The Homebrew Engine

Part Six

Building the mixer, timer, exhaust, cooling system and other parts.

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


06 July 2008:

Ever onward!  I made the exhaust pipe and got started on the mixer.


            The exhaust pipe and intake match plate.              The Intake plate with the start of the mixer soldered to it.

I cut the match plates from a chunk of 1/8" HRS.  The exhaust pipe is made from a piece of 1/2" galvanized pipe with the zinc turned off the O.D. and bored from the I.D.  I had what I thought was brazing rod that I found somewhere and it took everything my big mapp torch could do to get the pieces hot enough to stick 'em together.

Since the intake doesn't get near as hot, I silver soldered the scrap stuff that's going to be the mixer onto the plate.

Digging around the brass junk box found the pressure regulator from a defunct pressure washer pump.  With the nice threaded parts, I can unscrew the body of the mixer from the head without having to take the whole thing off the engine.

The start of the mixer on the engine.

You can just see the exhaust pipe on the left side of the head.  The throttle shaft for the mixer will be vertical so it can be worked off of the governor bell crank.  Since no one has a better theory, I'm going to make the venturi 1/4" in diameter and the throttle plate about 1/2" in diameter.  I'll use a spring loaded flutter choke on the air inlet a-la Fairbanks Z and a suction fuel system with check valve.

I've got a piece of about 3" diameter thick wall copper pipe I'll make the gas tank out of.


08 July 2008:

More work on the mixer.  I bored out the end of the piece you see above and tapped it to fit another fitting from the junk.

Throttle butterfly, shaft, stop plate, shaft and bellcrank.

It took a bit of whittling to make the throttle butterfly and shaft.  The throttle shaft is a piece of an 8-32 bolt that wasn't threaded for an inch or so.  I made a stop plate (shown below the throttle body) so I could set the idle if necessary and a wide open stop for the throttle.


The venturi piece in place.

The venturi came out at about 0.300" diameter and was an air conditioning fitting of some kind.  This part screws into the female thread in the throttle body.  The plan is to drill the venturi piece horizontally just outside the venturi and put the end of the main jet right in the middle of it.  With a horizontal jet, if I need to, I can drill a small hole just inside the throttle plate in it's closed position an idle jet.  I won't do that little job unless I need to.

The flutter choke assembly will slip over the turned O.D. of the venturi piece.  I've got a couple of candidate scraps for the choke.

The whole works showing throttle linkage and what I think I'll use for a cooling tank.

In the next couple of days, I'll finish the mixer, make a check valve for the fuel line, and make the fuel tank.


12 July 2008:

Finishing the mixer ended up being an exercise in "fiddly bits" as our friends the Brits say.

The rest of the mixer parts.

Delving into the scrap bins produced brass and copper to make the check valve (the fat part of the vertical piece in the photo above),  The jet is a press fit into the venturi body and the flutter valve assembly slips over the O.D. of the venturi body.  The needle valve is made out of a 10-32 steel machine screw.  The flutter choke is held in place by the 2-56 screw shown below.


The mixer on the engine showing the fuel jet.                                                                        The mixer complete with flutter choke. 

The raw materials for making the fuel tank.

I've gathered the metal to make the fuel tank.  The cylindrical thingy is a copper shield for a tuning coil from a long dead homemade radio.  The sheet copper is 1/8" thick.


13 July 2008:

More fiddly bits!  It seems that the closer to making smoke I get, the slower things seem to go.  It took all day to make the fuel tank and get it mounted.


One end cap bent and soldered.                                                        The other end cap bent and being soldered.

After cleaning up the cylindrical piece, I cut out the end pieces.  When I tried to bend them, the copper was too stiff so I had to anneal it.  Once softened, it bent just fine.  The ends were soldered on with plain soft solder.

The hole that shows in the left hand photo (above) was filled, using one of the brass rivets taken from the original mounting ears and soldering it into place.

And, yes Martha, I did melt the nylon thingy on the clamp.  Didn't need it anyway.

The finished tank.

I considered getting out the buffing wheel and polishing the tank but let sloth rule.  All I did was to rub it down with some old 400 emery paper.  The fill neck is on the right side (above), the vent tube is just to the left of it and the line to the mixer is on the left.  

I drilled out the fitting the fuel line comes out of so the 1/8" copper fuel line would go through it to near the bottom of the tank.  A rubber "O" ring is used to seal the line where it goes through the fitting.  I could have used a ferrule but figured I may want to change something later and didn't want to potentially waste the piece of tubing.

On the vent tube, I drilled and partially tapped the tank 6-32 then partially ran a die over the tubing (about two turns).  Doing this simulates a tapered pipe thread.


The tank fits below the cylinder with about a quarter inch to spare.

It'll be a couple of days before I can get back to the project.  If luck holds, I should be making smoke by the end of the week.  (Now that I've said that, Mr. Murphy will rear his ugly head and the schedule will slip!)


16 July 2008:

The cooling tank (made from an empty Mapp gas bottle) is mostly done except for paint.  Ditto for the plumbing.

The cooling tank

The brass cooling piping.

Next time I'm at an auto parts store, I'll get some 1/2" heater hose so I can connect the tank to the engine.  The tank is going to be painted aluminum to simulate galvanized steel.


17 July 2008:

I got the cooling tank painted and will be going out tomorrow so I'll get some hose.  I'm also hoping I remember to get some rust inhibitor.  That tank is pretty thin and it wouldn't take much rust to destroy it.

