MLA Diesel - Work in Progress

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Oct 28, 2009
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In 1997, I ordered the plans and kit for the “MLA Diesel” from Andy Lofquist, knowing that it would be some time before I would get around to building it. Well, that time is NOW.

I plan to make three of the diesels. One to fasten to my workbench. The second to give to my brother-in-law. He lives in southern California, and is big into model airplanes - primarily R/C sailplanes and Old-Timer style free flight. It would be cool to see one of my engines take to the air - and he's the man who can make it happen. Perhaps the third one will take to the air here in Salt Lake City.

In this photo, I've just finished turning and grooving the first engine cylinder for the "MLA Diesel".


The cylinder is cast iron, and rather heavy. It alone weighs 4.6 oz. (130 gm). About 10% of the material will be removed in subsequent machining, but it will still be about 4 oz. when completed. I haven't weighed the "Mate" diesel I just recently completed, but the drawings say it weighs 150 gm - in total. I'm guessing now that this engine will weigh about 12 oz - without a propeller. I am starting to make efforts to reduce the weight as much as practical.

The grooves are .063" wide and .445" deep. Since I have a tool block holding 1.25" indexable partoff blades on the back side of the cross-slide, I made a groover by machining a broken Iscar blade. They are made from something like 4140, but it worked great for the aluminum and cast iron fins.

Plunge milling the cylinder bolt holes.


I've made two cast iron cylinders, per the original design. But, in an effort to save reduce weight, I started my own re-design using a cast iron bore with aluminum cooling fins.

Here I've successfully pressed the cast iron sleeves into the aluminum blanks, and then grooved the aluminum cooling fins. Next I made a jig to hold the cylinders in the milling machine to drill the intake, exhaust, and transfer ports, as shown here.


The next step was to mill clearance slots for the connecting rod.


Then back to the lathe to profile the cooling fins to complete the part.


Now I have 4 cylinders - two of solid cast iron and two of cast iron sleeves with aluminum cooling fins. The cast iron ones weigh about 3.8 oz, and the aluminum ones weigh 2.5 oz, so I think it was worth the effort.

The cylinder head is next. Unlike most miniature diesel engines, the contra-piston in this design is entirely in the head, and sealed by a Viton o-ring, which will become obvious later. There is also an o-ring between the cylinder and the cylinder head.


This photo shows the face-grooving operation for the o-ring gland between the cylinder and the cylinder head. The spigot in the center will eventually be shortened, but the stub of it will extend into the cylinder bore. The spigot presents an obstacle to the grooving tool, so in this case I had to mount the tool upside-down and reverse the lathe spindle. I usually use tungsten carbide tooling, but have to use high speed steel for special features like this. Fortunately for me, I have a couple hundred lathe bits that have been sharpened by my dad and my Uncle Frank, but primarily by my dad's father, who was a tool-room machinist. Inevitably I can find a tool bit that will work for special jobs like this, and I suspect that a lot of them date back to WWII. I haven't had to grind a new tool bit for the past 15 years, and have probably forgotten how. I just paw thru those bits, find the right shape, hone it a little, and go to work.

I had already begun making two cast iron cylinders before I made the one with aluminum fins, so although I'm making three engines, I am making 4 cylinders. When milling the connecting rod clearance slots in the first cast iron cylinder, I inadvertently cut slightly into the bypass port. If I'm thinking this thru correctly, it probably wouldn't hurt engine performance at that location. However, the cylinder wall thickness is plenty adequate, and since I happen to have a .532" reamer that was handed down thru the generations, I decided to ream the cylinder to that size. It fixed the problem and I decided to ream one of the aluminum cylinders, too. Reaming any larger would compromise the head gasket o-ring seal. That cylinder was originally 70 grams, and after reaming it weighed 64 grams, for a surprising 8.5% weight reduction . Hopefully, that will come with a little more power, too. Those two cylinders will now have a displacement of .22 cu. in. The original design is .20 cu. In.

The next step was to mount the cylinder heads on the rotary table to drill and counterbore the bolt holes.


The cylinder head in the photo is the one for the .500" bore, so its spigot fit nicely into my existing rotary table center. The larger diameter of the .532" bores required a diversion to make the necessary bushing

The cylinder head will have a hemispherical profile. The building instructions give coordinates for roughing out this hemisphere. I don't have a radius turning attachment for my lathe, and this may be a good reason to make one. I have collected several magazine articles about how to make one, so I took a diversion here to decide whether I want to make one now.

