I been working on a horizontal 2 cylinder OMC engine for a friend,,, the  PO had cut wires and made a mess of things trying to start engine,,,,??? Starter is out and new one ordered,,SO,,I am trying to shade tree it to start. First tried my 1/2" Hi Torque  NAPA impact but engine rolled to the compression spot and would not go past that point ,,,,? I then dug out "Brutus" ,,my 1/2'Craftsman Hi Torque low RPM drill and ,,,,same reaction as the impact,,,!  I removed BOTH spark plugs for funs and the frigging thing would still stop at the compression spot,,,? I can roll the engine past the compression spot with one hand and is not binding but acts as if the spark plugs are still in engine,and bucking compression,,,,??

Anyone got any kind words of wisdom, what to look for,,,??

 Hey Dave Kamp,,,it sure good to visit with you, my Friend,,,,This is sure an ODD thing, Dave, as when you roll the flywheel back and forth at the place where it stops,,it feels EXACTLY LIKE when you are pushing against compression in the cylinders on the ignition stroke,,,,? Very puzzling to say the least. Taking the spark plugs out did not make any difference when rolling the engine back and forth,,that "spot" would be there at every revolution, but I do not think it is an internal piston obstruction,,rather it is just like when you reach the compression/ignition spot on the flywheel,,,,???

if it won't turn a 360 by hand 'somethings'  bad... maybe pour a 'decarbonizing liquid' in it over night or longer.

do NOT use anything but HAND power to spin it

BAD things ($$$$$) can happen !!!!

FYI Early 2 strokes (without tranny ) spin engine 'backwards' for reverse.

  WHOOPS,,,I might of mislead ya'll,,,it is a 4 stroke 2 cylinder engine with the 2 cylinders in an oppossed horizontal position kinda like them volkswagons and the older Corvairs.  Whatever is in  one or BOTH cylinders is what is pushing back on the flywheel from turning freely. I can roll the flywheel easy enough past the spot it trys to push back,,,,?? When engine is rolled right to the push back spot, I can roll it just a few degrees past the spot in either direction and engine will roll away from this "spot" of it's own doing. 

 Since I do not have a bore scope,,I'm gonna remove the head and take a look see, as it prolly is some build up of carbon and needs cleaning up and removed,,,,

Many Thanks for all the suggestions and help Guys,,,,

  Hey Thad,,That right there sure might be a consideration as what is happening happens at SAME spot in the engine rotation and sure could be the culprit,, 

  This engine uses what Cushman calls a "TiMER" with single contact points and condenser inside it.  Power from a  12 volt battery goes thru a "Resister" then goes thru TWO ignition coils,  (one for each cylinder,)  wired in series and on to the "Timer" or distributor with contact points and a condensor inside it. That wiring path kinda don't make sense to me as the "TIMER" only has the one wire on it's single connector,,,,??

 Am I missing something here,,,??

My Cushman uses a Kohler K-single, so I can't do a direct comparison, but I've worked on others with the OMC 4-stroke horizontally opposed twin.

This was a very unique motor for Outboard Marine Corporation... we expect, from their Evinrude, Johnson, and Lawn-Boy, that it'd be a two-stroker, but it's not... it's truely a unique beast for OMC.

The 'timer' is no different from any other ignition system, because of it's horizontally opposed arrangement, both cylinders are at TDC at same time, one is on exhaust stroke, the other is on compression stroke.  Both spark plugs fire at same time, one on a viable charge, the other on exhaust, so it is what is referred to as 'wasted spark' operation.  Simplifies ignition.  The ONAN CCK in my detassling platform, and in my Miller Bobcat welder are same, but instead of two coils, it uses just one coil that is 'double ended'.  There's good and bad to a double ended coil, benefits are that it's just one coil to mount, and services both plugs...  the bad is that it's just one coil, and if it goes bad, you lose all spark...

I suspect you've either got a ridge, or some debris in there.  Horizontally opposed engines are susceptible to that sometimes, particularly if debris can fall into the carb and migrate down in there.  Pulling the heads WILL help alleviate that.

The alternator on these was frequently a stator coil beneath the flywheel.  If you have debris in there fouling the rotation, it'll do that, but it also may just be tight clearance or strong magnet.  IIRC they used a charging stator very similar to, perhaps same part  as used on the SkiTwin/FasTwin/Industrial 40 two stroke outboard (it was an option on the ski/fast, and standard on the industrial 40hp, they all had electric start as an option, charging was an option on the Ski/Fastwin.  The magnet on those was just a sector portion, not a full circle of magnets).

Power from battery flows through ignition switch, through resistor, into one coil primary, out, then into to other coil primary, out, then through timer contacts to ground.

