Wont start! Help

[Jimmyg31b]

Ok I inherited my Grandfathers 1949 Cub a few years ago at the time it was running unfortunately the can blew off the exhaust and rain got into the cylinders and seized the engine, I pulled the head off and used penetrant oil in the cylinders and valves and after 3 days of tapping on the pistons and rocking it back and forth in gear i got it loose so i put it back together and tried to start her. I purchased a battery (6v) new starter, plugs, cables and rebuilt the carb and nothing! I do have spark but it doesn't even try to start....any guesses???

[Muletrain]

If you have new battery and cables, I would check for Ground first.

[Jimmyg31b]

If you have new battery and cables, I would check for Ground first.

hmmm i'm doing some reading i have a 6v battery is it a positive ground ? how do i know ? and if its reversed would that make it not start

[Denis]

It May be sticking valves! You say that you freed the pistons but did you make sure that all the valves were working properly?

[randallc]

If you have or can borrow a compression tester check the compression. Water in the exhaust can also effect the valves and hold some or all open.

[Eugene]

If you have new battery and cables, I would check for Ground first.

hmmm i'm doing some reading i have a 6v battery is it a positive ground ? how do i know ? and if its reversed would that make it not start

The Cub's 6 volt electrical system is positive ground, meaning that the cable from the positive battery terminal goes to the battery case. The battery case frequently gets rusty and makes a poor path for electrical current.

Move the positive battery cable end where it mounts to the battery box to the transmission case.

If the battery was installed with a negative ground, will that cause the engine not to start. No, it might degrade the spark quality a bit, depending on how the coil's secondary wire is grounded within the coil. There is a possibility that your new coil is faulty.

Conduct compression tests.

[Jimmyg31b]

Thanks for the input i have the positive cable from the battery right to the starter and the negative grounded, I do have spark (how hot i don't know) Two of the valves were sticking open and I had to work them as well, I used the same head gasket and exhaust gaskets my goal was to get it running then take it all apart again and paint everything then use the new gaskets. What kind of compression should I see out of the cylinders? One other question I have one single white wire that went to the battery but I'm not sure if it was attached to + or -

[Eugene]

White wire. Find out where it leads to before attaching it to the battery. Since you currently have the tractor negatively grounded, you want to hook the white wire to the positive terminal of the battery. You want the white wire on the battery terminal that is not grounded.

Suggest reversing the cables on the battery so that it's positive ground.

Conduct the compression tests, dry then wet. Report the results.

[Jim Becker]

You want the white wire on the battery terminal that is not grounded.

Unless somebody added a dedicated ground wire. First need to see what the other end is hooked to.

[Smokeycub]

As others have said a 49 Cub would have been originally a 6V positive ground set up. A 49 would also have had a magneto, if so, with the engine turning over on the starter then the mag will produce spark independent of the battery. The spark needs to be hot and bluish. An extra white wire going back to the battery? That would be something someone has added, hard to guess what it's for. As Eugene suggests, find out what it's for before you connect it.

Suggest reversing the cables on the battery so that it's positive ground.

Ditto.
Does your tractor have an external coil or the original mag coil? Compression ideally needs to be about 90 to 100 psi but if the valves aren't closing those particular cylinders will never get there.

[Jimmyg31b]

I believe its the original mag coil (side of the generator?) I took a compression test and the gauge pin bounces from 5-30 psi but will not stay up on each cylinder, when i add 30 weight oil to the cylinder the needle stops and stays at 120 psi as I keep checking it goes down to 90. So I'm starting to believe its a compression issue even though this tractor was running great before it went into storage. As for the white wire I think its for the rear lamp

[Smokeycub]

So it's turning over on the starter. If all four cylinders are near 120 psi in a wet test then by the results of your compression test the rings are not sealing well and the valves are closing. There is a possibility that they will loosen up and/or re-seat if you can get it running. Have you checked for a hot bluish spark? Are you getting a good flow of fuel to the carb? As an FYI the plug wires need to be solid copper core. Since it "ran when parked" the timing should be close enough to get it started. If the coil is an external type it would look like an automotive style coil, if it's a mag coil it would look like this

Courtesy of TM Tractor Parts
As mentioned before if it's running a mag coil then the ignition runs independent of the battery.

[Jimmyg31b]

Yes Thats it so i have a mag coil, Im thinking of taking the pistons out and replacing them with new rings, I see kits with pistons, Rings and rod bearings that are not to expensive, since I'm doing no machine work I guess i stay with the standard size pistons and bearings?

[Eugene]

I guess i stay with the standard size pistons and bearings?

The engine may or may not still be the factory standard.

You need to disassemble the engine, clean parts, measure and record measurements. Once this is accomplished you can determine if machine work is required, work to be accomplished, and parts to order.