TheAMCForum.com Homepage
Forum Home Forum Home > The Garage > AMC V8 Engine Repair and Modifications
  New Posts New Posts RSS Feed - MSD 8523 Dist with Factory Tach
  FAQ FAQ  Forum Search   Events   Register Register  Login Login

Click for TheAMCForum Rules / Click for PDF version of Forum Rules
Your donations help keep this valuable resource free and growing. Thank you.

MSD 8523 Dist with Factory Tach

 Post Reply Post Reply Page  <123>
Author
Message
 Rating: Topic Rating: 1 Votes, Average 5.00  Topic Search Topic Search  Topic Options Topic Options
White70JavelinSST View Drop Down
Supporter of TheAMCForum
Supporter of TheAMCForum
Avatar

Joined: Aug/08/2012
Location: Minnesota
Status: Offline
Points: 4867
Post Options Post Options   Thanks (0) Thanks(0)   Quote White70JavelinSST Quote  Post ReplyReply Direct Link To This Post Posted: Jan/25/2019 at 4:19pm
70 Javelin SST, second owner, purchased 1972
Back to Top
Someassemblyrqd View Drop Down
Supporter of TheAMCForum
Supporter of TheAMCForum
Avatar

Joined: Jul/02/2012
Location: Renton, wa
Status: Offline
Points: 456
Post Options Post Options   Thanks (0) Thanks(0)   Quote Someassemblyrqd Quote  Post ReplyReply Direct Link To This Post Posted: Jan/25/2019 at 8:24pm
Roger - In your top drawing from MSD, the assumption is a full 12 volts.  But the tach can’t handle the full 12v, or if you assume in the same drawing the voltage is 9.6v from the key to the tach to the coil, the power feed from the coil to the dist is insufficient for it to operate nominally.  The dist needs a full 12v. The tach needs 9.6v as does the charging system to operate properly.  




 
Greg E.
Back to Top
6PakBee View Drop Down
Supporter of TheAMCForum
Supporter of TheAMCForum
Avatar
Charter Member

Joined: Jul/01/2007
Location: North Dakota
Status: Offline
Points: 5454
Post Options Post Options   Thanks (0) Thanks(0)   Quote 6PakBee Quote  Post ReplyReply Direct Link To This Post Posted: Jan/25/2019 at 8:49pm
Originally posted by Someassemblyrqd Someassemblyrqd wrote:

Roger - In your top drawing from MSD, the assumption is a full 12 volts.  But the tach can’t handle the full 12v, or if you assume in the same drawing the voltage is 9.6v from the key to the tach to the coil, the power feed from the coil to the dist is insufficient for it to operate nominally.  The dist needs a full 12v. The tach needs 9.6v as does the charging system to operate properly.

 


Are you sure that the tach won't withstand 12 VDC to ground?  Think about this for a second.  What do you think the voltage is at the coil + terminal with the key on, the points open, and the engine not running?  I would bet that it is at full battery voltage.  So what is the voltage at the tach to ground?  Full battery voltage.  As the AMC tach that is being discussed is a series tach that operates from current pulses, not voltage, I am struggling with the concept that it couldn't be wired as I've shown and work.  I would also comment that the charging system (assuming this is a '69/'70 vehicle) does NOT need the 9.6 volts for proper operation as the regulator voltage sensing terminal is between the alternator output and the isolation diode(s).  The tie to the ignition system is for startup regulator supply only.

Full disclaimer:  I've worked a bit with Ford tachs that are similar to the AMC tachs but not with an AMC tach in particular.
Roger Gazur
1969 'B' Scheme SC/Rambler
1970 RWB 4-spd Machine
1970 Sonic Silver auto AMX

All project cars.

Forum Cockroach
Back to Top
Someassemblyrqd View Drop Down
Supporter of TheAMCForum
Supporter of TheAMCForum
Avatar

Joined: Jul/02/2012
Location: Renton, wa
Status: Offline
Points: 456
Post Options Post Options   Thanks (0) Thanks(0)   Quote Someassemblyrqd Quote  Post ReplyReply Direct Link To This Post Posted: Jan/25/2019 at 11:52pm
Are you sure that the tach won't withstand 12 VDC to ground?  No, I’m not sure, didn’t have an extra tach to sacrifice.  What I do know is the voltage to the tach is ~9.6v.   The pink resistance wire provides this reduced voltage from the ignition .

What do you think the voltage is at the coil + terminal with the key on, the points open, and the engine not running? ~9.6v.  The pink resistance wire, which connected to the yellow wire at the solenoid.  This yellow wire feed power to the I terminal on the solenoid.  The blue wire connected to the same terminal feeds power to the tach and on to the coil + side.


With regards to the charging system, I per port not to be an expert.  All I can say is I’ve read a lot of Billd’s write ups and he has stated that the exciter wire does not want the full 12v



  


Edited by Someassemblyrqd - Jan/26/2019 at 12:30am
Greg E.
Back to Top
6PakBee View Drop Down
Supporter of TheAMCForum
Supporter of TheAMCForum
Avatar
Charter Member

Joined: Jul/01/2007
Location: North Dakota
Status: Offline
Points: 5454
Post Options Post Options   Thanks (0) Thanks(0)   Quote 6PakBee Quote  Post ReplyReply Direct Link To This Post Posted: Jan/26/2019 at 7:43am
Greg,  I fully understand and appreciate your caution in moving forward with your project.  It's hard enough to get 50 year old parts without destroying them due to carelessness or poor choices.  That being said, I think that if you configure your car as I outlined, key on, engine off, points open (or - side of the coil disconnected if you do not have your points distributor) and measure the voltage at the coil + terminal, it will be full battery voltage.  If there is no current through the resistance wire (points open) there will be no voltage drop. 

