Hitachi dizzies - who understands them ?

[steptoe]

talking mechanical advance slots in the hitachi fitted to EA81

to access it I prised the electronics lobe off with two flat blade screwdrivers, then removed the two screws in the inside of the housing holding the plate down, lift that up and you have the spindle that the rotor fits on and at its base is the bit with the slots for the pins to locate in from the centrifugal advance weights

I have one from an electronic dizzy marked ~ "13" & "-10", and another from a points dizzy marked "12.5" & "+5"

A guess that the 12.5 and 13 is a timing value in mechanical advance ?? another guess that the +5 and -10 BLANK ??

the centre line of these slots when viewed from above shows they are not straight up and down
PHOTO COMING



Not a good photo but if you look closely the one on the LEFT has the lean // to the RIGHT at the top of each slot this is ponts dizzy bit
You need to look even more closely at the electronic dizzy slots, they lean \\ the opposite. The two are photo'd with the flat rotor button face facing same way

the one stamped +5 when viewed from above and looking at the one to the top looks like the top of it leans clockwise ( to the right) whereas the one stamped -5 the top of which leans anticlockwise( to the left)

The electronic one is what I had used in my LPG EA81 and brazed the extreme outer of the slots to reduce the maximum mechanical advance in order to get a total advance of no more than 28 degrees to suit the character of LPG combustion. It now has some slop in how the rotor button (NEW) fits so time for a newie shaft - otherwise I would reuse it and not be asking.


REASON FOR THIS POST...sorry

Does anyone understand the difference in timing advance in the way the advance slots are angled ?? Which one gives what ? I am trying to get my head around it. Because ( and many a teacher used to say don't start a sentence with 'because' ) LPG loves advance down low revs but not up high I would best to use the best one for the application. It may just be a suck it and see


expecting Disco to come to the rescue here




I should add that in the past I have brazed up the outer end of the slots to LIMIT mechanical advance to stop higher rev pinging. I also run an initial advance of 12 to 14 with the modded unit. I am just trying to fathom the advance characteristics between the two slot angles, keeping in mind that the rotor turns anti clock with the motor running. I sort of understand advance allowed by the increasing distance from the centre post but not what the different angled slots would allow

[steptoe]

C'mon, there must some snippets ??

I found this

Some Honda and Subaru engines from the same period also used same distributor. Check the number stamped on the distributor body, the one you want is the Model D4R81-## or D4R82-##. The last two digits indicate which advance curve is programmed into it and, as far as I can tell, the 82 has 10° total mechanical advance and the 81 has 15°.

and this:

For the Hitachi distributors, this is completely controlled by the length of the advance slot in the Cam Set (part number 22132-P7100). If you don't know where these are, open up your distributor, take off the rotor, and look under the Breaker Plate Assembly. Now force the weights out and look for where you see the pin moving in the slot. Once you have seen this, it is pretty easy to understand how to change the amount of advance. To get less, braze the slot so it is shorter. If you want more advance, then lengthen the slot.

On the bar with the slot in it will be a number stamped into the metal. It will be 8.5 or 9. These numbers correspond to the number of degrees that the rotor will advance relative to the base of the shaft. Since the crankshaft rotates twice each time the distributor rotates once simply multiply the number by two to get the total mechanical advance.

The second component of Mechanical Advance is the Advance Curve.

The Advance Curve is controlled by the shape and weight of the weights, shape of the cam (in between the weights) and the tension of the springs. If you install lighter springs, the weights will be able to extend out at a lower RPM. If you install heavier springs, it will take a higher RPM for the weights to overcome the force of the springs.

Since the Stator is fixed to the Breaker Plate Assembly, which in turn is fixed to the distributor body, and the Reluctor is fixed to the Cam Set, as the RPM changes, the weights move, and changes the relationship of the Reluctor to the Stator.

[discopotato03]

You may want to check the vacuum advance actuators details as well , these can vary between models with minor engine differences such as compression ratio .

Cheers A .

[Dave.k]

Just a side note. when i bought my brumby it had a 2 lt gemini dizzy. Dont ask me why or how but it's still on there and going ok.... i think. anyone herd of this?

[steptoe]

in my searches I found a fellow selling an electronic dizzie conversion for BMC models. His name escapes me at the moment....M.... anyway, he was leading the world n converting BMC's to the Hitachi electronc dizzy, but he tells me he gave up after some time fiddlng to get the right advance set up. This new dizzy is very clever as it conatins no mechanical advance but has user selectable choice of 17 advance curves to choose from. I have asked what he thinks of his dizzy (or the one he sells) being suitable for EA81 EA82 given they are suposedly similar to the Hitachis he was initially encouraging the world to source and convert to BMC vehicles. Awaiting reply. see it at http://www.tdcperformance.com

[steptoe]

I am just trying to work this slot system out

TURNS anticlockwise
DRIVEN by crankshaft and
as the centrifugal weights fly out advances the rotor button more clockwise, these slots are gong to give a different 'advance' pattern ~ still trying to get my head around it. Called in on a carby/dizzy fella who tells me he can no longer get many dizzy parts and sends his dizzies to precision distributors in Victoria