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Aussie Dave Offline
#1 Posted : Monday, 3 April 2023 10:53:14 AM(UTC)
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Hi everyone, need your advice again. A 253 HZ with initial advance of 42 degrees at idle and 50 total with the vacuum disconnected. The engine is happy at this idle advance, stalls if its too much lower. I have fitted a new the harmonic balancer in case the balancer had moved, this did not change any of the results. Have also fitted different distributors, also no material change. Car also has the correct carby, but as I said these results are with vacuum disconnected so the carby is not the variable.
I do not know the history of the engine, could the cam timing be out and the ignition timing is trying to compensate, or any other suggestions would be appreciated. Thanks again.
Dr Terry Offline
#2 Posted : Monday, 3 April 2023 11:45:42 AM(UTC)
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Originally Posted by: Aussie Dave Go to Quoted Post
Hi everyone, need your advice again. A 253 HZ with initial advance of 42 degrees at idle and 50 total with the vacuum disconnected. The engine is happy at this idle advance, stalls if its too much lower. I have fitted a new the harmonic balancer in case the balancer had moved, this did not change any of the results. Have also fitted different distributors, also no material change. Car also has the correct carby, but as I said these results are with vacuum disconnected so the carby is not the variable.
I do not know the history of the engine, could the cam timing be out and the ignition timing is trying to compensate, or any other suggestions would be appreciated. Thanks again.


I think you are correct with your first guess, if it won't idle at 10-20 degrees the cam timing must be out.

Dr Terry
If at first you don't succeed, just call it Version 1.0
Aussie Dave Offline
#3 Posted : Monday, 3 April 2023 3:48:43 PM(UTC)
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Thankyou, I thought it would be best to check before I started pulling everything apart. Appreciate the advice, thanks
KBM Offline
#4 Posted : Monday, 3 April 2023 4:19:04 PM(UTC)
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sounds like someone has put the timing chain on to chev specs as in both dots lining up on both cogs. Holden has bottom and top dots about 6 or 7 links apart.
Aussie Dave Offline
#5 Posted : Monday, 3 April 2023 6:26:20 PM(UTC)
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Thanks, the previous owner was heavily into big block chevs. I will check the cam timing tomorrow, I think Holden is 9 links. Thanks for your thoughts. Regards Dave (this is a possible duplicate reply, my last attempt seems to have disapeared.)
Smitty2 Offline
#6 Posted : Monday, 3 April 2023 9:31:11 PM(UTC)
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Originally Posted by: Aussie Dave Go to Quoted Post
Thanks, the previous owner was heavily into big block chevs. I will check the cam timing tomorrow, I think Holden is 9 links. Thanks for your thoughts. Regards Dave (this is a possible duplicate reply, my last attempt seems to have disapeared.)


yup.. Holden V8s are always 9 links between the links on the timing chain
(irrespective of what the bottom chain gear is, as some are quite retarded timing wise)
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Dr Terry Offline
#7 Posted : Tuesday, 4 April 2023 7:58:33 AM(UTC)
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It was very confusing the way GMH did the V8 cam timing. What was wrong with dot-to-dot, this was the waY 6-cyls were done as were SBC V8s.

Anyway for 253/308 it's 9 links from dot to dot INCLUSIVE, not "between".

