# Longboy's "OVERTIME" I/C Twin!



## Longboy (Dec 25, 2014)

About 3 yrs. since I built my first I/C twin engine. My "GEMINI" is a good start but I want another crack at an inline twin to address a couple of shortcomings in its build. Can I make improvements in service, durability and add a new feature using basic machine shop know how and NO PLANS  in the same scale? scratch.gif .....The story of "OVERTIME" starts this weekend!


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## Longboy (Dec 27, 2014)

With this engine being an open crank style, a 4 piece frame is the backbone of Overtime. Two end plates, a deck plate and base plate. The deck is overlapped to the endplates and the endplates are overlapped to the base. Eight, 6-32 socketheads holds it together. For servicing you can remove the deck with all top side components as a unit and either end plate for access and removal of the crankshaft. A couple of brass bearing holders for each end plate will be the crankshaft support. I'll be using Oilite bushings here, 3/4 inch long ( 1/2 in. shown). More bearing area than a set of roller bearings that also will work fine, just builders choice here!


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## Longboy (Dec 28, 2014)

A brass flywheel is secured to the crankshaft with a taper collet made from Delrin. A 3 screw retainer makes the press fit or actually draws the flywheel into the collet. This 1st collet was too short, didn't get the grip and a longer one was made without the split and tried out...the right length worked out better! The Delrin seems to compress enough without having the split down its side.


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## Longboy (Dec 29, 2014)

A fabricated 5 piece crank starts with 12L14 steel. A generous length of each web 5/8in. long for heft and support of a 5/16in main shaft and 1/4in throw pin of stainless round stock. Drilled & reamed as one piece then parted to length.


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## Longboy (Dec 30, 2014)

The webs are internally balanced to the piston/rod assembly. Two half inch through holes at 5/8 inch yields a hair under 1 oz. of removed material.


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## Longboy (Dec 31, 2014)

The shaft is joined to the web by press fit. A straight knurl gets the bite into the web. Some cold bonding agent, either thread locker or Epoxy, supplements the primary grip of the knurl when driven in. After pressing, the assembly is chucked in the lathe. The shaft is paralleled to the web with some light taps and the assembly is then set aside and repeated for the other side.


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## Longboy (Jan 2, 2015)

The weak link in a 360 Deg. crankshaft for two bearing inline twin is the throw pin. Its long and narrow and joins the heaviest parts of the crank. I used 1/4in. stainless round here, upsized from my GEMINI engine.






The pin is locked to the web with a 10-32 set screw instead of being pined or silver soldered to the web. The pin has to be removable as I am using roller bearings on the rods.


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## Longboy (Jan 4, 2015)

In the big end here I'm using FR168ZZ flanged bearings. The rods are beefier than need to be for scale to accommodate the 1/4in. stainless throw pin and hold the bearing. The flange makes the bearing support slightly broader around the pin and also shows more rigidness in the 90deg. relation of rod to crank. You want some lateral float for the rod on the pin between the webs. 











 In the lathe the throw pin is reduced in diameter a couple thousands by file between the lines here where the rod runs on the pin. Area is cleaned up with 400grit carbide paper and now the rod will "walk" between these lines.


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## Longboy (Jan 5, 2015)

The con rod starts out as a piece of 3/8in x 3/4in aluminum bar for the big end and 3/8in AL. hex stock for the piston end. The beam is hollowed by a tap drill for 6-32 threads and a stud joins the hex to beam. With two pieces the final beam length of the assembly will be determined later. R144ZZ bearings in the hex join the piston with a 1/8in pin and locked in position with 4-40 set screws. In this mock up I have a "too" long rod that would make a Diesel cry out. The beam is unscrewed from the hex end and shortened to where the piston rises to the top of the cylinder at this time. 






 Components are then scaled in to aid in the counter weighting.


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## Longboy (Jan 6, 2015)

Doing the static balancing here, you can see a 3rd crank web member between the con rods. Saw this on an Italian modelers twin engine. Don't know why its there but I had to have it and esthetically keeps the continuity of the crank webs the whole length of the crankshaft now. Internally lightened about 50% and is locked to the throw pin with 2 set screws. For balance note the neo magnets on top of the outboard webs. The weight of a couple of nuts completes the balance. I weigh the nuts (do not weigh neo magnets) and take the weight reduction externally at the nose  damper. Looks like I need a near half OZ. 











