Hubbard Marine Engine

[deverett]

Looking at my pictures, I've realised I didn't mention the crankcase door windows. They were milled flat and the window cut. There was very little metal left in some places.



The cover plates had previously been squared up and holes made for the securing screws (not shown on the drawings).



Both sides were done in the same way. Thinking about it afterwards, I wondered why the crankcase had windows machined when the doors were to be epoxied in place.

On now to the exhaust stub platform. When this was milled, the area was well undersize for the exhaust stub, so an application of JB Weld will be necessary.



The water inlet was drilled and tapped at the same setting. Afterwards, the casting was turned over and the water outlet was drilled and tapped.

The casting for the exhaust stub was rough-looking and remembering how poor the surface finish ended up on the crank brackets, I decided to ignore it and make the stub from a handy piece of cast iron (that would have been used originally, so that's a good enough reason for me to change it!)



The drawing shows an 8mm hole through the stub and a 10mm hole through the cylinder body. Looking at the shape of the casting, I think there may have been a mistake in the stub drawing. Anyway, I made an extension of the stub with an 8mm hole all the way through that fitted in the 10mm hole and if I am careful, I should be able to get it to a reasonably close fit against the cylinder liner. The extension was made overlong for trimming later.





Dave
The Emerald Isle

 

[Brian Rupnow]

Dave--You are doing a marvelous job, and I am following with great interest.---Brian

 

[deverett]

The engine side of the coupling seems to have been secured by a couple of set screws into dimples in the crankshaft. One picture I have shows what a mess this became after many years (ab)use.



My coupling started out as a piece of 1-1/8" round bar and I initially used a trepanning tool to make the recess but it didn't have enough clearance for the depth required and so a small boring bar finished the job off.



I will not be driving anything with the engine so the coupling will be in one piece with a groove to simulate the bolted joint. Four set screws were made from 3mm square bar and the coupling bolts are 10 BA.




Dave
The Emerald Isle

 

[deverett]

On now to the flywheel. The brass casting was very tight and try as I might, I could not get it set up to give me the full dimensions shown in the drawing.

I faced the first side then drilled the hole for the crankshaft 9.8mm, used a small boring bar to straighten the hole and then ream for final sizing. I got a nasty shock when I went to use the reamer and found it went straight through! When I used the boring bar, I didn't take into account the cut on the backstroke while withdrawing the tool. Nothing for it but to enlarge the hole and fit a new piece in place and start again. The new piece was press fitted in place with the addition of the Loctite.

Before drilling, I machined the eccentric which is used to drive the water pump and in full size, the ignition system. This was done to ensure there was still some wall thickness of original metal round the new insert. When done, the flywheel was reversed in the chuck and drilled out to 9.7mm. Using the boring bar cutting a few thou at a time, I enlarged the hole checking when the 9.9mm drill would just start to enter. Now it was time for the reamer and after trying, the crankshaft was now a nice light push fit.




The flywheel is held in place with a 1/16" taper key. I have a Dore slotting attachment that mounts on the cross slide. The smallest insert bar I have has a 1/16" cutter, but when I tried it the tool would not enter the hole. Reluctantly I had to remove the flywheel and make up a new slotting tool. The Dore type would be very difficult to make in a smaller diameter bar, but fortunately Michael Cox came to my rescue. He had designed a unique keyway slotter to put keys in a modified pulley wheel he was working on. That would do just nicely, thank you Mike. http://mikesworkshop.weebly.com/small-hole-slotting-tool.html
However, I didn't use his method of hammering the cutter through the hole! The clamp is to hold the heel of the cutter in place and also act as a length guide.

As an aside, for those who have not seen his site there are some quite good ideas that can be adapted for other machines.



Full size, the flywheel is fitted with a retractable starting handle. This is not shown on the drawings, but is easy enough to make. Using my centre finder, I lightly scribed a line that went through the keyway and this was carried over to the flange. The hole for the starting handle was drilled on this line at the half-way point on the flange. The handle itself was a piece of steel bar threaded at each end. On the inner end, a collar was attached and Loctited. The outboard side has a threaded brass button for the knob. A suitable light spring from the 'spring store' is the retracting mechanism.




The position of the holes should be rotated from that shown on the drawing and they were repositioned as far as I could without hitting the counterbalance weight. There are also an extra 2 small holes that should be drilled.



The pencil arrow was to remind me which way to offset the holes!



Dave
The Emerald Isle

 

[Brian Rupnow]

Nice work Dave.--And--You're not the first person to suffer from "Reamer Surprise".

 

[deverett]

Nice work Dave.--And--You're not the first person to suffer from "Reamer Surprise".

That was down to lack of concentration, Brian!

Dave
The Emerald Isle

 

[deverett]

I followed the drawings for the construction of the cooling water pump, but as usual I 'improved' the shape somewhat.

