# LONGBOY'S "JUSTABLE" MODEL GAS ENGINE!



## Longboy (Apr 21, 2020)

I got a phone call last month from "Bob Thomson" over at "NOR'WESTERN LOGISTICS"' They are a maintenance and infrastructure support company for the mining, lumber and oil industries and service U.S. and Canadian firms. He tells me that the little single, "Sentinel" engine I developed for them in 2010 was just ideal for their purposes. Durability, low service intervals and all weather performance. Asked if I would be interested in creating another with a greater capacity. Since I was wrapping up my build of the "Side Shafter" engine........I could most likely have a presentation built before Labor Day.

Starting soon, The Longboy "Justable" engine!

The Sentinel engine (2011)


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## Brian Rupnow (Apr 21, 2020)

Great looking engine. Just got to love all that brass and aluminum.---Brian


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## awake (Apr 22, 2020)

Very nice looking engine. Will the "Justable" be similar, just scaled up, or is that still a decision-in-process?


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## Longboy (Apr 22, 2020)

Same design language used for Justable.


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## Longboy (Apr 23, 2020)

The beginnings of JUSTABLE start with these two pieces. The 2 inch bore centerline cylinder head is a leftover from my first 2 cyl. engine, "GEMINI".  I couldn't get a center bearing to work by getting a proper line up of 3 bearings at the time. I duplicated a shorter cylinder head with 1.5 in bore centers and reworked a 2 bearing crankshaft and let a single long throw pin carry both con rods for that engine. Let the normal evolution of skill development take place in this hobby on later models.




On this head, the outboard holes for the head bolts are at 3.75 in. centers. The angle aluminum, left over from SIDE SHAFTER just completed, is 4 in. ! Now I can use this head on a project! With some .25 in. stanchions to mount the head to the deck, I have....." just enough room".....to mate these items and save a few days making another head!


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## Longboy (Apr 25, 2020)

JUSTABLE gets a three piece set of crankshaft webs. 










And the finished segments. There is one throw pin.....but three webs! Is JUSTABLE a single cylinder....or a twin?  Either way, are there the right number of crank parts here for a one or two cylinder engine....or too many, too few?    I'll let the forum play around with that question before the next posting.........


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## Longboy (Apr 26, 2020)

I'm trying out a hole saw on the deck for the cylinders, my original method before I bought a boring bar kit for the mill. Slow going with lube, the mini mill breaks circuit often if too much feed on one inch dia. and greater tools. Finished up with a basic China Special bore tool.








Barrel shape pistons with multi piece con rods tuck into the bores. Note the difference in the rod big ends between the two.




The camera's view alludes to a pair of over sized radiators upon the cylinder deck..... however they fit within the cyl. deck perimeter to bolt on the cyl. head. I had......"just enough room" to make it so.


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## Brian Rupnow (Apr 26, 2020)

I assume from the title of the thread that there is something adjustable on "justable". What is it?---Brian


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## Longboy (Apr 26, 2020)

Thanks Brian. There is nothing adjustable beyond a spark plug gap, ignition advance, carb needle setting or valve lash clearance. JUSTABLE's creation results from a series of circumstance around some leftover pieces that may never have come together due to tight spacing of its components.


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## awake (Apr 27, 2020)

I was thinking it meant "just stable" ...


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## Longboy (Apr 28, 2020)

Underneath the short angle frame piece goes the Tecumseh points. My favorite for their versatility mounting in tight quarters. The crankshaft offset from center of piece leaves little room on the outboard side to place them. Well.....I was "just able" to do such as you see. A ball hex wrench and 4-40 socket head substitute will allow access to adjust the gap easily.





A sample crankshaft stub with the points cam trigger through the bearing gives me an idea where the pivot point will be when the cam hits the rub block.





The spring and stud insulator stick out from the frame. The insulator will slot into a thin piece of hardware store angle aluminum and will make for easy connection with the ign.coil. Bolts up to the backside of frame tucked next to the bearing carrier. 





One other component goes onto the crankshaft, the cam drive. GOLLY!   ...it "just made it"!


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## Longboy (Apr 29, 2020)

I'm trying out and sticking with a new material for the valves.