Dr Terry
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Aussie Dave Offline
#8 Posted : Tuesday, 4 April 2023 8:16:41 AM(UTC)
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Thanks Dr Terry, I will try to get at it later today, so it will be interesting to see what I find. Will report back later. Thanks Dave
HK1837 Offline
#9 Posted : Tuesday, 4 April 2023 9:04:10 AM(UTC)
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Will be interesting to see how far advanced or retarded it is if that is what is done.
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Aussie Dave Offline
#10 Posted : Tuesday, 4 April 2023 5:31:26 PM(UTC)
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Checked the cam timing, all ok, 9 links. The crank sprocket has only 1 keyway option. Car is only partly reassembled, next to check another timing light. Currently using snap on with digital advance, I will get out my old timing light and try that.
MelbHZ Offline
#11 Posted : Tuesday, 17 September 2024 11:13:53 AM(UTC)
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Hi Aussie Dave, have you anything to report back on your findings with the issue you have?
I have the exact same issue with my HZ 253, I tried a brand new balancer and still got the same readings, then I installed a new cam, with the correct timing chain alignment, still the same issue, I have now changed the distributor to an electronic one, and guess what??
Still the same issue.....
I'm going to borrow a timing light from someone to test it, that's my last resort. In saying that, the timing light I have is not a cheapo, so will be very dissapointed if it is buggered.
castellan Offline
#12 Posted : Friday, 20 September 2024 5:00:52 PM(UTC)
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HX-Z V8 Distributor. What is the difference from the HQ etc. Regarding ADR27A and all this retarding the timeing in gears bar top gear !
So when you put such on a Dyno in any gear but top gear the reading will be wrong because the timeing will be retarded.

I seen a lot of people pulled of the wire to the Temp sensor to the head, that meant that they just destroyed perfomance and fuel economy.
And if they pulled the wire off the Gear box the same thing, you have a engine that is stuck in retarded mode.

But of the HX dizzy it's self ?
I have seen the Blue motors have this big box on the side ! can that bugger up or not work properly or retard the spark ?
I know all about the springs and weights in a dizzy in how they do function and the Vac advance canister.

So if one pulls off the wires to temp or gear box, how does the dizzy know to retard ?
Dr Terry Offline
#13 Posted : Friday, 20 September 2024 5:04:52 PM(UTC)
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Originally Posted by: castellan Go to Quoted Post

So if one pulls off the wires to temp or gear box, how does the dizzy know to retard ?


The temp sensor & the gearbox switch control the vacuum solenoid. Unless the engine is up to temp & in top gear, the dissy receives no vacuum to the vac diaphragm.

Dr Terry
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Smitty2 Offline
#14 Posted : Friday, 20 September 2024 6:54:54 PM(UTC)
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Originally Posted by: Aussie Dave Go to Quoted Post
Hi everyone, need your advice again. A 253 HZ with initial advance of 42 degrees at idle and 50 total with the vacuum disconnected. The engine is happy at this idle advance, stalls if its too much lower. ...............


if you lower the initial advance back towards 18 and at the same time INCREASE the carb idle speed adjustment
will it idle WITH the vac line re-attached?

doing it when in D is the trick here if its an auto

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stevo Offline
#15 Posted : Saturday, 21 September 2024 7:31:55 AM(UTC)
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only on a manual it wouldn't allow vac advance unless in top gear the first thing a young petrol head would do was to change that vac line so it came directly from the carby not that it achieved anything. What goes vac advance do when you have your foot flat to the floor. lol If ole mate above converted to an electronic distubtor did he get a full 12 volt to it?
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HK1837 Offline
#16 Posted : Saturday, 21 September 2024 12:06:59 PM(UTC)
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Originally Posted by: stevo Go to Quoted Post
only on a manual it wouldn't allow vac advance unless in top gear the first thing a young petrol head would do was to change that vac line so it came directly from the carby not that it achieved anything. What goes vac advance do when you have your foot flat to the floor. lol If ole mate above converted to an electronic distributor did he get a full 12 volt to it?


Autos have the spark control as part of ADR27A too. Its EGR that is auto only, manuals have a blanking plate where the EGR valve goes. As Dr Terry says, there is a switch on the back of the RHS head (engine side on 6cyl) and another one on the gearbox (3-4 selector manual and back of the box on an auto) The one on the gearbox just switches to 0V chassis, the one on the head is a switch. They simply give 0V (battery -ve, chassis) to the spark control solenoid when the car is in top gear and the metal of the engine has reached temperature. This will bypass by one of the thermal vacuum switches at the front of the intake on a V8 (thermostat housing on 6cyl) if the engine overheats, then it gives full vacuum advance to the distributor. This will cause the idle speed to increase and the fan to pull more air through the radiator.

