Home Model Engine Machinist Forum

Help Support Home Model Engine Machinist Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

This went well after re-reading very helpful advice from sprocket and others on this forum. The drawings also showed the outer dimensions of the drill rod reduced to allow better silver braze penetration and perhaps offset growth after heating.

Dressed the 7/16" and 3/8" drill rod using emery cloth in the lathe to a good sliding fit in the ball bearings ~0.4370" and ~0.3745" for the rod journals. Made the crank throws out of 2" x 3/4" rectangular hot rolled slices and gang drilled and machined as pairs. I didn't round over the throws yet. The alignment half circle pieces were a really good idea and super easy to make on the lathe and hacksaw in half. The wire is easily cut and spacers removed while the brazing continued. The black areas are the spacers and not the drill rod.
crank fluxed.jpg

The assembly remained flat (in plane) but is very blackened. I used the white flux this time because of the tight fits sliding drill rod inside of holes would be very hard with the black grittier type. I let it cool completely and then placed it in a citric acid bath while I worked on another part.

It didn't really flow well where the white arrows are, but that part is being removed anyway. I will need to be careful removing the excess fillets at the throws
crank brazed.jpg

I think it's a good part, but will measure it after cleaning and removing the excess materials tomorrow.

Made a pair of brass camshaft bearings and pressed them into the brackets instead of soldering. This kept my impatience at bay while the part soaked in the pickle bath.
camshaft bushings.jpg
Congratulations on a great looking crank shaft. I've made a few and like the process and results.. One thing I don't care for is the solder creeping onto the bearing surfaces. Any one know of a way to prevent this ala Whiteout to stop lead solder from flowing where not wanted?

Last crank I made this way I mig spot welded the pieces together to hold them in place while I checked everything was straight and square. Worked well and will repeat. I like the idea of being able to use good steel, drill rod, and the ease of construction.
Thank you Vietti, it turned out okay I guess.

It cleaned up nicely, and I removed most of the excess brazing carefully with swiss files and emery cloth while held in the lathe. I also rounded the ends of the throws. However the heat bowed the rotating assembly. I measured 0.004" total indicated runout, TIR, at one end and 0.005" at the opposite end with 0.0015" in the center. I created a crude sketch to better understand what happened so I wouldn't chase my tail.

checking runout.jpgas left1.jpgrelieving bow.jpg

I attempted to control the straightening by clamping in my mill vice with shims, but it just sprung back into the starting point. Round two was to mark the high spots and use a large adjustable wrench to bend. After this attempt, It was noticeably improved with just 0.0007" at the ends but still 0.0017" in the center. I estimated it might move again after cutting the webs so I did that next at the mill.

cutting webs.jpg

It did not appear to spring after the first side, but did spring 0.002" after the second cut. This time the wrench didn't seem to fit right, so i used a piece of copper pipe over the ends as leverage and a brass hammer to strike where I thought appropriate. I ended up with less than 0.001" at each end again, but still 0.0018" in the center. Not sure how or why. I decided to stop there and make the center bearing and measure after assembly before the next move.
Crankshaft-Center Bearing

Had a 1.75" OD slice of brass in the drawer that was used for the center bearing. I wanted to do like Sprocket did and make a groove so the bearing would be held captive in the center web. Started by cutting it roughly in half, machining the halves flat and soldering together with regular plumbers no lead solder and flux. This will keep it together throughout the machining. I never have had decent results with super glue, and my plan was to machine the OD on an expandable arbor that I had. This stresses the adhesive or solder pretty hard.

The bearing was bored to size and a generous inside chamfer machined in to avoid interference with excess brazing on the crankshaft. Axial thrust is maintained by separate parts on each end of the crankshaft.

soldering center bearing halves.jpgbore and face.jpg

The groove was made slightly oversize or deeper to allow for error in the bore. Planned to wick a small amount of green Loctite to affix the lower half later on. Then a trip to the mill to machine shoulders 0.100" above the split line and drill/tap for 2-56 SHCS.

groove.jpgshoulders N tap.jpg

The fitup was good so I witness marked upper and lower crankcases and bearing covers and tightened all fasteners. The thrust sleeves were 0.196" long at each end for my model. There was a rub at the center bearing right where the TIR was at a peak, so I attempted to analyze how to fix it again. When I chucked the crankshaft in the lathe at the ends, TIR was less than 0.0005" at the center so I decided not to turn it down any. With the crank held by the bearings, I got different results. The bearings are El-cheapos so there is nearly 0.001" TIR there depending on how you load them. The only meaningful flaw I noticed during examination was that when I held a straight edge across the throws there was visible light at one of them.

