Longboy's "BEST FRIEND FOUR" model gas engine.

[Longboy]

Flathead engines, an old design from the onset of internal combustion. Most notable characteristic is its cylinder head with nothing more than the spark plugs rising up from its surface. No camshaft or rocker arm assembly on top, its low profile stance calls attention to its named type. Valves in block along side the cylinders furnish the breathing.....except in this example! ( ...where did you put those valves Longboy?)

The Best Friend Four story coming up now!

[Longboy]

Here is a photo of another modeler's (PARKSY) crank cradle. Made for his steam engine, I felt the same could be used under a gas engine for my winter shop work. A block could be supported over this cradle by posts or a gantry set up in a change from how I have framed up my engines.



Here's my copy of Parksy's cradle.



Bearings and webs in brass, the aluminum cradle is 2 in. wide.



And in Satin Black!

[Longboy]

The crank cradle supported by a pair of slight S- bend raised cross bar stock. A set of motor mounts from aluminum angle are bolted to the block and join the bar stock legs using 3/8 in. rounds.



The block will get a set of .065 wall DOM cylinder liners of a 1 in. bore.

[90LX_Notch]

Following along Longboy.

-Bob

[Longboy]

With a billet piece of aluminum for the block I get to use my new boring head on this project. I'll be using 1/4 in.width bar stock for the connecting rods here which allow me to reduce the bore centers to 1-1/2 in. This is a half inch less than my FOREMAN engine where I used longer webs and 3/8 in.width con rod stock.



I bore the cylinders with the block bottom upright in the mill to accept the liners at a finger press fit and overbore here .040-.050 about 1/4 in. deep for a film of epoxy to bond in the liner with the block to the correct position later when the combustion chamber is bored into the cyl. head. The epoxy at the bottom of the cylinder is far enough away from the combustion chamber where engine heat would not soften up the bond.

[b.lindsey]

Nice start, and should be a fun build. Do you have a sketch of where you are hoping to end up appearance wise?

Bill

[Steamer5]

Hi,
 Ok pulled up my chair,  at the ready.
Nice work so far, keep it coming.

Cheers Kerrin

[Longboy]

Nice start, and should be a fun build. Do you have a sketch of where you are hoping to end up appearance wise?

Bill

Thanks Bill. No sketch-ups here. There will be some unique features that I haven't seen in models paging thru forums and Google images for BEST FRIEND though!

Dave

[Longboy]

The Chinese special boring bar makes a tapered groove around the cylinders for the O-rings that seal the cyl. head to block.




What looks like the beginnings of a water cooled engine was not to be. The mini mill doesn't allow a 6 inch long block to fit under a boring head for making the water jackets. BEST FRIEND will be air cooled!








Some finning can be machined into the side of the block for ambient heat rejection....but I will be using "cladding" instead.

[Longboy]

Trying something different here. On Ebay, you can find heat sink material in various sizes. Always in hardware store grade aluminum, it is easy to cut and shape.



Choosing some 3-48 SS screws to bolt to the block, they can also be bonded in place.



There is room for another row between the motor mounts if needed. The same can be used for cooling cylinder heads. These are listed in mm. sizes, on BEST FRIEND they have seven 3/16 in. fins and are nominal 3/4 in. width.

[Longboy]

The single piece cylinder head combustion chambers are bored 1/4 in. deep. The 10 mm. spark plug holes for CM-6 plugs are upright center.



Four head bolts per cylinder and intake/ exhaust cross flow porting drilled into head. Later the head will be decorated with some contouring /finning.



The liners are placed into block with their O-rings and then the head is mounted and torqued down. The liner bottoms out at the roof of head chamber and a reference mark is made where the liner is to be epoxied in the block with about .020 clearance from the chamber roof. Through the head porting, the liners are now through drilled into combustion chamber.



