The Homebrew Engine

Part One

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

In Part One, I will work on the crankshaft, the rod and the main bearing blocks

In Part Two, I will work on the engine frame and mount the mains.

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

In Part Four, I will work on the cylinder head and other parts.

In Part Five, I will work on the sideshaft, governor, valve gear and other parts.

In Part Six, I will work on the mixer, exhaust, timer, cooling system and other parts and get it running.

In Part Seven, I will make revisions, corrections and improvements and make it ready for display.


27 March 2008:

Yesterday, I decided to see if I have the machining skills to make a complete small engine from scratch.  On a whim, I started on the crankshaft.  Looking in the junk pile, I found some 0.75" hot rolled steel plate.  In the same place, I found some old 0.750" shafting. 

Laying 'em on the bench, I took a piece of scratch paper and sketched the crankshaft.  For no reason, I decided that the engine should have a 3" stroke.  I drew the cheeks of the crankshaft, made from the HRS to be 2.975" by 1.450".  Why, you ask?  Because that was the size that one piece of the HRS would clean up to.

Another big decision was to make the rod throw just a smidgeon over 1.00".  Why?  Who knows.

The main shaft is going to be about 3.0", which will make the shaft about 8.5" long overall.

Here are the pieces I cut out.  I laid the cheeks together in the mill chuck and flycut them all over so they'd look nice and be exactly the same size.

After cleaning up one side of each cheek piece, I punch marked them so I could always keep them in the same relationship.  The piece of shafting I used for the rod journal cleaned up in the lathe to 0.742", a nice round number.  The longer piece which is going to be made into the main shaft cleaned up to 0.734".

My first plan was to press fit both both the crankpin and main shaft into the cheeks then cut out the mainshaft between the cheeks.  This didn't work out because after I got the shaft done, I found that my big vise (that I was going to use as a press) couldn't open far enough.  Also, I wanted the press fit to be TIGHT so I wouldn't have to weld on it.  It was so tight, there was no way I was gonna press that mainshaft all the way through both cheeks and keep from galling it even if I did have a hydraulic press.

To make sure the holes in the cheeks were exactly aligned, I stacked them and clamped the stack in the mill vise.  I found the width center and located the rod journal holes.  After getting the rod journal holes to size, I stepped off 1.500" and did the main shaft holes.

I drilled each hole with a #1 bit then redrilled with a 0.5" bit I'd cut the shank on so it was short enough to fit into the mill.  After drilling a hole, I used my boring attachment to open the holes to size.  The size was about 0.0015" smaller than the shaft sizes so the fit would be tight.

Here is the partially assembled crankshaft, ready to have the other end of the crankpin pressed into the cheek.

To make sure the shaft was aligned when the final press fit was done, I laid the pieces on the flat table of my drill press and used a brass hammer to start the pin.  Then I transferred the assembly to my trusty vise and pressed it about 1/8".  I removed it from the vise and laid it on the drill press table again to check for alignment.  It was a little off so I simply held one side down flat against the table and gave the other side a belt with the brass hammer.  I pressed it about halfway and checked it again.  It was still aligned so I finished the job.


Here's the completed crankshaft.

When finished, I chucked one end of the shaft in the lathe and indicated the other end.  It was within 0.002" of perfect - plenty good enough for a toy.

I'm not sure what I'll do next.  Most likely it will be a series of sketches to work out the bore and length of the connecting rod.  Then I'll have to figure out just what materials to make the bearings, cylinder, head, etc. out of.


27 March 2008:

Today, I decided to do the right thing and actually design on it a little.  Using my old version of AutoCad, I did enough drawings to know how long the rod needed to be for a 2" bore.

Since I haven't worked the dimensions into the CAD drawing; if you're interested in being ahead of me, you can scale off of the piston which is 4" long and 2: in diameter with two 1/8"wide rings.  The ring grooves are 0.150" deep.  The rod is 10" center-to-center and the rod bolts are 1/4-28 and 2" long.


Do note that you will have to scale each drawing separately because I plotted them to fill the sheet for best resolution.

