16 replies to this topic

[73TORANA!]

Hi All,

Here is something interesting I have discovered. I have been chasing what feels like a weird kind of cam jerk in cruise, worse when hot, good when eng is cold. Not to go into details in everything I have tried so ill get to the point.

I found that my timing is spot on and stable when cold and the starts to become erratic when engine is hot. Timing at idle will jump 2 deg and at 2500 rpm when really hot it will jump up to 4 deg; No its not cam end float. Different dizzy tried with same results. A third dizzy, a stock old junker was tried and it was steady with only a slight jump, 99.9% better than my near new one; WTF. When my dizzy was graphed and reconditioned ( by a well reputed company ) they took off the near new metal gear and put a plastic one one saying"these are far better for spark stability and not  to use the metal" ok your the experts.. The second dizzy I tried also had a plastic gear; the third junker had a worn oil pump metal gear. So I swapped around the gears and mine is now 90% better with a worn metal gear. Also noticed with the plastic gears was that when cold there is a slight normal back lash in the dizzy gear with the cam gear; when hot the plastic gear expanded, this backlash was almost gone. 

Conclusion: When the dizzy is driven the nature of the helical gears pulls the dizzy shaft down against the internal thrust washers keeping it steady; It seem that if there is any sort of binding it will try to push the dizzy shaft and down?; as the shaft goes up it will tend to retard? the timing, in my case up to 4 deg at worst. The pitch on these plastic gears a slightly different from the metal ones and they don't seem to ware in. The hotter it got the worse it became.

 

Any comments, theories, welcome. Does any one have any similar experiences?

 

 Cheers Geoff.

[Shiney005]

I've never heard of it happening, but I don't know if I have ever seen the plastic gears either.  I would have thought the plastic one would be more stable than an iron one. (ie Grow less)

[Bruiser]

You got me thinking about the meshing between the cam gear and the dizz gear
Just checked what’s happening in motor on stand, you’re right again,
the rotation of the cam does pull downwards on the dizzy shaft.
Maybe the plate and bobweights in the advance mechanism have enough momentum
of their own to try and drive the cam gear instead of being driven by the cam while the cam is slowing down when
throttling off and end up being pushed upwards instead
If a dizzy wasn’t shimmed up tight enough, more up and down free movement would mean more advance
as it climbed up the gears.
If it’s real loose, it could mess things around by a couple of degrees

What if the dizzy shaft climbs and gains 4 degrees, picking up revs on it’s own
which might cause it to lose its 4 degrees again and slow down
and pick up that 4 degrees again?
Just a comically wild guess
Might be worth checking the shaft end float?

[Bruiser]

Something Clay wrote in the other distributor thread got me a bit worried about my mad theory in the last post🎺
He probably looked into that for himself, but I thought I would check for myself, rather than spread some
bullshit theory for everybody which really was a load of nothing.
A Google of “excessive distributor end float” came up with a heap of results of folks discussing the same thing as me
So I am not totally daft, after all.
Including the very first listing from pelican parts forum where the guy has exactly the same cold/hot symptoms as
you do, Geoff

https://forums.pelic...t-end-play.html

Not really a definite solution there unfortunately, but might lead to something resembling a clue.

Checked my dizzy for the sake of it, it had .021”. Never noticed a problem before, but added another shim and
got it down to .013”
Measured a plastic gear at 22.55mm wondering if they were longer or shorter than the steel ones
but they were both the same. Thought that might go some way to explain why so many people have
talked about the steel gear causing ignition problems at high rpm, and solving that problem by going
back to the plastic gears. There’s several old threads here about it.
I think that’s what dr Terry was referring to in the other thread
Could be the reason scorcher put a plastic one on yours

[Bruiser]

Probably should have checked first, but just found a float spec of .1mm - .25mm
In an old gregory’s VB commy manual, the only book with anything in it
That’s a points dizz, though. Don’t suppose an electronic would be any different?
That’s what, 3.93 - 9.84thou - pretty tight

[73TORANA!]

Great info Bruiser,

Ive got a new ( re manufactured ) one coming from EBay The guy recons its an exact copy so we will see. Will post results here Thx for the end float measurements, couldn't find it anywhere in my manuals.

