GMCforum: GMCnet » timing question

Home » Public Forums » GMCnet » timing question

Show: Today's Messages :: Polls :: Message Navigator

timing question [message #145499]

Tue, 04 October 2011 17:27

chasingsummer

Messages: 434
Registered: May 2011
Location: asheboro, nc

Karma: 0

Senior Member

first power up after timing chain replacement,
tach/dwell meter as well as timing light are old sears i bought on ebay.
start up and let run 3 or 4 minutes. no leaks.
turn off, hook up tack and start back up, (breather is off if matters) rpm reading of 500, sounds steady, turn off, pull vacuum line at dizzy and hook up timing light. start back, light slowly on/off so i assume the 500 is a good reading. look at timing mark and dead on the 8 mark. give gas to 800 rpm by tack, mark still on, advance rpm to approx 1100 and timing mark no longer at the 8. sake of argument i would say approx half inch past the 8 degree, but steady not waving. i did inspect balancer when it was off, no indication of it not being good.
i am low on gas, so no plan on driving around block til weekend,
i dont want to just start adjusting things without good reason. i am surprised my motor is as smooth as it is at the 500 rpm , and that is assuming tack is correct.
any input?
thanks bgk

brian asheboro, nc 75 eleganza, 74 build 119k miles and counting, DOG HOUSE

Report message to a moderator

Re: timing question [message #145503 is a reply to message #145499]

Tue, 04 October 2011 17:35

fred v

Messages: 999
Registered: April 2006
Location: pensacola, fl.

Karma: 0

Senior Member

chasingsummer wrote on Tue, 04 October 2011 17:27

sounds good to me. at 800 RPM the mechanical advance in the dist. may have kicked in. it shouldn't at that speed. normal idle is 7 to 800 and set the timing at that speed. the carb idle screw on the left side linkage should be backed off all the way. also plug the vacuum hose that you take off the dist. when you set timing.

Fred V
'77 Royale RB 455
P'cola, Fl

Report message to a moderator

Re: timing question [message #145506 is a reply to message #145503]

Tue, 04 October 2011 17:47

chasingsummer

Messages: 434
Registered: May 2011
Location: asheboro, nc

Karma: 0

Senior Member

vacuum line is plugged, golf tee,
my idle screw at linkage, based on my uneducated guess , but looking at other linkage pieces on same shaft, i would appear to me it is all the way out, or atleast amy more out has not effect on mechanical movement.

brian asheboro, nc 75 eleganza, 74 build 119k miles and counting, DOG HOUSE

Report message to a moderator

Re: [GMCnet] timing question [message #145540 is a reply to message #145499]

Tue, 04 October 2011 20:24

USAussie

Messages: 15912
Registered: July 2007
Location: Sydney, Australia

Karma: 6

Senior Member

Brian,

I have made the assumption that your ignition system is HEI.

Reference: MM X-7525
Section:
Page: 6Y-38

IGNITION TIMING

The ignition timing marks are located on the engine front cover. A saw slot on the balancer indicates engine top dead center.
(figure 33)

To adjust ignition timing, proceed as follows:

1. Remove air cleaner and plug manifold vacuum fitting.

2. Disconnect vacuum hoses at carburetor and plug fittings.

3. Connect tachometer and adjust engine speed to 1100 rpm with transmission in neutral.

4. With the use of a timing light, set timing to 8�BTDC by loosening the distributor clamp bolt and rotating the distributor until
the specification is obtained.

NOTE: The indicator has four "V" slots, each representing 4�.

5. Tighten the distributor clamp bolt and recheck timing to make sure distributor was not moved during tightening of bolt.

NOTE: If a tuned engine detonates with this setting, the cause is low octane fuel or excessive carbon build-up in the combustion
chamber. If these factors are not corrected, the timing should be retarded 2 degrees from the specified setting.

6. Remove plug from fittings and connect hoses to carburetor. Remove tape from manifold fitting and connect vacuum hose, install air
cleaner.