With a bore of 2" and a stroke of 3", the displacement will be 9.425 Cu. In.  I figure it ought to run pretty well with a 4:1 compression ratio so the unswept volume (using a flat head surface) should be 9.425 divided by 4 which is 2.356 Cu. In.  Doing the math gives me the unswept length of cylinder which is 0.75".  

Now, with a 4" long piston, a 3" stroke and 0.75" headspace, the cylinder will be 7.750" long end to end.

Later today I may go back and add cylinder detail and critical dimensions to the drawings.


28 March 2008:

Today, I did some more CAD work and modified the little end of the rod for a 1/2"  i.d. bushing.  I'll use a hardened dowel pin for the wrist pin.  It looks like I'll make the piston out of 6061 aluminum.  

The cylinder will be a hunk of 2" sch. 80 black iron pipe that I'll bore to 2" and hone smooth.  I have been advised that if I use cast iron rings, the steel cylinder will be all right.  As of now it looks like It'll be tank cooled.  The water jacket will be a piece of 3" sch. 40 black iron pipe.  The end plates of the cylinder and jacket will be 3/8" plate bored on the head end to just clear the cleaned-up cylinder pipe o.d.  The crank end of the cylinder will fit into a recess in that end plate and I will use a thin gasket to seal it.  I figure that the cylinder should stick out a few thousandths from the head end of the deck so, when the head is bolted on, it will crush the gasket on the crank end.  The water jacket will be welded to the end plates.

The rod will be a piece of 1/4" black iron pipe with a piece of 1/2" black iron pipe welded to it for the little end.  The big end will be a chunk of .750 stock, split for a split bushing and welded to the rod.

I figure that the bearings will be bronze bushings.

I haven't given the head much thought so far.  The main question to answer will be "wet" or "dry".  I tend toward "wet" because I may run a little generator with it and heat may be a problem.

Since I favor throttle governed engines, I may go for that approach.

It would be nice if I could work out a sideshaft arrangement for the governor and exhaust valve.  If I decide to make a hit-n-miss, it would be neat to make it a cam-stopper but that may be a bit too complicated.

I'm going to have to purchase ready made flywheels.  8" diameter seems about right considering that my lathe will only swing 9".  Once I get the drawings a little further along, I'll post 'em. 

Oh, well - off to dinner!


3 April 2008:

I haven't been goofing-off!  I am nearly finished with the drawings and have enough information now to go to the steel supply place to get the materials I don't have.  The jury's still out as to what I'll use for the cylinder.  On the drawing below, I've drawn-in some heavy wall steel tube but that's probably overkill.  If I've got time tomorrow, I may go to a junkyard and see what cast iron shapes are in the pile.  In case I get cast, I'll modify the drawing for a wet sleeve

Here's the plan view of the engine.  Notice that the image below is a camera shot of a printer plot of the file.  Behind it is the revised image of the converted file which has a lot more detail.  I cannot use a smaller version of the converted file because lines disappear.


4 April 2008:

I started on the bearing blocks today.


On the left is the piece of "freebie" 3/4" scrap I'm using for the bearing blocks.  On the right is the piece marked out about 1/8" oversize.


After I sawed out the big piece that is sized to make all three caps, I milled the sides parallel and to dimension (2.000").

Then I sawed the individual bearing blocks out.  They are rough and oversize.  And NO, the vise isn't rusty, it's just a trick of the light.

I milled the cut ends of the individual blocks parallel but they are still about 0.200" oversize.  

I'm drilling the rod block through 0.250 in two places and use 1/4-28 bolts with nuts.  

On the main bearing blocks, I will drill #3 all the way through then follow half way through with the 1/4" bit.  Afterwards, I will tap each block 1/4-28.  

Then I plan to saw witness mark each block then saw it in half (across the bolt holes).  Then I will mill the sawed edges flat.  After that, I will make up about 0.030" in shim packs for each bearing block, clamp the shims into the blocks with the 1/4-28 bolts and bore them to 0.999".  I'm ordering bronze bushing tubing that is 1.00" O.D. and 0.625" I.D.