I've counted up 23 articles in my files about how to make radius turning attachments for lathes. But making most of those attachments would entail a project of comparable scale to making this engine. In the 28 years that I've had a lathe, this is the first occasion I've encountered where I need to cut a hemispherical shape, so I wasn't sure how much I would use such a dedicated tool in the future. Fortunately, one of my articles is one that I had photocopied about 30 years ago from "School Shop" magazine titled "Ball and Arc Turning Simplified". It describes how to generate a hemisphere just using the lathe compound tool rest swept by hand. Unfortunately, my lathe's compound doesn't retract from its pivot point as much as the one in the article, so I had to figure out another way to hold my cutting tools. Here's my solution to the problem.


Since I had suitable indexable tool holders with 1" and 3/4" shanks, I just needed to fashion a clamp to hold the toolholders so the inserts were at the centerline of the compound and shimmed up to the lathe centerline. It took a lot more time to figure out WHAT to do than to actually do it. The downside to this approach is that I am limited to a diameter of 2 1/4" because larger diameters will hit the compound. And with the cutting tool retracted from the headstock this way, I couldn't use my regular chuck - the carriage hit its stop and the tool wouldn't reach the left end of the part. Since the stub end of this part had already been made, I was hampered but found that if I used my drill chuck with a precarious grip on the part it would just barely work. And it exceeded my expectations!

Just for giggles, I tried both a full radius insert and a 35 degree diamond, both shown here.



They both worked well. The full radius insert had an easier time in the interrupted cuts but had minor chatter. The 35 degree diamond didn't chatter but took more pounding in the interrupted cuts. Just as a text book might tell you! Since the parts weren't gripped well in the chuck and the drill chuck isn't made for side loads and was held only with the friction of the Morse taper, I kept my depths of cut at .008" or below, but it didn't take long before all three parts were done. Next time, if I make the stub long enough to use the regular chuck, I could get just a little more aggressive, but it would still be hanging out several inches from the chuck.

The original plans for this engine don't call for cutting cooling fins on the cylinder head. However, since the grooving tool that I had made worked pretty well and I saw that by doing so I could see weight savings without losing strength, I went ahead and grooved the cylinder heads. And since the rotary table was still set up, I increased the counterbores around the bolt holes to 3/8". It is a tough call to know when to call it "good" and to "leave good enough alone". There is always the potential for me to make a ham-fisted move and scrap all the work I have invested into a part so far. I've reached the point of diminishing returns, so I'm calling this part "good".


Before this grooving, the cylinder heads weighed 1.8 oz. Afterwards, they weighed 1.4 oz. The stub that fits into the cylinder will be shortened to adjust the piston clearance at final assembly, so I estimate that the final part will weigh about 1.2 oz. Grooving the fins had an additional bonus of providing a better gripping surface than the hemisphere for re-chucking to trim that stub.

Here are the cylinder assemblies to date.


I'm at the stage with machining skills that I wouldn't consider building an IC engine without step-by-step directions, but I'm starting to make more parts the way I want to make them rather than follow the instructions. So it is with the "cylinder jacket" - an aluminum sleeve into which screw the intake and exhaust ports radially, and into which the bypass/transfer port is cut axially. Effectively, one feature had to be cut in each of the three axes - x, y, and z. The written instructions suggest using an alignment gage along with a dial indicator to dial in each operation, which I would have done if I was only making one of these parts, but it sounds rather tedious when cutting three features into 4 parts. Being lazy, I conceived a way which minimized the use of the dial indicator and allowed quick repetition of each operation.

First, I turned the four cylinder jacket blanks - simple aluminum cylinders with a bore to match the cast iron cylinders. Then I made a mandrel that was a tight fit in the bores, and mounted the mandrel vertically on the rotary table, show here.


The bypass port calls for a vertical plunge mill operation that only partly engages the jacket ID, so I set up the spindle to the proper location and then , first, plunged the 5/16" end mill into the mandrel to provide the necessary clearance. Next, one at a time I slipped the four cylinder jackets onto the mandrel and plunge milled again.


