Home Tuning 101 - Setting the dwell angle.

Hi Folks,

Home Tuning 101 - Setting the dwell angle.

This should be straightforward, right?

I'd like to be able to measure the dwell angle on my '65 beetle which is still 6 volt. So I got hold of a self-powered (via a 9V battery) digital multimeter, you know the type, which I thought should be perfectly adequate for the task. Trouble was, it was completely incapable of reading the impulses from my 6V coil, the screen would flash on and off, stabilise for a couple of seconds and blank again and just go generally nutty. Assuming the meter was faulty, it was replaced with another, entirely new one with precisely the same outcome. OK, so maybe these devices are just calibrated to read 12v signals although why it won't measure from a 6v systems escapes me.

So I then picked up a much older, analogue model instead. This one at least could give me a reading BUT in order to get a dwell reading of approx. 50 degrees (25 degrees an an 8 cylinder scale), I had to gap my points to 0.035 rather than 0.016. I figure this can't be right either.

In the interest of keeping the car running smoothly, I'm leaving the points gapped to 0.016 for the present but this doesn't answer the question of the dwell reading and I CAN'T be the first person to have trouble with this!.

Any suggestions?

Reply to
Dangermouse
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I have an old Craftsmen 12Volt Dwell meter and just use a 12V battery to test the dwell on 6V engines. I have been known to eyeball the points settings and be right. I prefer to be a little more open on the points' gap or lower on the degree scale. AFAIK In your case, I think the 8 cyl setting may not be the right one to use with the dwell..............with RPM maybe but I am not sure about using it for dwell and doubling it. I could be wrong though since my meter has a

4 cyl setting. I have not heard of using a "digital multimeter" to check dwell, but I am still learning. ;-) Now are you talking about a digital "dwell meter" (AKA Engine Analyzer sometimes)? I have one of those too but rarely use it nowadays.

later, dave (One out of many daves)

"Dangermouse" wrote

Reply to
dave AKA vwdoc1

I don't think you can use multimeter because points would close/open fast and would not allow enough time for the meter to register voltage especialy digital ones which are slow. I am not familiar with procedure, only thinking of runing engine and rate at which points would open and close. If this is not the case you can disregard this thought.

Ant> I have an old Craftsmen 12Volt Dwell meter and just use a 12V battery to

Reply to
anton

Hi Dave,

The multimeter I was referring to is one of these...

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Disappointing that it doesn't seem to work on my car :-(

- DM

dave AKA vwdoc1 wrote:

Reply to
Dangermouse

Ok that one IS an Automotive Multimeter that is designed to test the dwell and rpms of engines. Maybe yours is defective if you wired it up correctly to test for dwell. And the 2nd one too. Did you contact the seller/manufacturer to see if it would have any problems with your 6V system? Did this multimeter work on any other vehicle?

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Reply to
dave AKA vwdoc1

Well I did connect it up pretty carefully; I connected the red terminal to the #1, negative terminal on the (6 volt) coil (the same terminal that the condenser wire attaches to), and grounded it to one of the bolts that attaches the coil to the fan housing. The reading just never stabilises, or even stays on for that matter. Same problem if trying to measure duty cycle but the other functions, including tach, work normally so I'm assuming the meter is not fundamentally defective. That and the fact that an entirely new replacement meter exhibited the same problems.

I did of course wh> Ok that one IS an Automotive Multimeter that is designed to test the dwell

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Reply to
Dangermouse

then I agree with you............probably not compatible with a 6V system for every function of the meter. I think I use an external 12V system (or 9V battery for my digital meter) and only have to hook up 1 lead to the neg side of the coil.

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Reply to
dave AKA vwdoc1

I don't think it's a problem with 6V system incompatibility. The signal from the points, is not a clear 6v - 0v pulse, it has high voltage spikes and RF noise, which is not easily filtered by a digital multimeter. The digital multimeter (most of them) would only read correctly if you had a pointless ignition, which provides a cleaner pulse. Many cheap digital multimeters can't even read the voltage on the generator / alternator outputs while the engine is running (there is also too much electrical noise and spikes on the generator outputs).

You can try to replace the condenser, which may be faulty. The condenser clears a bit the signal from the points, and try to find an analogue tool (with a needle) to get a dwell reading.

Other than that, just keep the gap of the points to 0.4mm. It is more important to keep the correct gap, than set the dwell exactly to 50 deg. Anyway, you would'n notice any difference if the dwell was in the range of

40 to 60 degrees.

Bill, '67 Bug.

Reply to
Bill Spiliotopoulos

Thanks for the comments folks. Makes sense that modern meters would be designed to measure electronic ignitions and might have difficulty with breaker points, I guess. That would certainly explain the symptoms anyhow.

The condenser itself is already new, I replaced it when I changed the points. I have tried using an older, analogue meter, like this one...

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which did appear to reliably take a reading but to get a dwell of 25 degrees (8 cyl scale) I had to open the points way out to 0.9mm. Is this not daft?

I don't want to get overly anal about this and I realise the car's perfectly happy with the points simply gapped in the usual fashion; I'd just like to be able to measure my dwell angle like all the big kids.

Its a long weekend coming up down here and I'm off to Brisbane for the week! Hooray! 28 and climbing - now THOSE sort of degrees I can cope with ;-)

- DM

Bill Spiliot> I don't think it's a problem with 6V system incompatibility.

Reply to
Dangermouse

If the analogue meter reads 25 degrees for 8cyl, then this is equivalent to

50 degrees for a 4 cylinder engine. If it is rated to %, then you should be aiming for 55% regardless of # of cylinders.

Bill, '67 Bug.

Reply to
Bill Spiliotopoulos

You can accuratelly measure the dwell angle withoul a dwell meter, with just a lamp connected between the points side of the distributor and chasis.

Disconect the center HT lead from the distributor cap, and earth it somewhere away from gasoline.

Then with the ignition on, turn the engine pulley with a whench. When the lamp just turns off, make a mark on the crank pulley. Continue rotating. When the lamp just lights, make a second mark on the crank pulley. Continue rotating, and make a third mark when the lamp turns off.

You can switch off ignition now.

Get a tape measure now and make two measurements on the circumference of the pulley. The first measurement is from mark 1 to mark 2, let's call this A. The second measurement is from mark 1 to mark 3, let's call this B.

You can calculate the dwell angle with this formula:

Dwell = ( A / B ) * 90

You can check your dwell meter reading against the angle you calculated, to see what should be the "correct" reading the next time you are going to set the points.

Bill, '67 bug.

Reply to
Bill Spiliotopoulos

Ooops, correction to the above.

Measurement A should be from mark 2 to mark 3.

Reply to
Bill Spiliotopoulos

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