Reference: MM X-7525
Section: 6Y - Engine Electrical
Page: 6Y-59

HIGH ENERGY IGNITION SYSTEM SPECIFICATIONS
(*) Set with Vacuum in Retard Position.
IGNITION TIMING
Idle Speed (RPM): Federal / California - 1100 / 1100
Distributor Setting: Federal / California - 8�BDTC 8� BDTC
* With Distributor Vacuum Ports on Carburetor Plugged

Regards,
Rob M.
Sydney, Australia
AUS '75 Avion-The Blue Streak TZE365V100428
USA '75 Avion-Double Trouble TZE365V100426

-----Original Message-----
From: Of brian

first power up after timing chain replacement,
tach/dwell meter as well as timing light are old sears i bought on ebay.
start up and let run 3 or 4 minutes. no leaks.
turn off, hook up tack and start back up, (breather is off if matters) rpm reading of 500, sounds steady, turn off, pull vacuum line
at dizzy and hook up timing light. start back, light slowly on/off so i assume the 500 is a good reading. look at timing mark and
dead on the 8 mark. give gas to 800 rpm by tack, mark still on, advance rpm to approx 1100 and timing mark no longer at the 8. sake
of argument i would say approx half inch past the 8 degree, but steady not waving. i did inspect balancer when it was off, no
indication of it not being good.
i am low on gas, so no plan on driving around block til weekend,
i dont want to just start adjusting things without good reason. i am surprised my motor is as smooth as it is at the 500 rpm , and
that is assuming tack is correct.
any input?
thanks bgk
--
brian
asheboro, nc
75 eleganza 2 74 build
118k miles and counting,
DOG HOUSE

_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist

_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist

Regards, Rob M. (USAussie) The Pedantic Mechanic Sydney, Australia '75 Avion - AUS - The Blue Streak TZE365V100428 '75 Avion - USA - Double Trouble TZE365V100426

Report message to a moderator

Re: [GMCnet] timing question [message #145644 is a reply to message #145540]

Wed, 05 October 2011 17:44

chasingsummer

Messages: 434
Registered: May 2011
Location: asheboro, nc

Karma: 0

Senior Member

Robert
you are correct with me having the hei dizzy
i will see this weekend how she runs, but before gear set she ran fine, chain was alightly loose, if i had to guess, maybe 4 degrees of slack.
i am not convenced i need to increase idle to 800,i thin 800 would be spec. ???
i also wonder, since it seems my mechanical advance kicks in at approx 1000rpm, if i set timing at 8 degrees with idle up at 1100 which is after my mechanical advance kicks on, then at idle i will be the other side of tdc, which then i assume idle will be terrible. i do wonder if my dizzy may be one meant for a car and that maybe my advance happens too soon ?
i sure hope to receive more input before i adjust anything.
otherwise, i did read the manual, my marks have been painted so they are easy to ID. i did not have vacuum lines removed from my carb, only the one at dizzy, i will remove and plug them, but i dont see that truely changing the readings i presently have.
i also did not check with trans in neutral, only in park. driveway is slight incline and bogies are aired down onto blocks. it is hard to get much done after work and before dark so most stuff waits till weekend.
presently seeking as much info as i can get. i understand it may not be set up by the book. i also understand if it aint broke than dont fix. i have not had any backfiring, and correcting my vacuum lines a while back took care of my dieseling issues. but i was surprised to see that after timing chain replacement that timing mark was dead on the 8 at idle
this sure has been a learning experience,

brian asheboro, nc 75 eleganza, 74 build 119k miles and counting, DOG HOUSE

Report message to a moderator

Re: [GMCnet] timing question [message #145651 is a reply to message #145644]

Wed, 05 October 2011 19:31

jhbridges

Messages: 8412
Registered: May 2011
Location: Braselton ga

Karma: -74

Senior Member

Mine idles happily and smoothly warm at 500 on the tach.� That's hwere I would set it if I were you, and that's where I'd time it.� As long as it's running, the slack of the chain is not on the pulling side.� Thus unless it's so loose it skips a cog, slack isn't a problem as far as setting the timing with the engine running is concerned.� (Not so for static timing)
�
--johnny
'76 23' Norris
'76 Palm Beach

________________________________
From: brian <chasingsummer@triad.rr.com>
To: gmclist@temp.gmcnet.org
Sent: Wednesday, October 5, 2011 6:44 PM
Subject: Re: [GMCnet] timing question

