No response on the truck side yet OT but MoPar

[Reg Evans]

http://www430.pair.com/p15d24/mopar_forum/showthread.php?t=16595

[randroid]

Reg,

I had dual points in a '55 Plymouth sedan. It was a small OHV V-8 but that was when I was in High school and I don't remember any details.

The concept of dual points was rather brilliant in that the distributor would move at half the speed of a normal one, thereby lowering the incidence of 'bounce'. That was the concept, but in reality they were a pain in the butt to set because you needed to block-off one side while adjusting the other. They never became a favorite with mechanics.

-Randy

[Plymouthy Adams]

think you are a bit confused as to the dual points..

[randroid]

Tim,

That's how it was explained to me, and it makes sense. Do you have a different answer?

-Randy

[Reg Evans]

There are 8 lobes on the dist. shaft and the second set of points just opens a little later than the first set or is it vice versa.

[Plymouthy Adams]

distributor speed is the same with either setup..the purpose of the dual point is that the opening and closing overlap and thus saturate the coil for a hotter spark for high speed opertion..no spark will occur until both set of points are open

Reg..the first set closes and before it opens the second set closes..they are parallel so the circuit is yet unbroken..when the second set opens you fires the coil ...

Edited July 17, 2009 by Tim Adams

[Don Coatney]

Tim is correct. Dual points offer an overlap in dwell time to give the coil more saturation time. I have been running dual points in my engine sence I installed it.

[Don Coatney]

There are 8 lobes on the dist. shaft and the second set of points just opens a little later than the first set or is it vice versa.

Reg;

Only 6 lobes on the distributor shaft. The point mounting plate has an off-set so one set of points opens, then the next set of points opens, then the first set of points closes, then the second set of points closes. This gives more duration and coil saturation time.

[randroid]

Gents,

I stand corrected after forty years of misconception, and thanks for setting me straight.

-Randy

[Plymouthy Adams]

Don...being in Jacksonville..drive on over tomorrow for a steak...will try to get the Lou-man to show up also...give me a heads-up if this is doable..or any other day that you may have free while this close..

[Dodgeb4ya]

Reg,

I had dual points in a '55 Plymouth sedan. It was a small OHV V-8 but that was when I was in High school and I don't remember any details.

The concept of dual points was rather brilliant in that the distributor would move at half the speed of a normal one, thereby lowering the incidence of 'bounce'. That was the concept, but in reality they were a pain in the butt to set because you needed to block-off one side while adjusting the other. They never became a favorite with mechanics.

-Randy

Randy,

I special ordered a new Mallory "Rev Pol" distributor-think that was the name of it for my 51 Plymouth in 1969. I wanted a optional 3 lobe cam for higher RPM-just what I needed or so I thought. I used to be able to get to 5000RPM in 1st gear=30 MPH. Anyway the 3 lobe cam gave smoother transition for points to open and close with out point bounce like what you mentioned. Distributor shaft speed is normal-1/2 speed of the crankshaft.

This is a picture of it today still in the same car. Still works good, and I see that I need to clean it up a bit-little oily. Like me I don't rev it to 5000 RPM anymore either!

Bob

[randroid]

Bob,

Thanks. It's reassuring to know I wasn't entirely wrong.

-Randy

[Plymouthy Adams]

controlling/preventing point bounce is the job of the contact point spring..very similar to that of valve springs..higher rpm requires stiffer springs to ensure closing to prevent 'float' condition..the replacement points in Mallory distributors, due to the implied higher performance, will ensure one is getting a stiffer contact spring.

[Dodgeb4ya]

controlling/preventing point bounce is the job of the contact point spring..very similar to that of valve springs..higher rpm requires stiffer springs to ensure closing to prevent 'float' condition..the replacement points in Mallory distributors, due to the implied higher performance, will ensure one is getting a stiffer contact spring.

Just as in the design of a performance engine camshaft and valves- both the cam lobe ramp contour/speed of rise ect. and spring pressure are important design issues to prevent valve float-same theory with the 3 lobe distributor cam. I also have a "Spaulding Flamethrower" 4 lobe cam in my Chrysler Hemi engine. They -(Spaulding) touted the higher attainable RPM's with the 4 lobe cam design.Too much spring pressure can cause premature wear on contact point rubbing blocks and distributor cam lobes so they created back in the day this 1/2 cylinder lobe design as a new high performance marketing? -solution.

Bob

[1955 plymouth]

It looks exactly like the dist in my '55 Belvederes with the v8 engines, I have two and they are exactly like that, badge and all.

I would be interested to purchase if you figure you don't need it any longer.

[Reg Evans]

Don,

My dual point setup is for my 315 Poly V-8. Same principal as the 6....just two more cylinders.

Reg;

Only 6 lobes on the distributor shaft. The point mounting plate has an off-set so one set of points opens, then the next set of points opens, then the first set of points closes, then the second set of points closes. This gives more duration and coil saturation time.

[Plymouthy Adams]

true, ramp angle plays an important part especially in the closing of the points to try and prevent slamming and wear....in the 3 lobe for 6 or 4 lobe for 8 application of pictured distributor..the speed is the same, the points still open at the same speed..the only thing here is that 3 cylinders are fired from one set of points and three from the other..the one set is closed while the other is open..in this design I will agree that the 1/2 cycle of the point by alternating their application in the firing order will prevent high speed bounce..further..am not sure without seeing the position of the points as to their offset if the longer ramp of the 1/2 number of lobes will equally go toward saturation..though it is dual points..it is not the original dual point concept of the stock distributor..

[Don Coatney]

Don...being in Jacksonville..drive on over tomorrow for a steak...will try to get the Lou-man to show up also...give me a heads-up if this is doable..or any other day that you may have free while this close..

Free time off? I dont think so. As much as I would like to visit I will not be able to do so on this trip. But thanks for the invite.

Randy,

I special ordered a new Mallory "Rev Pol" distributor-think that was the name of it for my 51 Plymouth in 1969. I wanted a optional 3 lobe cam for higher RPM-just what I needed or so I thought. I used to be able to get to 5000RPM in 1st gear=30 MPH. Anyway the 3 lobe cam gave smoother transition for points to open and close with out point bounce like what you mentioned. Distributor shaft speed is normal-1/2 speed of the crankshaft.

This is a picture of it today still in the same car. Still works good, and I see that I need to clean it up a bit-little oily. Like me I don't rev it to 5000 RPM anymore either!

Bob

Interesting. I had not given any thought to a gearset reducing the distributor speed to 1/4 crankshaft speed. The dual point setup with the 1/4 crankshaft speed should not need a heavier spring but instesd a lighter spring in my thinking. And the dwell time may be increased but I need to do the math to figgure it out. Interesting concept. Makes me wonder how much efficiency is lost in the extra gears required to reduce the distributor speed.