The pump cylinder was the first part. Just a simple turning exercise. The full size one had a gland on the top, mine is a dummy. The cross bar was from a piece of thick wall brass tube, with the outside reduced a bit and bored out a tad. These two parts were silver soldered together and the cylinder bore was drilled all the way through and then reamed.

The pump piston was turned to a tight fit then lapped to the cylinder. The drawings wanted a 5mm O ring as a seal on the bottom of the piston, but I don't have any so what I have done is to put 3 grooves in the piston to act as a labyrinth water trap. If it doesn't work, I can enlarge one of the grooves and use some Teflon string as a seal.

The bottom of the cylinder was sealed with a silver soldered plug.



The pump uses two balls in the horizontal bore as a check valve. Three inserts within the horizontal part trapping the balls form the guts of the pump check valves, the side extensions accept the cooling water hoses.

On any water pump that uses balls for check valves that I have seen always have notches filed on the upstream side, or some other way of allowing the water to pass. On my drawing these are not shown or even mentioned. Any potential builder not aware of this would find that their cooling pump would not work!



The sphere part of the check valves were made with a form tool. The valves being brass I just used a piece of 3/16" x 3/8" steel. A hole was drilled in one end and the end machined away to a bit less than half diameter. A clearance cut on each side and the horns were rounded over. The tool was then case hardened.



The check valves were machined as a pair. Slow speed and no chatter gave a good finish. The swarf came off in nice curls as the ball was formed.



After the spheres were turned, the filing rest was set up and a hex was filed on either side of them.



A pilot hole had already been drilled through the pair and this was enlarged so that they would fit on the pump. They were then parted off as two pieces and then the hex ends were brought to length. A recess was milled in the spheres to take the screwed cap, which would be Loctited in place. The screw head was filed square and stuck in place.



Pump finished



Dave
The Emerald Isle

 

[deverett]

The cooling water pump and ignition are driven from an eccentric on the back of the flywheel.

The plans show a piece of bent wire soldered to a brass ring for the eccentric strap that would have been a casting in full size. I made the strap in 4 parts silver soldered together. The strap will not be adjustable - the bolts are dummies. The ring started as a slice of brass bar and after rounding the circumference was sliced in half with a 1/8" slitting saw.



The bolting flanges are a piece of 1/8" brass bar trimmed to the right size. In order to keep these three bits lined up during soldering, I drilled 2 holes in each part for dowels.



Once these bits were silver soldered, the rod anchor was filed up and a notch milled in the top of the disc.



The disc and rod anchor were silver soldered in a second operation. The rod will be trimmed later.



The top fitting on the eccentric rod - the connector to the pump rod - was drilled clearance for the connector bolt. It was then shaped while still attached to the parent stock



After being parted from the parent, the part was filed to shape and drilled/tapped for the eccentric rod.
Final assembly looks like this:



Dave
The Emerald Isle

 

[Brian Rupnow]

Very nice, very finicky work Dave. I didn't build that part on my home-grown clone of that engine, because I already had a gear pump made to handle the water circulation. I do appreciate the amount of work that goes into a simple assembly like that.---Brian

 

[deverett]

There have been some serious distractions that have taken me away from the workshop for a while - watching Ireland and Munster rugby teams perform. Still a few more matches for Munster, so more distractions to come and from tomorrow a week away, hopefully in the sun.

I have to confess that if they had degree courses in procrastination, I would graduate with honours. I've done everything to delay machining the cylinder and piston but I've run out of reasons not to go ahead, so out with the seamless steel tube supplied for the liner and into the 3 jaw chuck with it. Fortunately it was supplied in a generous length for easy holding. It had to be made with a step to sit in the casting. I aimed for a few thou clearance to give room for the gasket goo sealant. One of my worries is to make sure that when finally fitted there will be a good seal between liner and casting. If not, cooling water will leak into the crankcase and probable disaster.



The bore was machined out to the correct diameter, less an allowance for lapping. I'd read that most 2 stroke engine builders aimed for a very gradual reduction in bore towards the head end to ensure best piston seal for ignition, this done during the lapping process. I nearly followed suit, but then realised in time that most 2 stroke aero type engines have the cylinder bolted to the crankcase and the piston enters the cylinder from the bottom. This engine is assembled by passing the piston down from the top, so the tapering wouldn't be possible.

I have a few AcroLaps, but of course not the correct size for this application. Looking at the lap, there didn't seem to be anything very difficult to making a new barrel. A piece of brass bar was turned, drilled and tapped as required. Afterwards, 5 lengthways slits were put in with a slitting saw and hey, presto a new lap. That's the new one at the bottom compared to the nearest existing size, using the same stem and adjuster.



