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48 Plymouth flathead starting problems


Wanderlust

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Hi, I’m new to the group and have a question about my old Plymouth I’m restoring. Backstory my dad gave me the car out of the barn and the car was running up until 2009 where it was parked after he became ill. I’ve drug it out and have started working on it the past couple years. The car will turn over and will run when pull started but not off the starter. Had starter rebuilt as I thought that may be the issue. Now car winds really slow and still no luck starting it with the starter. Any suggestions on what to check/try next? Thanks. 

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What year, what engine, positive ground? 12 Volt? 6 Volt? Has there any wiring done? (Assuming positive ground) If you run a jumper from the negative side of the battery to the negative side of the coil. See if it starts then. it may rule out a switch problem. (Or check voltage on the negative side of the coil while cranking) 

Edited by Dodgy49
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What are the condition of the battery cables? They need to be a large size with clean connections. If the cables are too small, or there are corroded connections, there could be enough voltage drop under cranking that the ignition can’t fire the spark plugs properly. 

Edited by Merle Coggins
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It’s the original flathead that came in the 48 special deluxe and is on 6 volt system. Cables have been replaced with the heavy duty ones from tractor setup as suggested on a previous post here. Will try the voltage check on the coil. Thanks. Other suggestions welcome ?

Edited by Wanderlust
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If your starter is turning very slowly, check your battery and all your cable connections.

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59 minutes ago, greg g said:

What sparkplugs are in it?  Current Champions are junk.  Been running AC 45 , got 40k on the set in there since rebuild.  Starts great.

How is you compression?  What vacuum are you pulling at idle?

"CURRENT Champions are junk???" I had Champions die in a stock 48 Ford panel truck in less than 100 miles the 70's. I will smack anybody that puts a Champion plug in anything I own.

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13 hours ago, knuckleharley said:

"CURRENT Champions are junk???" I had Champions die in a stock 48 Ford panel truck in less than 100 miles the 70's. I will smack anybody that puts a Champion plug in anything I own.

I would NOT use Champion plugs if they were free, and payed me to put them in. Auto lite is the way to go on Mopar flatheads.

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Get some NGK replacements. 

 

I researched plugs by testing a bunch of manufacturers for the same application on primary resistance. NGKs are consistent at 5 Kohms, on a sample of 8.

 

Of those tested, champions were the most variable and resistance was upwards of 15 to 20 Kohms. Significant because of ohms law - higher resistance = less spark energy. Furthermore I believe the high resistance causes more stress on the rest of the ignition system. I used to replace coils on my lawn boy once every 1-2 years. Since I put in an NGK plug the coil has lasted 5 years and is still working fine.

 

I now insist on NGK when replacing a plug, and my mowers, snowblowers, cars, anything with an engine run better and start easier.

Edited by Dartgame
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9 hours ago, Wanderlust said:

Got it... check plug brand if they are the champions immediately discard in trash angrily while yelling obscenities. ?? 

If he doesn't live too far away,you might consider going over there and beating the snot out of him,too.

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  • 2 weeks later...

I replaced the plugs and checked grounds.... and she finally started on her own. Super happy with that. The timing may be a little off so I’m going to work on that as well. 

 

Now onto the next big task of replacing the flywheel. Any advice/suggestions there? 

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1 hour ago, Wanderlust said:

I replaced the plugs and checked grounds.... and she finally started on her own. Super happy with that. The timing may be a little off so I’m going to work on that as well. 

 

Now onto the next big task of replacing the flywheel. Any advice/suggestions there? 

 

Why do you need to replace the flywheel?

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1 hour ago, Wanderlust said:

It’s worn from a bad starter head that got put on before I had the car. Now it has the right starter head but the teeth are worn on the flywheel

 

You may get by by just flipping the ring gear. But to do so the flywheel must be removed. Suggest you mark the flywheel using a center punch and or a paint stick as pictured. The fly wheel bolts are not concentric so the fly wheel must go back on exactly as it came off.

 

es5.jpg

 

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Well after a long weekend and a little help from my stepdad we got the flywheel replaced and everything reassembled. We switched the ring gear as suggested. The wealth of information on this site is so helpful! While taking the transmission out of the car there was a part that was not hooked up and looks to have been disconnected for a while. I looked in the service manual but it wasn’t very descriptive on what it was either in the diagram. I’m attaching a photo if anyone could help? 

 

 

9EA84047-5A89-46A0-9E95-9ABE73213D60.jpeg

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  • 2 years later...

My 48 Plymouth P15 cranks very slow and it eventually will start but when I turn it off it cranks real slow like the battery is drained.  I checked the battery and us fully charged. Please advice on what to check. Thanks

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Sounds like it could be undersized battery cables, such as the skinny ones a 12v car will use rather than the fatter ones a 6v car needs.  Bad, loose or dirty connections for those cables can also cause a similar issue.

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