As a few people seemed to like the build thread that Allan did on his Victoria and I feel we could do with some more similar threads on here I'm going to post the more detailed build of the Monitor engine that I have been showing bits of in the What did you do thread. So here goes, its a bit picture heavy but as its not the mag I hope you won't feel its being padded out and want a refund

I had long fancied doing this engine and would often visit Pacific Model Designs website to eye it up. Unfortunately they went out of business so it looked like I would not get to make one, I did almost buy one of Lone Star's Engine Works similar style engines but the opertunity to make one of the PMD kits came up so how could I refuse.

The engine is of the 4hp version and modeled in 1/3rd scale. All but one of the castings are supplied in cast iron, the exception being the carb body which is bronze. These are the castings with a 12" rule to give an idea of size, the plastic bag contains the two timing gears.

The logical place to start is with the crankcase which is quite a heafty lump at 11" tall

But before I could get going on that my fixed steady needed a little bit of surgery before it could be used for one of the suggested machining processes so I have included this picture especially for JS.

After a lot of careful measuring and marking out I decided on the position of the crank drain hole which was only centre drilled for now so that the casting could be supported by the tailstock while the head end was adjusted in the 4-jaw to get the outside of the cylinder to run as true as possible then the base was machined.

Who says carbide tooling does not like interupted cuts?

At this same setting a very light skim was taken off the lower part of the cylinder so the fixed steady would have a surface to run against.

It was then over to the mill where the casting was shimmed up and a squaring cut taken across the base, this would be my datum for most of the other machining.

The opposite side and then the ends were squared to this first face

With the casting stood upside down the datum face was clocked true, centre located and the 4 mounting holes drilled a tight fit on some 1/4" Whit cap head screws. I had to resort to a keyed chuck here as I could not get the longer keyless on in the space available with the X3 head right at the top of the column

Back to the lathe and the crankcase was clamped to the faceplate and set to run true with a DTI against the previously turned portion. When true the fixed steady could now be positioned to add support while the casting was faced and bored, the bore for the liner needs to be about 6" long. I used the Warco supplied 4-way tool post as it takes larger tools than my usual Dickson QCTP

I'll stop there incase I loose the posting.

J

Edited By JasonB on 24/03/2014 17:34:49

Before the bearings housings could be bored I needed the bearing caps so these had their ends cleaned up but left over length and then the mating surface was milled down to size.

They were then flipped over and the stud holes drilled & spotfaced, the wick oiler tube hole drilled and a large counterbore cut to hold the oil.

It was around this time that I confirmed my earlier suspicions that the whole casting was a bit narrow, 0.100" or there abouts. There was not enough room inside the crankcase for the crank to turn let alone the flanges of the bearings. This shows the cross section with what I actually had marked in red.

A plan of action was decided upon and the caps held in place with caphead screws for now. The casting was set up on the lathe cross slide and a long series 1/4" drill put through first. before opening upto 9/16 in a few steps.

A 1/2" boring bar was then used to take the bore upto just over 18mm

This allowed me to just sqeeze in a between ctrs bar to take the bores to the final 3/4"

I made use of the side access hole to change the bit to a side cutting one and counter bored the insides to take most of the bearing flanges so I could keep the crank as wide as possible.

The final job was to face back the bearing caps to match the narrow crankcase using a flycutter in the lathe, fit an angled bit and cut a decent chamfer – probably larger than needed looking at it now. I also marked the caps with punch marks

As you can see from above due to playing about with sizes and the position of the caps the fit was not ideal, so a bit of time with files soon had things looking better on the outside too.

The cylinder liner had been roughed out a bit earlier and allowed to settle. The bar in the end is just incase it came loose as there was a lot sticking out the chuck and the bore was too large for my Ctr.

It was now finish bored and turned, you may be able to see a couple of changes in the pattern on the outside this is because the top nearest the chuck is a couple of thou larger than the bottom and the area between the two smaller still. This allows it to go most of the way into the crankcase before final pressing in with some Loctite for good measure.

J

As the inlet and exhaust valves are on the side of this engine the actual cylinder head was quite an easy job. The odd legs were used to swing a few arcs to get an average centre position and the casting then held in the 4-jaw to get this running true.