From SPEEDY METALS with a full line of diameters of 12L14 steel rounds. Ordered some valve material as well as flywheel rounds at 3.75 and 4.0 inch dia. I'd say an easier cut than SS. No galling or chunking and a clean finish with no follow up treatment in the seat area of valve.









As for flywheels.  Still a chore. Slow going removing metal from large diameter stock on the mini lathe.


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## moose4621 (Apr 29, 2020)

Longboy said:


> He tells me that the little single, "Sentinel" engine I developed for them in 2010 was just ideal for their purposes.


I am interested to know what the purpose of this engine was, especially considering the company profile.


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## Cogsy (Apr 29, 2020)

Longboy said:


> I'm trying out and sticking with a new material for the valves.
> 
> 
> From SPEEDY METALS with a full line of diameters of 12L14 steel rounds. Ordered some valve material as well as flywheel rounds at 3.75 and 4.0 inch dia. I'd say an easier cut than SS. No galling or chunking and a clean finish with no follow up treatment in the seat area of valve.



I've never contemplated using 12L14 for valves as I'd be afraid of how quickly the stuff likes to rust. It'll be interesting to see if it causes you any troubles. I agree it's nice stuff to machine though.


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## Longboy (Apr 30, 2020)

Cogsy said:


> I've never contemplated using 12L14 for valves as I'd be afraid of how quickly the stuff likes to rust. It'll be interesting to see if it causes you any troubles............


Thanks Cogsy.  The fuel mix with WD-40 plus the combustion carbon coat has both valves "covered" for corrosion intrusion. For wet sump splash models, a dribble down the valve stem of lube should cover the top end for long term storage. I have flywheels in unpainted C.I. and steel as large external parts with no rust.........that's just indoor display conditions and you will be all right using steels for model parts fabrication!


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## Longboy (Apr 30, 2020)

moose4621 said:


> I am interested to know what the purpose of this engine was, especially considering the company profile.


Thanks moose4621.  There will be a "story" at the premier of the JUSTABLE engine!


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## awake (Apr 30, 2020)

Dave, it sounds like this might be the first time you have used 12L14? Yes, it machines like a dream; that's exactly what it is made for, with both sulphur and lead added to the alloy for just that purpose.

As Cogsy notes, however, it also rusts in a half-second, far, far more quickly than cast iron or 1018 or similar mild steel. And, just in case it ever comes up, it is not recommended for any sort of welding, as in, it will bubble up with all sorts of porosity if you try.

As you point out, the lubricant-rich environment may make its tendency to rust a moot point ...


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## Longboy (Apr 30, 2020)

awake said:


> Dave, it sounds like this might be the first time you have used 12L14? Yes, it machines like a dream; that's exactly what it is made for, with both sulphur and lead added to the alloy for just that purpose.
> ...................As you point out, the lubricant-rich environment may make its tendency to rust a moot point ...


Thanks awake.  I learned about 12L14 steel with it's lead content somewhere along in the forum years back and have been using this grade steel for crankshaft webs in 1.75- 2 inch diameter. Maybe the steel barons heard the call from hobby machinists to come up with this alloy!      Since crank webs are the only steel parts of size in my models that need cutting, drilling, thread tap and facing, I appreciate the difference in easy of working, especially on my tabletop machine tools which are a hair underweight working C.R.   Now trying 12L14 for the same reason with flywheels and the clean cut needed for valve faces.  The webs get steady droplets of oil from the bottom of the cylinders post combustion.


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## Longboy (Apr 30, 2020)

The lower deck piece is 2 x 2.25 in. surface. I need two items upon it, the cam drive and a distributor. 





The cam sprocket location is the difficulty here. 




I measure for an approximate position for the camshaft bushing through the vertical leg of the cylinder deck, go to my belt length calculator ( Timing Belt Calculator - Belt Length Calculator | B&B Manufacturing) and order a MLX 81 tooth. The arc in the upper left corner is my margin of position. It is  a 2 inch center line, crank to camshaft.
 If the belt is low to the left......I am running the lifters too close to the edge, right off the upper deck and with the belt upon its sprocket, the belt slot will be beyond the left edge of lower deck. 
If I follow the arc up and to the right, I'm running the cam lobes right into the underside of the upper deck.  Had to sit and think about this for awhile........and I got a solution!


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## awake (Apr 30, 2020)

Longboy said:


> Thanks awake.  I learned about 12L14 steel with it's lead content somewhere along in the forum years back ...