When the adjuster is screwed in, it puts a slight hump in the middle of the barrel. Using a mixture of very fine lapping compound and thin oil wiped over the barrel, it was quite easy to pass the liner back and forth over the lap until the clearance felt the same along the length. Keeping the liner over length during the process ensured that there would be no bellmouthing at the top end.

Still to do is to machine the ports and ignition hole.

Dave
The Emerald Isle

 

[deverett]

I'm back on the case again - at least for a little while.

Before putting holes in the cylinder liner for the ports, I made a start on the cylinder head. This is basically an inverted top hat that sits in and on the liner.



The central hole on top is for the cylinder priming cup in full size. With the basic turning done, it was put in the vice and the six holes for the head studs were drilled.



The engine body was put in the vice next and the holes for the studs were drilled and tapped. I wanted to put the holes as far from the outside edge as I dared so that the cylinder head nuts didn't overlap the edge. 7 BA nuts are too large across the flats, so I'll have to drill out and tap some 8 BA ones. I was mightily relieved that the holes were tapped without any problems after my experiences with the crankcase holes.



The casual observer will notice some filler on the casting. When I slipped the head into the cylinder liner, it was flush in places and proud in a lot of others. The cross section of the casting resembled the moon 3 days before full. The only way I could think of making it round and to the correct size was to apply some (plenty) filler. It was over 20 thou thick in places at the top to get it circular.

The reason I made a start on the cylinder head now was that I can temporarily bolt it in place to clamp the liner for drilling the exhaust port and glow plug hole. The drill tip will mark the head so that I can be sure the recess will be put in the correct place.

Dave
The Emerald Isle

 

[deverett]

I know it's been a while but other things have been distracting me from the job in hand.

Now it is time to put in the exhaust and transfer ports. The liner was slipped into the cylinder and clamped by the cylinder head; the exhaust manifold was secured to the casting to use as a drilling guide. After putting the casting in the vice, a piece of 8mm bar was used to line up the exhaust hole.



Once lined up the exhaust port was drilled through. The liner was then removed to get ready for the inlet port. The transfer passage is a good 13mm wide, but the inlet port is only 11mm wide - plenty of leeway. Just to be sure there was no cock-up, I used a handy narrow 6 inch ruler that happened to fit nicely in the transfer passage and the limits of the passage were marked on the top of the cylinder casting.



The liner was then replaced and the piece of 8mm bar was put through the exhaust again as a lock so that the position of the inlet port could be marked on the liner - hopefully in the correct orientation. Then it was out with the liner and off to the vice where it was lined up and the inlet port was machined with a 3mm slot drill.



There were some burrs where the holes had been put in the liner, so I needed to put the lap through the bore again to remove them. In hindsight I should have waited until this point before starting the lapping process in entirety.

Slipping the liner back in the casting I was pleased to note that with the exhaust lined up, and testing the inlet port with a bent scriber, the inlet port came midway between the transfer passage walls as closely as could be judged.

The reason why I didn't just put the transfer port directly opposite the exhaust port is that the cast in passage and the exhaust were not exactly 180 degrees apart - about 8 degrees out as far as I could tell. It won't make any difference to the running of the engine, but if I had just gone ahead and machined without checking, the transfer port would have been partly obscured.

Dave
The Emerald Isle

 

[deverett]

The last hole to go in the cylinder was for the glow plug. Back near the beginning I said I had modified the design to get closer to the original. Before putting the glow plug hole in the casting I used the stub from the bottom of the main casting which I fortuitously saved. This was a test to check that I could safely tap the cast aluminium and to check the recess depth for the copper washer. With the modification, the washer sits below the diamond shaped plate and the circular part of the plug has to compress it while out of sight.



Fortunately the threads came out satisfactorily and the washer recess was a good depth. With that test done, a bar was put through the exhaust port to lock the liner and the head was refitted. The engine casting was then set up on the milling machine table to put in the real hole.
Using a sticky pin, the centre of the glow plug boss, previously centre popped, was picked up. The actual hole is 50 thou below centre to take into account the modification.



Before drilling, I added another hold down for added security. Don't want to let anything move unexpectedly!
The glow plug tapping drill went through the liner and into the head but the thread was only in the casting. A quick test with the plug screwed in place showed it will seal OK.



The head was removed and set up at a 45 degree angle to mill out the combustion chamber recess. The bottom of the head sits well down in the liner and without the recess, the fuel could not be ignited.



The engine, liner and head ready for assembly.



Dave
The Emerald Isle

 

[Jhawk]

Dave, glad to see you're well along and doing a fantastic job! I've not started on mine and watching your build is very encouraging and makes me want to get back on it. Hopefully soon. Best wishes......