There WAS (initially, but possibly eliminated sometime) a wire that went from the START solenoid to the first ignition coil, to bypass battery power AROUND the resistor during starting.  The reasoning for this is frequently misunderstood:

When the engine is running, and the generating system is recharging the battery, you're seeing about 14.2ish volts on the electrical system. 

To make the coils survive 14.2v, they must be wound to run well at 14.2.

When the engine is CRANKING, however, system voltage gets pulled down, could be down around 9-10v.  Coil won't work too well there.

So they make the coil work well at 9v... but once the engine is RUNNING, it's getting pounded with 14.2.

So... when engine iS RUNNING, coil current is limited by the resistor.

When CRANKING, the resistor is bypassed.

 Hey Dave Kamp,,Many Thanks for taking the time to explain this for me. On the wiring diagram I downloaded,,it DOES show the start solenoid with two small connections in addition to  the two BIG connections for the battery input and the outlet to starter. One of the small connections on solenoid does have a wire going to the positive side of first coil. The other small connection quite possibly was removed as the wiring diagram does show a wire on second solenoid terminal but this dwg is so fuzzy I cannot follow where it terminates,,,, got any ideas,,,??

 OK, I "WAS" going to buy two new 12 volt coils but with your info will this design require special wound coils by Cushman,,,?? you know the word "special wound" means HIGH Dollars,,,,???

DJ, do me a favour, post the model number info.....please

I do NOT want to go 'north 200 feet'...

prefer to surf the web !!!!!

ANYTHING but go to 'contractors BBQ ' !!!!!

 Sure thing, Jay,,,,it is a 1980 Cushman Three Wheeled Turf Truckster It has the 18 HP OMC 2 cylinder horizontal opposed cylinders with the 3 speed Transmission with reverse. Tag on dash reads : Model: 898515-8010. No other numbers anywhere. I was informed the first two numbers AFTER the dash designates the year produced,,,,All this other info I have gleaned from several Cushman forums. Hope you have better luck than I have as there appears to be a huge lack of documents left from Cushman with an even worse situation about parts availability AND pricing,,,,,  I wish you all the luck,,

 Well,, I got a bit of an update  on the OMC engine.I figured I was gonna have to pull the cylinders or pull whole engine out so I was removing the flywheel and LO AND BEHOLD when it came off,,,,there was the danged'est bunch of UGLIES stored in there by RATS,,,,maybe at least a 5 gallon bucket full for sure,,!!! After cleaning all that BS out of there,,,I slip the flywheel back in there and ,,,,,,,,it rolls like it is supposed to free and clear,,,,I'll just be danged,,,!!!! ALL that frigging work and then to find that BS,,,,!!

  AND,,,I still have a NO SPARK sitiation on the engine. I tested both coils , one at a time using the battery and a spark plug and they both tested good,,altho spark was not to big ,,it was a spark,,,?? Hooked both coils and the timer (distributor) as per Dave Kamp suggestions and still NO FIRE at either spark plugs or at the points,,!! For funs I installed the old condensor and still NO FIRE,,,!!!  What the heck could be the problem,,,???? How do you "TEST" the timer,,(distributor),,?

welcome to 'my world of pain'..

wad a B&S motor in a rider,go both ways but NOT round and round. For SURE it has to be busted con rod(seen that ). Yank engine out of rider, drain oil, tear cover off, WTH ??? con rod IS good...OK, morning shot...WHAT stop crank from going round and round ???

Well for me it was 3/4s of the MAGNETS that are SUPPOSED to be glued to the flywheel !!!

6 decades of turning wrenches on small engines and that was the FIRST time I'd seen that....

sigh, I need a new hobby...

 Well, Jay,,,at least you did not find a king sized Rats nest in your project like I did,,,,!!! That was amazing at the amount of garbage them rats had "RATHOLED" in the space behind the flywheel,,,!!!! Prolly what burnt the starter up,,,!!!

 What could possibly be wrong at the timer, (distributor) the distributor sees 12 volts negative coming at it and goes thru the points and on to ground which makes the contact points go" fitzzze" when they are forced open (spark) so,,,why no spark on this OMC,,,??

The 'timer' is nothing more than just contact points.

Pull out the coils, install a double-ended coil for an Onan CCK-series, it'll work fine.

To run two coils in series, they need to be 6v coils, not something you'll find in many environments nowdays.

   WELL, Dave Kamp,,,you're a Champ,,,but Ummmmm,,,you wouldn't ,,,,by chance,,,happen to know of a PN I could throw at one of them current style of parts persons,,,,that savey these things,,,,huh,,,?

 But,,,,I'll give it a go post haste this very morning,,,,,sigh,,,,,

 WAIT,,,,WAIT,,A Minute,,,let me run this Double ended coil for a Onan by Ms. Google,,,, ,,,,you know how these parts peoples are these days,,,,,,,

 On the "No Spark"   sitiation,,,it almost has to be the timer (distributor) that is not grounded properly as THAT is what provides the spark that goes back to the secondary windings on the coils which then provides the spark to the spark plugs,,,,right???

