The Homebrew Engine

Part Two

Making The Frame And Assembling The Mains.

You can click on any of the photos to enlarge it.

5 May 2008:

While rooting around in the junk shelves, I found an end piece of 5" shafting.  That ought to do fine for the head.  With a big piece like this, I won't have to fiddle with piecing the head together from a lot of little parts.  The hard part is going to be cutting it to length.


I'll make the head out of this chunk of 5" shafting.


8 May 2008:

I've started on the engine frame, the part that holds the main bearings and the cylinder.  It's kind of tedious because it has to be done right for everything to align correctly.


Main bearing slots hogged out with bandsaw.

fThe side rails were first.  I rough bandsawed the outside dimensions then milled them to final size.  Then, I laid-out the main bearing slots undersized and bandsawed out the rough openings.


Milling main bearing slots to size.

The main bearing slots were milled to exact dimension minus about 0.0005" so the mains have to be driven into place.  I may have to file a little on the slots to make them fit but I will do this after the frame is assembled.  I will only file on the left end (away from the cylinder) of the slots, leaving the right end (toward the cylinder) alone, as that end of the slots is now at the exact dimension it needs to be. 

Note, that in all milling operations on matching parts, I've machined them while sandwiched together.  This will eliminate small tolerance variations in the parts.


Side rails showing main bearings partially driven in place.

Here are the nearly completed side rails.  Attachment holes will be drilled and tapped in these parts.  I've decided not to weld anything because of the warpage and stresses that would be set-up from the heat.

I've drilled and countersunk holes in the bottom halves of the main bearings.  When I drive the main bearing blocks into place in the side rails, I'll drill and tap the rails and screw-in #10-32 flathead screws to make sure they don't get the urge to wander.  Just to add some more solidity, I'll use JB Weld as a seating compound.

Next, I'll probably make the end bridge (at the back end of the side rails) and do some drilling and tapping to tie them together.  This part ought to go fairly fast because there's not much to the part.  Then, I think I'll make-up the bottom plate and tie it to the rails and bridge.


9 May 2008:

I started off the day working on the CAD to get hole locations nailed down.  Then I went out and made the little end plate that ties the back end of the side rails together.


On the left is the end plate and on the right is the end plate holding the side rails together.

I had to make a small change in the detail of the back end of the engine.  Since the end plate is 1/4" and I drilled and tapped it for 10-32 screws, I needed to set the plate toward the cylinder by 0.200" so the heads of the bolts don't hang over the end.


Side plates with base plate mounting holes drilled and tapped for 12-24 bolts.

Drilling and tapping the side plate to base plate holes was tedious.  I drilled the holes and started the tap in the mill because I could accurately step off the dimensions.  I made the hole spacing in multiples of 1/8" because that's how the lead screws in my mill are set up.  I would have preferred to have the leads made for 0.100" per turn but I suppose I can't be too critical.  At least I have a mill that will do accurate work.

I may have overkilled on the number of bolts holding this engine together but I want it to be stiff when it is finished.

I still have the clearance holes for the spreader plates and the tap holes for the main bearing blocks to do then I will be -mostly- finished with these parts.  I will have to re-visit them when I design the sideshaft mountings.


10 May 2008:

Today, I made the base plate and finished drilling the holes in the side plates.


The completed side plate.

As I did with the side plates, I used the mill to lay out and drill the holes.  I laid out the first hole manually then used the leads on the mill to step-off the holes.  I had one problem and that was that I couldn't move the table far enough toward the column to drill the holes in the side closest to me.  What I did was to drill the holes on one side then remove the base and manually lay out the first hole on the other side.  Then I  re-mounted it in the vice and re-indicated the first hole and finished it up.



The assembled engine frame.

The engine frame was assembled assembled with the parts I have made so far.  The main bearing bottoms were a "squeeze-the-heck-outta-it" fit using the the vise.  You can see the "insurance" screws in the bottoms of the journals.  As insurance against insurance, I punched the head of the screw to the countersink so it won't try to work out.  The fit is tight enough that I decided I didn't need the epoxy.


