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1948 8N Misfires after rebuild

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Rons1948

10-18-2006 17:05:47




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I recently replaced rings and valves in my 48 8N. When it finally started, it was misfiring on 1 & 3. What I've done to date: Compression checks in at 95 PSI on all four cylinders after rebuild. Plugs (2 sets) are AL 437s. New copper core wires installed. Distributor refreshed with points, condenser, rotor and cap (stock 6v), no wobble in shaft. All adjustments according to I&T F04 manual. Turned engine over with all four plugs out and connected to wires; spark was healthy, blue and sequential with no misses. Removed head and verified valve adjustments and movement were correct. After head re-installed, same roughness with 1 & 3 appearing to be the culprit (based on reading the plugs). Spark plug wire hookup verified multiple times. Haven't messed with carb as it ran OK when I tore it down and it would seem it should be random if it was carb related. The reason for the rebuild was low compression, ranging from 40 to 80 PSI. I have searched the archives and verified various other things that might have been vaguely related. I'm at a loss, any additional ideas? What am I forgetting? Thank you.

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RP-40-9n

10-18-2006 22:00:18




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 Re: 1948 8N Misfires after rebuild in reply to Rons1948, 10-18-2006 17:05:47  
ron, did you replace the valve springs, are you sure that 1 and 3 are getting oil and not trying to stick, and did you use a straight edge to be sure that your manifold was flat and true? since it is 1 and 3 related it will probably be valve related. one other possibility is plugs. i just put a farmall together and installed new champions and they have coated up with heavy- black-dry-soot three times and havnt burned three gallons of gas yet. back to store tomorrow. RP

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Dell (WA)

10-18-2006 19:15:55




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 Re: 1948 8N Misfires after rebuild in reply to Rons1948, 10-18-2006 17:05:47  
Ron..... ..you write..... "Haven't messed with carb as it ran OK when I tore it down and it would seem it should be random if it was carb related. The reason for the rebuild was low compression, ranging from 40 to 80 PSI"..... ..well guess what? its yer carb!!!

Why? because it was probably adjusted to make yer worn-out engine just barely run and now you have good compression and miss-adjusted carb. Simple, eh? Much to the dismay of environmental bureacrats, each engine and each carburator needs to be adjusted together for optimial running. That is why carbs have handy-dandy tweak'ems.

Iff'n yer uncertain how to adjust yer carb, ask. And I tell you how I do it..... ...Dell

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Bruce in 100 mile house

10-18-2006 19:14:42




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 Re: 1948 8N Misfires after rebuild in reply to Rons1948, 10-18-2006 17:05:47  
When you replaced the valves did you have adjustable lifters? If you did ,did you set them properly? If they were non adjustable lifters did you grind the stems or the seats to set the gap?



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Bruce (VA)

10-18-2006 18:07:54




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 Re: 1948 8N Misfires after rebuild in reply to Rons1948, 10-18-2006 17:05:47  
You're missing something right in front of you. Don't worry; we all do it. You have done all the right things, but you have not done something right. Take it from a guy who spent 10 minutes tracking down a no-fire situation after a simple tune up only to find the rotor laying on the bench. Start with one step at a time. Look at the distributor cap and make sure it is not cracked. Then, look at the numbers on each nipple and remember it fires 1-2-4-3, CCW. Check that the #1 nipple goes to the number one plug, etc. You get the idea. It will be something simple.

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Marks8N

10-18-2006 17:34:39




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 Re: 1948 8N Misfires after rebuild in reply to Rons1948, 10-18-2006 17:05:47  
I have been converted to a hard core Ford tractor nut, or obsession, or addiction in the last 3 months and still love my Chevrolet’s.

I don’t know for sure on an 8N still learning, but on a Chevy car motor if the distributor is 180 degrees out of time it will misfire like you describe. Sounds like the distributor might be 180 degrees out of time. If you removed the distributor you could have installed it a 1/2 turn out of time this being 180 degrees out of time.

I don’t remember from the last time I worked on my father in-laws front mount distributor 2N if you could possibly install the distributor 180 degrees out.

Well first I should have asked if your 8N is a front mount or side mount, but I do think you could put either in a ½ turn out of time.

Some body else let me know if you could put a front mount dist in 180 degrees out I"d like to know?

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Dell (WA)

10-18-2006 19:04:34




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 Re: 1948 8N Misfires after rebuild in reply to Marks8N, 10-18-2006 17:34:39  
Mark..... ..the 2-bolt frontmount distributor has an "off-set" cam slot direct drive scheme and is "impossable" to install 180 outta time. (unless you use a BFH) and in that case you have busted yer distributor body..... ....Dell



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Bruce (VA)

10-18-2006 18:01:26




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 Re: 1948 8N Misfires after rebuild in reply to Marks8N, 10-18-2006 17:34:39  
It's a front mount & wouldn't be running at all if it was 180* out.



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