Twin cylinder open crank marine engine

[fourstroke]

Hello again

I thought I would share with you my latest efforts, as the title says this is my version of a twin, open crank, marine type engine. It has a 32mm bore and 40mm stroke. I'm going to call this one "The Mariner" as the aluminium for the castings came from my late fathers greenhouse frame who served 12 years in the royal navy
It seemed like a good use for the metal but it has proven to be a bit "chewey" when machining

The patterns were made and the base and cylinders cast in aluminium, the head was cast in brass, it took two attempts to get the head right but then I ran into my first problem. If you look at the picture of the head drawing, it was designed with 5 holding down bolts, a close look at the head pattern and the finished casting will show that when I was in my shop making the pattern, the number of holding down bolts increased to six!!
Normally this wouldn't have been a problem but as I plan to hollow out the head for water cooling then this put one of the studs directly over the exhaust passage and complicated things too much. Also the finish on the casting was far from ideal, fortunately I have had an offer from a member on here, Abby, to make me a new head casting so a new pattern has been made

The first few pics are the patterns in the raw and then painted with high build auto primer, the finished castings are next along with some pics of the cylinder core followed by the drawing of the head showing how it should have been made

The base of the cylinder casting was filed flat and it was clamped to the mill table to make a start on machining. The top was skimmed to level it then it was flipped to take the base to its final thickness. Once the centres for the cylinders were marked on some plywood and lined up the holes for the liners were bored and the top cut to final thickness. The casting was bolted to an angle plate to skim the cylinder bosses, the two on the front are for mounting the carb, the large rectangular one will be the mounting plate for the magneto and the final round one on the end is the water inlet

Enough rambling for one post, enjoy the pics and as always any comments, thoughts or suggestions will be appreciated

Regards

Dougie

 

[kuhncw]

Dougie,

Thanks for posting your progress on this very interesting engine. It should be a real chugger with the 32 mm bore.

Could you please post a link to a photo of a full engine like the one you are modeling?

Chuck

 

[fourstroke]

Hi Chuck

This engine is loosley based on the frisco standard engines I saw on the net
I have made mine more freelance than copy but something like this

Regards

Dougie

 

[kuhncw]

Thanks, Dougie. I've seen a running model Frisco at our NAMES model engineering show. It is a nice model.

My hat is off to your fellows who make your own patterns and pour your own castings.

I'm looking forward to seeing your build as it progresses.

Chuck

 

[Cogsy]

Your castings look great and it's obviously too late for any advice, but I have vastly improved the machinability of random aluminium casts by adding around 3% copper by weight to the mix. I have no idea what it does to the rest of the properties of the metal but it does reduce 'chewyness'.

 

[fourstroke]

Hi

The next stage involved machining the base casting.
The bottom was trued up with a file and belt sander till there was no rocking when it was placed on a flat surface. Clamped to the mill table, first the bearing surfaces were brought to height followed by the pads for the four corner pillars and then the pads where the cam driveshaft bearing and water pump will be fitted
The extension to the rear of the casting is where the gearbox will go and these mounting surfaces were machined as well. The bearing caps were held in the mill vise by the spigots cast in to them and the underside machined to size, these were drilled tapping size for 5BA and the caps were glued to the base while the holes were transfered then tapped. The caps and base were cleaned of glue then fitted together to mark the crankshaft centres

Now, the next operation was a first for me, I have never machined anything clamped to the lathe cross slide before. There was a lot of measuring, marking and measuring again to get everything lined up. I made a base from some 10mm plate bolted to the cross slide and mounted a couple of box section peices that had been milled to give the correct centre height, the box section and the casting were secured with some home made clamps as nothing else I had gave me enough clearance.
The casting was lined up against centres in the tailstock and headstock, clamped as tight as I could get it and the first bearing pillar was centred, drilled in stages, then reamed 12mm. This was done as I made a centre drill from 12mm silver steel that would be long enough to reach the last pillar furthest from the chuck and the first bearing hole was used as a steady for the second and consequently the third.
I used a long drill to open up these holes to a tad under 9/16 then a long reamer to finish the holes to size.
At this point I breathed a huge sigh of relief that the whole thing had went witout a hitch. Before the casting was removed the holes were counterbored wilth a 3/4 cutter I made to allow the bronze bearings to clear the taper on the pillars