Remember the large adjustable wrench method I used? I must have induced some twist at the throw. I twisted it straight again and everything was back in tolerance. Gee these brazed crankcases are easy to assemble, but tedious to straighten back again. Also a downside to the brazed fillets at each journal. I'll be fighting that battle next as I make the crank rods.

Anyway its all free spinning now....and it looks more like an engine

adjust thrust clearance.jpgfree spinning.jpg
Nice work and very helpful insights for me that I can as I'm in the process of building my own 2-cylinder engine.

Do you plan to make a chamfer to the side plates or a undercut to the bushings that hold the outer bearings? In the left picture it looks like these bushings are not flush with the side plates as there is some interference in the corner.
Good eye Xander,

I'm still awaiting the flat head screws to secure those bearing holders, so they look worse than I hoped them to be in that picture. I went ahead and undercut the inside corners as you suggested to be sure.

Thank you!
Connecting Rods

The book calls for silver brazed assemblies here instead of a billet. It also takes advantage of dissimilar metal sliding friction and suggests cast iron for the big and little ends. I had a few scrap wafer valve castings that had really seasoned gray cast that machines well for small parts like these.

Started out by squaring up the scraps to dimension. Then the bolt holes were drilled and tapped for each big end. Used the slitting saw to cut the cap off....
Then drilled and reamed the 3/8" bores. Put a generous chamfer using a countersink to avoid interference with crankshaft brazing fillets. Lastly they were rotated 45 degrees and corner chamfers added.

small ends.jpgsmall end spiltting.jpg

The small ends were drilled and reamed 3/16". Then the hole was used to rotate them while clamped over a center transfer punch milling the radius in steps rather than trying to hold in the rotary table. I also scribed the end to visually align in the vice for the taper. Used a radius gauge and hand filing to make them pretty. Somehow I messed up here reading the vernier surface gauge and they are 0.100" longer than they should be.

small end bore.jpgsmall end chamfer.jpg
To compensate the error, I made the drill rod connector a little shorter. Then I worried that they may contact the inside of the piston recess, so I brazed them on just the rod and turned a shoulder in the lathe.

Before the final assembly I fitted the big ends to the crankshaft journals. They interfered with the excess brazing on the sides, so more file work on the crankshaft webs using a Swiss triangle file. It only took a few minutes and they spin nicely with very little side to side end play.

fitting on throws.jpgrod fixture.jpg

Every thing I have brazed has warped so I was a little concerned about the parallelism of the bores on these rods. I also wondered about restraining them too much during the heat as surely the center piece needed to expand as it was heated and might buckle. I had already pre-brazed the small ends and chose aluminum as the jig material because it was such a good heat sink and might grow with the assembly. I undercut the space below the big end 0.030" to compensate for the different thicknesses of the ends. Also undercut 0.120" where the heat needed to go. Perhaps the aluminum wasn't such a great idea, because I needed the largest turbo-tip to get it hot enough. But we prevailed and they both came out with good looking joints, and the cap bolts even came apart! They cleaned up nicely after taking a dunk in citric acid. I never verified the length of the drawing as I figured I could compensate with the pistons. They are up next 🤔
The pistons were made 0.002 under the bore as the plans suggested. The bores ended up a few tenths different as did the pistons, so the sets were punch marked to be a proper fit during reassembly time.

started by making a 1 inch split sleeve to avoid marring the finish as I flipped the pistons end over end in the lathe. 1st operation was cutting ring grooves, and as always found that I had to over compensate the measured axial tool travel to achieve a 0.045" groove as measured with feeler gauges. The pistons were then turned and the recess operation started.
piston ring grooves.jpgpiston recess.jpg

Onto the mill for the slotting operation and here I fumbled twice.

:confused:1) Should have drilled and reamed the wrist pins first, as the indexing for the perpendicular slots would have been easier to measure. I ended up using feeler gauges to accurately measure the horizontal-ness.
wrist pins.jpg
:confused:2) Milled the slot using a 3/16 end mill and removed the part from the setup without verifying that the 0.094 radius in the corners would work. It didn't and had to redo using a smaller 1/8 endmill.