The bushings will be cut to length then sawed in half.  I will mark them then clamp them in their blocks and mill the edges flush with the bearing block mating surfaces.  When they are finished, I will make six shim packs with one 0.020 shims and five 0.002" shims in each pack.  These shims will extend almost to the journal and will lock the bushings in place in the blocks.

Then, I will put the bearings and shims together and bore the bushings to fit the journals.

I THINK this plan will work.  I should end up with round bearing block bores and bushings.  If anybody's got a better way to do this, email me and let me know.


9 April 2008:

Yesterday, I went to town and visited the steel supply company.  My order from McMaster-Carr also arrived.  I now have enough materials to keep me busy.

The large pipe is the outer water jacket.  The heavy walled steel tube will be the cylinder.  The long bushing will be cut into three pieces and made into the rod and main bearings. The chunk of 2-1/8" aluminum will make the piston (and others).   The small bushing with the dowel pin inside it is the wrist pin and bushing.  I also went to a local scrap yard and found the slightly bent piece of 1.2" bar stock among other stuff..

I've revisited the connecting rod because I can't seem to find 1/4" black iron pipe locally.  I'll use some of the 1/2" bar I found at the scrappers.  Instead of welding on the rod, I will drill and tap the big and little ends to 12-20 and thread the ends of the rod.  I'll jam the threads into the little end and use a lock nut to hang on to the big end.  Note that the image behind this one shows the revised rod.

Here's the revised rod design.

The bearing blocks have been cut in two and milled to size.


In the right-hand photo, the rod bearing block is in the middle, the mains on either side.

Tomorrow, I hope to finish the connecting rod and maybe get started with the cylinder assembly.  As of now, I'm thinking of redrawing the cylinder for the 2" I.D. tube to be a wet sleeve in case I need to tweak with it.  I'll post a drawing of the cylinder assembly tomorrow.


10 April 2008:

Despite a few goofs necessitating rework, I've got the rod mostly done except for boring the big end.


The connecting rod nearly finished

Since I re-designed the connecting rod, I had to make a new cylinder end half of the connecting rod bearing block.  It has to be long enough to be able to screw the rod itself into it and allow for some adjustment.

Now, I can realize why it's good to do the drilling BEFORE splitting the halves.  When I laid out the new piece and drilled and tapped it, the parts missed by a few thousandths of matching up and I had to re-do the cap.  In retrospect, I should have scrapped both pieces and made new, drilling and tapping before cutting them apart.  They would have matched better.

The two bearing blocks were drilled and bored to run a 1/2-20 tap into.  The rod was cleaned up and a 1/2-20 die was chucked in the lathe and the threads chased square with the rod.

The rod is interference screwed into the little end and on the other end, the center-to-center distance is adjusted by unlocking the nut and going a half turn at a time to get the length right.  I knew that, using the threaded connections, I couldn't get it exact but it is now within about 0.010" of being right on 10.00".

The wrist pin rides in a bronze bushing.  The wrist pin is a 0.500" dowel pin.  The O.D. of the bushing was 0.625" and the pin fit was a little loose in the I.D. so I bored the little end to 0.624" and pressed the bushing in.  The pin is now a very snug fit and I will work it with oil for a while to break it in to a running fit.

Next time, I'll probably bore the rod and main bearing blocks, then it's on to fabricating the crankcase.


11 April 2008:

I almost got the connecting rod done today.  Along the way, I learned something and I don't know why I didn't think of it.  I'll 'splain it in a minute.

Since I don't think this engine is going to work real hard or get a whole lot of hours on it, I made up shim packs with one 0.015" shim and two 0.002" shims on each side and bolted the cap to the bearing block with these shims.

Then I located the big end (it's there underneath the pile of cuttings) in the mill and used a 3/4" two-flute end mill to start on the bore.

Mext, with the boring bar (REALLY boring!) I opened the bore to 0.998" to accomodate the1.000" bushing with some squish.

THEN is when I made the revoltin' discovery that there was no way I was going to split that 1.0" O.D. bushing and have it tight in a 1" bore.  Since this bushing material is all I have, I made do.  Not elegant but it should work.

