Benson engine

[crueby]

That looks great! A little bit of time with the needle files and ghe slots will be done. Excellent!


 

[Don1966]

Been with you Kurt just been quiet but enjoying your build. Getting close are you making the flywheel or purchasing one?


Don

[kvom]

Don, I bought a pair of finished flywheels of the correct size off the consignment table at Cabin Fever.  There's a pic on replay #77 from March 19.

I started to do some filing on the various cotter/wedge/holes for the conrod, but it was slow going.  The cotters and wedges are very hard to hold onto.  I also managed to knock one of the strap-bearing combos off the bench and onto the floor, where the shop elves confiscated it.  They're not too hard to remake, but I decided to give the filing a rest in hopes that they show up.  For the remaining two straps, i redid the holes by making an additional pass around the edge and employing corner relief with a 3/64" endmill.  Here's one of the results:



So I won't need to file these anyway. 

Couple of smaller tasks got done.  I drilled and reamed the hole in the bracket through which the piston rod passes,    I could have done so when the rest of the part was made originally.  Here's the setup I came up with:



And the trial fit:



I can move the piston rod, but the tightness of the bracket's mounting screws can cause binding.  The hole is .126", but I may use a #30 reamer to give it more space.

Last job of the afternoon was turning the "big end bolt" that connects the conrod to the crank.  Turned from 1/4" drill rod and threaded 3-48 on the end.



Still waiting for my buddy to powder coat the entablature.

[kvom]

Finally got the entablature powder coated.  I don't think it looks too bad.  Test fit on the column:



With the crank at its bottommost position I can tell how much to take off the piston rod next time in the shop.



Rest of today's shop time was filing and fitting the cotters and wedges to the conrod.






 

[crueby]

Looks great with the wedges in place!

 

[kvom]

Did a bit of adjustment to be able to mount the conrod to the piston rod and free up the motion, including reaming the bracket hole with a #30 reamer.  Also made the 2 crosshead pivots (part 24).  Then with the conrod and flywheel connected to the crankshaft, I found that the rotary motion is quite smooth.  Of course this flywheel is oversize (7") and quite heavy, so the rotational mass overcomes any sticky spots.



The next steps will be to mount the eccentrics on the crankshaft and to then figure the lengths of the two eccentric rods.

[Art K]

Kurt,
Good to see the progress. I must admit the flywheel looks oversized and undoubtedly will overtake any rough spots.
Art

[kvom]

Today's goal was to assemble the crankshaft with the eccentrics and skew gear, then fit the eccentric rods.  This was fairly straightforward as pertains to the eccentric rod for the pump, and the length is not super critical as long as the dummy ram stays inside the pump body.

Ran into a glitch on the valve eccentric when I discovered that I had neglected to through drill the head of the valve rod.  So I had to unscrew the valve rod in order to do so.  Then I had a problem re-installing it since apparently the valve nut must have moved.  I removed the column and everything on it in order to get access to the steam chest, but was able to nudge the nut back into place and screw in the rod without removing the steam check cover.

Reassembly and finishing the valve eccentric rod will wait for another day.  I want to do a little better fitting on some pieces first.  Also, the length of the eccentric rod needs to be more precise in order that the valve travel is centered.  There's about .2" of adjustment possible from the fork end.

[kvom]

I attempted to attach the governor pivot to the entablature today and discovered that it interfered with the crankshaft.  Turns out I had made it from 3/16 stock instead of 1/8.  I'd also modeled it incorrectly in SW (as 1/8 round instead of 1/8 square).  When I modeled the assembly in SW I see that the clearance is still very small.  We'll see how close it is once I machine off the extra material and reassemble.  Looking at JLs engine photos, I can't tell what the clearance is but it's not large.

[Jasonb]

You will probably only have 1/32" between shaft & pivot, my larger one looks about 3/64"

[kvom]

I've decided to remake the bracket so that there's a bit more more space.  Even after reducing the diameter of the pivot it's too close for comfort.

[kvom]

Finished remaking the valve eccentric rod.  This time I just turned the tip of the eccentric end down to 1/16 from 3/32 rather than drilling and gluing in some 1/16 in the end.  For some reason I had originally thought that op would be difficult.   

I was able to do an initial assembly of the the eccentrics and adjust the position of the fork on the valve eccentric so that the valve does move through a 360 turn of the crankshaft.  Any further need to center the valve in its travels will be done by turning the valve rod itself.

I did find a problem brought on by not following Mount's dimensions exactly.  I made the entablature cross piece wider than the bearing carriers, and as a result they interfere with the jam nuts on the eccentrics.  With the eccentrics moved inboard to clear, the eccentric rods aren't vertical as can be seen here:



So next time in the shop I need to disassemble to remove the entablature and machine vertical grooves in the ends to clear the nuts and rods.

I ordered a dental mirror on eBay to be able to look at the valve position through the acrylic steam chest cover.  Once I have that and the above fix I should be ready to attempt a run on air.

[crueby]

Looking great! I'll go make some more popcorn for the first run video....   

[kvom]

I had an interesting thought last night.  Normally to time a slide valve engine you adjust the eccentric and fix it with a grub screw.  On this engine the tapped hole for the screw is only .045" long meaning a 2-56 screw has only 2.5 threads engaged.  OTOH, the grub screw holding the crank has 8.5 threads of engagement possible.  So would it make sense to secure the eccentric to the crankshaft with loctite. and then set the timing using the crank?

[Jasonb]

Once you have got the timing right, loosen off the grub screw and slide the eccentric to one side, file a flat where the screw bears and then put it back together. That way you don't need to apply any large forces to the grun screw to hold the eccentric in place as it is unlikely to slip against the flat. I have two grub screws at 90deg on my eccentrics

Crank would not likely have had a grub screw originally eiother forged /shrunck onto teh shaft or pressed on with a key. Eccentric would have been adjustable to allow the desired running direction to be set when on site.