Redo for my horizontal 2 cylinder compressed air engine

[cfellows]

Earlier this year, while setting up my engines for display, I dropped this engine on the concrete floor, rather severely bending the crankshaft. I tried straightening it, without much enthusiasm, but couldn't really get it straight. I've never really cared much for this engine anyway. It seems kind of misshapen and I could never get the air supply balanced properly between the two cylinders.

So, I've decided to make some changes to it and see if I can make it more to my liking.

The first thing I've decided to do is make a new crankshaft. This time, I will have the two pistons in phase instead of 180 degrees apart. Since the engine is 4 stroke in operation, each piston will fire on alternate revolutions. So, here is the pictoral of making the crankshaft.

I started with a piece of 1" x 3/8" cold rolled steel 5" long. After marking it out, I used my bandsaw to cut too axial slits along side the future main journal. This will relieve the stresses before I finish marking and center drilling the ends. I also center drilled the spaces between the webs that will need to be cleaned out.

Next I drilled holes where I had center drilled

Then used my bandsaw to cut out the waste metal from between the webs

With all the stresses relieved, I marked out the centers on the ends

And center drilled them so I could mount the crank between centers in my lathe

After putting a 3/16" screw between the center webs to keep the gap from collapsing, I mounted the crankshaft between centers in my lathe

To turn the connecting rod journals, I use 3 different cut off blades. The first two, a left and a right, are sharpened at a slight angle so I can have clearance when turning the sides of the webs.

Here you can see the right face cutting blade mounted at a slight angle so only the point contacts the side of the web. I've turned both journals down to a little bit over size using the angled cutoff blades.

Here I'm using a squared ended cutoff blade to turn the journals down to finished size.

And here you can see my progress so far, along with the old crankshaft that it will replace.

Next, I'll cut out the other waste and turn the main journals.

Chuck

 

[ttrikalin]

So why didn't you simplify the crankshaft further (asterisks mark the big ends of the connecting rods)

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instead of the design (i think) you use :

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perhaps for balance?
but then the 180 out of phase is better, no?

this is an honest question.

tom in MA

 

[b.lindsey]

Chuck,

The Mis-shapenness doesn't really show in the pic though I am sure it is glaring to you or under operating conditions. Glad you are picking it back up though and trying to fix it, its a fine looking engine. The new crank looks great so far too, but I share tom's question, won't timing both cylinders the same tend to unbalance it more? Again just a question for my own enlightenment. Please keep posting on the progress.

Regards,
BIll

 

[cfellows]

Thanks, guys.

Yes, balance is typically more of a problem when the crank throws are in phase, but it will be a slow running engine and the engine is heavy enough that balance shouldn't be a big issue in this case.

I'm making the crank a little more complicated than it needs to be mostly for strength and aesthetics.

Chuck

 

[b.lindsey]

Well that "splains" it then...looking forward to a video when you have it running again

Bill

 

[ttrikalin]

OK... figurs...

in any case, the trick with the bolt (to avoid collapsing) is very neat...

tom

 

[cfellows]

Finishing up the Crank...

First, I tested the fit of the existing connecting rods to the journals before removing the last bit of waste. This is in case I needed to do some additional turning using the centers on the ends of the waste.

Everything fits nicely, so next I cut off the last bits of waste.

And, a couple of hours later, here is the finished crankshaft. This is probably the best crank I've ever made in terms of fit and finish.

Now I have to make a new cam with the lobes 180 degrees apart instead of the current 90 degrees.

Chuck

 

[kustomkb]

Ouch!

Sorry to hear about the mishap, or should that be mis-shape.

A real beauty of a job on your new crank tho'

 

[winklmj]

Very nice. That's a cool looking engine--reminds me of a double-barrel shotgun.

 

[krv3000]

HI thats a briil way of making a crank

 

[b.lindsey]

Chuck, the crank turned out very nice. A little rework on the eccentrics and you will be back in business. Might even become one of your favorites after the changes, but if not at least the memories of its run in with the concrete floor should be dulled some There will be a video won't there??

Bill

 

[cfellows]

Here's some pictures of the new camshaft being made. I didn't take any pictures of the lathe work since that was pretty straight forward. I started with 1/2" diameter cold rolled steel 2 3/4" long. I center drilled each end since the process of turning included driving the work with a 5c collet and supporting the outboard end in a live center. I then turned down the ends to fit the bearing holes in the engine frame. I then turned down the inside of the cam to 5/16", leaving the cam lobes full diameter of 1/2".

After drilling and tapping the end of the cam, I mounted the timing gear on it. This first picture shows the cam in my milling vise where I'm preparing to form the cam lobes by milling away the unwanted material. I'm actually using the cam gear as an indexing mechanism. You can see I'm using an allen wrench as the detent in the gear.

Here you can see I've finished milling away all the unwanted stuff, leaving small facets all the way around.

And finally, after a little file and emery cloth work, I have a passable camshaft. It actually looks a lot better than the photo portrays it. I'm now ready to reassemble the engine and see how it runs. After that, I'll consider other cosmetic changes to improve its looks.

Chuck

 

[dreeves]

Chuck,
Are the lobes 90 or 180 apart?

 

[cfellows]

Chuck,
Are the lobes 90 or 180 apart?

The lobes are 180 degrees apart.

Chuck

 

[cfellows]

OK, finally got a video made. I was going to wait until I finished any other cosmetic changes, but decided to put those on hold for now. Just can't get excited about this engine for some reason. Back to my hot bulb engine!

[ame=http://www.youtube.com/watch?v=-gyovVhjGRQ]http://www.youtube.com/watch?v=-gyovVhjGRQ[/ame]

Chuck

 

[kustomkb]

Well I got excited. Great runner!

All the best with the hot bulb.

 

[putputman]

I like the strong sound of the engine.
I am surprised that it is that well balance with both pistons & throws on one side of the crank.

 

[cfellows]

I like the strong sound of the engine.
I am surprised that it is that well balance with both pistons & throws on one side of the crank.

It's actually not well balanced at all. Hard to see in the video, but I have it clamped to the workbench. Otherwise, it would be hopping all over the place!

Chuck

 

[lathe nut]

Chuck, Hoop or not it runs great, love the sound and thanks for the play by on how to cut the crank, learned again, thanks, Lathe Nut

 

[blackfoxsteam]

Chuck
I am interested in your comment about difficulties with two cylinders operating out of phase including balancing the air supply. I am attempting a two clyinder beam engine (my second project, my first departure from plans) and I intend to have them 180 deg. out of phase.
Dave