On the bright side I now had wrist pin holes to use as an external indexing reference, and my mill has both X-axis, purple arrow, and Y-axis travel stops, orange arrow, making the journey around the perimeter much easier and safer for such a tiny endmill.
piston slots.jpgpiston assembly.jpg

I don't have any cast iron left in the material bin for the piston rings so I will work on the camshaft while I order up some more materials
Happy Holidays!
Nice work and an interesting build thread.

Thank you Chuck. This is a fun engine to build with new to me work techniques. The cam lobes were a mathematical challenge today.


I used a right angle triangle along with the arc sine function to estimate the rotation of the ramps on the camshaft and incorrectly cut the first one.
After studying the drawing again and making a sketch of the rotation (flipping the paper over while looking at a light helped) I attempted it again and it came out correctly. I needed to add 180 degrees to the calculated angle before traversing the Y-axis. See sketch below.


not sure if this photo proves its correct or not. The caliper is set where the land is supposed to be (0.328") Not too easy to measure it at this point. I guess the proof will be once its mounted on the camshaft and rotated with a dial indicator measuring the valve lift. Any other suggestions...?


I made two cam lobes at a time and sawed them apart and milled to final thickness. The drawing calls out little bitty 2-56 set screws to hold them in place. I may be overtightening these but they seem to strip the hexes out very easily. The shortest set screws also stuck out to far and I made a tapped scrap piece to mill them shorter. The first two worked, but the second pair just backed themselves out when the endmill touched them so I filed the next set instead of milling.

Once I make and mount the gears, I will cross drill and pin these cam lobes to the cam-pair-holder thingies. The cam pair holder thingies have to remain removable the way the design is, but I will be able to file small flats and divots where the screw lands. Or I could drill right through?

The gear blank material arrived today along with the cast iron for the rings 🙂

thank you for the suggestions on the 2-56 set screws. I may just have a poor quality (Amazon) set. I can hold the screw in my fingers and twist the hex key and feel slipping. Have ordered some from McMaster Carr made from black oxide alloy and two new 0.050 hex keys. I need some for the valve spring keepers also.

this is a first time for making the valves from two pieces. Made 6 total so I can BOZO 2 and still have enough. Stems from 1/8 drill rod and valve discs from an offcut of 303SS which machines very nicely unlike all other austenitic stainlessness'. Metallurgy is magical isn't it?

I appreciate builders on this forum very much when they share their experiences in detail. Used a jig idea from Sprocket to hold the valve discs in place while brazing. I embellished the jig one step further by making a small nut to set the valve stem tip at the correct height which left a small divot for the braze to fill while heating. (I parted the discs at 0.015" oversize to allow truing later) White flux didn't work on the first attempt and switched to using black flux and a tiny nip of silver placed on top. Worked the flame on the stem and the disc until it melted. The last one stuck to the jig and was deemed defective

It was a tricky setup in the mini-lathe to cut the valve angle while holding the stem in the collet chuck. I ended up inverting a very small carbide boring bar and running in reverse in order to get the clearance needed. I also set the compound approximately 1 degree over 45 degrees to reduce the valve to seat contact area. They seem to fit very very well by visual inspection. I may not need to lap them at all??

The stem to valve guide sliding friction is also nearly perfect. Overall I like this process versus attempting to make from one piece. Glad that I purchased this wonderful book by Doug Kelley.

valve parts.jpg

adjust valve tip.jpg

braze valve.jpgdefect.jpg
After fabricating the valve spring retainers and push rod adjusters, I assembled the valves into the seats and leak tested using an El-Cheapo brake bleeder. I simply grease the end of the plastic adapter and hold it in the exhaust and intake ports. My goal is to see if I can create a vacuum in a few pumps and how it compares cylinder to cylinder. Only one was decent.

Soooo... break out the 220 grit clover and twist each one back and forth for 2 minutes each. Looked pretty good judging by the dull ring on each valve and seat. The vacuum improved so I did another 2 minutes each using 600 grit after disassembly and cleaning with WD40. I have to set a timer because 2 minutes seems like an eternity when I'm lapping valves or even brushing my teeth LOL.😬

The valve stem twisting worked very nicely on this particular engine by just using a 1/4 open end wrench on the push rod adjusters and letting the valve spring control the seating pressure.

