Little Demon V8 - helpful hints (hopefully)

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Cylinder liners done. I started making them as I described, cutting the material to length to get 2 liners. Drilled them with a 14.5mm bit (.571"). I wanted to get close to the finished diameter to not leave too much to bore out, but not go over with any drill wandering. That size worked out well.

Machined the first few on the CNC lathe. Did one end, flipped it around and did the other end. Only issue was once machined the one end was not a good size for any collet I had, so I made an adapter to hold the machined end while the "new" end was being machined. Worked out OK but I wasn't thrilled with it. Material blank (5/8" diameter 12L14), adapter piece to fit in a 1" collet and hold the machined cylinder, double piece finish machined, after being cut.

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I had left enough material to cut the double length piece apart, but after machining I realized that I cut it very close and there wasn't enough length on the large diameter in the middle for a band saw blade thickness, or even a normal cut-off tool. So I used the thin cut-off tool I made for grooving the valves and it worked perfectly to separate the 2 with only a .020" kerf. Then cleaned up the cut end of each on the lathe.

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After the first few I realized that the bore in the lathe head is larger than 5/8" and I could drill about 1 1/2" deep on one end of the full length bar on the larger manual lathe, machine a cylinder on the CNC, then cut it off, drill the hole deeper in the bar, and proceed with another cylinder. So basically worked with the full bar without needing to cut off a length until a cylinder was machined.

The set of 8 done:

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Installed with red loctite:

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Some of them were a touch tight and some were a touch loose, but the loctite should retain and seal them. Even a tight fit needs something to seal liquid-tight.

Next, the pistons.

With the cylinder liners done and installed, time for the pistons. The CNC lathe did the turning, the bore in the bottom (with a 5/16" end mill centered and then with it offset, used as a boring bar, to give the correct ID), the grooves, and then the parting off. Once again the little grooving tool I made came in handy.

Then onto the CNC mill for the slot in the bottom. Yes, I try and do as much as I can on the CNC mill and lathe.

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While I was there, I machined a fixture to hold the pistons for the pin hole drilling.

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Clamped the fixture in the vice and drilled the holes......manually, no CNC!

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Now the piston rings were much more of a challenge.....
The piston rings. I did a lot of research on how to make these. There are many ways to do it, with the most popular needing a heat treating oven. My wife has a kiln for glass work, but it would be a really bad idea for me to use that. So, other ways...

I have a bar of cast iron I bought for a project some time ago. It is about 2" diameter and 5' long so should give me enough material. I think I bought it for a piston for a Sterling engine and since that was the only piece the supplier had I bought it. I figured I would use it all eventually.....if I live long enough.

I tried the method of machining the ID and OD, slotting it the full length, clamping it in the lathe with the slot closed, and machining the ID to final size. I parted off a few rings and then decided that trying to hold them with the gap closed while machining the OD to final size was going to be a real pain. I knew how to make a fixture to hold them, but it still didn't seem like the way I wanted to go. So more research showed people using this method...

Machine the OD and ID to final piston ring size, and part off the rings.

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It went well, but when parting them off it leaves a large burr on the ID, since the rings break off before the cut is complete:

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OK, "large" is relative, but even with this fixture to hold them, it is a bit of a pain to sand off this burr.

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Then I came up with a brilliant idea..well, I thought it was brilliant and nobody in my shop argued with me. I remembered where some people use hot-melt glue to hold parts for machining, so I filled the blank up with the glue:

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As I parted the rings (with my thin parting tool) I could cut right through the metal and the glue held the rings in place. Looks a bit like an air-cooled cylinder head:

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A stack of rings:

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Softening the glue in hot water let me pull the rings off and they were very cleanly cut. They only needed a quick sanding on some 500 paper and they were done....almost.

Breaking them for the gap is very easy with rings this small; holding them with needle-nose pliers and a very small twist does it. Now the method says to hold the gap open with a metal rod or plate, heat the rings red-hot, and they fall off the fixture and are done.

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They seem springy enough to close the gap and still spring back. They fit nicely in the cylinder. I'm not going to open the gap up as from what I've read they will wear in and the gap will open slightly.

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These rings are very small and fragile, so certainly make extras as you will break some. I still have enough material for replacements:

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I'm close to getting this assembled as a short-block now. I have to re-work 2 of the connecting rods that don't fit the crank journals as nicely as I'd like. After that, assembly time. I think the lifters and camshaft have to go in before the crank assembly. At that stage maybe I should run it on the lathe slowly with oil to let things wear in. That will be an nice stage to get to.

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Thank you Michael. I'm not really happy with the rockers I've made, and still need some operations on them to finish; mainly figuring out how to make the slot. So looking at your build thread, I've "borrowed" your method of using the 4th axis to produce them. I've made a couple so far to fine tune things and am really happy with how they came out with the 4th axis method. I'll post some pictures soon. So thank you very much for that idea.

Got the rings installed, only breaking 1.