I also started on the ignition.

The cam with the magnet glued in and the Hall-Effect transistor that will sense the passing of the magnet.

The ignition timer will be mounted on the housing for the sideshaft bushing at the cam end.  I will use a magnetic pickup.

I had a bunch of small rare earth magnets so I spot drilled a hole 0.120" in diameter in the cam shank and set it in place with some Gorilla Glue.  The sensor will be mounted on a brass bushing that rides on the sideshaft bearing housing and I will build it so it can be rotated to change the timing.

The dead pressure washer pump gave up another piece for the cause.

I cut off another piece of the pressure washer pump and turned it so the I.D. is a slip fit on the sideshaft bearing housing.  I'm planning to use a setscrew with a nylon tip to give the sensor bushing some drag and will use a bolt (or something) as a handle to move the timing sensor.

The cam with magnet in place along with the sensor bushing.  Note the little screw to the right of the swivel screw on the cam follower roller bracket.  This is to limit the movement of the follower roller bracket so it won't flip off of the cam.

I'm not sure about my time for the next couple of days so it may be a little while before I'm back to it.


18 July 2008:

I got a short reprieve from the Honeydew projects so I spent a little time with the engine.  Today was one of those days when I figured I wouldn't get much done but, after getting the cooling tank hooked up and starting on the ignition, before I noticed it, I was finished!  I got going so well that I didn't take a picture of the completed timer.

The timer bushing marked and the PC board that the transistor is going to be mounted on is laid up for marking.

I used a small piece of 1/16" printed circuit board material to mount the Hall-Effect transistor to the timer bushing.  It is attached by a couple of 2-56 screws.  I engraved the copper (big deal, I sliced off the copper where I wanted to seperate the conductors) and soldered the transistor in place then soldered the cable to one of my Solid-State ignition modules.  Where you see the cross point is the place where I drilled and tapped it for an 8-32 binding post thumb screw.  With this, I can loosen the screw and turn the timer back and forth to set the timing.  After setting the timing, I tighten the thumb screw to lock it in place.

After making a spark plug connector, I put-in the plug.  Just for the heck of it, I decided to put a little gas in the tank and motor it some to see if it would fire at all.


First, with the ignition turned off and the timing set a little after TDC, I motored it and used a rag to choke it to get fuel up to the mixer.  When I could smell the naphtha in the exhaust, I turned on the ignition and lo and behold, it started firing.  A slight tweak of the fuel mixture and a slight advance of the ignition timing, and it ran steadily.  I turned off the motor and it sat there and chugged merrily for about a minute before I turned it off.

The photo is a little grainy because I turned off the flash on the camera to show the motion of the flywheels, governor, etc.  Also, I didn't run it any longer because I hadn't put any water in the tank.

Maybe tomorrow, I can take it outside and add water and run it for a while to break in the bearings and rings.  


20 July 2008:

I ran the Homebrew Engine in the driveway for about an hour and a half today.  I quit when the heat of the day started getting to me.  It's HOT here in Florida, honeychild!

The timer setup.

Here's the promised photo of the timer setup.  You can just see the little magnet in the lower part of the cam shank.  The Dykem on the cam itself is so I can find the high spots on the clearance portion to file them off so the valve doesn't lift during the power stroke.  I noticed that the other day when it first ran.  I ended up having to take off about 0.005" so I can run about 0.010" clearance when it's warm.

Mr. Homebrew happily putt-putting along in the driveway.

I moved it out to the driveway and filled the cooling system and, once I'd checked to see that there were no leaks, I added a dollop of rust inhibitor.  Filled the oiler and grease cups and gave the gears a dab of grease and cranked it up.  Today, I left the motor belt off and actually managed to get it started by pulling over the flywheels.

I did learn something and I've got a couple of scraped knuckles and some road rash on my right wrist to prove it.  What I learned is how to crank the little engine without injuring myself..........I learned the hard way by injuring myself!  In all the fiddling I did with it, I guess I started it about a dozen times.

Here are some things I noted:

- GOVERNOR....The governor is not as responsive as I'd like although it does work.  When a load is applied, there is a lag before the governor opens the throttle.  This is not a critical issue and may resolve itself as the governor linkage loosens up.

- CRANKSHAFT SPEED....With the timing retarded and running slow enough to almost stop on the compression stroke, I recorded about 375 RPM.  Not too shabby for such a small engine.  With some tweaking and after it breaks in, it may run at around 300 RPM.  

- BALANCE....It seems happiest at about 500-600 RPM.  Above that speed, imbalance causes it to shake a lot.  I may do some rough calculations and make a set of counterweights for the crankshaft to alleviate some of the shaking.

- TEMPERATURE....After running for several minutes at various speeds and ignition timing settings, the water temperature stabilized at what I'd figure to be about 160 degrees.  In the future, I may plop a thermocouple into the tank to see exactly how hot it gets.  When I run the motor/generator, it will undoubtedly run hotter.

- NOISE....About halfway through the run, I started hearing a faint connecting rod big-end knock. By the end of the run it had gotten slightly louder so I'll adjust it before the next run.  I sort of expected this to happen because of having scraped the bushing to relieve a slight alignment problem.  In retrospect, I should have left the rod bushing unfinished until I had the cylinder and piston done then assembled it without rings and lapped the rod bearing with piston in place.

The exhaust side.


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

Questions or comments?  Email me at:

[email protected]