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Cub won't start after rebuild

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Kermit

11-26-2006 09:37:43




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I just rebuilt the engine on my 1950 Cub. Crank was read and polished. New rings, main and rod bearings, and seals were installed. It turns over, but the starter is laboring to spin the engine more than a dozen turns after the rebuild. I thought it might be a weak battery or a bad ground, but even after trying two fresh 6V batteries and checking Rx all down the line, it still acts the same. What's more, I doesn't sound like any of the cylinders are even trying to fire. I've checked the spark at the magneto wire and it's nice and blue, I've checked the spark down the spark plug wires all the way to the plug and they are all sparking well. I've got fresh gas in it, no clogs in the fuel line. I've taken the Carb apart several times, and cleaned it out - everything is clear. The float and needle valve are working fine. I can feel a nice draw on the intake manifold when the engine turns over, so no obstruction there. I checked timing by putting a pressure gauge on cylinder one. Everything seems ok there, the pointer is at TDC at the top of the compression build on cylinder#1, the dist rotor is pointing to #1 postion on the cap, and I can hear the Magnetor trip at the top of the compression stroke. This Cub was a great runner before the rebuild, and would fire and try to run even on a couple of cylinders The spark, fuel and timing all seem good, but I'm not getting so much as a sputter - even with a healthy shot of starter fluid. Does anyone have any suggestions?

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El Toro

12-03-2006 06:52:01




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 Re: Cub won't start after rebuild in reply to Kermit , 11-26-2006 09:37:43  
Did you get the Cub started? Hal



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El Toro

11-27-2006 18:47:48




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 Re: Cub won't start after rebuild in reply to Kermit , 11-26-2006 09:37:43  
I noticed the firing order got messed up. Hal
2-1
4-3



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John M

11-28-2006 03:26:56




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 Re: Cub won't start after rebuild in reply to El Toro, 11-27-2006 18:47:48  
1-3-4-2, but in reverse, right?Cubs are backwards rotating right?



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El Toro

11-28-2006 08:34:44




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 Re: Cub won't start after rebuild in reply to John M, 11-28-2006 03:26:56  
According to my manual the rotor turns clockwise.
Hal



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El Toro

11-27-2006 14:11:27




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 Re: Cub won't start after rebuild in reply to Kermit , 11-26-2006 09:37:43  
Did you get the tractor started? Hal



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El Toro

11-27-2006 14:11:26




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 Re: Cub won't start after rebuild in reply to Kermit , 11-26-2006 09:37:43  
Did you get the tractor started? Hal



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El Toro

11-27-2006 03:31:29




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 Re: Cub won't start after rebuild in reply to Kermit , 11-26-2006 09:37:43  
Check your plug wires to make sure they're in the correct firing order. Should be on you cap and to the sparkplug in this order. Hal
PS: Check that valve clearance too.
2-1
4-3



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kermit

11-27-2006 14:25:17




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 Re: Cub won't start after rebuild in reply to El Toro, 11-27-2006 03:31:29  
Hi Hal,

Plug wires are in order.

I'd be more worried about the valves if I'd had the cam out, but I left that in. I did have the valves ground, and did lap the valve seats when I put them back in, But the lifters, valve springs, cam, etc. all stayed in the block. I checked the valve lash when I put the engine back together - most were very close, just a turn or two to get them into spec.

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El Toro

11-27-2006 16:27:01




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 Re: Cub won't start after rebuild in reply to kermit, 11-27-2006 14:25:17  
I would do a compression test to see what that is. Do you remember how the punch marks were aligned when the crankshaft was installed? It seems like something is out of time. Hold your hand over the throat of the carburetor and see if there's good suction on your hand while someone cranks over the engine with the starter.
Hal



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gene (missouri)

11-26-2006 21:00:53




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 Re: Cub won't start after rebuild in reply to Kermit , 11-26-2006 09:37:43  
Plug wires mixed up?



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gene (missouri)

11-26-2006 20:52:27




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 Re: Cub won't start after rebuild in reply to Kermit , 11-26-2006 09:37:43  
Tight engine. Inserts and cylinder walls getting dry.

1) Put several tablespoons full of oil on top of each piston - need to lubricate the cylinder walls.