This not only cut the necessary bypass port, but provided a way to quickly align the cylinder jackets for their subsequent drilling operations. Next, the rotary table was positioned so it held the parts horizontally, and dialed-in square to the table movements.


In this way, one of the ports was center drilled, counterbored, drilled and tapped on each of the four parts, the rotary table was indexed 90 degrees, and the second set of ports was completed. The black rod with a short thread is the 5/16" pin I used for aligning each part.


Hi Bob,

This is a very good thread, very educational, the pictures with the very good write ups with them, makes this a very interesting thread to follow.

I like the details of your explanations, it really helps in understanding more about the machining processes in this hobby.

Great looking parts, very nice job altogether..

Welcome to the forum Bob.

Thanks for the detailed thread. Your work looks great. I'm sure your brother will be thrilled.

Keep it coming!

Professional quality thread with great photos and explanations.

Hi Bob, wEc1 I really enjoyed reading your thread (I'm an old aeromodeler) and am looking forward to seeing your progress to the end.

Way to go Bob. A nice thread. I'd like to make some R/C engines myself some day.

I like the idea about sweeping the compound to get a radius. I'm gonna have to try that. I've looked at a lot of designs for making radius attachments too but they all look like a lot of work and it's hard to tear myself away from building the engine when I am in the middle of it. I will make one some day but that day is not today.
Sometimes, I'm not sure whether I am machining, or taking a history lesson. Here comes a history lesson.

Making the cylinder jacket required tapping a 5/16"-24 thread. The recommended tap drill is a "Letter I" drill. I seldom need to use lettered drills, and have never bought any. But, in my drill drawer, I have a handful of them that I have inherited. I didn't find any "I" drills, but I did find two "N" drills inscribed with the initials "USAAF" - "United States Army Air Force".


A quick internet search tells me that the USAAF existed from 1941 to 1947. I'll never expect "The History Channel" to run an episode titled "The Twist Drills that Defeated Hitler", but I can't help but wonder what role these drills played. Do I dare use them? I don't dare to even wash the grunge out of their flutes! To the best of my knowledge, none of my relatives were machinists for the USAAF, so I don't know how these came into my dad's possession, but I suspect they had belonged to one of his friends, Joe Gerard, whose initials are inscribed on many of my precision tools, and confusingly, are the same as my dad's, Jerome Grant. I'd have to guess that the average age of the tools I am using is older than I am.

Back to Machining

The next part I made is the compression screw. For a "lathe-only" part, I found this simple part to require quite a few tooling changes, and I was grateful to have a quick-change tool post to help produce a run of three parts. I turned 1/2" diameter steel rod down to .250" for a length of about 1.3", and then cut a 1/16" full radius thread relief groove.

(History lesson) "Thank you, Grandpa." Once again, I found that you had provided me with a "ready-made" tool bit of the right width and radius - and so free cutting that it didn't chatter, despite the fact that my tool block prevented me from using the tailstock center. Could this be due to the positive side rake? (Not evident in photo)


I cut the thread with a die, rather than with the lathe, so a thread relief wasn't strictly needed, but it looked good, to I cut it anyway. On the 2nd and 3rd parts, I cut this groove after threading with the die.


The next step was cutting the o-ring groove.

(History lesson) "Thank you, grandpa." You provided me with a .042" wide grooving tool that was perfect for this. Although it was apparently made for use with an Armstrong holder and had negative rake in my quick change holder, it worked very well. You may notice that I used a transfer punch for a tailstock center since my Morse taper centers were too fat and my PeeWee centers ( my dad's nomenclature) were too short to reach past my tool post. And you can see that I made a practice cut to the right of the groove, in the section that would be removed later.

Now I needed to cut the knurls for the "gription" of the compression screw. All of my knurling tools are ancient, too, and I haven't been happy with my past attempts to use them, so for the first of the three compression screws, I tried something different. By laying my 35 degree VNGG insert holder on the side, I could cut a nice groove by cranking the carriage toward the headstock. In other words, I used my lathe as a shaper.



But without a spindle indexer, how would I space them evenly? Being too lazy to make a dividing head for the lathe spindle, I realized that the lathe itself provided a 40-tooth gear synced to the spindle, and by putting the shank of a small drill into the gear mesh, I could stop the spindle at the appropriate spacing for a 40-groove-per-circumference knurl.


