Twin cylinder open crank marine engine

[kuhncw]

Dougie,

Thanks for posting your procedure for making rods. What is the porous surface you are using for silver brazing?

Nice work.

Chuck

 

[fourstroke]

Hi Chuck

The porous material is a burner plate from a gas fired commercial fryer, its made of some kind of ceramic.
I salvaged some from a unit I replaced in a Mcdonalds a few years ago. Its good for making ceramic burners for model boilers as it can be cut to shape easily.
Its also good for silver soldering as it reflects the heat and if I need to I can thread thin steel wire through the holes to hold parts in place while they are soldered

Regards

Dougie

 

[fourstroke]

Next, in the grand scheme of things, were the cylinder liners.

I didnt have any cast iron but did have some EN1A leaded steel, I posted a question on this forum and on the model engineer website asking whether this would be a suitable material for liners with alumimium piston and cast iron rings. The replies I got confirmed that this would be ok and a number of builders have used this setup without any problems.
So, the first few pics show the steps I took, the blank was drilled out to 1" dia then bored to a few thou under 32mm, the outside was turned a little under the 35mm bore of the cylinder casting to allow for the JB weld that will be used to seal the liner to the casting. The cylinders were honed to finished size of 32mm. Each liner extends from the base of the casting by 5mm.

Pistons next, simple, right?

Not quite.

On a "normal" IC engine, with an enclosed crank, the lubrication of the little end is usually by splash. In this instance, with an open crank, things get complicated ( well for me at least ).
I posted a couple of questions on this forum and the model engineer website asking how lubrication on this type of engine works for the little end, sadly no one replied with a solution.
So what I decided to do, and jump in here if my logic is wrong, was, instead of having the gudgeon pin fixed to the piston and free to move in a bush in the little end of the con rod, I have fitted the brass bushes to the piston and will fix the gudgeon pin to the conrod with a grub screw. I copied this from one of my full size vintage engines.
My thinking is this, it will be easier to get some oil into the ends of the gudgeon pin bushes from the oil that is fed into cylinder from the lubricator, rather hoping it would get to the little end via a series of holes drilled through a hollow gudgeon pin which was my other option.

The next pics are the pistons, some of them are "posed", after the fact, as during the machining the batteries on my camera packed in.
What I did was centre the aluminium bar in the mill vise, drilled and reamed to 5/16". I made a bush 5/16" od x 1/4"id, loctited this into the blank then carried out all the turning of the OD to 003" below bore size, cut the ring grooves, 2 for iron rings above the pin and one for an o ring just below the pin to help collect the oil and feed it into the piston bushes, I transfered this to the mill still attached to the parent bar, set it up square to the pin and cut a little flat across the pin centres, again to help collect oil.

The final pic ( sorry for the quality ) is one of the crank, conrods and pistons all assembled.

Regards

Dougie

 

[Mechanicboy]

On a "normal" IC engine, with an enclosed crank, the lubrication of the little end is usually by splash. In this instance, with an open crank, things get complicated ( well for me at least ).
I posted a couple of questions on this forum and the model engineer website asking how lubrication on this type of engine works for the little end, sadly no one replied with a solution.
So what I decided to do, and jump in here if my logic is wrong, was, instead of having the gudgeon pin fixed to the piston and free to move in a bush in the little end of the con rod, I have fitted the brass bushes to the piston and will fix the gudgeon pin to the conrod with a grub screw. I copied this from one of my full size vintage engines.
My thinking is this, it will be easier to get some oil into the ends of the gudgeon pin bushes from the oil that is fed into cylinder from the lubricator, rather hoping it would get to the little end via a series of holes drilled through a hollow gudgeon pin which was my other option.


Regards

Dougie

For a open crank case engine use the needle vavle type oil cup lubricator with sight glass to adjust amount of oil but can give a messy engine if fault adjusted or run with too little oil to wear out engine --> to check oil amount is correct: A little oil smoke from exhaust.

Wick oil lubricator can give give less messy engine and a little oil smoke out of exhaust pipe.

My engine with open crank has wick oil lubricator mounted on cylinder who give less messy engine. The wrist pin/little end of connecting rod is lubricated by oil from cylinder who is lubricated by wick oil lubricator. The big end of connecting rod is lubricated with oil can before starting engine, it's no problem for me. You can mount the closed oil cup with wick to give small amount of oil into the big end since your engine is not hi reving engine.

 

[fourstroke]

Thankyou Jens Eirik
Thats good information
Regards
Dougie

 

[fourstroke]

Hi,
Once I assembled the crank into the base I discovered my first problem. I had reduced the rear of the crank to 5/16" for the cam drive gear but hadn't reduced it further for the connection to the gearbox.

