Rebuilding distributor

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jcmeyer5

jcmeyer5

Token Ford Guy
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I am working on the distributor for the 340. First off... this housing is cast iron! I’m a Ford guy. Our stuff is aluminum. Anyway...

I have the unit apart. It’s a dual points unit. Stock for the 340. I am going to switch it over to Pertronix. The shaft and bushings are tight. Everything needs degreased, but all the hard parts are in good shape.

Unfortunately, the advance parts have a couple issues. First, the mechanical advance springs are shot. Need new ones. Second, I think the vacuum canister is shot. It won’t pull with vacuum from my vacuum pump. Finally, I have no idea which Pertronix to use.

I see the vacuum canister at Mancini’s. Good god that’s not cheap. Between that, the springs, and what I am guessing is a $125 Pertronix kit, I can darn near just buy a new Pertronix distributor. Am I missing something?
 
How do you know the springs are shot?
Are you staying with the emmisions timing at idle?
vac can's can be expensive. New diaphram can be put in - also not cheap. Which type is on that prestolite?
For performance, the Chrysler distributor for the engine is the best advance curve - except for the emmissions deal. That can be adjusted so you can use a pre-CAP initial timing on the order of 10-12* BTC at 600 - 650 rpm.
 
jcmeyer5 said:
I am working on the distributor for the 340. First off... this housing is cast iron! I’m a Ford guy. Our stuff is aluminum. Anyway...

I have the unit apart. It’s a dual points unit. Stock for the 340. I am going to switch it over to Pertronix. The shaft and bushings are tight. Everything needs degreased, but all the hard parts are in good shape.

Unfortunately, the advance parts have a couple issues. First, the mechanical advance springs are shot. Need new ones. Second, I think the vacuum canister is shot. It won’t pull with vacuum from my vacuum pump. Finally, I have no idea which Pertronix to use.

I see the vacuum canister at Mancini’s. Good god that’s not cheap. Between that, the springs, and what I am guessing is a $125 Pertronix kit, I can darn near just buy a new Pertronix distributor. Am I missing something?
Click to expand...


Don’t guess. Get it on a machine and then you’ll know what it is. I’m am no longer a fan of anything Pertronix. I’d use the points long before I went to a Pertronix unit.
 
I think the springs are shot because it looks like a beaver chewed on them. All stretched out and they don’t do a good job of returning the weights. Someone has been in there before. It also looks like someone ground the pins on the weights to give it more advance. I’m starting to think I should just store this one and get a different one to run. I really wanted to use the stock casting though.

@yellow rose I’ve had a different experience with Pertronix. They’ve always worked well for me. Haven’t had one fail yet. That said, I’ve stayed away from the fancier products and use only the Ignitor II series.
 
Factory timing specs for '68 Plymouth if initial set at spec. Dodge was sometimes a little different but similar.
Initial could be increased or decreased a couple degrees depending on fuel, altitude etc.
upload_2020-4-28_21-46-20.png


With the automatic it should be no problem using 10* initial using premium. Even if the advance is near the max of the specs, timing will only be 32* at 3000, and 35* at 4000 rpm. That's in the ballpark of what that engine will like. It's easy enough to adjust when the secondary spring engages if it needs a little timing above 1500.

I know some Ford performance engines had very different curve. Different engines have different combustion efficiencies (and flame development) and also the difference in piston dwelling at the top etc etc.
 
jcmeyer5 said:
I think the springs are shot because it looks like a beaver chewed on them. All stretched out and they don’t do a good job of returning the weights.
Click to expand...
That's a bummer. These things sometimes do get hacked over the years. :(
The heavy spring (aka secondary spring) has a long loop and only engages when the weights are already out 15-20 degrees.
The light spring definately should return the weights easily even though it has a fairly low spring rate.
Halifaxhops might have what you need. But might have to put it on a machine and try a few to get the advance right. I'm sure he'll respond in the AM.
 
Only high performance Mopars had dual point which were Prestolite distributors. All others had single point aluminum castings, until electronic around 72-ish, and those used pretty much the same/ similar aluminum casting. Frankly if you want to convert to Pertronix, that dual point may be more valuable to a collector "as original." I would scare up a single point distro and convert that to Pertronix if you desire. Be careful, some, I think 383 dist are similar length to 340, but are not the same and rotate opposite direction. You can not convert them to a SB mopar. High deck, 413/ 426/440 are longer shaft yet.
 
@67Dart273 Im thinking of doing that. Still, I really like the look of this casting. Dad always hated the dual points though. Not in a hurry I guess. Engine is not even done yet
 
How about you post some photos of the insides. I used to be a Ford guy too, and a lot of Mopar stuff while similar is just a bit different.

One of the counter weight springs looks all stretched out but that is normal. It doesn't effect anything till the weight gets out a bit.
 
I am kind of with 67 dart find a la alum core and build it. By the time you get new springs, weights , petronix and vac advance probably over $500 easily.
 
So the decision has been made. I am going to go with the Mopar electronic ignition. I go this route for a few reasons, not the least of which is the cost. I was looking at $250 or so to rehab the stock Prestolite and fit it with Pertronix. Instead, I am going to reassemble the stock unit, mark it "needs calibrated" for future me who will forget, and stick it on a shelf.

Thanks for the input everyone! You have been very helpful. Until this thread I didnt know there was basically a drop-in alternative from Mopar for electronic ignition. I have very much learned something.
 
Hope your looking at the repop MP unit the Rick E-berg is selling. That looks to be the closest to providing a matching curve. @halifaxhops might have an older one in good shape.
 
Not sure who Rick E-berg is, but if you can point me in the right direction, I'd be happy to check it out.
 
jcmeyer5 said:
Not sure who Rick E-berg is, but if you can point me in the right direction, I'd be happy to check it out.
Click to expand...
He was a writer and editor at Mopar Action for a long time. Like any of those who were succussfulk in that biusiness; a mix of colorful writing, product placement, and better than average tech. Entered and ran the One Lap of America a few times so not all talk.

Here's the kit he's offering for LA engines.
For MOPAR 318 340 360 HiRev Electronic Ignition Kit Resto Plymouth Dodge Chrys | eBay

Claims to be a copy of the Chrysler built Direct Connection/Mopar Performance distributors. If so, then the advance curve is probably as close as you can find to the 273 Hi Po or 340 as can be bought off the shelf new. You can also buy the distributor alone if you're using a different ECU.
@318willrun has used the Hi-rev 7500 ECU successfully so I would be willing to give that a try.

I measured the timing of an original MP distributor on my previous 340. Subtracting the initial, the advance plot looks like this.
upload_2020-4-30_9-14-10.png


There's probably more like 25* in the advance mechanism, but all electronic ignitions steal some advance in the higher rpms.
Maybe more important, at the time I measured, 900 rpm was as low as I could get a good measurement. It may have started to advance at 700 or so. So there's a a couple degrees that could have been missed at the low rpm.

That's all easy to adjust - once you know how. The initial spring tension is adjustable by turning the perches.
 
I'm using this distributorFireCore Vacuum Advance Electronic Distributor now , the stock mopar electronic one broke ,before that had the Petronix which orked well , but if i broke down parts would be hard to find so it sits in the spare 340 . So far the firecore is working well
 
i used the hi rev 7500 from Rick , it worked as well as the stock ECU , seems like a good deal for the whole kit , i'm just not crazy about the new mopar distributors , 2 have gone bad on me over the last 6 years . Don't know where they are built these days , but they don't have the quality of the older units the old ones lasted years .
Good luck however you decide to go
 
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