TR7 & TR8 Mailing List

Electronic ignitions

0 Members and 1 Guest are viewing this topic.

"Jim Altman"

Electronic ignitions
« on: September 14, 2017, 10:15:17 PM »
So, following our heat soak discussion, which symptoms I have suffered, the

application of sudden cooling assistance (aka water) it appears my heat soak

is coming not from the afm, but my cranecams xr700 ignition module.  This

unit has been in my car for at least ten years, maybe more.


So, I am thinking of replacing it.  It appears that Crane has sold their

ignition products to a company called FAST, but it's unclear to me that they

actually still make the xr700.  Amazon still lists several sources for the

xr700.  It looks like there is a pertronix unit (ignitor lu181a) listed for

the lucas distributor.


Anyone got a more recent ignition purchase and can make me a recommendation?

I have an ignitor (pertronix) unit in my 240z and am happy with it.  It's a

completely inside the dizzy unit without the external box the crane had.



Jim Altman




Archives provided courtesy

Kelvin Dodd

Re: Electronic ignitions
« Reply #1 on: September 15, 2017, 08:58:53 AM »

Speaking officially for Moss Motors Tech Department. We have seen no change in

quality or operation of the XR700 amps since the purchase of Crane and the

later change to FAST packaging.

We did lose the V8 cutting wheel a while ago and sometimes the points wheels

have not had the retaining spring clips installed. But the amp reliability

appears to be unchanged.

I'm still happy recommending them.

Btw. For a while now the amps have a signal LED that makes them easier to set.


Sent by smoke and mirrors.


"Jim Altman"

Re: Electronic ignitions
« Reply #2 on: September 21, 2017, 02:42:00 PM »
Well, here is the next chapter.  I went into the dizzy to look to see if new

XR700 units use the same optical pickup as old ones.  (Could I just replace

the control unit?)  Inside the dizzy was an UNBELIEVABLE quantity of packed

dust.  I took things apart and I have no idea where the dust had come from.

There is no indication that anything was rubbing on anything.  The trigger

wheel is not grooved or cut into, the sensor was nice and evenly spaced above

and below the wheel.  I had put a new rotor and cap on last spring and both

appeared fine.   Nor was there any dust in there last spring. But, the gaps in

the trigger wheel were seriously impacted with dust.  I cleaned it all out and

been driving around and it now seems fine.  The engine clearly is running

better and cooler.

So, electronic gurus (Jim T?), could obstruction of the light beam, separately

from making the car run like crap, cause overheating of the control unit?

It's easy to anthropomorphize the control unit and say it had to "work harder"

with weaker signal from the sensor, but it either gets a sufficient signal and

triggers a spark or doesn't.   The "kinda" signal ought to be enough to

trigger the unit or not.  But, then I have not seen a schematic of the control

units innards to really know what's going on in there.

So, I have a replacement unit (Thanks Ted) which for the time being is going

to sit on the shelf while I see what happens next.


Jim Altman



Re: Electronic ignitions
« Reply #3 on: September 21, 2017, 06:04:36 PM »
Depending on how the dust was effecting the shutter wheel it is possible that the light beam was being interrupted intermittently during the period that the wheel had a slot positioned over the light beam.  This would cause the transistor to switch at a high rate of speed which could cause a greater amount of switching losses and cause an overheat.  It would also mean the coil current would not build up to the appropriate level causing  poor running.



Dave Massey

"Jim Altman"

Re: Electronic ignitions
« Reply #4 on: September 21, 2017, 08:13:36 PM »
I knew there had to be a reasonable explanation that did not ascribe human

qualities to an electronic device.  The only electronic device I own that has

human qualities and emotions is my PC.

I wonder if the dust might not have been attracted by static electricity from

an imperfect connection by the rotor to the plug wire connecting points inside

the dizzy cap.

Thanks Dave

Jim Altman


Re: Electronic ignitions
« Reply #5 on: September 22, 2017, 07:43:43 AM »
They say that the definition of insanity is doing the same thing repeatedly and expecting different results.  Yet, that is exactly what happens when you use a computer.  I dunno if that qualifies as human qualities and emotions, maybe it does.


I don't know the source or the nature of the dust but perhaps there was some oil that caused it to become attached when it normally would have passed on by.



Dave Massey