Robert
you are correct with me having the� hei dizzy
i will see this weekend how she runs, but before gear set she ran fine, chain was alightly loose, if i had to guess, maybe 4 degrees of slack.
i am not convenced i need to increase idle to 800,i thin 800 would be spec. ???
i also wonder, since it seems my mechanical advance kicks in at approx 1000rpm, if i set timing� at 8 degrees with idle up at 1100 which is after my mechanical advance kicks on, then at idle i will be the other side of tdc, which then i assume idle will be terrible. i do wonder if my dizzy may be one meant for a car and that maybe my advance happens too soon ?
i sure hope to receive more input before i adjust anything.
otherwise, i did read the manual, my marks have been painted so they are easy to ID. i did not have vacuum lines removed from my carb, only the one at dizzy, i will remove and plug them, but i dont see that truely changing the readings i presently have.
i also did not check with trans in neutral, only in park. driveway is slight incline and bogies are aired down onto blocks. it is hard to get much done after work and before dark so most stuff waits till weekend.
presently seeking as much info as i can get. i understand it may not be set up by the book. i also understand if it aint broke than dont fix. i have not had any backfiring, and correcting my vacuum lines a while back took care of my dieseling issues. but i was surprised to see that after timing chain replacement that timing mark was dead on the 8 at idle
this sure has been a learning experience,
--
brian
asheboro, nc
75 eleganza 2 74 build
118k miles and counting,
DOG HOUSE

_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist

Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons. Braselton, Ga. I forgive them all, save those who hurt the dogs. They must answer to me in hell

Report message to a moderator

Re: [GMCnet] timing question [message #145670 is a reply to message #145644]

Thu, 06 October 2011 00:00

USAussie

Messages: 15912
Registered: July 2007
Location: Sydney, Australia

Karma: 6

Senior Member

Brian,

Setting the idle to 1100 rpm is for the purposes of timing, I copied the following procedures for setting the Slow and Fast Idle
from the MM as noted. By the way it's NOT easy to find these two procedures that's for bloody sure!

Ref: MM X-7525
Section: Engine Fuel System
Page: 6M-23
Step: 12 - SLOW IDLE ADJUSTMENT

CHOKE VALVE WIDE OPEN AND CAM FOLLOWER OFF STEPS OF FAST IDLE CAM

1. ENGINE AT NORMAL OPERATING TEMPERATURE. REMOVE AIR CLEANER DISCONNECT AIR CLEANER VACUUM HOSE
AT INTAKE MANIFOLD, THEN PLUG FITTING.

2. CHOKE OPEN AND AIR CONDITIONING OFF.

3. SET PARKING BRAKE AND BLOCK DRIVE WHEELS.

4. DISCONNECT CARBURETOR HOSE FROM VAPOR CANISTER (PLUG HOSE).

5: DISCONNECT DISTRIBUTOR VACUUM NOSE AT DISTRIBUTOR AND PLUG.

6. WITH DWELL AND TIMING PROPERLY ADJUSTED AND TRANSMISSION IN DRIVE ADJUST IDLE SPEED TO OBTAIN 600 R.P.M.

7. CONNECT DISTRIBUTOR VACUUM AND CONNECT CARBURETOR HOSE TO VAPOR CANISTER, CONNECT AIR CLEANER HOSE AND INSTALL AIR CLEANER.

Ref: MM X-7525
Section: Engine Fuel System
Page: 6M-23
Step: 13 - FAST IDLE ADJUSTMENT

CAM FOLLOWER ON LOW STEP OF FAST IDLE CAM AGAINST SHOULDER OF NEXT HIGHER STEP

1. ENGINE AT NORMAL OPERATING TEMPERATURE REMOVE AIR CLEANER, DISCONNECT AIR CLEANER VACUUM HOSE AT INTAKE MANIFOLD, THEN PLUG
FITTING.

2. CHOKE OPEN AND AIR CONDITIONING OFF.

3. SET PARKING BRAKE AND BLOCK DRIVEWHEELS.

4. DISCONNECT CARBURETOR HOSE FROM VAPOR CANISTER AND PLUG

5. DISCONNECT DISTRIBUTOR VACUUM ROSE AT DISTRIBUTOR AND PLUG.

6. WITH DWELL AND TIMING PROPERLY ADJUSTED, PLACE CAM FOLLOWER ON LOW STOP AND AGAINST SHOULDER OF NEXT HIGHER STEP. ADJUST FAST
IDLE SCREW TO OBTAIN 1100 RPM (TRANS. IN PARK).

7. UNPLUG DISTRIBUTOR VACUUM HOSE AND RECONNECT TO DISTRIOUTOR. UNPLUG VACUUM FITTING AT INTAKE MANIFOLD AND RECONNECT AIR CLEANER
HOSE CONNECT CARBURETOR HOSE T0 CANISTER. INSTALL AIR CLEANER AND RECHECK IDLE RPM.

