PM Research #4 Build Log

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.
Hi Ved

I am busy with the final touches on mine and should start painting in the next 2 weeks if all goes to plan. I am using 2K epoxy paint for my models which dries in any weather.

Happy machining
On to the cross head. This is a casting with no obvious ways to machine it. It doesn't have any cast in bosses for holding the part.

The last time (on the PMR #6) I made this part my initial thoughts were "How the hell am I going to machine this thing?!?!" This time around my intial thoughts were "How the hell am I going to machine this thing?!?!" :p

So first I spotted/drilled/tapped where the piston rod connects. This gives me a place to attach a threaded rod for chucking into the lathe. Against the drawings, I drilled all the way through the cross head. This gave me a place to apply the live center.






Cross Head #2

It took a couple of trial fits, but the cross head fits acceptably in the engine frame.

Then it was back to the mill for drilling the connecting rod journal and facing the width.

I drilled/reamed the journal first. This allows (with the help of a 5/16" rod) flip the cross head for the width facing. Again, I fit the parts to the connecting rod instead of strictly by the drawing.




The last part for today was the Cross Head pin. It's a comparatively simple part, so the pictures should be self explanatory.

After I finished the pin, I could temporarily assemble the bottom end of the engine. (short block?) It moves freely with no noticeable knocks. Thus far, I'm quite pleased with it.

(If you're curious, the red stuff on the Con Rod is engine assembly lube. I have a bottle left over from when I overhauled the turbocharger on my Corvair.)






Next is the eccentric strap. This is another CI casting with not obvious holding position, so after some pondering on the cut order, I forged ahead.

First I drilled the strap. After cutting the casting in two, I used a fly cutter to clean up the sawed surfaces.

Then after tapping the holes, it was off to the lathe to bore the inner diameter...






Eccentric Strap #2

After facing the strap to width, it was back to the mill for drilling out the push rod connection point.

With that part completed, it was on to the eccentric. This part is fairly simple, the most important thing is fitting the part to the eccentric. It took a few trials, but in the end it fits good.









A running engine is within grasp. The last components are the valve linkages.

I'm fortunate enough to have a mini-mill that I converted to CNC. So for the upper and lower linkages, I used the CNC to mill the radius and drill the holes.

After profiling each end of the provided bar stock, I used a hack saw to cut the linkages in two. Then I could clean up the sawed edge and drill for the linkage bar.

Now for the slot in the link I used a slitting saw. THESE THINGS SCARE THE HELL OUT OF ME!!!! I was well out of the way when cutting the slot.

There was some filing necessary to get the parts to move freely, but it's all good.






There's no use in showing pictures of bending bars and fitting parts, but in the end I have created life!!!!!

There's still more to do, like painting and making the oil cups, gaskets, and lagging. But I couldn't resist trying to run the engine.

There's nothing like seeing a creation run for the first time. It's exhilarating. After a few minutes of running, the engine will barely run on about 3-4 psi, but it idles reliably at 5 psi (as shown in the video).


I would like to thank all those people (especially Albert) for following this thread.

Unless something truly interesting comes up, I probably won't be adding much to this. For looks, I plan on strips of balsa wood as lagging and I'll show that, but from here on out updates will be scarce.

Again, thanks for all you followers.

You are welcome Ved, I was watching your steps and realized many similarities as far as methodology goes between the 2 of us.

I painted mine on Saturday and now for final polishing and assembly. I will post few pictures of that on my thread. I will share the link with you.

I also converted an old wiper motor into a little generator which works well. I am now busy with the lamp pedestal...will see how it comes out

However, stay in contact with me on [email protected]


I would like to thank all those people (especially Albert) for following this thread.

Unless something truly interesting comes up, I probably won't be adding much to this. For looks, I plan on strips of balsa wood as lagging and I'll show that, but from here on out updates will be scarce.

Again, thanks for all you followers.

Apologies for hijacking an old thread but I've found all of this very useful and want to add my 2c worth with my own PM4 build.

Firstly, many, many thanks to Vederstein. I've read all of the posts in great detail and they've helped me enormously with my build.

Also, thanks to all of you others who have contributed to this thread. Many times, wondering what to do, I've been helped out by your advice.

There's very little on the 'net on the machining for this kit. This is by far the most comprehensive thread I have found.

There's also a Youtube video series on the PM6 by GI Customs here.

And this on the PM6 by Don Giandomenico.

So. Here we go!
Last edited:
In mid 2020, courtesy of covid, I found some YouTube videos on making a small model steam engine.

It was the PM Research PM1, and both Blondihacks and Joe Pieczynski have excellent video series detailing it's manufacture.

I ordered one, and mostly, by copying what Joe and Quinn did I managed to make it. AND IT WORKS!!

Making this model improved my machining skills by an order of magnitude.

I finished the kit in October 2020. The Devil, as they say, finds work...

Joe Pie's next series is to be the miniature lathe offering from PM research. I bought it, but it's terrifyingly small and complicated. I need to buy some tiny tooling, so I'm waiting until Joe gets started so I can copy him.

In the meantime I wanted something bigger. After perusing PM's catalogue, I ordered the PM4 as well.
Last edited:
So. Why bother to post this?

Well, to be honest, because the PM4 kit presents some challenges to the novice home machinist (people like me).

Parts of it are too big to fit in our little lathes.

Some of the design has flaws that can lead to failures in components.

And the castings require us to think outside the square to produce acceptable tolerances, and a machine that will run.

I love a challenge!
Last edited:

I started out with the cylinder. Fairly straightforward setup in a 4 jaw.

I elected to use an angle grinder to remove the surface scale layer to make initial machining easier and to get the top surface approximately flat.

To make setup easier I machined up a mandrel out of round bar.

This is a clever trick I picked up from Quinn, and for more detail see how she did this with her PM1 build (link to Youtube above).

The main diameter was a fairly close fit to the ID of the casting, and on one end I turned it down to 1/2" so it would fit into my drill chuck in the tailstock. You mount the mandrel in the chuck, slide the bore over it and you are 95% centred for the 4 jaw.

All that weight off centre meant that I had to run the lathe slowly but I got the bore to dead on 1.500" and the top surface flat.
Last edited:

As I needed to do the valve cylinder bore and drill holes in the mill, I opted to machine the other face parallel at the same time.

I used the chamfer on the end of my drill chuck to centre the piece. I double checked the centre with an edge finder and it was very accurate.

So I bored the valve.

I then glued the cap (prepared earlier) onto the cylinder with good quality cyanoacrylate glue and drilled the holes for the lower cylinder cap.
Last edited:

Latest posts