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Discussion Starter · #1 ·
In my car, when I tighten the hold-down clamp of the distributor the advance increases. If I set it correctly with the bolt loose, when I tighten it will advance to about 2-4 degrees (directly related to how much I torque the bolt), so I have to set lower advance, and estimate where it will fall, tighten, check and repeat (4-5 times) until it is spot-on... This makes the proccess time-consuming, difficult, and even frustrating sometimes.

What could be causing this? Could it be a distorted hold-down clamp? Any ideas would be appreciated...
 

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tomking
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You are possibly loosening it too much when you adjust it. Just loosen it only enough that you can rotate it by hand. You dont want it loose enough for it to come up any. And you dont want it loose enough that it can rotate on its own. Then when you tighten it you should not have to turn the bolt more than about half a full turn in order to get it tight again.
 

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Discussion Starter · #3 ·
I just loosen it so that it will still need some hand-power to turn, and you are right, it tightens up to about 3/4 of a turn. But during these 3/4 the advace increase happens...
 

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Senior Contributor
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Sounds to me like it is a gear "lash" problem. Could be that either the distributor gear is worn or the gear on the crank is worn or a little of both.
 

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I just went through this on the turbo engine two days ago. I was using the thick cork distributor gasket, and it left very noticeable slop in the gear meshing, meaning the timing could randomly fluctuate on its' own. I put a thin paper gasket in there and the slop was 100% gone. Plus, as you mentioned, the hold-down bolt torque spec alters the gear mesh (and therefore the timing) because the thick cork is compressible.

Bob
 

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Discussion Starter · #6 ·
I assume I have a paper gasket there too (I have never needed to remove the distributor) because as seen from the side it is very thin, less than 1mm. Maybe it is the torque of the bolt that makes the difference...

Thank you!
 

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Actually, it is the helical gears that cause the problem. As you tighten down the distributor you force it down into the gears and it will turn the shaft, similar to a worm drive but not as severe.
 

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Opeler
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namba209 said:
Actually, it is the helical gears that cause the problem. As you tighten down the distributor you force it down into the gears and it will turn the shaft, similar to a worm drive but not as severe.
Without being inside your disributor, I do know that the helical timing gear's key and keyway WILL wear and allow the gear to "free-play" to whatever the extent of the pressure put on it. Just something to check....

Bill B.
 

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Opeler
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Since we are on the subject, can I ask a quick question regarding timing and the distributor?...Can the timing be set by ear by slowly turning the distributor one way or the other according to how the engine reacts or sounds?
 

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alolmo said:
Since we are on the subject, can I ask a quick question regarding timing and the distributor?...Can the timing be set by ear by slowly turning the distributor one way or the other according to how the engine reacts or sounds?
Not very accurately or safely. I know of someone who timed their engine this way, and when I checked the timing with a timing light it was almost 15 degrees overly advanced. This could cause engine damage, and does not necessarily make more power.
 

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Opeler
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OK thanks, yea I thought it would be too easy.
Thank you.
 

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Discussion Starter · #12 ·
It now makes sense why my idle speed differs between cold/just warmed up engine(choke-off, still about 500-600rpm) and hot (after about 10 mins of highway run, or 20 minutes of city driving).

Engine temperature propably affects the tightness of the distributor hold down clamp (as described above), by metals extracting.

I thought of it yesterday night, and today I felt like investigating and verifying my thought. I warmed up the engine really well, then went through hell to perfectly adjust dwell/timing/idle speed. When all was done, I made a mark with a marker on the crankshaft pulley opposite the timing cover's indicator, to when the points open (like the static timing process, but reversed...).

After sitting for 3 hours (and the engine bay is still warm), timing is already off by about 2 degrees, and I estimate that when it will be stone-cold this could go to about 4 degrees... This is why it doesn't want to move when it is cold, and idles higher later...

Time to start finding causes here...

Gasket (as RallyBob suggested) will be the first thing to go, but sometime next week, that I will propably have my new (hopefully correct this time) distributor.

Can anybody think anything else appart from what has already been mentioned in this thread? Any thought would be appreciated!!!
 

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Now you know why every auto manufacturer, engine builder, and every manual states that the timing and any carb adjustment should be made with the engine up to "normal" operating temperature. It's so that the various metals have had the opportunity to reach their optimum expansion caused by the heat. It just doesn't make any sense to dial the engine in when it is below normal operating temps, it doesn't stay there and except for first startup of the day for a very short trip, you don't do any driving in that temp range. HTH.
 

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I am bringing back this old topic, since today I found something interesting concerning this problem, that I still have...

So far, when tuning-up the engine, I did it in steps, to avoid having a ton of tools and intruments in the engine compartment. So after adjusting dwell I removed the dwell-meter and connected my timing light.

Today, luckily, I forgot to remove it and during timing I noticed that when I loosen the hold-down clamp to time the engine, it is not timing that changes, in fact dwell increases by 3 degrees, and when I re-tighten it dwell goes to what I had set (50*). And this negative change in dwell during tightening causes the timing to advance by 2-3 degrees...

How on earth can the hold-down clamp's torque affect dwell I can't understand.:banghead:
 

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Old Opeler
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Worn ...

Yep - sounds very much like a worn distributor - as you tighten the clamp it pushes the drive gear or oil pump drive against the other parts and closes the points gap when the shaft is 'tweaked' out of square.
The clamp is just on one side of the distributor so this probably causes some of the misalignment - especially if the distributor is a bit loose in the front cover before being clamped.

All sounds pretty normal for a mass produced GM motor!
 

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Discussion Starter · #18 ·
I see... Well, I should start looking for a distributor then...

I'll check Bob Legere's document with distributor's curves, and if I find one that suits my engine (1.6S) I'll post it to see if anybody has one in good condition.

Thank you very much guys!
 

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Old Opeler
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Pretty Close ...

Don't rush away to find another distributor - 2 or 3 degrees is pretty close tolerances for a stock distributor !! With the fuel pump and oil pump being driven off the bottom of the distributor shaft I doubt that much less 'spark-scatter' can be expected. That sort of variation is even pretty hard to measure accurately with a timing light and big marks on the front pulley - you can "phsyc" yourself out over trying for too much accuracy!

(There speaks a Toolmaker - who is a bit "anal" about accuracy :lmao: )

If you really want to 'excite' yourself - try moving to the other three cylinders and see how much variation there is between cylinders .... :D
 

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Opel Rallier since 1977
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If you adjust the distributor and points setting so that it is correct when the engine is running, does the car run OK? If so, maybe it is something to not worry about too much. Older cars with points in the distributor will never have the consistency in operation that a newer computer driven car will have.

Is there some operational problem with the car that you are trying to fix in setting the ignition timing and dwell?

Regards,
Mark B.
 
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