Enjoy the pics, more details of the split bearings in the next post

Regards

Dougie

 

[fourstroke]

Most of this work was carried out over the christmas holidays when I had some time off.
There is normally some point in a build when I realise I dont have some material I need and this was it.

I wanted to make the split bearings but had no bronze bar and with it being the holidays, no chance of getting any. What I did have was a 4"dia bronze bar that I, ahem, aquired, a few years ago. Needs must so I cut two 13mm slices, machined one side of each flat and soldered the two together.
From this I cut a 26mm square section across the mid point to give me the bearing material
Mounted in the four jaw chuck this was drilled and reamed 1/2", then the outside rough turned round.
This was then loctited to a 1/2" shaft, mounted into my collet chuck and the three bearings machined to final size with a parting tool.
Once split into seperate peices they were mounted on a short spigot to face to final width, the black electrical tape is to hold the halfs together as at this point they had been split
The final picture is the trial fitting of the bearings and the silver steel that will become the crankshaft
As always, comments or advice appreciated

Regards

Dougie

 

[cwelkie]

Beautiful work Dougie!
This will a very nice project from concept through patterns, castings and machining.
Very impressive!
Charlie

 

[10K Pete]

I really like the bar for the center drill. Great idea! On the reamer; did you
make the pilot or buy the reamer that way?

This is going to be a great build to follow!

Pete

 

[fourstroke]

Hi Pete
The reamer came fom my favorite tool store, Bill's Tools in Glasgow.
I bought it as it is, I have no idea what it would be used for originally but this store sells lots of second hand tools, frequently ex MOD, and often like this was, unused.

I have had it for a year or two and bought it with no idea what I would do with it till this project came along

Regards

Dougie

 

[10K Pete]

Thanks Dougie,

The reamer is so perfect for the job I just had to believe you made it. But
it was fate!! I think that's why we collect things; just in case....

Pete

 

[bmac2]

Hi Dougie, Great work. I’m looking forward to following along and have my chair pulled up and the kettle on. I hope you’re not getting hit with any of the nasty weather I’ve seen on the news.

 

[fourstroke]

Hi Bob,
Nice to hear from you again, how is your whippet build coming along?

Like Bob says we have had a lot of rain here lately and December temps of
13 Deg C. I suffered from a persistent leak in the shed roof that drove me mental, eventually I traced and fixed it

The next stage in this build was the crankshaft, this method may have been described here before but this is how I make all my cranks.

A length of 1/2" silver steel was reduced at one end to 5/16 to take a helical gear salvaged from an earlier abandoned project. Four pieces of 10mm plate were cut, glued together to make pair of blanks and machined to a finished size for the crank webs, these were clamped to the mill table, drilled and reamed 1/2" for the crankshaft and 10mm for the crankpin. The ends were rounded and the pairs split, each web was machined on the rotary table to cut the clearance of 1.5mm needed for the taper on the bearing pillars and cutouts on the base casting
The next picture shows the "kit" of parts needed to complete the crankshaft

The shaft was set in the bearings on the base and the first web was glued into position with 603 loctite, next, using the centre bearing as a spacer and a flat plate as a base the opposite web was glued at 180 deg fom the first. Leaving these to set for a bit, each matching web from the respective pair had the crankpin glued into position. After a few minutes each web and pin assembly was slid onto the shaft, glued and slid into its final position using a short length of 10mm rod to give the correct spacing for the con rods.

The nearly finished crank is shown next set into the bearings, complete apart from the pins and central parts of the crank still to be cut out.