This manual operation allowed me to skip the last tooth and create a visual indicator of the compression screw's position, which is more obvious in person than it is in the following photo, but the shiny spot in the center of the knurl pattern is a "skip-tooth" position indicator.


To avoid chipping the tungsten carbide insert when used as a shaper, I limited the depth of cut to .002" per pass, and relieved tool pressure on the return stroke. But at 10 passes per groove times 40 grooves per screw, this became quite time consuming. I think you might have to understand that I enjoy crossword puzzles - a 2 dimensional puzzle. I have grown to view this hobby as a 3, or actually 4 dimensional, puzzle by asking myself "How do I transform a 2 dimensional drawing into a 3 dimensional part, and in which time dimension (the 4th) do I perform each operation?" I have a fair idea, from selling cutting tools, how a production machine shop would do it, but how can I do it with a strictly limited budget? And I've learned that producing 3 parts for three MLA Diesels makes me think differently than if I was making only 1 part. So I dug out my knurling tools, and once again had to say "Thank you, Grandpa", for leaving them for me. And this lead me away from machining and into another history lesson.

(History lesson) One of my knurling tools has a wooden handle on it, and an inscription that reads "Goodell-Pratt Co." A quick internet search located a site with several pages of historical background on this company from Massachusetts, including an ancient tool catalog from the company. It was only at this time that I realized that the wooden handle of this tool was hollow, and when unscrewed, it contained two more interchangeable knurling dies. The range of tooling in this catalog suggested that Goodell-Pratt was an early competitor of Starrett, and this induced me to search my dad's Gerstner tool chest to see what other Goodell-Pratt tools it might contain. I found an inside caliper and a thread gage made by them. This company collapsed during the Great Depression. Dare I use these tools any more without incurring the wrath of the God of History?


Luckily, I had another knurler, which was probably older, but without pedigree from Google, so I used it to knurl the screw heads without (too much) fear of heavenly wrath.


The knurling wheel is inscribed "8C" and "A.S.F.&T. Co., Eliz. N.J." All I've been able to learn about this tool is that Elizabeth, New Jersey, dates from 1664, so this tool must be newer than that.

I referred to the article "A Mathematical Approach to Knurling" from "Projects in Metal" magazine form August 1997 to determine the proper diameter for knurling with this wheel. The math dictated that I turn the .500" rod down to .497" diameter, and, by golly, it worked better than anything I have ever knurled before!


And, yeah, since the compression screw will be one of the most obvious parts of this engine, I buffed their heads well enough that it really does reflect the dimensional arrow from the print! A new skill for me! (I've come a LONG way in the last 12 months.)

Very nice work, Bob,
I like your attention to detail, excellent ideas on your setups, and the way you trouble shoot a potential problem and your means of working it.

The machining of your parts are very well done..
Nice subject. Andy still sells the engine. I fly R/C planes and have long considered buying his kit or plans.
very instructive thread Bob, thank you
I like (and hate too!) these little diesel engines: I too built a 'Mate' some times ago, but it didn't run really well, only sporadic revs occasionally

I'll follow this thread with interest to learn how to build a better diesel next time :D
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A delightful thread Bob, I do so much enjoy your methods and ways of creative thinking. Also the "thank you Grandpa" part, I most certainly can appreciate. You have to wondwr how they know. Somehow they just do.

Thank you, everyone, for your encouraging comments. It helps make the time consuming effort of posting this worth while. I'm having fun building this engine. Andy's instructions and customer service have been a great help, too.

The engine mounting plate was next. First step was to mill three identical plates from 3/16" thick aluminum. Drilling the holes for the mounting screws and the cylinder bolts for this was the first, and perhaps last, operation where I could stack all three parts in one setup, and took very little more time than if I was making only one engine.


The center drill is shown, which was followed by a thru drill. I drilled the pilot hole for the cylinder first. This provided a 0,0 coordinate, a way to clamp all the plates together, and a way to locate each plate on the lathe's faceplate for the next operation. This setup would have been more rigid if I had aligned the long axis of the part with the vise jaws, but the holes are so close to the edges I would have had to remove the parallels for every thru hole. So I made a compromise. Even at that, I had to remove the parallels for the mounting holes.