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 And ready to roll.


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## gus (Jan 6, 2015)

Hi LongBoy,
Gus will be following this thread. Your engine is on my KIV build list.Am about to jump in to build the Howell V-2 Engine.


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## Longboy (Jan 7, 2015)

Thanks Gus. Even though I build without plans there will be many photos of Overtime presented so others who want to tackle their own version should be able to get a good start.Thm:


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## Longboy (Jan 7, 2015)

I make camshafts by pieces. Starting out with 5/8in CR round in the lathe with one jaw shimmed (or a jaw offset in chuck) and drill for a 3/16in. shaft. Your amount of offset will determine the baseline lobe lift.  I'll be using a prototype lobe with the engine and will need to make 3 new lobes. Dye the end of shaft and I put my lobe on a short length of shaft, insert into new stock and trace the profile to new stock. 











With the stock overhanging in the machinists vise, in 5 steps ( each side of lobe nose) mill to the scribe line your rough profile. 






 This what it looks like. The shaft is cut back between the lobes for part lines and to drill & tap for a 6-32 set screw to lock the lobes to its shaft.


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## Longboy (Jan 8, 2015)

In the bench vice file over the milled facets to blend into a traditional shape finished lobe. You can get them perpendicular flat to their shaft by filing without being machine cut perfect and they will work fine.






Without a degree wheel the only thing I can check is the lobe lift running the profile on the lathe. Shows .180in lift here but for its duration, do I have a race profile.....or a RV profile? 
	

	
	
		
		

		
		
	


	




 Looking for a smooth idler I will have to wait till assembly of Overtime and see the relations of valve open duration to the crank degree position.


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## Longboy (Jan 9, 2015)

I had two pairs of timing gears available for Overtime. Using the larger dia. set of the two, I set the meshing using a transfer punch into the bore of the cam drive and finger spin. Then make the mark and drill both end plates for the camshaft bearings......it was shortly later I saw reasons that my cam to crank centerline would be too close together. My "added feature"(  whats Longboy up to !) would interfere with the nose damper. To set the cam farther from the crank I ordered some Delrin idlers and then used my smaller diameter pair of gears. 
	

	
	
		
		

		
		
	


	




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The deck plate then had to be shifted over toward the cam side so the lifters would be over the camshaft . Since I didn't have the deck bored for the cylinders yet, it was a minor operation.


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## Longboy (Jan 11, 2015)

On top of the cyl. heads go a pair of rocker pedestals. 3/8 x 3/4in brass bar is free style cut to something that looks like it will work  with a roughing mill and a clean finished mounting tab that screws into the side of the heads. Its pattern is traced onto the bar stock and the duplicate is cut and drilled.


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## Longboy (Jan 12, 2015)

This is called "rocker arms on a stick'. Not to be confused with a county fair treat.  CR steel here a pair at a time, their counterparts are a mirror image by a staggered cut. Brass bushings for the pivot and stainless 4-40 socket caps for the pushrod with homegrown lock nuts.






A 3/8in brass rod is threaded down about 3/4in and a straight knurl is run across the threads for a superior finger grip in setting the pushrod length. Drilled and threaded for the stainless screws.






Finally the rockers are flame colored to a plum/ violet hue for contrast. I like the effect and here a matched pair are done!


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## Longboy (Jan 13, 2015)

The radiator is bored for a DOM tube that takes 7/8in. dia. pistons. Separate block style heads will sit on top.






To reduce the bore centerline distance, the radiators are milled & fly cut.... and butted together on the deck.











The shinny arc inside of the radiator is a slight overbore to a 1/4in. depth from the bottom. A film of Epoxy here bonds the cylinder. to the radiator as a unit.


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## Longboy (Jan 14, 2015)

The deck is bored oversize to the O.D of the cylinders, squared up to the crank centerline and a trio of 4-40 screws tie them together. Though it ended up not necessary, the deck overbore when the crank is close to the underside and a longer stroke displacement or just shorter rods can aid in clearance with rod angles. I had enough clearance with a 1 inch stroke without shaving the deck underside or narrowing the rod beam.