Hawk

 

[deverett]

The piston was a piece of cast iron bar, not overly generous on length. To ensure adequate holding in the chuck I first turned the top part where the baffle would later be milled so that I could work on the main part. The design of the piston has a piece of brass tube silver soldered across the bore to take the gudgeon pin but I didn't like this idea. I have read that brass can be silver soldered to cast iron, but it's not something I have done so I made my piston in more conventional style, keeping the wall thickness a suitable dimension to support the pin and slotting the piston to allow the con rod to swing. It will be a heavier construction, but I don't envisage it creating any problems on this low performance engine.

When the diameter was to size, the piston was put in the vice to put in the con rod hole which was drilled and reamed. I will put a bushing on the small end of the con rod and allow it to swing on the gudgeon pin.


The piston was now upended in the vice ready for the central hole to be made into a slot. To ensure the slot was perpendicular to the hole, a piece of gudgeon pin diameter bar was passed through the hole and using a DTI running along the bar the piston was adjusted to give no deflection.


It was now easy to mill the slot for the con rod.


Back to the lathe and the top end needed a slight taper where the baffle would come and put in the oil retention grooves.


Then back to the milling machine to create the baffle. The same process as before was used to line up the gudgeon pin hole so that the baffle would be correctly orientated.


It was then just a matter of milling away the top of the piston to leave the baffle and another part done.


Dave
The Emerald Isle

 

[deverett]

The con rod was supplied as a piece of aluminium section. This was drilled and reamed for the two holes. The bottom end had a bronze bush pressed in. The drawing showed the little end as just a bare hole in the ally. As there were oil holes in both ends, I guess the con rod swings on the gudgeon pin but the design of having a brass tube to support the gudgeon pin seems strange if it not to be a bearing. Anyway, I didn't like that idea, so decided to bush the top end as well and use that as the bearing.


To shape the rod, I got a scrap piece of steel and drilled it for two pegs the correct distance apart so that the con rod could slip onto them. It was now an easy matter to cut away the waste on each side.


The rod was now mounted on the rounding over jig and swung back and forward (always cutting against rotation) to round over the big end. I had previously used filing buttons to round the small end.


As mentioned earlier, I don't like the idea of the gudgeon pin bearing on plain aluminium so as I had to make a bush for the big end, I made another for the small end. There may be many instances of aluminium running on steel shafts, but I think bronze to steel is a better combination. Last job then was to drill the oil holes in each end.



The gudgeon pin was simply a piece of steel drilled through and a rounded over brass plug fitted in each end.



I now had a trial assembly of the working parts. I was pleasantly surprised that there was no binding of the piston in the bore. It felt reasonably tight so there is hope yet for acceptable compression.

But unfortunately there is a potential problem: When I rotate to crankshaft, the piston uncovers the inlet port completely but only comes down just over half way on the exhaust port. I checked all my measurements and I don't see any discrepancy from the drawings, so an email to Heinz to ask if my situation is correct. He said my con rod must be too long. Recheck and it is the correct length. Hmm.

I can think of two possible work-arounds: 1. to machine the exhaust side of the piston down so that the exhaust port will be completely open at BDC but by doing this the compression ratio will be lowered considerably, probably unacceptable without other modifications to restore the compression ratio

or 2. to machine a small half-round cutout in the side of the piston to achieve the desired result of getting the exhaust port completely open. This is my preferred option at the moment. Whichever way, the piston at present is about 100 thou too high.

Dave
The Emerald Isle

 

[Brian Rupnow]

Dave--I am following this thread. I will really be interested in what rpm your engine will run at. The clone I built of this engine runs well but the lowest speed I can run it at is about 900 rpm. I know that it is supposed to run at 300 to 400 rpm, but I think that is pretty optimistic.---Brian

 

[deverett]

Workshop time has been severely limited recently and will be for a few weeks hence. However, I managed to get an hour or so this afternoon.

Well, after some deliberation and without any other thoughts or suggestions, I went ahead and put in a cutout on the side of the piston. Before taking the piston out of the cylinder, I used a scriber to mark the piston where it covered the exhaust port. The piston was set up in the vice using the previously used method of passing a DTI along a bar in the gudgeon pin hole for alignment. Using a round nose slot drill I made the cutout 100 thou deep and 250 thou across to match the scriber mark as near as I could judge.


A quick try of the piston in the cylinder afterwards and it looks OK.

Dave
The Emerald Isle

 

[Blogwitch]

Hi Dave,

I know exactly what you mean about putting extra bearings in, so here is a chart I have shown before where you can easily determine if the two materials act well together.

Just follow the material selection down and across and where they meet, read the result.

John

 

[Jasonb]

Dave a lot of the model aero engines run without bearing material in the con rod, provided you use 2014 there should not be any problems. The 30cc lightweight 2-stroke I made is about the same size as your Hubbard and faster reving and that has no bearing material.

More of a problem may be stretching of the now thinner conrod ends if 6082 (HE30) was used.