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I had a good look at the block before installing the pistons to make sure there was no more machining on it to do. And there was. I had not machined the hole for the distributor. That meant assembling the heads and intake onto the block:

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I did have to open up the intake manifold holes a bit so all the screws would fit in nicely. I'm really pleased with how it all fits. I have the head and manifold gaskets in place and there is virtually no gap between the manifold and the block. In the real engines there is a gap here that a seal, and sealant, goes in.

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I'll probably put a bit of sealant on that surface when it goes together for good.

A cordless screwdriver with a hex bit makes for much faster work when installing/removing all the head bolts:

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The hole in the intake manifold that looks like it is for the distributor is an undersize hole I used to clamp it down for machining. Set up on the mill I first used a 3/8" end mill for the hole:

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Then the boring head to finish it off:

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And it fits:

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And with the cam in place it rotates nicely. I realized I hadn't machined/modified various gears yet, so decided to do that before assembling things. I think it is ready for piston installation now.

Oh, as you can see, the intake and exhaust ports in the heads haven't been drilled yet. I'll be really careful with those as to mess up the heads at this stage would not be nice.

Gudgeon pin? Reminds me of the manuals for my first car, 1969 MGB. Bonnet, boot, dynamo, petrol, spanner.... :)

But I digress. It is a press fit into the rod. From what I remember (I made the rods a while ago) I used a .124" reamer for the rod holes and .125" in the piston. The pins are .125 drill rod and the tight fit was just right. Cut a small 'V' in a piece of wood to support the piston and pressed them in on the mill using it as a drill press.

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Nice work. Just curious about your tool. Is it made from a slitting saw blade or uni-blade with relief or...? Reason I ask is it looks nice & thin & I have to do some deeper & thinner cooling fins soon.

Finally, I have a camshaft!

I know I could have produced the cam in a fraction of the time it took me if I made it in the traditional way; indexing it around on the lathe and taking cuts every 5 degrees or so. But I was determined to do it on the 4th axis of the CNC. And after many weeks of trials, incorrect software settings, and broken cutters, it is done. It was cut with a carbide 3/32" 4 flute ball nose cutter, with very conservative speeds (after breaking too many cutters). Thus, 6 1/2 hours of CNC.

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After the lobes were CNC'd, I did mess up the end that the gear goes on. Got it just a bit undersized. So I machined it down to about 1/8" diameter and made a thin steel tube to press/locktite on. Then machined it to the proper dimensions.

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One interesting thing I found (that turned out to help me a lot) is that with the spacing of the lobes at that end of the cam it grips in the 1/2" collet perfectly centred, as you can see in the picture.

My wife says she never wants to hear the word camshaft as long as she lives.....or maybe just as long as I live?

Hullo would you share your camshaft file I cannot get mine right, cheers Peter
Nice work. Just curious about your tool. Is it made from a slitting saw blade or uni-blade with relief or...? Reason I ask is it looks nice & thin & I have to do some deeper & thinner cooling fins soon.

There is a little more info on it in post #57. It is a piece of blade from one of these:

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I just snapped off one of the sections and used that. It is .0196" thick and extremely hard and durable. I've used it to cut the grooves in the valves, the piston ring grooves, small groove at the end of the thread for the rocker studs, slice off the piston rings from the machined stock, re-machine the piston ring grooves (more on that later), and slice off many parts on the lathe in brass, aluminum, and steel. I have used it so many times with this little engine I have to say it is one of the most useful little tools I've made.

The blade is used just as it comes, no modifying or cleaning up the cutting area, other than grinding off the original sharp part for safety. I'm using the back of the blade for cutting, not the "pointed" part; see post #57.

I made a little fixture from a scrap of wood to hold the blade to make the hole since it is a fiddly operation. A carbide end mill produces the hole.

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Starting assembly of this little engine. Not that everything is made yet, but the major rotating components are done. So I thought it would be fun to assemble it. I was wrong.

Turned out to be a pain. Most of it my fault. First thing I did was make a small guide bushing to insert the pistons in the cylinders while compressing the rings. There are a number of ways to do this, but the big boys that build engines have dedicated tapered sleeves, based on the piston size. This one has the bore diameter at the bottom and the expanded ring size (plus a bit) at the top:

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Insert the piston/rod assembly into it, hold it against the block, and tap the piston in. In theory. I found that the rings weren't compressing enough to slide though the bushing. When I made the pistons I didn't cut the grooves quite deep enough. Turned out to be not a huge deal. Fortunately the piston/rod assemblies fit in a collet chuck to hold them to deepen the grooves a bit. Of course I had to take all the rings off again:

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Now the little tapered fixture worked well to install the pistons. BUT...