It's the Goldilocks problem of any on-line forum, especially for a relative newcomer like myself - am I assuming too little, too much, or just right? Fortunately, you were much more gracious than Papa Bear even though I told you something you already knew.


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## Longboy (May 2, 2020)

The best way was to pull back from the 2 inch crank to camshaft centerline.  Lower and to the right, under where I want the lifters to be. 





Belt slot will end before running off the deck and if too much slack in the belt, can reorder. Most likely a MXL78 tooth. 

Trying an idler to take up the slack now and it will work fine with the 81T belt. Locate with a couple of transfer punches and drill the frame.








One caveat with the choosen location of cam sprocket is its flange sits right on top of the short deck now. With a slitting saw, I milled a shallow trough in front of the sprocket to the end of the deck for the clearance. Trimming the flange back about .025 in. would have done the same..... but I was looking for adventure with the slitting saw!  

Still going to be tight under the lifters. So I re-bush the sprocket for a 1/8 in. shaft now. These cam lobes start form 5/16 in. 12L14 round stock secured with 4-40 set screws to their shaft. 
	

	
	
		
		

		
		
	


	



Back on the other side, I shorten the lifter guides to be flush with the cylinder deck underside and cut back the lifter heads so they have some space between the lobes and guides. Of course....I just made it!


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## Longboy (May 4, 2020)

JUSTABLE's distributor sits on the back corner of the short deck. Its bracket is a piece of the angle aluminum milled for the correct angle along the apex.





 With the camshaft at 1/8 inch through the brass bushing to end of sprocket, I need a 3/16 in. shaft for these 20T .5 mod gears. They come holed at 3-4mm and I re drill for this size shafting. An inch long piece is drilled the eighth inch and pressed fit over the cam shaft with some epoxy. There is a flat for the set screw under the gears.





These gears are tiny and on an eighth in. dia camshaft.......to prevent flexing and going outta mesh screwing up the ign. timing, an R166 bearing supports the tail end.






Now if you look closely!  (  not again Longboy). Oh yes.......the distributor gear........"just fits" between the sprocket bushing and drive gear!     (ah- huh  )


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## Longboy (May 6, 2020)

Can an overhanging crankshaft be developed for a 360 degree two cylinder inline engine? Perhaps best described has a hybrid as one crank throw supported in two webs, and the other crank throw.....not supported by two webs. What does that look like?

A third crank bearing is supported under the deck between the cylinders.  With two bearings in the vertical portions of frame, a transfer punch is inserted.




The bearing block is 1/2 x 1 inch stock.  A bearing cap bolted to its bottom, the butt joint is slightly below the crank center line for trimming up to the correct match up with the point on the transfer punch.




There is an Oilite bushing on the crank segment for this bearing block. The crank webs are assembled onto the crank segments with the rotating assembly. The front two webs are pressed fit to the shaft with the Oilite bushing with two thin SS washers properly spaced for some slight thrust movement and capped in the lead bearing block.




The bearing block shank has been reduced substantially as it is obviously too meaty in appearance here. The illusion presented upon completion is that JUSTABLE's crankshaft appears to be hanging out in space under its cylinders.


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## Longboy (May 8, 2020)

Working on the under framing. This set up not giving me enough clearance for the flywheel.





Going with a couple of skid members and transverse bars with the rubber feet.





Another week or so to go..........and then it looks like it is finished!  





Some changes, trouble shooting, photos and video.....and then!




"LONGBOY'S "JUSTABLE" ENGINE .........THIS WEEKEND"!


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## Longboy (May 10, 2020)

Welcome to Longboy's "JUSTABLE" engine presentation!





An inline 360 twin. 1x1 inch bore & stroke. 






Work began on JUSTABLE 1st week of March.





And completed 2nd week of April  (5 weeks)






Special features!  






Cantilever frame construction.






Projected floating crankshaft.


























See it run and thanks for following!    Dave.


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## ShopShoe (May 11, 2020)

Congratulations.

That turned out well and it seems to run nicely.

Thank You for posting.

--ShopShoe


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## minh-thanh (May 11, 2020)

Great engine and I like the sound of the engine . Congratulations !
thanks for shared .


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## awake (May 11, 2020)

Very nice!


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