Fingers crossed,,,,,

   dot,,dot dit,dotdit, dit, ddotdeeeeeeeeeee, that right there is morse code for,,,,,"I HAVE SPARK AT THE PLUG WIRES AND THE TIMER",,,,!!!!! YEA,,,YEA,,,YEA I am stoked, Guys,,,!!

   I used a hot wire to the terminal at the timer and jiggled, moved,  pushed condensor and all wires around and finally seen where the main terminal at the side of the timer was going to ground and stopping everything right there!  Made a fiber washer and repositioned the terminal where the points and condensor would not ground out on the timer case,,,WHEW,,,!!

 Now on to more interesting things,,,like putting a spark in the engine and hear it run,,,,?? 

MANY THANKS for all who worried on this thing with me,,,,

Ok...progress !!!

Now, I wanna SEE a pickture of youe new beastie !!!!

  OK, Guys,,as I have repaired the 12 volts going to ground at the timer,,I am on to completing the wiring in engine compartment and now find one of the two resistors is possibly bad. The 12 volts will not go thru it,, from either direction. on one corner of the porcelin  body it has the following : 60 followed by the OHM icon, 10%25 W,,,? What do I order??,,,Or does the engine even have to have  it to run? There is a second resister that did not have any wires connected to its terminals,,,??

  Hey Jay,,I ain't forgot you, I still am having issues with trying to post pics hoping ole Buckskin agrees to help me get all my pics in one place so I can find em,,,,,????

that's a sixty ohm, 25 watt resistor though I suspect it might really be a SIX ohm ( get  extra eye power and see IF it's says 6.0 ohms. Itty bitty decimal point between the 6 and the 0.

  Well, I have no idea what the reasoning was for the TWO resistors in the engine compartment,,,one of the persons on the Cushman Forum I been pestering did say the one of the resistors was for having full 12 volts while cranking and when engine started,,the resistor would cut back to lower voltage when full 12 volts not needed,,,,,??? How does the resistor KNOW when that happens,,,??

 I used an old magnifying glass but the  numbers on the porcelin are not clear enough to be sure,,,if there is a dot between the 6 and the 0,,,I cannot see it,,and I agree that it is most likely 6.0 instead of 60,,,,,

On old tractors that have been converted to 12v, the use the resistor to cut the coil voltage to 6 volts ALL THE TIME... start or run...  I think a 6 volt coil is about 1.5 ohms and a 12 volt coil is 3 ohms...... not sure where the 6 or 60 comes from ???

   According to one of the members of a Forum I been bothering that did venture of a wire at the key that does drop the voltage to the coils when key is turned to start,,then drops out when engine starts,,,? As with purists of every group,,,,he strongly cautioned me to replace the bad resistor with a new one post haste,,,,but,,I also received several suggestions to remove or bypass both resistors for better spark quality and better performing engine,,,,???

BUT,,,,BUT,,,,the best news of the day is,,,,,,(lets have a drum roll, DIYDAVE,,

  These OMC 2 cylinder engines have a  highly questionable intake piping that includes a rubber " T " that on most Cushmans have deteriated over the years by developing cracks in the rubber almost big enough to poke your finger in the cracks.  (Please no dirty comments here)  Mine was that way, so I been fashioning a replacement from a 1" copper tubing T  that is almost a direct fit to the intake piping ,,but did take many  Installs and removals to get it just right so nothing leaks...... AND FIRED THAT MOTHER UP,,,!!!! Engine runs many wonderfuls and sounds great with NO smoke out the exhaust,,,except

 the dang KEIHIN carburator kept leaking at one of the bolt holes,,? I had opened it up and it was very clean but will pull it tamarrow to check it out  and reset the float level.,,,,,, ps,,,I bypassed both resistors, Steve)

If the coils are original, they're most likely wound to fire at either 4.5v, or 9v.  They'll run at 6v or 12v (respectively) and at 7.3v or 14.4v (when charging), however, they will flow considerably more current doing so.  When used in an 8 or 6 cylinder engine, these coils will operate and survive simply because the more frequent ignition events reduce the coil's total 'dwell time' over a course of an engine rotation, than in a single-cylinder application.

They'll work without ballast resistance, but usually, within a dozen hours of operation or so, they'll overheat and expire.  They'll frequently, but not always burn up contact points... if they're good quality plated points, they'll tough it out.

The other aspect of smaller engine coil design, is vibration.  Small, lightweight air cooled motors with few cylinders shake the bejesus out of components... that's why Kohler K-singles don't last long with an ordinary store-shelf ignition coil, and that's why they wear out strange things like carbeurator float pivots.