  A concern of mine is that the porting is drilled low in the combustion chamber just above the O-ring. Hot exhaust may penetrate the gap between liner and block deteriorating the seal then. The solution is to bridge the gap with a tube installed into the port through the liner if needed. On this test piece the liner is ground through to the hole so the cyl. head with tube protrusion can then be dropped down upon the block then. This can be done while still installed in the block. 

[Longboy]

The cradle, block and head pretty much completed, the body is there. Now ready for some internal organs to come and external appendages!

[zeeprogrammer]

Nice picture!

I'm not saying much but I'm following along. 

[Roger B]

Following along in the background    The use of commercial heatsinks is an interesting idea 

[Longboy]

Points ignition working well for me and so equipped is BEST FRIEND. A change here to Kohler engine points. Brian Rupnow found these pushrod actuated points.....I'd thought I would try them out. Mounted to the front of the block they are crankshaft triggered.



The elephant faced brass piece is the pushrod guide. A tiny steel barrel sits on the rod against the points rub block and a brass barrel rides the points cam on crankshaft. The condenser ended up later under one of the screws on the end bearing block.




I find that the Kohler points has extraordinary stiff spring pressure for model engines. I radiused the flats on the points cam and sphered the bottom of the brass barrel for a softer ride over on the cam. Also with a needle nose pliers bent the spring to take some pressure off and it rides
well now.

[Longboy]

The very basic barrel piston and a plain shape connecting rod fabbed from 1/4x 3/4 aluminum bar. I don't find Viton O- rings in my size at Ace Hardware. A plumbers O-ring made from....black stretchy stuff, makes the seal.



A pair of R144ZZ bearings ride in the small end. In a tutorial by Brian Rupnow, he mentions aluminum con rods can be their own bearing riding on the crankshaft throws. This would allow narrower 1/4 in. bar stock to be used. BEST FRIEND uses 3/16 in. throw pins and the 3/4 in. wide stock can also run on 1/4 in. pins using 4-40 rod cap bolts.

[Longboy]

On each side of the cylinder head will be the valve blocks mounted in outrigger fashion. On the ex. side, a strip of painters tape on each block face, some RTV sealant and eight ss 3-48 screws hold it together. The exhaust block is 9/16 in. wide and the valve guides are 3/8 in. and it was difficult putting on the RTV around the guide without contaminating the valve head or guide face tightening the screws down.  After about 3-4 tries, it was leakage free.



On the intake side, I tried furnace tape on the faces.....it was too thin. I went to some .060 gasket paper with RTV.......still leaks.  The gasket paper would get saturated with fuel and on compression stroke, would foam out between the two pieces! Not much margin here either from valve guide to edge of bar stock....and the screws are tightened.  Would have to find sheet rubber gasketing, remake using wider bar stock.....or sum-tin else.

[Longboy]

The valves are stainless in brass guides and the block has enough room for my solution.



Some 1/2 x 3/8 in. O-rings will have enough support on the block!
The guides were removed and a seat around their perimeter was cut in for them...



..and they leak no more!

[Longboy]

Another area that has to be leak free is the porting between the cyl. head and valve blocks. The brass tubing is blue Loctite in head but I want the valve blocks removable from head.



A set of eight collars for both valve blocks were made with O-rings to slip over the tubes. Three 6-32 bolts draw the blocks up to the head against the collars for the seal. The tubes do not penetrate the valve block port too deeply, the valve guides are close to the edge of block.

A side note with this valve arrangement is the porting volume, from cylinder to valves, becomes part of the combustion chamber volume for figuring the compression ratio. In BEST FRIEND, that would be 2 inches of 3/16 in. diameter porting between cylinder and valve guide per cylinder or .901cc.......ah, just forget I mentioned it.

[Zephyrin]

I find that the Kohler points has extraordinary stiff spring pressure for model engines...

