9N, 2N, Early 8N vs. Late 8N Points Gap

[nkaleida]

Hi all,

Was paging through my manual and noticed the points gap for a side mounted (late 8N) and a front mounted (9N, 2N, early 8N) distributor is different -- got me
thinking a little bit. Side mounted distributors take a 0.025" gap while the front mounts specify 0.015". Anyone have any idea why the change?

Nathan

 

[JMOR]

Cam geometries are different.

 

[nkaleida]

Even if the cam geometries are different, you shouldn't need a larger gap to break the contact between the points right?

 

[Indiana Ken]

(quoted from post at 07:13:44 09/10/20)
Even if the cam geometries are different, you shouldn't need a larger gap to break the contact between the points right?

The important parameter is "dwell" which determines the time the coil has to build voltage - befre the points open. The cam geometry and gap setting determines the dwell time. Since the cam is different it requires a different gap setting.

 

[lha]

If you change the gap,you'll also change the timing. All older dirt bikes,lawnmowers used the point gap to set the timing. Before everyone starts ragging on me,look it up. I know that these machines are different,but not the design of the basic point systems.

 

[JMOR]

(quoted from post at 10:13:44 09/10/20)
Even if the cam geometries are different, you shouldn't need a larger gap to break the contact between the points right?

ven a 0.001" gap will break contact.......but it won't run because most of ignition coil energy will be lost in the point gap arc & not delivered to plugs. The engineer had to compromise/trade-off several factors. He would like a gap wide enough to minimize the arc and open it as fast as possible. However, the cam profile has to be of a shape/profile such that point rubbing block can follow without bouncing. The front mount distributor design is such that the ratio of cam peak-to-flat difference translate directly, that is, 0.015" rubbing block movement to 0.015" point gap opening.
Later designs such as side mount 8Ns & later Fords such as NAA, 600, 801, etc. have a design that multiplies the point gap to about 1.6X the rubbing block movement. This makes it possible to achieve a larger gap without a cam profile that rubbing block can not follow. This is mentioned to make it obvious that you can not just open the gap from 0.015 to 0.025 and expect your front to perform properly, if at all.