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castellan Offline
#17 Posted : Saturday, 21 September 2024 2:21:02 PM(UTC)
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Originally Posted by: Dr Terry Go to Quoted Post
Originally Posted by: castellan Go to Quoted Post

So if one pulls off the wires to temp or gear box, how does the dizzy know to retard ?


The temp sensor & the gearbox switch control the vacuum solenoid. Unless the engine is up to temp & in top gear, the dissy receives no vacuum to the vac diaphragm.

Dr Terry


This is what i thought but in regards to why the HX 5.0L 4sp were so gutless, even with dual exhaust, i know the manuals did not have EGR entering the intake to be burnt like the Automatics did.

So me was thinking, now if your foot is flat to the floor, the vacuum advance has no regards to power at all when flat to the boards, but the Dizzy should work just as a HJ one would ? with the springs and weights ! So that can not be the issue ! unless them springs and weights are the issue ?

Then i was thinking of the Blue motor dizzy has that big box on them ? now why is that so and can that bugger up or interfear with timing in anyway ! plus their is a electrical box with fins on it i think they bugger up and most mecanics gave no regard for them. I have heard of CL Valiants had problems with such things when they got old, for such just were hammered with heat that destroyed them from working.
I had a Dyno Tune dude do my car and he did not even detect that the vacuum adv was not working in fact ! i though how stupid can he be. they have no regard for that ? Applause that's the main thing to make sure is working.

I had a mate with a WB Statesman in 1988 and it just would not perform, it was like the advance in the dizzy did not work, that's what i said to him that i think it's like and to get it cheked out, he did and said they claimed it was fine.

I know that the vacuum adance is only a fuel economy device truly.
castellan Offline
#18 Posted : Saturday, 21 September 2024 2:31:54 PM(UTC)
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Originally Posted by: stevo Go to Quoted Post
only on a manual it wouldn't allow vac advance unless in top gear the first thing a young petrol head would do was to change that vac line so it came directly from the carby not that it achieved anything. What goes vac advance do when you have your foot flat to the floor. lol If ole mate above converted to an electronic distubtor did he get a full 12 volt to it?


No one changed from a red motor to a Blue motor Dizzy hear that i am talking about. I think that goes back to 9 volt if you do with points, or 12v will fry such.

Blue use 12v ? and make sure you have a good earth. a mate had spent a fortune on his Torana engine and totally painted, but she just would not perform ! until it was correctly earthed.
castellan Offline
#19 Posted : Saturday, 21 September 2024 2:36:57 PM(UTC)
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Originally Posted by: HK1837 Go to Quoted Post
Originally Posted by: stevo Go to Quoted Post
only on a manual it wouldn't allow vac advance unless in top gear the first thing a young petrol head would do was to change that vac line so it came directly from the carby not that it achieved anything. What goes vac advance do when you have your foot flat to the floor. lol If ole mate above converted to an electronic distributor did he get a full 12 volt to it?


Autos have the spark control as part of ADR27A too. Its EGR that is auto only, manuals have a blanking plate where the EGR valve goes. As Dr Terry says, there is a switch on the back of the RHS head (engine side on 6cyl) and another one on the gearbox (3-4 selector manual and back of the box on an auto) The one on the gearbox just switches to 0V chassis, the one on the head is a switch. They simply give 0V (battery -ve, chassis) to the spark control solenoid when the car is in top gear and the metal of the engine has reached temperature. This will bypass by one of the thermal vacuum switches at the front of the intake on a V8 (thermostat housing on 6cyl) if the engine overheats, then it gives full vacuum advance to the distributor. This will cause the idle speed to increase and the fan to pull more air through the radiator.



Have to bypass the lower gears setup.

In regards EGR, that should not work when your flat to the floor ? so it should not drop max power at all when flat ! but for part throttle i believe.
stevo Offline
#20 Posted : Sunday, 22 September 2024 9:58:48 AM(UTC)
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VB VC VH 6 cyclinder auto commodore where was the vac advance in first and 2nd disabled? I dont rember pissing it off I would , what does vac advance do? It doesn't matter when the foot is flat to the floor as all the vacuum is being pulled thru the big hole.
GM bleed us dry and run away.
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