The first couple of pics are my solution to this. I made a couple of "jacks" from two M6 nuts and a short length of rod, these were placed between the webs to counteract any force from the turning, the end to be reduced was held in the revolving centre and very light cuts used to reduce the diameter to 3/16"

With this complete I decided to make a start on the gearbox. The base casting was returned to the mill and clearance cut in the rear supports.
The main body of the gearbox is made from a chunk of brass, two groves were cut along its base to let it sit into the main casting, the centre line was marked and the height of the crankshaft was transfered onto this from the crank end
From this centre the brass was drilled and reamed 1/8" for the drive gear, using the next two gears positioned with a bit of cigarette paper between each one for clearace, the lower gear centre was marked using a point turned on a short piece of 1/8" silver steel, drilled and reamed.

Another piece of brass was silver soldered to the top to bring it up to the required height and the top rounded

Six holes were drilled 1/4" around the edge for bolting bosses that are just short lengths of brass rod drilled through tapping size for 6BA, these were also silver soldered into position. The tops of the bosses were milled level then the top of the gearbox was cut from the base using a slitting saw

More pics of the rest of the assembly in the next post

Regards

Dougie

 

[fourstroke]

The first couple of pictures in this next lot show the main body of the gearbox set up on the rotary table to mill out the inside, once this was done a small block of brass was silver soldered onto the top. The access hole was milled through and the stud holes finished

The carrier for the two idler gears is made from two pieces of brass and two silver steel pins 1/8" dia. The assembly was silver soldered using tipex to prevent the solder sticking to any of the bearing surfaces.The input and output shafts have been increased to their final size of 3/16". The bushing is 9/32" od by 3/16" id, a couple of pics of the completed assembly are next, the gears are held on with washers and 1/32" split pins

The gear change lever is made from steel plate with a bush soldered into place to match the gear carrier. I made the detent pin from 1/8" square steel.
Shown in the picture is how I like to hold little square sections in the lathe using a pin vice, this saves changing chucks for one little job, this was faced and drilled for the pull rod

The compled lever is next, the little brass pieces are rivited and soldered on, the bush at the base has been split to clamp it on to the gear plate.

A few views of the completed gearbox are shown last, sealing bushes have been soft soldered to the ends of the shafts and the selector plate with the locating notches for forward, reverse and neutral fitted.

As always comments or suggestions always welcome

Regards

Dougie

 

[cwelkie]

You make it look so easy Dougie ... a sign of a master!
Very nice gearbox.
Charlie

 

[fourstroke]

As I said in my first post in this thread, the head pattern I made was wrong.
I'm now at the stage where I need the head casting to fix the position of various other components so I made a new one
This set of pictures show the new head pattern being made and then cast.
I spray the pattern with high build auto primer and finish it with clear laquer

For this pour, I bought some oil bonded sand, bentomix. I have never used this before but I was well impressed with how easy the patterns came out of the sand and how the finish is improved compared to greensand.
The last few pics show the casting straight out of the sand and then after it has been trimmed and given a going over with a wire brush
Now I just need to figure out how to hold the bloody thing for machining!!

Finally some pics of a switch I replaced in a grill, not engine related you might think but when I stripped it I got four pairs of contacts, each with a little tungsten pad and complete with their own flat spring. I'm sure they will come in usefull at some point
As always, comments or suggestions welcome

Regards

Dougie

 

[bmac2]

Hi Dougie
What can I say that gear box belongs in a gallery. Your silver soldering skills are amazing I’m not a member of the “slop on lots and grind club” but I definitely need more practice. The new head looks great. The finish from that petrobond / bentomix sure looks good.

 

[fourstroke]

Thanks Bob
The secret is tipex or some other correction fluid.
I paint it wherever I dont want the solder to run and it stops the flow in its tracks.
This works for silver or soft solder.

Dougie

 

[bmac2]

Actually I think my biggest problem is patents in my setup. I get frustrated trying to keep the parts aligned while heating them, practice, practice, practice. I’ve got some Correction fluid/Tipex but it’s getting hard to find most places only carry the correction tape.
Can’t think for the life of me why I never thought to try it with soft solder.:wall:

 

[fourstroke]

Now that I had a decent casting it was time to make a start
The base of the casting was ground smooth to give a level surface
The first pictures show the holes for the head studs being drilled then the top of the bolting bosses being brought to a level height

Next I made a double sided jig to hold the head while it was machined, its just a piece of 1/2" thick flat bar with slots cut in one side to clear the camshaft and tappet pillars, a length of 1" square bar is used as a spacer. The stud holes from the head were transfered to both, drilled through 6BA clearance and countersunk both sides, the head stud holes were tapped 6BA, this is just temporary to hold it to the jig

The head was screwed to the jig right way up to clean up the front face which will eventually have the inlet and exhaust cut into it, then it was flipped over and the lower side faced back, I had to remove quite a bit of brass to get under a lot of slag that had accumulated when it was poured, I reduced it from 21mm to 16mm thick

When I cast the head I included a couple of dimples on the base marking the cylinder centre position, I drilled and tapped these 6BA 5mm deep, the next pic shows why. I made a couple of ply discs that fit the cylinders tightly, these are screwed to the head and then the cylinder block is fitted to make sure I have enough metal left all round and to check that the head studs will drill and tap wthought fouling anything. This simple set up was used to secure the head while the stud holes were spotted through to the cylinder block.