As far as the rest of your comments go I see the following words; guess, maybe, think, wonder, seems, assume, etc. You also note "if
it ain't broke don't fix it." The only way you will KNOW if it's broke or not is to check everything step by step as per the
Maintenance Manual.

Aussie Tradesmen have a saying; "she'll be right, Mate, no worries!" Whenever a tradesman says that to me I START worrying! ;-)

Regards,
Rob M.

-----Original Message-----
From: brian

Robert
you are correct with me having the hei dizzy
i will see this weekend how she runs, but before gear set she ran fine, chain was alightly loose, if i had to guess, maybe 4 degrees
of slack.
i am not convenced i need to increase idle to 800,i think 800 would be spec. ???
i also wonder, since it seems my mechanical advance kicks in at approx 1000rpm, if i set timing at 8 degrees with idle up at 1100
which is after my mechanical advance kicks on, then at idle i will be the other side of tdc, which then i assume idle will be
terrible. i do wonder if my dizzy may be one meant for a car and that maybe my advance happens too soon ?
i sure hope to receive more input before i adjust anything.
otherwise, i did read the manual, my marks have been painted so they are easy to ID. i did not have vacuum lines removed from my
carb, only the one at dizzy, i will remove and plug them, but i dont see that truely changing the readings i presently have.
i also did not check with trans in neutral, only in park. driveway is slight incline and bogies are aired down onto blocks. it is
hard to get much done after work and before dark so most stuff waits till weekend.
presently seeking as much info as i can get. i understand it may not be set up by the book. i also understand if it aint broke than
dont fix. i have not had any backfiring, and correcting my vacuum lines a while back took care of my dieseling issues. but i was
surprised to see that after timing chain replacement that timing mark was dead on the 8 at idle
this sure has been a learning experience,
--
brian

_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist

Regards, Rob M. (USAussie) The Pedantic Mechanic Sydney, Australia '75 Avion - AUS - The Blue Streak TZE365V100428 '75 Avion - USA - Double Trouble TZE365V100426

Report message to a moderator

Re: timing question [message #145835 is a reply to message #145499]

Fri, 07 October 2011 15:06

chasingsummer

Messages: 434
Registered: May 2011
Location: asheboro, nc

Karma: 0

Senior Member

i did get a responce from dick patterson which made sence to me, so i will follow it. my corcerns with the book were that at the 1100 rpm, my mechanical advance was on, so if i set to 8 degrees there, then at idle i would be on the other side of tdc. it appeared i would stay on the wrong side of tdc til approx 1000 rpm. i am new to this but i did understand that would not be correct.
plan is to increase idle, i may not go as high as 750 as suggested, or i may depending on how she drives, then adj to 12 degrees, then i may need to back up to 10 degrees, again depending on how she drove .

at 750 rpm my mechanical advance is not on, so i will still be on proper side of tdc. \
thansk to all for there input
bgk

brian asheboro, nc 75 eleganza, 74 build 119k miles and counting, DOG HOUSE

Report message to a moderator

Re: timing question [message #145843 is a reply to message #145835]

Fri, 07 October 2011 16:06

Ken Burton

Messages: 10030
Registered: January 2004
Location: Hebron, Indiana

Karma: 10

Senior Member

I think you are making more out of this than necessary.

GMC Ignition timing is based on the components. Base or static timing, mechanical advance, and vacuum advance.

Your are trying to set the static or base timing. In order to do this you need to make sure the other two components are not providing additional advance while you are look at the timing mark light with a light.

Crippling the vacuum advance is simple. Just disconnect the hose at the distributor and block it while you are adjust the static timing.

Crippling the mechanical advance is done by running the engine slower than the point where the advance begins to take effect. If the mechanical advance starts at 1000 RPM then setting the base timing with a light at any engine speed BELOW 1000 RPM should achieve the same results.

The end result is the slower you run engine when setting the base or static timing the more likely it is that you will get it correct.

Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana

Report message to a moderator

Previous Topic:	electric fans (again) checking the math
Next Topic:	How do I clean the inside of a small plastic fuel tank.

Goto Forum:

-=] Back to Top [=-

Current Time: Sun Nov 17 15:58:28 CST 2024

Total time taken to generate the page: 0.00940 seconds