Modern electronic ignition solves the dwell-time circumstance by doing all the 'hard' work electronically, and only flowing coil current when necessary.

Lots of marininized setups use a 'resistance wire' rather than a resistor module.  Imagine about 8 feet of flameproof cloth wrapped nichrome wire included in the wiring harness of a boat engine... that's what many did.  nichrome is significantly less willing to carry current than standard copper wire, so they used it instead.  There's still a bypass lead coming from the starter solenoid, so that the coil gets full battery on crank, but release the key and coil current flows through the nichrome.

The giveaway that a coil resistor has failed, is the 'starts but won't run'... as you're cranking, it fires, but as soon as you release the key, it looses spark.

The converse circumstance (poor starting, or no start) is often a weak cranking spark, from the bypass circuit not being operational... it's trying to crank and fire limited spark whilst doing so.

 Hey Dave Kamp,,,,,So, what range of resistor(s) do you think should be in this service,?? There were two resistors that were different from each other bolted on next to the two coils but since the PO was not too terribly judicious  about taking care of the engine neither resistor was hooked up to any thing,,,no wires ,,nothing. On one of the forums I been visiting,,one of the members did mention a resistor of 60 ohms.

   I cleaned the one resistor and it was a 60 ohm,, but then ole Jay questioned if the resistor might be  a 6.0 ohm,,, The other resistor did NOT have any writing on it.

  I did get the engine running by deleting the resistors and the engine started and did run but I did not let it run longer that 5 minutes for fear of burning up the new points and condenser,,,!!

 What do you think??

Hay DJ

Please measure the resistance of the coils. It'll probably be low, less than 10 ohms.....

'Points' typically like less than 4 amps through them ,else they pit and burn up.

Once we know the coil ohms, can figure out the resistors you should have ( or at least 'safe' ones ). BTW the ones in purdy colored finned aluminum are much better that the old ceramic logs.

The formula for current flow through a resistor is:

I = P/R

where

I = Current

P = Potential in Volts

R = Resistance in Ohms

So if you were to connect a resistor directly across a 12v battery:

12/60 = 0.2A. 

IF you connected a coil across that circuit, it would need to be able to fire at 0.2A... and that's not anywhere CLOSE to what an ignition coil will draw.

A typical 8-cyl 12v automotive ignition coil 's primary winding will be around 1.5-2.5 ohms...  if it were run on straight 12v, that would put it around 5-8 amperes with no ballast resistor... but at 14.6v, that would be 6-9.75amperes.  Cold Cranking, though, pulls the system/battery voltage down to about 9v... which means there's only 3.6 to 6A at the coil.

A typical 4-6 cyl automotive ignition coil's primary will be somewhere 2.5-4 ohms... that'd be 2.5-3 amperes... with no resistor.  At fully charging 14.6, that'd yield 3.6 to 5.8 amperes, and down at 9v,  that's 2.25 to 3.6v.

These coils MUST be able to sling a hot spark when cranking at 9v... but when the engine is running, and charging system is up above 14, they need to be limited somehow to keep from being burned up. 

The difference between cold-cranking and running-warm-charging can be significant... going from 9 to 14.6v is a 160% change.

So to get the reliable starting under cold cranking, the coil is wound to fire well around 9V, and the ballast resistor limits current so it'll be reliable up to 14.6 or so.

Typically, the resistor will EXHIBIT the same general range as the coil's primary.  a 3 ohm coil would be protecting a 3 ohm coil... as that would cut the operating current in half.

As Dmiller noted- ceramic ballast resistors tend to 'drift' with temperature.  Like the 'resistance wire' I described earlier, a ceramic ballast resistor doesn't use carbon film or other types of materials that a precision electroncis resistor uses... instead, they use a ceramic coated nichrome wire element, that changes resistance as it warms up.  Let's say you test a 3-0hm ballast resistor... At -30F, it may be 2.5 ohms, but running on a hot day, the shell might be 180F, it'll be almost 4 ohms.

60 ohms is out of reach for that application.  You probably have a 60 ohm resistor there, but it was either put there in error, or it was supposed to be for some OTHER purpose (like powering a temperature gauge, fuel level, or oil pressure circuit).

  60 ohms is out of reach for that application.  You probably have a 60 ohm resistor there, but it was either put there in error, or it was supposed to be for some OTHER purpose (like powering a temperature gauge, fuel level, or oil pressure circuit).

 BINGO,,,,!!!  Hey Dave Kamp,,,Me thinks that is exactly what has happened here,,,whether the PO thought the previous resistor was bad or whatever,,and just installed one from who knows where is very likely,,,prolly what I would of done in a pinch,,,SO, maybe the resistor that is in there now (bypassed) is prolly a 6.0 instead of a 60,,,,???