Next, each plate was centered individually on the lathe faceplate, using milling clamps. This required a longer than comfortable reach for a small metal boring bar, but with light passes in aluminum, it worked. The hole for the cylinder was bored to size, and then counterbored 1/32" deep and 1" diameter to match the cylinder jacket.


Then back to the milling machine to plunge mill the slots for the connecting rod clearance and the bypass port.


I just made that vise stop about a month ago, when I got the second-hand set of parallels that allowed me to allowed me to space the fixed vise jaw (finally, after 15 years) over a flat surface and allow a lip for the vise stop to grip (THANKS, MIKE) so it felt good to have a legitimate use for it. Since these were clearance slots and the dimensions weren't critical, I located the mill spindle just once and indexed each part twice in the vise. I should have made the vise stop about 1/8" taller, for it just barely caught the 3/16" plates when using my tallest parallels. Duh - learn by doing! Thanks, Andy, for not making the plates 1/8" thick.

Here's a photo of the finished mounting plates, after deburring, chamfering the edges, and hand sanding the surfaces.


The next part is the backplate, which calls for a 1.370"-32 thread to match the crankcase. I probably cut threads less than once a year on the lathe, since I primarily use taps and dies, so my threading skills are a little sketchy for such a fine pitch thread, especially for two matching aluminum parts. I need to review my reference materials and do some trial threads before I take the next step. Suggestions are welcome.

Bob G
For the fine-threaded backplate connection, I'd make a steel male thread first, to use as a plug gauge for the female crankcase thread, perhaps to use as a fixture to hold the crankcases for other operations, and finally to get practice making threads. Make the backplate threads match the plug gauge threads by measuring with thread mics or by using the three-wire method. Then, when cutting the crankcase threads, test with the steel plug gauge. Once that fits nicely, you know the aluminum backplate threads will fit. If you try to use the backplate threads as gauges for the crankcase threads, you risk seizing the connection, because aluminum-on-aluminum threads love to seize.

I love single-point threading, such that I seldom use dies on my models. I also confess to having a CNC that can do helical interpolation, so I can cut threads using it. That is really sweet for making short threads that run as close to a blind shoulder as possible, and to thread multiple parts all almost exactly the same, including with respect to phase angle. Additionally, I can thread anything I can hold on the mill, which is more than I can hold on the lathe without a lot of futzing around, and I can do the thread in one pass (though a second finish cut makes for a nicer thread).
Before beginning the backplate, I re-read several articles about threading and refreshed my memory of some things I had forgotten. Since the backplate is threaded up to a high shoulder, I also decided to switch my lathe’s drive pulleys to the low speed range, apparently something I had never done in the 15 years since I inherited this lathe from my dad, for the v-belt was too short to switch from the high range to the low range. The problem stems back to about 14 years ago, when the original Taiwanese motor burned out, and I replaced it with an American made motor. The two “cans” which hold the starting capacitors on the top of the new motor restrict the amount that the motor can pivot, and it took the greater part of the day to modify the motor mount and get another belt one inch longer.

The plans call for cutting a 1.370”-32 thread on the backplate. However, since the thread depth of a 24 tpi thread is only about .007” deeper than 32 tpi, and there was plenty of material thickness on both the backplate and the crankcase, I elected to go with the coarser thread. This allowed me to cut the backplate’s external thread with the “full-form” threading insert from my Valenite threading kit, shown below.


The three inserts on the left are “partial-profile” and resemble HSS threading tools in that they cut a wide range of thread pitches by cutting just the root and flanks of the thread. The remaining inserts are “full-profile”, meaning that they cut the root, flanks and crest of the thread, but each insert is dedicated to a single thread pitch. These inserts have allowed me to cut the nicest looking threads that I have ever made, and although I don’t have a kit for internal threads, I felt that they offered the best chance for me to make an aluminum-to-aluminum thread interface without seizing. The finest pitch in this kit is 24 tpi, so that influenced my choice of thread pitch!

Following a tip from rklopp (Thanks!), I first made internal and external thread “gages” from steel. This provided a little “refresher” course on threading, a gage to assist in making matching threads in all three backplates and crankcases, and mounting plates for holding the parts in the lathe and mill for subsequent operations.


Cutting male thread gage


Cutting female thread gage with one of my grandfather’s homemade threaders. Thank you, Grampa!