And the spigot turned to a nice fit in the top of the cylinder.

It was then just a case of reversing the part and facing off down size then turning the recess in the top. Final job was to drill the five 2BA clearance holes.

The hopper is quite a lump, weighing it at 2.5kg and measuring 5.5" diameter. To make sure I got the top and bottom holes in line I first machined a disc to fit snugly in the top opening and clocked that in on the mill table.

I could then slip the hopper over this disc and using a small height gauge get the central bead as horizontal as possible with the aid of some feeler gauges as packing. With a clamping bar inside it was then just a case of using the boring head to open out to the required 2.5". I do like these indexable bars from Glanze, they seem to work very well in all metals and will cut down to a 12mm dia hole.

I then skimmed the bottom surface back to the required size.

Before drilling another four 2BA clearance holes for the studs

Next it was over to the lathe so that the recessed hole for for the lid could be done, as its a fair size casting and the cut some 5" from the chuck I added a length of studding through the spindle just to be sure it would stay put.

The hopper lid was not the easiest to hold either so I put a bit of brass bar in teh tailstock chuck just to make sure it would not work its way forwards while the spigot was turned.

It was then easy enough to hold by this spigot while the rim was finished.

J

With that bits that go onto the ends of the crankshaft done I though the next logical parts should be what goes in the middle.

The conrod is supplied as an iron casting with another casting for the bearing cap, one unusual feature is that the cap is pivoted much like a hinge on one side with a single bolt to the other as there is only access into the crankcase from one side.

Making use of a step in the casting halves and the machining allowance at the other end the main rod was taken to width and a light skim taken along its length so I could hold it by the "I" section if needed.

Luckily the ends just fitted in the vice so held by them the central part of the hinge was milled to width, then the part reversed to take the face back to the joint line.

The bearing cap was machined in much the same way adjusting the hinge gap until it fitted snugly onto the conrod.

Then using a G clamp to hole the two halves together, the vice to stop it all moving about and some 1-2-3 blocks for support the hinge pivot hole was drilled and reamed.

With a length of silver steel (drill rod) as a temporary hinge pin the hole for the bolt was then drilled with the job held to an angleplate with assorted clamps.

Now I could make use of the skimmed side of the "I" beam to support the rod while the little end was drilled and reamed and at the same setting a boring head was used to open up the big end to 3/4"ready to take a bearing.

Finally a bit of hand filing to clean things up and a quick whizz around in the rotary table to make the big end look a bit more presentable.

The big end bearing was made in much the same way as the others, tin two bits of bronze, sweat together and then machine.

The small end bearing is just a simple turning gob and then pressed into the casting and thats another part ticked off the list

J

The ones on the "What have you done today" are upto date but there are just a few odd ones, these cover the whole build in a lot more detail and are not so upto date.

J

Due to the cooling hopper being on the top end of the cylinder there is not the normal cylinder head arrangement on this engine, instead the valves, plug and carb fit into a block on the side of the cylinder and there is a slot from that into the combustion chamber.

First job was to shim up the casting and get the surface that mates to the cylinder nice and flat, due to the previous chilled spots I used a carbide tipped "littel hogger" to do this

This flat surface was then placed against the vices fixed jaw and the top machined flat.

Followed by drilling and tapping the carb mounting holes and the larger hole which will create a space below the inlet valve where the fuel/air mixture is ignited (plug goes into the dark central boss on the front) The bottom of this hole has the seat for the exhaust valve and a hole right through for its stem.

The casting was then turned 90degrees keeping the same face against the vice and the hole for the exhaust pipe drilled & tapped 3/8" BSP. using a pointed rod in the drill chuck to guide the tap, I find tapping like this better than a separate tapping guide/tool as you can always ensure the work is directly below the axis.

The last thing to do on this was to spot face the four mounting holes and spark plug hole, drill 3/16" for the 2BA studs and tap M10x1mm for the CM-6 plug.

The "carb" also houses the inlet valve, A chucking spigot is provided and was lightly cleaned up with a file so it could be held in a collet, the end lightly faced and centre drilled so that the tailstock could give support while the boss and flange were turned.

