Longboy's "FOREMAN" model gas engine.

[Longboy]

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

 

[Longboy]

Top of the deck plate, four 1 inch dia. DOM cylinders inside air cooled radiators. Bore spacing is 1 -7/8in. 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.

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[Longboy]

A set of valves, guides and spring cages along with a better view of the head to cylinder offset.

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

 

[Longboy]

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

 

[Longboy]

A pair of cam towers sit on top of the deck and are mounted with one #6 hex screw to the end plates.


Smaller diameter CR round stock cam lobes. On FOREMAN, I am using .375 CR round stock. I find I can get enough offset drilling to receive a a .1875 shaft and have up to a .100 in. lift at the valve with 1:1 rockers. Hand filed lobe profiles are easier too on this diameter with less metal to remove.
Camshaft with sprocket guard and distributor base on the towers. The sprockets are pair of 25/50 MXL. Distributor 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.

 

[ozzie46]

Nice work,Longboy.
Keep it up.

Ron

 

[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 balancing 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 might be enough to shift the pins in the webs. 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 set screws. If I ever have to service the con rod bushings a little heat will release the bond here then.

 

[Longboy]

The points trigger cam resides up against the web and the end plate. Tecumseh points set at the end of the plate. A plunger rod in a brass carrier bearing transmits the action to the rubbing block on points.

Cylinder sealing at the heads is provided by an O-ring. The protruding end of the cylinder rises into the combustion chamber of heads. A tapered groove was machined into the top of the radiator to seat the o-ring, providing the squeeze against the cyl. on compression. On FOREMAN, I tried set screws to lock the cylinders to the radiators from the bottom. It didn't go well. The DOM cylinders are thin wall and the set screw deflected enough at the bottom of their stroke to choke the pistons at the bottom. I went back to previous practice and epoxied them together with just a light turn of the set screws then.Thm:

Valves are made from grade 5 hardware store bolts.

Where stainless, brass, bronze and nylon get together! Delrin tapper lock mounts the flywheel to crank. Stainless acorn nut for the starter drive. About a pounds worth of bronze flywheel. Found at a garage sale....I thought it was some discolored, dirty brass till I started machining the stock!

 

[Longboy]

All major parts fabricated and a static mock-up assembly a couple weeks before initial run in.

Figure out an intake and exhaust. Make a fuel tank, distributor wire loom....try to find a carb on EBAY and some paint work. My cog belt should arrive from China any day now!

 

[Longboy]

After paint..... Lookin' great in satin black!


[

 

[Longboy]

A block of Delrin was contoured into an intake with brass tubing into the heads. A Thunder Tiger carb is borrowed from another engine. The fuel tank shown here is too small for a 4 cylinder and will be up sized.

The manifold tubes are a light press fit ( by hand) into the heads. The porting into the intake valves is two stage drilling. Straight along in for the tubing and then a right angle into the valve guides from the side. Access hole in the sides of heads are sealed up with Permatex RTV then.
The translucent items on the tubes are silicone fuel line for model airplane engines. Slip over the tubing you use, measure its diameter and drill about 3/8th in. into the port for a positive seal to the head. I taper the fuel line putting the brass tube into a cordless drill with the silicone on the end. Spin it against the bench grinder and cut to length for a quick self guide install.

 

[Longboy]

"Zoomies" guide the exhaust stream from the heads. The port was drilled straight thru to the ex.valve guide. You see the valves on one pair of heads are reversed order from the other pair by the opposing diagonal insert into the heads. In setting the cams onto their shaft.....I did catch myself setting the exhaust timing phase for an intake valve.......but it gets worse than that!

Another look at this view below reveals that I have the heads reversed on cylinders 2 and 3. The clue is the wide gap between them. Somewhere along then I layed out the intake ports for these heads on the wrong corners!

A couple of aluminum plugs conceal the error on the intake side. The valve guide itself was not drilled here and covers the thru port mistake internally. Experts have determined that the cause was, " Continuing the project early the next morning....before the lead guy had his bowl of COCOA PUFFS"!

 

[Longboy]

Between the lifter and rocker arm go some "very short" push rods of piano wire. The knurled lock nuts here are a little short (.312 in) on diameter and were remade on some .375 in. threaded rod for a better finger/ thumb grip .
Flame tint steel rocker arms hang from brass hex stock.

CM6 spark plugs....the friend of I/C builders everywhere! Thm: Some shallow fins will be cut into the corners of the outboard heads for looks.

Finishing the front of the crankshaft is this door knob looking brass nose damper.

For the larger fuel tank a nice feature is a sight window. I'm looking up "glass disks" on Ebay and nothing much comes up. But if you look up "cabochons"......you're in to what you need. I thought a cabochon was some kind of weird seafood appetizer! Got a whole bag for like 4 buck$. The filler neck is from a miniature liquor bottle.

Electrics are done and FOREMAN"S build is complete! Thm:


Come in later for the showroom photos and the running reveal of FOREMAN! woohoo1

 

[Longboy]

Welcome forum members to the premier of "FOREMAN".

Built along the lines of my "OVERTIME" twin, Foreman was started 3rd week of October and finished the end of March.

A one inch bore and stroke, Foreman yields 52CC displacement.

A free standing engine, Foreman weighs about 12 lbs.

New feature.......The "underhead camshaft"!

But I don't expect any awards for this layout.

And after hooking up the battery and fueling....

....this is what you get!Thm:

[ame]https://www.youtube.com/watch?v=XXU9-uhhAj0[/ame]

Thanks for following this consolidated build log on Foreman's construction. Time for summer recess now! Dave.

 

[10K Pete]

Out freekin' standing!!!

Pete

 

[terryzilla]

Awesome! I love the sound.
I guess with the drum style webs on the crankshaft means you don't need much a flywheel. It's built in.

Terry

 

[ShopShoe]

I've been following along. You've done a nice job with this and it's nice to see it running. All the parts look basic, but show a fit and finish that proves you have been focusing on detail throughout.

I like how you've highlighted the individual features in the video.

Thanks for posting.

--ShopShoe

 

[Longboy]

Awesome! I love the sound.
I guess with the drum style webs on the crankshaft means you don't need much a flywheel. It's built in.

Terry

That would probably double the idle speed without some bulk of the flywheel. Dave

 

[Blogwitch]

Dave,

What a wonderful journey.
It started off fairly slowly, but once you got a few of the bits made and put together, people started to take notice, until now, where it becomes a must read article.

You have made a very nice engine indeed, not too complicated, so even someone with a little machining experience could take it on, and it runs absolutely fantastic, not a single missed beat despite running rather slowly.

Very well done and I hope it gets recognised as an engine of the month contender.

Just one criticism, every time I watched the vid, I expected the camshaft to bend like a banana because of no central support, but it looks like I thought wrong.

Great project and result

John