Bearing shells anchored in bore.

What I did was to drill and countersink each bearing half and use a brass screw to anchor them in the bore.  There's a split but, it won't matter.  If it gives a problem, that is a detail I can revisit after the engine's finished and running..


Here is the rod all done except for boring the I.D. of the big end bushing.


13 April 2008:

Yesterday, I bored out the big end bushing.  Before boring it, to keep the bushing shells from trying to move, I placed some lead solder into the gap in the bushing then torqued down the cap, squashing it and holding the bushing firmly.

Today, I finished the rod. 


Here, you see the lead after the boring job is finished.  Also, note the #45 hole I drilled through the cap and into the bushing for greasing.  I redrilled the hole on the outside of the cap about 1/4" deep and partially threaded it with #12-24 thread.

Later, I will make a little brass grease cup and partially thread it 12-24.  The partial threads will be sort of like a small pipe thread and should self-seal.


Here, I apply the lapping compound to the big end journal.

I used a product called "Timesaver Lapping Compound".  It comes in several grades, Green Label is for hard metals like steel (valve seats), etc. and the Yellow Label is for soft metals like babbitt and bronze.  I chose to use the finest grade (#100) of the Yellow Label compound.  

Following the instructions, I mixed some motor oil with a small amount of the #100 to make a thin paste.  I then applied some of it to the journal and mounted the crankshaft in the lathe and assembled the rod to it without shims and just tight enough to make a moderate drag.


The crankshaft and rod assembly in the lathe.  Note #55 oil hole with the 1/4" counterbore for a funnel in the wrist pin end..

While holding the rod, I ran the lathe at low speed for a couple hundred revolutions then disassembled the rod for inspection.

This photo shows the lapping compound loaded with bronze wear material.


After cleaning off the lapping compound.  The shiny streaks are spots that are a few ten thousandths of an inch high.  The steel I made the shaft out of is not what I'd call a premium quality machinable alloy.

I put it back together and ran it in oil this time for a hundred revolutions or so.

Here's what it looked like after running in oil.

After cleaning the blackened oil off the bushing and journal.  There are still a few slight high spots but I can't measure them so I figure they will wear-in when the engine runs.

After final cleaning, oiling and reassembling with "Break-In" shims in place.

When I reassembled the rod to the crankpin, it was locked to the shaft.  I had planned to take just slightly less out of the bushing than needed for a fit but it's difficult to accurately measure a bore so it ended up a little more than 0.002" under the size of the pin.  After lapping, I had to add an extra 0.002" shim to each side.  Now, when the bolts are torqued, the rod barely drags on the shaft with no tight spots. 

I figure I'll remove one or both of the shims after the engine has run for a while.

Next, I'll bore the main bearing blocks and rough fit the bushings.  I may waste some of the bushing material to make the bushings fit flush to the shims.  The only way I can think of to do that is to split two sets of bushings for each main pretty far off center so there is more than enough meat on the ends of one of each of the sets to be able to mill them flush with the cap and base.  I'll have to toss the two short halves into the scrap bin.  If you've got a better way to do this, please let me know.

After assembling the frame and main bearing blocks, I'll lap the main bushings to fit.


21 April 2008:

Just a note to say that the project has been put on hold for a few weeks so I can take care of other projects.  


5 May 2008:

Today, I got back to the project and got the main bearing bases and caps milled and bored.

Main bearing bases and caps finished.


6 May 2008:

I'm about done with this part of the engine.  Today, I finished the mains.


On the left, the unevenly cut bushings. One of each makes a bearing half.   On the right, milling the excess flush with the caps.                

The finished main bearings.

I bored the bearings to about a half thousandth undersize.  Once the bearings are mounted in the frame, I will scrape and lap them to fit the crankshaft.  

Also note the 10-32 screws in the caps.  These are to hold the bearing in place and they are also drilled with a #50 bit so I can make up some little grease cups to screw on them.  Oh, yes - I'll trim the long one.


In Part Two, I will work on the engine frame and mount the mains.


You can always contact me via email at: 

[email protected]

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