Here I’m parting off the threaded backplate. I usually cut a thread relief groove at a shoulder like this, but my threading lever sometimes resists being dis-engaged, and I couldn’t spare the space for a wide relief groove. So I cheated this time in order to cut as close to the shoulder as possible. With the motor off, I engaged the threading lever, and then pushed the “jog” button until I was in the last thread, and then turned the chuck by hand to a precise stop point. And with such a fine thread pitch, I fed straight in with the cross slide, rather than at 29.5 degrees with the compound.


Next, I made a pin wrench, mounted the steel thread gages on the rotary table to act as fixtures, and spaced the holes to match the wrench.


The cavity in the backplate is flat-bottomed, so I roughed it out by sequential plunge milling with ½’”, ¾”, and 1” end mills.


Then the cavity was finish turned in the lathe.


Finished backplates and wrench.

Now, can I thread the crankcase to match?

Bob G


Somewhere inside this chunk of aluminum was a crankcase. I needed to find exactly where it was.


The first step was to turn the OD to 1.875”, then bore out the ID, which was then threaded the same way as I did with the steel female thread gage. The concept of making thread gages for this non-standard thread really worked well. This is the first time I have ever had to make more than one pair of matching threads, but the gages made it easy to ensure that all three backplates threaded into all three crankcases – and none of them seized up – a new accomplishment for me!


By chucking the male thread gage in the lathe, this made it easy to mount each of the three crankcases in succession for profiling the nose. The prints called for a ¼” radius at the root, but when burrowing thru my Grandpa’s HSS lathe bits, I found a full-radius, high positive tool that was somewhat smaller. Since this wasn’t a critical dimension, I made an ad hoc design change to make use of this tool. Grandpa’s HSS tools have never failed to meet my needs, and never failed to please. I must have dozens of brand new HSS bits, but I’ve never had to grind a tool from scratch. Thank you, Grandpa! You have always helped me tackle any new challenge I encounter.


The next step was back to the mill to make the flat for the mounting plate.


This was followed by drilling and tapping the 6-32 holes for the cylinder hold-down studs. To prevent break-thru into the crankcase, these holes are only 3/16” deep, which allowed only 4 or 5 threads, even when using a tap that has been ground flat. The photo shows a tap held in a drill chuck, but the chuck shank was loose in its collet and turned only by my fingers. The mill was only used as a tapping guide.


(History Lesson) – This is the wooden box in which I keep my #6 taps. The lid says “S. W. CARD MAN.’F’G. CO., MANSFIELD, MASS, U.S.A., MANUFACTURERS OF Taps, Dies, and Screw Plates.” I believe that this box had belonged to my Great-Uncle Frank, from Buffalo, NY.
An internet search tells me; “S. W. Card Mfg. Co., was one of New England's most important late classic period manufacturer's of taps, dies and related cutting tools (and) operating between 1874 - 1908 before being bought out by the Union Twist Drill Co. of Athol, MA.”
Uncle Frank lied about his age in order to join the Army in WWI, which means he couldn’t have been more than 8 years old in 1908, so it is unlikely that he bought his box new. The only thing I know about HIS dad is that he was a saloonkeeper, and that the going rate for a 4 ounce jigger of whisky in 1900 was 5 cents.

BTW – I had never heard of a “screw plate” until just now. It is a steel plate with threaded holes that serve as dies for making small screws. They are apparently still used by jewelers.


The bore for the cylinder was plunge-milled in successive diameters, finishing with an 11/16” milling cutter that gave the appropriate clearance for the cylinder. Then the table was indexed over to plunge with a 5/16” cutter for the conrod clearance/by-pass port holes.


If I had strictly followed the prints, I would have been done with the crankcase at this point, but I saw an opportunity for further weight reduction by reducing the crankcase OD from 1.875” to 1.811”. This reduced the weight from 3.6 ounces to 3.3 ounces without compromising strength. The male threading gage was still mounted in the lathe, which made this operation easy. Additional weight was squeezed out of the nose.


Still lusting for lightness, I decided to remove .100” from the radius of the crankcase, except where that thickness is needed where the cylinder mounts. This required ten .010” passes, using the rotary table. The crankcases now weigh 2.3 ounces, for a total savings of 1.3 ounces. I did this with two of the crankcases, leaving the third one at full diameter.