I installed the crankshaft and installed a piston and found that the connecting rod was hitting the block and not allowing full rotation. Tried a number of pistons/rods and found the same thing. The rods were too wide (at the point in the above picture with the red arrow). It was hitting here:

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After hunting around, checking my machining dimensions and the drawings, I found the issue. The drawing of the connecting rod does not actually give the width of the rod. The angle of the taper is dimensioned, but not where the angled parts are located. So the rods can be various widths and still meet all the drawing dimensions. Unless I missed something. When I laid out the rods for machining I estimated where the tapers were located to look like the drawing. Obviously I made them a bit too wide. Once I figured that out it was not too big a deal to touch them on a spindle sander and take them down a bit where the interference was.

I've got the camshaft, lifters, crankshaft, gears, and half the pistons installed. Finicky oily work, but it's getting there. And it does rotate!

The short block is assembled and I ran it with the lathe to break in the piston rings. I assumed that would be a good idea.

It was fairly stiff to turn over, but after running for a couple minutes it was quite a bit looser. Not sure how loose it should be at this stage. I can turn it over easily with the gear (see video), but can't quite turn it by gripping the crankshaft ends that stick out.

I ran it for a minute or so, then swabbed out the dirty oil from the cylinders, put some fresh oil in them and ran it again. Cleaned that out and then put some WD-40 in to try and flush the stuff out and into the oil pan. Is it a good idea to run it like that until the oil in the cylinders doesn't generate debris?

I put together a short(ish) video of the major components being made and then running it in. I had some 3D printed gears from a failed project that worked nicely to couple the engine to the lathe.

The valve train components are coming along nicely. Not without some hiccups of course.

I had made the rockers earlier but wasn't really happy with them. You can see how I made them in my earlier posts. Nothing really wrong with how they came out, but I was trying to figure out how to cut the slots in them accurately. Then I saw Michael's method of making them with a 4th axis (rotary table):

michael-au rotary machining of rockers

Michael, I owe you a huge thanks. Next time you are in Bolton the beer is on me (Bolton, Ontario, Canada that is, not the UK). I didn't think of making parts that are in no way round on the 4th axis, so now I got to thinking how to do it.

I had modelled the rockers previously and I tried simulating the machining with Deskproto, which does 4th axis stuff, but they weren't looking good. I came up with another method that doesn't actually require 4th axis software at all. Also, I wanted to minimize tool changes from the 87 changes that Michael has. OK, maybe not that many, but I don't have fancy tool holders so to change tools means to stop things, swap cutter in the chuck or collet, zero the cutter on the work-piece, and continue. Also, I don't like drilling small holes with the CNC. I've done it, but I've also messed up now and then, so I prefer to just spot drill them with the CNC, then drill all the holes in all the parts later on the mill (as a drill press). So this is what I came up with, since I am getting more familiar with G-code and modifying code.

I use VCarve for most of what I do. Though it is generally thought of as something for making signs and similar stuff, I've used it for most of the CNC work I do. I drew the profile of the rocker and used VCarve to cut it. Then I took that code, added a 90 degree rotation at the end of it (G0A90), drew and programmed the side profile of the rocker, and added that to the code. Then just continued on with it to machine the top profile with the oval hole, the side profile with the round hole, the .100"wide slot, and parted it off.

Some decisions I made after some tests. I started out with a 1/8" end mill for most of the work, then a 1/16" end mill for the thin slot and parting off. I also had a spot drill for the 2 small drilled holes. So that was a bunch of tool changes, times 16 rockers....makes a lot. I realized I could get away with a single 3/32" end mill for all the features except for the 2 small holes. I used the same end mill to produce the counterbore for the #2-56 screw hole.

This shows how it went. Cutting top profile and oval hole:

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90 degree rotation and side profile and hole cut:

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Another flip and the counterbore cut:

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Flip again to machine the thin slot:

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Part off:

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Then clean up the cut end of the rod and move the cutter back to the start position:

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Then it was a matter of loosening the chuck, moving the 3/8" diameter rod out to touch the cutter, and hit start again. Cranked them out like a production line.

A couple operations left. The counterbore made it fairly easy to locate for the #2-56 tapped hole. I made a small fixture that located in the counterbore with a hole to guide the drill. The hole in the fixture may not look centred, but it is; some of the material is filed away to clear the radius on the rocker.

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The rocker was pressed onto the protruding boss and the hole drilled:

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The other small hole was done like this. Pressed a pin in a piece of aluminum and zero'd the mill above the centre of the dowel. Then offset it to the location of the small hole to be drilled:

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Put the rocker over the pin, pressed another piece of stock against the flat side of the rocker to align it, and drilled. No issues.

The only other thing was to clean up the thin slot. The cutter leaves the corner radius too large. I came up with all sorts of complicated ways of doing that, then resorted to a small file to square up the corners. 16 rockers finally done:

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Very well done Rick, happy to have inspired you to use the 4th axis, yes I did have a lot of tool changes but having all the tools in holders it Was not really a problem

would be nice to have that beer 🍺😀

your engine is coming along very nicely, I have taken a short break from the V8 and working on a single cylinder Thompson Engine, I will post a build log for it soon


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