan if you let her rip. At normal speeds its really smooth but with no counter weights on the crank it bounces BAD at high speeds. With the bore and stroke this things has it would take more than an average hobby boiler to ever get it that fast though.

[TomG]

(12-22-2018, 02:28 PM)Dr Stan Wrote: Those look great, but what about the balance of the engine?

It looks like they are pretty much 180º opposed on the crank so any inertia they impose on the engine will cancel out.

Tom

[f350ca]

Actually the cams for the valves have 24 deg lead or lag depending on which way I connect them. Expect its supposed to be lag, opening the valves after TDC.
The imbalance is on the crank, no counter weights there, may bolt weights on. If so do you balance just the crank or crank rod and piston assembly.

[Hawkeye]

I was thinking about that last week (for when I design my hit-and-miss engine). I concluded that I should just balance the crank. The rod and piston will be on the opposite side of the crank as much as on the same side.

[f350ca]

That was my thinking too Mike, but recall (memory isn't what it was) something about adding half the weight of the rod piston weight. Could be totally wrong on that one though.