I also cleaned up the top face of the flange at the same time which needed to be done with a parting tool to clear the elbow.

I then held it by the spigot to machine the outside of the valve guide

Flipping it back around again and held more firmly on the now turned guide the spigot and flange were given a final skim before drilling and reaming the hole for the valve stem, counter boring and machining the valve seating.

Then over to the mill in a collet block to firstly drill the mounting holes

bore the intake at right angles to this

And then drill and tap for the needle valve body at right angles to the other two holes

Finished part, save for a bit of cleaning up.

J

Thanks Jeff.

The needle valve body screws into the side of the carb, this is just a brass turning with a threaded spigot at right angles. After turning a pocket is machined into the body with a 2-fluted cutter

The two are then silver soldered together

Nothing too special about the needle valve though I did put a slightly more tapered point onto it. (The square nuts are for the flywheels which have already been covered)

I deviated slightly from the plumbing shown on the drawing as it was a bit tight to get things in and not as the full size seem to have things. The non return valve is from P M Research as is the street elbow.

There is a venturi that is inserted into the carb intake but I did not take a photo of that. What I like about this carb position is that you can see a burst of fuel being sucked in on each "hit" stroke but thats getting a bit ahead of outselves

The valves were cut from 16mm stainless bar for a 5/8" finished dia, I made the stems a bit over length so a centre hole could be used for support while turning the shaft.

The back of the head was then machined to profile and unusually for a valve the end of the stem was threaded.

While the valve was still on the parent bar I used that as a handle to grind the valves into their seats with some 1000g SiC powder and a drop of oil, you can see the matt area where the valve head has been ground.

Once sawn off the bar the heads were cleaned up and given a slightly convex surface

And the finished pair, the exhaust is slightly larger than the inlet.

J

So with all the machining done its time to start the finishing touches. First up is to go through all the parts and clean off any remaining casting flaws which are mostly where the two parts of the casting boxes may have been a little out of line and also I like to run over the cast surfaces with a grinding stone in the Dremel to knock off any small lumps. This was followed by a wipe down with thinners and then body filler applied where needed. The main areas where to blend in where I had to turn a surface around the cylinder for the steady to run on and also reprofile the corners of the crankcase side holes. Then a good rubdown, I'm not aiming for a dead smooth finish as I want the parts to still look like they are castings

Following another wipe over with thinners I sprayed on some high build primer (etch on the bronze castings) which tends to show any blemishes that can be attended to. Being a light colour it showed up quite a few pin holes that were not obvious to the eye, compare this shot of the bearing caps to the painted one and the one that has been second filled behind it.

Once all the blemishes were sorted and the primer touched up it was on with a coat of red. You can see that the machined mating surfaces have been masked and holes pluged with whatever seemed to fit.

Once the paint had been allowed to harden for a few days it was out with the paint brushes and ruling pen to add a few pinstripes and pick out the "Monitor" logo on the fuel tank. I used a gold acrylic for this as the pigment is quite fine and diluted it slightly with an airbrush extender medium as this works better than water. The acrylic is also not affected by the fuel proof clear coat that went on next.

It was then assembled on the base. I went with an ignition from S/S which easily fitted inside together with a battery box for 4 AA size batteries. The wires that are visible were done in old style cotton covered wire complete with a flat sparkplug clip not an unsightly steel braided wire and big metal cap.

And thats about it, so a few pics of the finished engine.

Thanks to all who have commented throughout the thread and a big thanks to Dave for giving me the chance to build this one.

J

Edited By JasonB on 07/12/2014 17:33:19

Edited By JasonB on 07/12/2014 18:26:52

Thanks Chaps

Fizzy you are right the bottom end uses splash lubrication. I just added a few drops of oil to the big end for the test runs which were only a few minuits long as if it had needed a strip down things would be a lot cleaner. Once I got it running right there it was filled with oil, I also fitted the two plates that close in the open areas around the bearing caps and sealed with a small bead of clear silicon, again not something I wanted to remove if possible.

Jeff the longest I have let it run is about 5mins and by then it is starting to get about as warm as I would want it too so any longer runs would best be done with the hopper filled.

J