Indecently the ol EH dizzy that was perfect had about 25 thou and mine from Scorcher has got about 35 thou. Will fit metal gear to my dizzy and not change anything else and then after I shim it to what your VB book says.

one final thing. On the ol EH dizzy there is a very very slight ware on the non driven side of the dizzy gear so to me that would indicate a kinda over run condition like you mentioned, I dont know but will see what happens with a new steel gear.

And yes Shiney 005 that is exactly what Scorcher said but for what ever the reason in my set the plastic is causing scatter maybe because the gear is 10 years old ???? 

 

Stay tuned,  

[Bruiser]

Just found another blurb that says around 20 thou play
Might pay to get a third opinion

[claysummers]

I couldn’t find any specs for it in the factory HQZ manual, or the Gregory’s VH I have.


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[73TORANA!]

Hey Clay does your rocket breath much through PCV? A friend years ago had an XU1 carb set, they suck a fair bit of oil through the PCV. His was knocking but as soon as we blocked it off for a test it was way better as oil fumes will cause it to knock. Just a thought. 

[claysummers]

Not that I have noticed at all. I did notice at one point that the vacuum hose was off the front carby, so mixture up front may have been out. I seem to have solved the issue with a diz that’s been “curved” to top out advance early on.


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[73TORANA!]

On the subject of end float tolerance Ill throw this out there.

So the old EH Bosch dizzy has a totally different fly weight set up for advance it uses lighter weights and lighter spring.

Now my later Bosch dizzy uses the same fly weight set up as the later HEI commodore set ups and I believe the same as HZ VB era??

The old EH dizzy has around 25 thou clearance while the commodore HEI is like 10 thou, if that.

Maybe the difference in the rotational mass is the reason for the difference in the manuals hey Bruiser.

So I going on that theory I'm not sure why scorcher gave mine so much clearance at around 35 thou.  

[Bruiser]

No much knowledge about the specs, Geoff
I just had a look around for whatever I could find.
Googlage led to the idea that tighter is better, but allow some for heat
expansion in the gear, shaft and dizzy body so the thing doesn’t lock up
There is a fibre washer involved in the stack of shims, though.
Found a broken one in one of mine here
Not sure if all the dizzys there ever were all had them, but did
wonder about the possibility of yours disintegrating and disappearing
giving you some more gap - if you had one in the first place
Maybe a call to scorcher to find out what they set them up at would help

[73TORANA!]

Yeah cheers Its worth a phone call, I will let you know

[Shiney005]

Well I'll be.   I didn't even know they were still going.

I am only going by the jumper Brock is wearing, but I am guessing that would be around 78 or 79?  I have the distributor from his Patterson A9X, and its not a Scorcher.

[73TORANA!]

So the dood at Scorcher said they usually set them up for about 5 thou. Thats odd cause they set mine at 25. Massive siegh

[Bruiser]

Nice one Geoff
I thought our eunUCh here was being daring going to 3 thou
He’s pretty on the ball

[73TORANA!]

Here you go.

A friend has a factory LC Torana service manual and we found the shim specs for the dizzy; between 4 and 10 thou. I managed to get mine to 5 thou and fitted a steel gear from earlybitz3 on ebay, NEW METAL DISTRIBUTOR GEAR DISSY GEAR TO HQ HJ HX HZ WB VB VC VH HOLDEN | eBay

 

Results: Timing is now rock solid at idle and up to about 2500 rpm cold or hot and varies no more than 2 deg at 3k+ rpm; may be this is the balance weights and springs acting on the gear backlash which is bugger all when compared to the plastic gear or maybe its a combination of that and the cam gear end float that upon installation was 3 thou, don't know but its so much better and seems to be smoother at around 60Kph in top ( 1800rpm ) not as much cam jerk / hesitation feel in cruise, jerk is prob the wrong word as it feels more like wind buffeting the car 

Would be interested in hearing  from others as to how much the timing moves around on their engines at about 3k?

Remember mine is rock solid on the dizzy machine so its got to be engine related.

All in all its way better and probably would not even notice if it wasnt my car.

 

Just a note on the Ebay gear. The one from this seller is a perfect copy of an original, exact dimensions. There is a cheaper one but in the description for it says its for a blue black dizzy and I discovered the gear face area is about 1mm smaller but the overall height of the item is the same meaning it will shim the same.     

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