I dont know for this type of points, but I agree that all commercial points I have found are all very stiff. However, in my last engine, a 8 cm3 mono 4 cycle , with a contact breaker from a moped, it worked perfectly without modifications, contrary to the many homeshop made points i did, with too weak spring giving lots of misfiring...

A great thread to follow, thanks to share.

[Longboy]

I find that the Kohler points has extraordinary stiff spring pressure for model engines...

I dont know for this type of points, but I agree that all commercial points I have found are all very stiff....

A great thread to follow, thanks to share.

Thanks Zephyrin. I've been using these Tecumseh points set on my engines and will continue. Pretty compact, they tuck up around the cam trigger and the spring tension is right. Part # 30547.

[Longboy]

The cam drive is a pair of 20/40 MXL sprockets using a .25 in. belt. There are tooth belt calculators to determine the number of teeth needed for your set-up. I use this one!
http://www.bbman.com/belt-length-calculator/.



The cams just keep getting smaller! I'm using a 1/8 in. ss shafting with 5/16 in. cr lobes. This is the smallest I can manage for cam making stock.
Easy to hand file the profile after a couple passes under the mill creating the ramps. 4-40 set screws lock the lobes to shaft.



The lobe shows plenty of lift at around .085 in.

[Longboy]

The bucket lifters are threaded to the valve stems and evened out to same level. Valve lash is covered then by moving the camshaft up to the lobes, the mounting brackets for cam are slotted.
Initially the shaft would flex on valve spring compression, the span between bearings is over 5 inches. The ex. valve springs here were rewound using .020 piano wire to eliminate that issue, the .025 wire used too stiff. Another solution would be an added center shaft bearing.......but the Budget Dept. memo'ed back that there was no funding for that.



A distributor cap base and sprocket guard are mounted to the camshaft brackets using a pair of 3-48 ss screws. R144 ZZ bearings support the shaft in the brackets.

[Longboy]

A candy bar's worth of Delrin becomes the intake tract for BEST FRIEND. Is the best material here since mankind crushed rocks to make aluminum.   The cyl. head sculpted now.



A 1/8 in. brass modified plumbing elbow mounts the OS carb on top of pendulum. I really didn't care for the carb right angle stick-out. What to do.....

[Longboy]

Turning the carb 90 degrees and swinging it over the intake gives a better integrated look. The fuel metering needle screw now over its top and the fuel line will tuck in between manifold and valve block.



The finalized intake was trimmed to width then. It is just a thumb press fit over the valve block port tubing.



The exhaust pipes come into the ex. valve block at an angle. I want to assure the forum that only the best quality steel shafting..... ever to be found in a Korean made VCR..... was used in their development!



This is BEST FRIEND FOUR's story.  Coming next will be the studio photos and the running reveal.    See you there!    Dave

[Jo]

  looking forward to hearing her go Vroom, vroom.

Jo

[Longboy]

Welcome to my presentation of the BEST FRIEND FOUR flathead engine.



The block and cylinder head were started back in July.



Work was set aside for the cooler days of Fall & Winter then.


Completed in February.



Being different with outrigger valve blocks.



And re-purposing electronics items for engine radiators.   




And now....see how to burn a bottle of Coleman Camp Fuel in four easy cylinders!    Thanks for following along!     Dave.

<a href="https://www.youtube.com/watch?v=2bRFujsk8LU" target="_blank">http://www.youtube.com/watch?v=2bRFujsk8LU</a>

[Admiral_dk]

Nice engine and a very easy starter 

[Flyboy Jim]

Fantastic!  I love how the moving parts are out there in full view.

Jim

[vcutajar]

Congratulations.  A great runner.

Vince

[fumopuc]

A very nice runner. Congratulations.

[zeeprogrammer]

Wow! That didn't seem to take very long. Seems like yesterday I began watching.

Congratulations! Very nice model. 

[Roger B]

Excellent runner    Well done 

[mike mott]

An interesting engine and looks like a good one to experiment with.
Congratulations on the run.

Mike