Duraspark 2 swap - distributor issue - HELP
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Laughing Gas
Joined: Aug 2010
Posts: 983
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From: Northern Kentucky
Duraspark 2 swap - distributor issue - HELP
Vehicle is a 1984 F150 351W. Carb is swapped, emissions gone, wiring all ready. Go to swap distributors and the Duraspark distributor is shorter than the TFI distributor by 1/2 inch from the bottom of the mounting flange to the end. The new distributor is for 351W from 1983 -1987 according to the part number. Everything seems to measure the same except for the length of the shaft below the gear. The replacement is 1" long and the TFI distributor is 1-1/2 inches long. It almost looks like an extension pressed into the end of the shaft but it sure doesn't seem removable. Can anyone tell me what distributor I should be looking for or offer any ideas?
Laughing Gas
Joined: Nov 2011
Posts: 1,033
Likes: 11
From: Wausau, WI
The dizzy you bought should work fine. For some reason, the newer ones have a longer shaft. BUT, you might want to double check that it is engaging the driveshaft correctly.
Is this a motor swap? Just wondering because an '84 should have a duraspark dizzy already.
Is this a motor swap? Just wondering because an '84 should have a duraspark dizzy already.
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Laughing Gas
Joined: Aug 2010
Posts: 983
Likes: 49
From: Northern Kentucky
Thanks for the reply. No, This is not a motor swap: it's the original motor. As I understand, only the 351W HO with 4 bbl carb. was still Duraspark II in '84.
I did get the distributor installed. I used a wood dowel to check the length from the flange at the top of the block to the top of the oil pump drive pin. There was enough length for engagement with the new distributor. It appears that the extra length is all depth of the socket that engages the drive pin.
When Ford designed the TFI distributor it appears that they decided to use a longer length of engagement and a slight taper on the socket to ease installation of the distributor over the drive pin, but didn't change the older style distributor. At least that's what I hope happened. We'll see when I fire it up. If I get oil pressure then all is well; if not then I have a problem.
I did get the distributor installed. I used a wood dowel to check the length from the flange at the top of the block to the top of the oil pump drive pin. There was enough length for engagement with the new distributor. It appears that the extra length is all depth of the socket that engages the drive pin.
When Ford designed the TFI distributor it appears that they decided to use a longer length of engagement and a slight taper on the socket to ease installation of the distributor over the drive pin, but didn't change the older style distributor. At least that's what I hope happened. We'll see when I fire it up. If I get oil pressure then all is well; if not then I have a problem.
Cargo Master
Joined: Dec 2004
Posts: 3,362
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From: Florence, SC
Now that I think back on it, I think my distributor shaft was about 1/2" shorter or so as well when I did my own Duraspark swap. And I think I came to the same conclusion as you did. I did this swap on my truck four years ago and haven't had any problems yet, nor have I heard of anyone else having a problem switching from the TFI distributor and the Duraspark distributor.
Now that you are doing the Duraspark swap, I would strongly recommend that you try to use MOTORCRAFT parts if at all possible. Cheap, aftermarket ignition parts from parts houses that are made in China are notorious for failing early, especially the ignition modules.
In 1984, the 351 was a 2-barrel, and it would not have had the Duraspark ignition. In 1985, the 351 H.O. replaced the earlier 351 and came with a 4-barrel carburetor, and it did have the Duraspark ignition.
Now that you are doing the Duraspark swap, I would strongly recommend that you try to use MOTORCRAFT parts if at all possible. Cheap, aftermarket ignition parts from parts houses that are made in China are notorious for failing early, especially the ignition modules.
Originally Posted by 81ChopTop
Is this a motor swap? Just wondering because an '84 should have a duraspark dizzy already.
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Laughing Gas
Joined: Aug 2010
Posts: 983
Likes: 49
From: Northern Kentucky
Thanks guys, that's comforting to hear. When I saw the difference in length, the first thing I did was call the parts house and check the part number and they said it was correct. Until I did the measurements I was pretty bummed, and put the project down for a while. After a drive and a cup of coffee, I thought about the dowel trick and when I checked I felt confident enough to go ahead. Hearing other people found the same thing and it worked out will make me sleep better tonight
FTE Legend
Joined: Jul 2010
Posts: 32,875
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From: Northeast, OK
By the way, when I did that swap I had the devil of a time getting the dizzy to engage the oil pump drive shaft. It went in only so far and wouldn't drop all the way down, apparently because the hex on the drive shaft didn't align w/that of the dizzy. My nephew said to just crank it over and it would drop down, which I did and it did.
But, I didn't really like that solution as I didn't truly know where the rotor was going to point exactly when it did drop down. So, now I reach down with a priming tool and turn the oil pump shaft slightly and try the dizzy. If that didn't get it I do it again, and again until it does drop down. Usually only takes a couple of tries.
As for what I use for a priming tool, I have an old dizzy that I took the gear off of. But, before that I taped a 5/16" socket to a long 1/4" extension and used a ratchet to turn it. The tape was to ensure the socket wouldn't come off and fall into the engine.
But, I didn't really like that solution as I didn't truly know where the rotor was going to point exactly when it did drop down. So, now I reach down with a priming tool and turn the oil pump shaft slightly and try the dizzy. If that didn't get it I do it again, and again until it does drop down. Usually only takes a couple of tries.
As for what I use for a priming tool, I have an old dizzy that I took the gear off of. But, before that I taped a 5/16" socket to a long 1/4" extension and used a ratchet to turn it. The tape was to ensure the socket wouldn't come off and fall into the engine.
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FTE Legend
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From: Northeast, OK
Actually, I didn't explain completely. To line the pump shaft up I just turn the dizzy's shaft by grabbing the mechanical advance. But, for priming I hook my cordless drill to the shaft. However, unless I REALLY tighten the chuck it sometimes slips, so I'm thinking brazing something to the shaft like a nut.
Laughing Gas
Joined: Nov 2011
Posts: 1,033
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From: Wausau, WI
Gotcha! Learn something new every day. Thanks for clarifying that.
I do pretty much what Gary does for aligning the shaft. For aligning it, I use a socket taped to an extension and turn it a little until it drops in.
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Laughing Gas
Joined: Aug 2010
Posts: 983
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From: Northern Kentucky
Well I probably flirted with danger but I got away with it. I just used the 5/16 socket on a long extension - no tape. My socket snaps on that extension with authority but I was still mighty careful pulling it back out. If there is a next time I think I will use tape.
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