2) Prime the oil system. Use the allen plug on the left side of the engine.

You have compression so the major problem is ignition.

3) Ignition timing is off. Check with a timing light. If engine fires at TDC you are 180 degrees out.

4) Retard the timing a bit - fire just after TDC.

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Hermit

11-26-2006 19:17:37




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 Re: Cub won't start after rebuild in reply to Kermit , 11-26-2006 09:37:43  
If the valves aren't adjusted so they open wide enough, that would cause a labored starter and no fire since not enough fuel is getting to the cylinder. Good luck.



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El Toro

11-26-2006 18:04:50




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 Re: Cub won't start after rebuild in reply to Kermit , 11-26-2006 09:37:43  
Have you pull one of sparkplugs and ground it against the engine with the plug wire attached
to see if the plug fires when cranking? Hal



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Kermit

11-26-2006 18:46:11




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 Re: Cub won't start after rebuild in reply to El Toro, 11-26-2006 18:04:50  
Yes, checked all four - all have good spark.



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El Toro

11-26-2006 18:59:21




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 Re: Cub won't start after rebuild in reply to Kermit, 11-26-2006 18:46:11  
That's sure weird. Have you measured the compression. When you had No1 piston on the compression stroke, did you look at the valves on
on that cylinder? Hal



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Kermit

11-26-2006 19:14:17




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 Re: Cub won't start after rebuild in reply to El Toro, 11-26-2006 18:59:21  
No, I haven't checked the compression. Do you mean did I check to see if both valves are closed during compression? I did have the valve adjustment plate off when I was installing (timing) the magneto and it looked like both valves were closed as #1 hit the TDC mark on the pully.



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El Toro

11-26-2006 19:22:18




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 Re: Cub won't start after rebuild in reply to Kermit, 11-26-2006 19:14:17  
That's where they should be. I guess we will have to sleep on it tonight. Hal



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Bigdog

11-26-2006 13:26:32




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 Re: Cub won't start after rebuild in reply to Kermit , 11-26-2006 09:37:43  
Don't forget that with the cub you must time the governor and then time the magneto because the mag is driven off the governor. The timing marks for the governor can be hard to find for those not familiar with the process.



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Kermit

11-26-2006 16:44:45




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 Re: Cub won't start after rebuild in reply to Bigdog, 11-26-2006 13:26:32  
I did have the governor out during the rebuild, and it was tough lining up the marks, but I"m pretty sure I got the governor timing mark lined up to the idler gear marks. I"ll check the timing on the magneto, I got several comments on that.

Thanks.



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El Toro

11-26-2006 13:02:53




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 Re: Cub won't start after rebuild in reply to Kermit , 11-26-2006 09:37:43  
If you pulled the mag off during this rebuild you may be timed on the wrong stroke. Pull No1 plug near the radiator and bring No1 piston to TDC on the compression stroke. Once you have it at TDC
pull the cap on the mag and see where the rotor is pointing. Should be at the No1 plug tower.

Squirt some gas into the plug hole and see if the engine tries to run. Like the Magman says keep an eye on that oil pressure. Post back if there's no pressure and don't keep running the engine. Hal

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Kermit

11-26-2006 17:36:38




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 Re: Cub won't start after rebuild in reply to El Toro, 11-26-2006 13:02:53  
I just double checked the timing. Rotor is definately pointing straight to the #1 plug tower at the top of the #1 compression stroke.

I tried squirting starting fluid into the plug holes - with no luck - not even a backfire.

I'll watch the oil pressure - assuming I ever get her running again!!

Thanks. Kermit



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MAGMAN

11-26-2006 12:34:31




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 Re: Cub won't start after rebuild in reply to Kermit , 11-26-2006 09:37:43  
I am not sure why its not firing up for you but I have one thing to add since I have been reading posts here and the cub board alot of people have problems with fresh C60's getting oil pressure and have to prime them if you have not and you do get it running watch your gauge if it does not pick up pretty quick shut her down and prime the gallery or what ever they do to them. JON

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Kermit

11-26-2006 17:14:00




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 Re: Cub won't start after rebuild in reply to MAGMAN, 11-26-2006 12:34:31  
I did see several comments on the message board regarding priming the oil pump on recent rebuilds. From what I understand, there is a small hex-nut behind the hydraulic lines that can be removed and oil squirted in to prime the pump. I'll make sure to do that if the oil pressure gauge doesn't come right up

Thanks.