In the end it may be better to have your tach converted and driven from the tach output on the MSD distributor.  Good luck.  

As to the charging circuit, I stand by my original statement. 
Roger Gazur
1969 'B' Scheme SC/Rambler
1970 RWB 4-spd Machine
1970 Sonic Silver auto AMX

All project cars.

Forum Cockroach
Back to Top
White70JavelinSST View Drop Down
Supporter of TheAMCForum
Supporter of TheAMCForum
Avatar

Joined: Aug/08/2012
Location: Minnesota
Status: Offline
Points: 4867
Post Options Post Options   Thanks (0) Thanks(0)   Quote White70JavelinSST Quote  Post ReplyReply Direct Link To This Post Posted: Jan/26/2019 at 8:44am
I took a couple of pictures this morning, probably won't help anyone a lot, but know that the White70JavelinSST is wired like this.

Three wires from the distributor,

Orange wire to negative side of coil
Red to positive side of coil
Black to ground

Yellow wire from 70 Javelin factory in dash tachometer to positive side of coil.

Disconnected the yellow and pink (or on this car it looks tan/light brown but could be color faded) wire from the solenoid, (not used).


The distributor wire connector is ty-wrapped to the oil fill tube. There is no gray wire on this MSD RTR Billet Distributor. The underhood has never been restored on this 50 yr old car. The engine has never been out so please forgive the appearance.

The tach works fine. It has worked fine for probably ten years wired this way.

The two yellow wires wrapped in the factory thermal cover and just to the front of the voltage regultaor go to the starter side post of the solenoid. The black ground wire from the distributor is grounded to the horn relay mount (wire is seen just above the large red cable to the amplifier and between the two SS braided AC lines). The disconnected yellow and tan wire with a blue piece of tape around it can be seen in front of the voltage regulator and a bit below it.

I do not have a MSD ignition box installed nor is there some other type of tachometer adapter being used.
It's just the MSD 8523 RTR Billet Pro-Distributor, Blaster 2 coil and factory AMC 8k tachometer.



Edited by White70JavelinSST - Jan/26/2019 at 9:39am
70 Javelin SST, second owner, purchased 1972
Back to Top
Bucks AMX View Drop Down
AMC Apprentice
AMC Apprentice
Avatar

Joined: Oct/18/2015
Location: Michigan
Status: Offline
Points: 88
Post Options Post Options   Thanks (0) Thanks(0)   Quote Bucks AMX Quote  Post ReplyReply Direct Link To This Post Posted: Jan/26/2019 at 9:10am
To solve the issue of can't shut car off go to this link (MSD Tech Support) and click the Engine Run On tab. Follow directions, it worked for me. I have the factory tach as well as an Autometer tach and both are operational with the RTR distributor.
1970 AMX 390 4spd Golden Lime
Back to Top
Someassemblyrqd View Drop Down
Supporter of TheAMCForum
Supporter of TheAMCForum
Avatar

Joined: Jul/02/2012
Location: Renton, wa
Status: Offline
Points: 456
Post Options Post Options   Thanks (0) Thanks(0)   Quote Someassemblyrqd Quote  Post ReplyReply Direct Link To This Post Posted: Jan/26/2019 at 1:39pm
Roger - agree, good discussion.  With my ‘70 AMX, I wanted to stay with the original wiring and electrical system schematics.   I initially used Armand’s (White70) wiring diagram for my MSD 8523 dist.  because of common wiring - it didn’t work, hard starting, popping, shuddering, etc.    I believe this due to Armond’s dist being 10years older, no grey wire for tach wave signal, which my dist has.  I believe this is why other current 8523  dist owners are experiencing hard start/run issues.

By adding a discreet 12v line to the dist tied into the ignition wire before the pink resistance wire, I accomplished the best of both old and new:  modern 12v dist, integrated into the original ‘70 wiring, no tach upgrade expense.

Thanks. Greg

Greg E.
Back to Top
PHAT69AMX View Drop Down
AMC Addicted
AMC Addicted
Avatar

Joined: Jul/07/2007
Location: West Virginia
Status: Offline
Points: 5903
Post Options Post Options   Thanks (0) Thanks(0)   Quote PHAT69AMX Quote  Post ReplyReply Direct Link To This Post Posted: Jan/26/2019 at 2:14pm
Probably no help, this worked with MSD Box and a UniLite Conversion,
which obviously is different than a Magnetic PickUp, HAL Effect, or HEI

Back to Top
White70JavelinSST View Drop Down
Supporter of TheAMCForum
Supporter of TheAMCForum
Avatar

Joined: Aug/08/2012
Location: Minnesota
Status: Offline
Points: 4867
Post Options Post Options   Thanks (0) Thanks(0)   Quote White70JavelinSST Quote  Post ReplyReply Direct Link To This Post Posted: Jan/27/2019 at 10:19am
I purchased a second MSD 8523 about four years ago for use in a fresh build 70 390.

I just opened the box to verify.

It has the grey wire, so I'll be using Someassemblyrqd's wiring method probably.

What I find interesting is the popping and sputtering some one posted about earlier. That almost sounds like a way out of time setting problem. Like 180 degrees out of time.
70 Javelin SST, second owner, purchased 1972
Back to Top
 Post Reply Post Reply Page  <123>
  Share Topic   

Forum Jump Forum Permissions View Drop Down

Forum Software by Web Wiz Forums® version 12.03
Copyright ©2001-2019 Web Wiz Ltd.

This page was generated in 1.734 seconds.
All content of this site Copyright © 2018 TheAMCForum unless otherwise noted, all rights reserved.
PROBLEMS LOGGING IN or REGISTERING:
If you have problems logging in or registering, then please contact a Moderator or