Finally after letting the loctite set properly the webs were drilled and pinned using 3/32" selloc pins, the central parts of the crank between the webs were cut out with a hacksaw and the ends smoothed in the mill. The finished crank is the last pic, the holes for the pins will be filled and smothed over later.
Regards

Dougie

 

[bmac2]

So far the only tricks the Whippet knows are “Sit” and “stay”, living in a box on the shelf. Between my wife’s family and my own, almost all the birthdays and anniversaries fall between the end October and the end of January. Toss in Christmas and New Years and I have three months each year of limited shop time. I’ve started to get set up to do gear cutting but for now I have to live vicariously through everyone else’s work.;D

The crank looks great. With all the reading I’ve been doing on gear geometry that little helical on the end gives me a shiver :hDe:.
Thanks for posting . . . Bob

 

[Longboy]

This surely is a beefy crank and throws for it's displacement. Will you be going for a low RPM torque cam profile for a marine application? I can't help but wonder if there is a project vessel your engine will power down the road.

 

[fourstroke]

Hi Longboy
I dont know anything about cam profiles for specific aplications, as usual, on this build, I will decide on the lift I want and simply file the cams to a point to give that effect
I know its not scientific but it works. I am hoping for a low revving engine but dont envisage ever putting it into a model boat, sometimes they sink

Regards

Dougie

 

[maury]

FOURSTROKE, a couple of things.

First, Very nicely Done! The castings look great and it looks like you are modeling castings everywhere it is possible to within reason. This will be a big plus on the final model, and the looks will give the appearance of the original.

Second, it is quite gratifying to me to see there are still a few in the model engine hobby who are willing to take the time and effort to make castings for their models. I commend you on the nice work, keep it up and help teach others to follow in your steps.

maury

 

[fourstroke]

Thanks for your comments Maury, I appreciate it.

So
With the crank made the logical next step was the con rods

I turned the taper on the central part of the rods from 1/2" steel, EN1A leaded, then drilled and tapped the lower end 6BA. A piece of 1/2"x1/8" was drilled centrally and countersunk, these were fluxed, screwed together and silver soldered, the first picture is one of the rods ready to heat.
Once this cooled it was transfered to the mill to cut the flats for the litte end, clamping the flat bar to the mill table ensured that the flats for the piston pin were paralel to the big end bearings

The bearings were made from 1/2" square bar, the ends were cut with a slot drill to let me solder the 1/4" round bar to the ends to make the brasses look like castings, the two halfs of each were glued together and the stud holes spotted through to the bottom half, these were drilled and tapped 6BA. The blanks were glued square to the conrod and the stud holes spotted through onto the con rod base

The next few pictures show the bearings bolted to the rods and ready to have the big and little ends drilled and reamed. Once this was done the brasses were clamped to a stub of 10mm steel in the lathe to reduce the main body of the bearings to 8mm wide and leave the central round boss a shade under 10mm wide, I used some electrical tape on the 10mm stub to give the bearings something to grip
The last job was to mark the width of the brasses onto the base of the conrod and mill them to match. The rods were then split from the parent bar and the ends of the rods rounded using a pin in the rotary table chuck and turning the rods by hand
A finished rod is the last pic

As always, comments or advice greatly appreciated
Regards
Dougie

 

[xpylonracer]

Pete

I have some very similar reamers, mine were used for finish reaming the kingpin bushes on car steering components and have 2 sets of cutting flutes with a reduced diameter part in between, the width between was the distance between the top and bottom bushes on the part.

Emgee

 

[10K Pete]

Pete

I have some very similar reamers, mine were used for finish reaming the kingpin bushes on car steering components and have 2 sets of cutting flutes with a reduced diameter part in between, the width between was the distance between the top and bottom bushes on the part.

Emgee

Yep, that application makes sense. I've never owned a reamer like that, but
I have put a home made long dead center in the tail stock with the point
in the center drill of the standard reamer. Worked pretty well though
not quite as rigid as the one piece.

Pete