Clamped together, scribing a perimeter line around radiators to help locate the screws.


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## Longboy (Jan 15, 2015)

With the cylinders now located on the frame work begins on the cyl. heads. A 3/16in. deep combustion chamber bored to the O.D. of the cylinder here.






The cylinder rises above the radiator 1/8in and a 1/16in O-ring is laid over. No need to make gaskets, the head sits on the O-ring to make the seal.






The side of each head is fly cut to match the radiators when sitting on top of the cylinders. The heads are now ready for drilling ports, spark plug, valve guides, rocker pedestals and head bolts.


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## Longboy (Jan 16, 2015)

Valve guides from 3/8in brass rod test fitted here.






The horizontal V-groove in the machinist vise provides an arbitrary head angle for the spark plugs. Shown is a flat being cut in the chamber with a 3/16 end mill for a 90 deg. approach by the center drill, then tap drill for CM6 sparkies.






From the top side of heads the CM6 hex will not clear the opening to engage the head threading. Since they don't make a reduced shank 13/16in end mill to fit my machine, the China special boring bar will broaden the space. ;D






The heads are cross milled & fly cut parallel to plug angle to a point exposing the hex to get a socket around them.


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## Longboy (Jan 17, 2015)

The valves are made from 1/4-20 long stem hardware bolts. 






The do cut and work fine! Thm:


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## Longboy (Jan 19, 2015)

Five head bolts are used due to the porting, one intersecting the butt of the heads. Between the plugs, the exit ports for the intakes.






Outboard valves are the exhaust, inboard are intakes. A two step port drilling is needed to get between the plug boss, valve guide and head bolt. 1st step starting at the butt into the valve guide seat and then the 2nd.step drilling an exit straight outside along the butt seam. From this 1st. access point a transfer punch is used to mark the valve guide when placed. Removed and drilled separately, then epoxied into the head. Access point is then sealed off with short 10-32 set screws.











A diagonal is milled at the head corners and then arc filed for styling. I may add fins later to heads.


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## Longboy (Jan 20, 2015)

Tecumseh ignition points are located on the end plate and are camshaft driven. I like their compact size that wraps around the cam trigger. The coil stud attached to the tension spring is low and inside on the plate here. I want to bring that to the outside edge of frame for an easy connect point.







An eyelet over the stud with a brass rod encased in a Delrin tube threaded to a bracket mounted to the side of plate solves the location issue. Condenser to be mounted opposite side plate edge.






When the bottom plate is joined to the end plate the stud sits on its top for a ground out. A relief area is milled out for the stud here for isolation.






Now ready to work on the "special feature"! ....anybody see it yet?:idea:


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## Longboy (Jan 21, 2015)

On my "Gemini" twin, I have a dedicated dual fire coil and 6 volt battery ignition mounted with the engine on a oak board. For "Overtime", I wanted a free standing engine and be able to use my traveling 3 volt battery pack & coil. To do so requires a distributor.






From Home Depot, I picked up both a 1-3/8in and 1 inch PVC end cap and bag of #8 brass machine screws & nuts. Used the 1 inch cap on the engine. Three drilled and taped holes located for coil and plug leads.






The rotor is Delrin with brass strap, stainless #4 screw. The coil screw is dished out to a ball & socket mate with the rotor screw head with a round nose tool bit on lathe. Threaded into cap from the inside, when placed over the distributor base it is threaded down till contact with the rotor screw and locked nutted in place.






Rotor brass is located on the camshaft for line up with the plug leads. Distributor base is machined with a wrap around to the side of frame end plate and a matching piece serves as a timing gear guard at other end.
















Plug lead screws are threaded in till contact and locked. Being a sweep contact, fine tune by finger rotating camshaft and feeling for it then. The screws were replaced with longer studs to fasten the wiring. Though a press fit to the base, a finger screw was added later to hold cap in its base.......cuzz I like doo dadz on the engine!


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## Longboy (Jan 22, 2015)

Overtime went to the cobbler last month. Some steel tabs, hood bumpers and custom nuts mounted to the bottom plate should make it as stable ....as a turtle!


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## Longboy (Jan 23, 2015)

Delrin intake is used with .10 to.15 size carburetor. Press fit brass tubes join intake to engine........I didn't like the looks with the carb jutting out from the engine too far and a duplicate was made at a right angle shown on engine here. 