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John M

11-26-2006 10:09:27




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 Re: Cub won't start after rebuild in reply to Kermit , 11-26-2006 09:37:43  
Mine did the same thing. It was just so tight that the starter would drag on 12 volt. Pulled it a few feet and it fired right up!



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Kermit

11-26-2006 16:59:32




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 Re: Cub won't start after rebuild in reply to John M, 11-26-2006 10:09:27  
I did try that, but during the rebuild I drained the Cal. Chloride from the wheels and took off the wheel weights. Now it's so light that when I tried pulling it, the tires just spun on the pavement or dug up the turf - even in 3rd gear! I plan to get some of my buddied to stand on the tow bar to add a little weight and try it again.

Once you got yours started and ran it for a while, did it loosen up so the starter didn't labor so much? How long did it take to loosen up?

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John M

11-26-2006 18:16:43




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 Re: Cub won't start after rebuild in reply to Kermit, 11-26-2006 16:59:32  
Id have to guess, but I do know the next time I tried to start it, it fired right up.I ran it maybe an hour before I cut it off and finished the paint.Maybe another week had gone by since it had ran.



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Dellbertt

11-26-2006 09:48:03




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 Re: Cub won't start after rebuild in reply to Kermit , 11-26-2006 09:37:43  
Did you take the plugs out and see if they are wet with fuel.

Did you try starting fluid.

If air, compression, fuel, spark(timing) are good.

Try pulling it.



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Kermit

11-26-2006 17:07:28




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 Re: Cub won't start after rebuild in reply to Dellbertt, 11-26-2006 09:48:03  
That was one thing that was bothering me - the plugs did not seem to be wet w/ fuel, even after cranking it over a few times. but like I said, the carb seems to be clear - no obsturctions, and there is a nice draw from the intake manifold when the engine is turned over - so no obstruction in the manifold.

I did try starting fluid, I even sprayed some into the plug holes in the cylider head - just to see if I could get a pop on at least one of the cylinders, but didn't get anything.

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Nat 2

11-26-2006 21:18:28




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 Re: Cub won't start after rebuild in reply to Kermit, 11-26-2006 17:07:28  
Starting fluid is a good way to ruin all that work you did and money you spent on the engine rebuild.

I would guess that somewhere along the line, what you think is, isn't. You think you've got the timing right, but maybe you don't? You think the carburetor is working, but maybe it isnt? That's the kind of stuff I'm talking about.



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RP-40-9n

11-26-2006 19:39:48




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 Re: Cub won't start after rebuild in reply to Kermit, 11-26-2006 17:07:28  
when i redid my cub , after i checked tdc and timeing mark, it wouldnt fire and i turned the distributor about a half inch and it fired right up. also recheck your plug wires and fireing order to be sure they are in order. RP



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Kermit

11-27-2006 14:15:16




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 Re: Cub won't start after rebuild in reply to RP-40-9n, 11-26-2006 19:39:48  
Thanks for the suggestion RP.

Wires are where they should be. I tageed them before I did the rebuild, and also double checked them against the diagram in my manual after I put the engine back together.

I"ve rotated the magneto in about 1/4 inch increments from one edge to the other trying the engine w/ each move - without any luck.

Kermit



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lowboy

11-27-2006 16:05:40




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 Re: Cub won't start after rebuild in reply to Kermit, 11-27-2006 14:15:16  
Hi came late on discussion just wondering did you get it cranked ? If motor is to tight did you clean ring groves



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Kermit

11-28-2006 13:12:39




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 Re: Cub won't start after rebuild in reply to lowboy, 11-27-2006 16:05:40  
I didn't get it started yet. I'm going to try pop-starting it again, but need to get a few friend over first to stand on the draw bar and add a little weight over the wheels.

I did clean all the grooves very well, the new rings moved freely when I set them in the piston.



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lowboy

11-30-2006 19:27:29




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 Re: Cub won't start after rebuild in reply to Kermit , 11-28-2006 13:12:39  
did you check ring gap in the block also



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