The next post shows the progress so far
Regards

Dougie

 

[fourstroke]

The progress so far

I couldnt resist having a look at how the engine was shaping up now the head was half done
These pictures show things loosley assembled, I have, at the moment, two options for the flywheel, one in CI and one in brass. They are both 5.5" dia, I am thinking that it might look better with a 6.5" dia flywheel. So at this point I would like to ask for opinions of the members, brass or iron, 5.5" or 6.5"?
Will a larger flywheel let it run slower?
The engine stands 9" tall and 12" long
Comments welcome

Dougie

 

[kuhncw]

Dougie, your twin cylinder is looking great. A larger flywheel usually means higher inertia, and that will help the engine run slower. Brass has a higher density that iron, so large diameter and brass would be the way to go in theory anyhow.

I said "usually" regarding the inertia, because, as you know, inertia depends on where the material is relative to the center of rotation.

I'm looking forward to hearing your engine run.

Chuck

 

[fourstroke]

Now that the head position was sorted I decided to mark up the location of the camshaft drive gear bearing holes. I used my usual method of meshing the gears with a bit of paper between them for clearance, this time it was .003" thick.
Once the centres were scribed onto the base I clamped up the engine assembly onto an angle plate on my surface table to transfer the marks to the head casting. This done both holes were drilled and reamed 3/16" to trial fit the shaft.
Things might move a little when everything is eventually tightened up so a trick I use to avoid binding is to drill the holes in the base and head a little oversize, then I turn up the bearings proper with a good reamed fit for the shaft but make the part of the bearing that fits in the hole a litte undersize so that I can adjust the shaft to its perfect position with a good free running shaft and minimal bearing backlash then glue the bearings into their holes with epoxy

Next the head was marked up for the valve positions, spark plug and the cutout where the intake elbow will fit. The casting was clamped to the angle plate on its jig and the cutout milled, ( sorry about the shaky pic). Next the mounting faces for the fuel tank brackets were cut and finally the valve seat pockets and the spark plug holes were drilled, milled and tapped

Regards

Dougie

 

[fourstroke]

Next job was to cut the intake and exhaust passages. Again, the casting was set up on an angle plate and bolted to the mill table, the holes were drilled and reamed 3/16".
Now, here I have a question, the passages will be lined with some 3/16" od x 5/32" id bore tube for reasons that will become aparent later.
Will that size of inlet and exhaust passage be large enough for this engine?
Its 32mm x 40mm bore and stroke.
If anyone has an opinion or experience please say before I go any further.
My thinking is that the smaller bore will pull air quicker through the carb and intake tubes and help with carburettion.

With all the major holes in the head cut it was time to cut the water spaces. The rotary table was centred on the mill and the casting was centred on each bore in turn and milled. Apologies for the quality of the pics. First a slot was cut 10mm wide 2mm deep, next the slot was deepened to 10mm in the middle, 1/4" wide. This slot cuts through both the intake and exhaust passages and all the head stud holes.

This is where it gets complicated.

The inlet and exhaust will be lined with the brass tube mentioned earlier to seal them from the water, likewise the head stud holes will be sealed with short lengths of brass tube to seal the water passage and prevent leaks

Two brass discs were turned to a close fit in the head, parted off and marked up to be filed where the two met in the head casting. A bit of carefull filing got them both to size ready to be soldered into the head

So, before I solder everything together, has anyone anything to add regarding the diameter of the intake and exhaust passages?

Regards

Dougie

 

[xpylonracer]

Hi Dougie, like many others I have been following your excellent build article and must compliment you for your design and engineering abilities with even casting your own parts.
With reference to the port sizes the inlet pipe does seem small but as you say this will encourage the charge to speed up, because of the envisaged length there is likely to always be some mixture ready and waiting in the intake passage to pass the inlet valve.
I have searched the article again but can't see any reference to which fuel you intend to use, you do however state spark for the plug, what fuel will you be using ?

Emgee

 

[fourstroke]

Hi Emgee
thanks for the reply. I intend to use uleaded fuel or perhaps colemans fuel
At the moment I am thinking that I will increase the port sizes from 3/16" od to 7/32" od. Once the ports are soldered into place and the covers fitted to the water passages it will be impossible to increase the diameter but if needed I could decrease the diameter by sleeving another tube into the first
Regards
Dougie

 

[WSMkid]

Fourstroke,
This is my first contribution to the forum in probably 3 years but I spend about an hour a day on the site.

About your intake runners. When you mentioned your concern about there size I automatically thought about the old (Buick?) nail head big blocks. I have no personal experience but my buddy talks about them all the time. I digress. They had super small exhaust valves (comparatively) and produced fantastic low end toque.
With this being said I would think that if anything your small runners will help keep your idle low and smooth and for a running model (I have not seen a mention of putting it to work) this would be ideal.
I love the water space design in the head. I had never thought of doing anything like that.
I will be following along with the rest of the build like most others.
Fantastic work,
GJ