A gathering of parts for the fuel tank. I used the decorative steel tube with a nickel finish for both the tank & muffler.






Cutting off the neck of mini liquor or energy drink bottles.... makes great fuel filler necks for fuel tanks.











The exhaust port is threaded for a stud that is thru drilled and tapped for socket heads ( fillister heads cut off) to secure muffler. Stud is cross drilled to exit into muffler after spacing out with brass collars.


.wEc1.....Hey come back this weekend to the conclusion to Overtime's build with some tips, troubleshooting, the beauty shots and maybe a video!wEc1


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## Longboy (Jan 24, 2015)

Instead of a press fit for the lifter guides, set screws are used to secure them to the deck. The lifter heads are small enough to pass thru removing them with the guides otherwise, depending on how long the lifter stems are, you may have to pull the cam to drop them out the bottom. 






The brass collar in front of the timing gear is the collet knockout. Pushing and twisting the flywheel, as it will ride over this collar pops the collet for removal then.






Flywheel retainer is drilled & tapped for a stud and brass acorn nut. Socket on the cordless drill for a starter drive!






One of Overtimes cylinders had no compression. To reveal the leak, some dish soap suds over combustion chamber, a blow off nozzle from your compressor set to 10PSI into port shows where. In this case some epoxy dried on the valve guide seat preventing the seal.


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## Longboy (Jan 24, 2015)

With the valve train set up now, I see that my lift and duration on the lobes is too great. The valve keeper bottoms on valve guide stem. Re-profiled the lobes and cut lobe lift back by .035 and I have a nice idle cam profile.






Checking the spark here. The distributor cap rocked some as the rotor made contact. Some filing of the rotor tip and a spin of the camshaft with electric drill for wear in left some brass dust under cap and proper clearances.






Some paint work in black and polishing the bright work...... and it looks like I'm ready to go!Thm:


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## Longboy (Jan 25, 2015)

wEc1..... to the reveal of my new engine! Work on "OVERTIME" started on Sept. 25th and first signs of life happened Dec. 15th.







I meet my goals & benefits of a distributor ignition, stronger crankshaft and boxed open frame.






Pleasant solitude hours in the garage, trips to metal supply and hardware store.






And then its time!Thm:

















....Well that about does it for Overtime........(not so fast LONGBOY.... .....WHERE'S THE VIDEO?) ...Geez you guys are a tough crowd! 

[ame]https://www.youtube.com/watch?v=qh09Fsku3ZU&list=UUSN_jfvtt4ISxTJ-9cKND8w[/ame]

Hey thanks for following along on OVERTIMES story. See my other model engine projects on YouTube, Longboy4. Thmave


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## gus (Jan 25, 2015)

Hi LongBoy,

Great Engine. Your Prefabbed/bolt on crankcase proven and stood up very well. Will find time to build a single cylinder engine.
Meanwhile spending ample time read and comprehend Howell V-2 Prints before jumping into the cold water.Material coming in midweek. Weather warming up there??


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## Swifty (Jan 25, 2015)

Congratulations on a great build, the engine sounds as though it will run all day at that speed.

Paul.


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## Cogsy (Jan 25, 2015)

Great result. Runs very nicely.


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## Longboy (Jan 28, 2015)

Overtime gets a new underslung fuel tank to extend run times to 14 minutes.


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## minh-thanh (Nov 23, 2018)

Longboy said:


> (not so fast LONGBOY.... .....WHERE'S THE VIDEO?) ...Geez you guys are a tough crowd!





Thanks for sharing !


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## peter2uat (May 20, 2019)

Am following your build with open mouth!!! fantastic!!!!!
missing the pictures of the distributor build (and a lot others too)


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## Longboy (May 20, 2019)

All the photos are JPG files Peter. They show up for me on this forum. Maybe try one of my other logs for distibutor views.  ....    Dave


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## peter2uat (May 21, 2019)

Longboy said:


> All the photos are JPG files Peter. They show up for me on this forum. Maybe try one of my other logs for distibutor views.  ....    Dave


Well, totay they are here - yesterday just x-ed icons for over 15 pics - the mysteries of the internet... 
Thanks nevertheless
P


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