The full diameter crankcase is flanked here by the two lightened ones. The nose has been left about a quarter of an inch too long, and will be trimmed to size in a later operation.

Bob G
Bearing Sleeve

The bearing sleeve was the most straight-forward engine part so far. I chucked some ¾” bronze rod in the lathe, drilled it undersize, and then reamed it with a 3/8” reamer. The OD was turned to .5005”, except where the flange OD was 5/8”. I chamfered the end, and then parted it off.


The crankcase had already been reamed with a ½” reamer, so the sleeve dimension should have resulted in a slight interference fit – but the first sleeve slipped right in. OOPS. The reamer must have cut the aluminum crankcase a bit too big. The written directions that came with the MLA Diesel suggest that using thread locking compound was a viable alternative to a shrink fit, so that’s what I did. I turned the next two sleeves to .501”, heated the crankcases in a 500F oven, and pushed the sleeves home.


Bob G


I began the crankshaft by turning the front end to .250” and using a die nut to cut the ¼”-28 thread.


The rest of the shaft up to the crank throw is 3/8” diameter, and the transition between the two sections was tapered 10 degrees on a side by setting over the compound slide. The drive washer will seat on this taper. A slight stress relief groove was cut where the taper joins the ¼” diameter.


Parting off the crankshaft. The engine plans call for using “Stressproof” alloy steel for the crankshafts. I had enough Stressproof for only two parts, so I made the third one from 416 Stainless. Stressproof smells distinctly different than 416 while being machined! Who knew? I never learned that from any textbook.


The crankpin is to be pressed into a hole .500” from the centerline of the crankshaft. To facilitate drilling this hole for all three crankshafts, I made a simple jig using a piece of scrap aluminum, drilling a 3/8” hole, and then moving .500” on the Y axis. This C-clamp is the one I made in my Milling class in college. I don’t often find a use for it, but it worked perfectly here.


It later occurred to me that this same jig would work to locate the counterweight cutouts. This operation worked so smoothly that I found myself wondering what I was doing wrong!


The crankpins were cut from 5/32” drillrod. This is the smallest part that I’ve made for this engine, but it has caused the most frustration. I won’t enumerate how many failed parts I made. But my lathe chuck won’t grip small rod properly, or without causing flats on the rod. I don’t have a 5C lathe collet for 5/32”, and couldn’t justify spending $20 to 30 to buy one to make just three parts. My attempts to cut sleeves for larger collets proved to be slightly eccentric (both physically and psychologically!) But it then occurred to me to use a pin vise. This is absolutely the largest diameter rod that my largest pin vise will accept, but it worked. My #28 drill cut a .142” diameter hole in the crankshaft throw (as best I can measure), so I turned the pins down to .143” for a .001” interference fit. To insure that the pins are pressed in straight, I added a .100” long stub of .141” diameter for a slip fit guide into the hole, which will be ground off after installation. In this photo, the tip of the insert is precisely at this size transition.


The crankpins were made of W-1 drillrod. This is the first time that I have made anything from a known alloy which needed to be heat treated. I didn’t want these pins to be too brittle, so I somewhat arbitrarily aimed for a Rc hardness in the mid-50’s. I put the pins in a small stainless steel cup to make them easy to handle, heated them in my electric kiln to 1450F, and then dropped them in water. Using the residual heat of the kiln, I tempered them at 600F. Heat Treating – a new skill for me! I wonder how well it worked!? My garage temperature is now in the mid 40’s (F), so this process at least gave me an excuse to do something productive in the house last night.


I lightly removed the scale from pins, and used the vise to push them home. After grinding off the excess crank pin length, the crankshafts were done.

I considered lightening the crankshafts by drilling the center of 3/8” diameter portion with a ¼” drill. I calculate that this would reduce the weight by .3 ounces. But the open end of this hole would need to be plugged, or else the increased volume would reduce the crankcase compression ratio. I elected not to take this step, but if weight is an issue, it could be almost as easily done in the future.

Bob G
Bob, those little engines are coming along quite nicely. I'll be filing away some of the procedures you've used for some shop jobs here. I fly R/C planes and would love to build one of Andy's engines.

Also, on a note of old tools.... You have a real gem there in the form of that little wooden box. I just love old stuff like that and am quite jealous. A truly nice, and useful, bit of memorabilia.

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