Can pull 25 inHg on each port now and its relatively slow to bleed off.

Thank you Green Twin!

Rocker Arms
These pieces look deceptively easy as drawn, but involve a fair bit of mill work and rotary table foolery to get right. I didn't have the recommended 7075 aluminum which is a little harder as I understand it. I used some past project scrap as they are only 3/8" square by 1-1/2" long rough cut. The roller pivot hole was too close to the edge (0.14") and I thought I might add 50 thousand to this area to keep from worrying too much about error.

started by sawing up rough blanks in bandsaw, squaring off and bringing to dimensions. Then drilled, reamed and cut the slot on the end while I could still clamp the parts effectively on end.

Then we slotted the clearance for the cam rollers and messed one up by flipping it wrong. You can see the result the difference below. I realized it when I removed the part from the vice, but went ahead and did the other operations as a trial before attempting the four good ones. I don't know why it is so annoying to redo a part, so I tried to ignore the frustration and enjoy the fact that I already worked out the steps as I made a replacement. This is only a two cylinder, so part repetition syndrome didn't really set in compared to an 8 or 16 cylinder would have been.


Radiused the edges on the rotary table and reduced thickness at each end to give it that "forged dog-boney" look. Then I experimented with the wrong one using rods to give the profile that looked best. Finally I used the needle files to blend all radius' and debur the surfaces. Upon examination it looked like a trip to the sandblaster would soften them up so I used that.

This sandblaster was a past Christmas gift and is about half scale of the Harbor Freight versions. I really like it and it's made in USA. It's different in that the body is a tough plastic rather than metal so no seams to leak. I provide a negative pressure using an old shop vac and homemade cyclonic separator (bottom right) so the fines don't contaminate the precision equipment inside the garage area. Works pretty good on the small parts I make.

I super glued the roller axles. The glue wicked through and stuck a couple of wheels. Epoxy is suggested, and that's probably why.
As I remember there is very little space between the rocker arms once they are installed, so I had wondered about putting epoxy there.
thanks for that tip Sprocket. I was wondering about the epoxy suggestion also. I think of something thick like JB Weld when that word is used. Maybe just a toothpick dab of it is what is meant?

The brass for the gears arrived so I started them today. The cam gear will have 120 teeth because I am using a 20 pressure angle 48 diametral pitch cutting set based on Mr. Ivan Law's book GEARS AND GEAR CUTTING. I already have a #2 cutter ready to go. I will design the cam gear with a hub that will mount over a smaller 0.750 hub that will be pinned to the 3/16" camshaft. Two #6-32 set screws will be used to index the gear to set the valve timing. This way I can just pin the smaller cam lobes and take apart the engine as much as I want to without relying on those tiny 2-56 set screws.
brass stock.jpg
Started by rough sawing the blank and soldering it to a scrap bronze hub I had in my micro-scrap drawer. I tried using a white paint pen to keep the solder from sticking to the steel centering part. It worked well! Just like some have said typing mistake fluid worked in years gone by.

paint pen.jpg

Reassembled onto the center/mandrel and brought to the calculated gear blank diameter (2.542"). I then indicated it true in my crappy non-adjustable 4 jaw chuck on the rotary table. I adjust it with the 4 bolts holding the chuck plate to the table. Then set the depth of cut to 0.045" started cutting away the parts that didn't look like a gear.

roughing blank.jpgcentering blank.jpgcutting teeth.jpg

While it was still on the mandrel I drilled the web holes and deburred everything. Put a zip tie over the new teeth in a real adjustable 4-jaw chuck in the lathe and bored the center and recessed hub area. The smaller hub is test fitted in the image below. Upon visual inspection I believe this gear is a good one. The crank gear will be much easier as there is no hub and its half the teeth.

drilling web.jpgboring index hub.jpg
Gearmaking is somethink I need to master.

I have the cutters and indexing head to do it, but I would need a good gear chart that shows blank sizes, and would need to get a feel for exactly how to set the cutter height and depth of cut.

Then there is learning exactly how to use the indexing head to get the right number of movements.

It would be best I think to start on some scrap material, or perhaps even some 3D printed blanks.


Latest posts