The base with the crankshaft and rod temporarily in place.

The crankshaft and rod were put-in to see how it all fit together.  Now I can see it is actually beginning to actually look like an engine.


Lapping the bearings in the lathe.

Then, I removed the rod from the crankshaft and lapped the bearings. 

First, I used the coarse lapping compound mixed with oil and ran it in the lathe for a couple of minutes, slowly tightening the caps while monitoring the drag.  After disassembling it I cleaned all the lapping compound and wear material out of the bearings and journals.  Then I reassambled it with fine lapping compound and ran it in the lathe for a couple more minutes.  By the time this was done, I could almost tighten the main bearing bolts with the shim packs in place.

Again, I took it apart and washed everything thoroughly then assembled it again with oil only.  Back in the lathe, after about ten minutes at about 200 RPM, I torqued the caps tight and there was only a slight drag.



The crank and bearings after lapping and running in.


Once more, I took it apart and washed everything off.  The bearings have about 90% contact area and are nice and smooth.  I put it back together with 0.004" of shims under both caps and, torqued tight and oiled, the shaft is almost free-running.  With the fit as good as it is, I probably won't have to remove a shim for quite a while.

I'll be finished with the frame once I get the "spreader" pieces made and assembled.  That should be pretty fast.


12 May 2008:

I had to do some parts hunting yesterday and today, first off, I had to fix the oiler on my mill.  After that, I didn't get a whole lot done and even then, I made a boo-boo.


The "spreader" plates are made and in position.

The spreader plates are small but have ten holes each, six of them are tapped.  The plan was to use #12-24 machine bolts to hold the spreaders to the side rails.  Well, I drilled the four cylinder mounting bracket holes in each spreader then carefully laid out the five holes that were to be threaded for the bolts that hold the spreaders to the side rails.  After I'd finished drilling one of the spreaders, I found that I hadn't changed the drill bit and drilled them for clearance.  Kinda hard to tap a clearance hole!

After muttering some unmentionable words, I thunk on it some.   I really didn't want to start over on those parts.  The way it worked is that the clearance holes for #12 bolts still leaves enough meat to tap the holes 1/4-20 so I changed the drill to a 1/4-20 tap drill and finished up the other spreader.  Then the side rail clearance holes were drilled out to 1/4".

The center distances of these bolts is too small to be able to use 7/16 hex bolts so the next challenge was rooting through the big box of 1/4-20 stuff to find ten socket head 1/4-20's.  As you can see, I didn't quite get a matched set but they'll do.  

So far, this is my biggest boo-boo so, since this is my first try at making an engine from scratch, I don't feel too bad.

Tomorrow, the cylinder mounting brackets will be made and added and this part of the project will be finished and on we go to the cylinder.

Oh, yes - I've been thinking about what to do about the flywheels.  I've gotten some really good suggestions from the guys on the Stationary Engine List and Smokstak.  Suggestions include buying some rough model engine flywheel castings, using barbell weights and big pulleys.  I've also thought about hitting a junkyard and finding a cast iron auto or truck flywheel and roughing out a couple of small flywheels from that.  

So far, I've found the castings to be a bit pricey and am now leaning toward making a couple of thick wheels out of the stock I have pictured on the top of the page.  It's about 5" in diameter - a little small - but if they are wide, they will provide enough inertia to carry the engine over.  The only problem with using that stuff is that I will have to machine a LOT of steel off the blanks.

I'm still a-thinkin' on it.


13 May 2008:

I spent some time today working with CAD, refining the cylinder, liner and water jacket.  I added a water inlet at the bottom of the jacket and added an oiler port in the cylinder that runs through the water jacket.

Then, I got to the fun part and finished this stage of the project.  


The cylinder mounting rails are now in place.



Next up is the cylinder assembly.



In Part Three, I will work on the cylinder and liner. 

Comments?  Suggestions?  Email me at: [email protected]