Longboy's "FOREMAN" 4 cyl. model gas engine.

[Longboy]

Overhead cams, cam in block.....there has to be a middle ground for four stroke engines......right?  I got my FOREMAN engine done before it gets too hot in the shop as May temps begin to show up here! A short pictorial on its build highlights to follow the next few days.

[Perry]

What a teasing photo, more please

[Longboy]

Air cooled radiators on top of the deck with the start of their heads on top. Four 1 inch dia. DOM cylinders inside of them. Bore spacing is 1.875in. between cyl. 1-2 and 3-4 and slightly wider between cyl. 2-3 to accommodate a crankshaft support bearing. Individual rectangular profile heads to show a pronounced overhang to the cylinder centerline.

[Roger B]

As Perry said this looks to be interesting but there seems to be something strange in the way the pictures are formatted/posted. What I see is a very small picture in the corner of a large area with scroll bars suggesting that there is something more 

[Jo]

That's a feature of Photosuckit    If you leave the URL address in before the address of the image file it can do some strange things.

I normally delete that lot and just keep the image bit from [ img ] upto and including   [ /img  ]  (without the spaces)

Jo

[Longboy]

Showing a better view of the offset from combustion chamber to edge of head along with set of valves, guides and retainers.



Valves are made from ordinary hardware store grade 5 bolts!    They machine cut pretty well for the purpose.

[Longboy]

The heads have some common bolts shared between them threaded into brass studs fastened to the deck plate. Outboard cylinders heads use 3 and the inboard have 4 bolts.



The heads are drilled to receive a set of brass lifter guides opposite the combustion chambers. They are locked in with #6 set screws.......... "Lifters in the heads Longboy"? 

[Longboy]

Shown are individual cam lobes on .500 CR stock for my OVERTIME engine. On FOREMAN, I used .312 CR round. I find I can offset enough of the lobe stock to drill for a .1875 rod for the lobes and still have up to .100 inch lift valves with rocker arms at 1:1 ratio. Hand filed profiles to the lobes are easier as less material removal is involved then. 6-32 set screws tie the lobes to the rod and allow for a static variable valve timing on the rod.

[Longboy]

Mounts for the camshaft in the form of these towers sit on top of the deck and held in place with a 6-32 hex screw to the end plates.



The towers showing the camshaft with sprocket guard and distributor cap base. Sprockets are 25/50 MLX and the rotor is Delrin.

[Longboy]

The crankshaft is a 3 bearing multi piece build up. 12L14 steel, 1.625 in. dia. drilled down the center .312 in. and the crank pins are .250 in. Each crank half to the center bearing was done separately. A scribe line was dragged across the stock for orientation then needed lengths are parted on the lath. The crank ends are knurled and pressed onto the end webs. The center segment web pin is knurled and pressed with an Oilite bushing between the two webs as the center bearing.




Brass bearing carriers in each frame end plate holds a pair of R1810ZZ bearings completing the crank support. Bronze bushings for the rod big ends slip fit over the throw pins. The pieces are set back into the frame bearings, lined up and a series of #10 set screws lock the throw pins after rotational alignment of all segments for further bonding of the pins to webs. Looking at the throw bushings you can get another sense of the spread between bore centers here.

[Roger B]

An interesting crankshaft    How easy was it to keep it all aligned during assembly?

[Longboy]

Thanks Roger. The set screws will hold the crank components in assembly and line up in the frame. However they are not strong enough to grip the throw pins when starting or running. See further upcoming posts!
Dave

[Longboy]

A crankshaft with these drum style webs is going to be heavy compared to bar shape webs. All the crank webs and shafting added up to 44 ounces and with internal lightening ended up at about 32 oz. A lot of inertia spinning over with the drill on starting.



I felt that the the set screws are not enough here to hold everything in place. A kickback from too much ign. advance and other misfires in troubleshooting might be enough to shift the webs on their pins. The short web's throw pins are silver soldered. The pins with a reduced shank about a 3rd into the web to accept the solder.





The pair of long webs are locked in with Loctite 640 with the double set screws. If I ever have to service the con rod bushings a little heat will release the bond here then.

[mnay]

Great looking engine and beautiful work.
Is that your own design?
Mike

[Longboy]

Yes it is Mike. I build with no plans common engine configurations and sometimes unique looking models like this.
Dave.