Misc: Ignition ATD

[Chris Launders]

Chris
On my Rapide I run a twin points ignition system that I made 30 years ago where its just a machined housing with basic shaft with a cam on one end operating the two sets of points and the other end has the standard ATD from a magneto and in 30 years I have had no problem with the opertation of the ATD apart from the original ATD was a bit worn and so had too much advance. So 15 years ago I replaced it with a new ATD unit from Roy Price who was still making them at the time.
I have never put a strobe on the bike though so have never observed what the timing is doing advance curve wise, assuming its even a curve.
Simon

Hi Simon, that's exactly the same as I have. Maybe I need to check the ATD out, it was 2nd hand when I fitted it but in 30 years has only done 5.000 miles (too many other bikes to use)

 

[vibrac]

Two comments
first the ATD was built to react when 38 BTDC fully advanced was a suitable setting because we still had decent petrol
The slop we have nowadays has necesitated moving the timing towards 35-34 BTDC and speaking to Roy Price shortly before he died he was thinking (or actually was reducing?) the throw of his mecanism to allow for this.
personally I think measuring the throw of the ATD is the first step. if we think 4*deg BTD is a kick start figure then a throw of 15 degrees should be in the ball park
* alter to taste

 

[Simon Dinsdale]

Two comments
first the ATD was built to react when 38 BTDC fully advanced was a suitable setting because we still had decent petrol
The slop we have nowadays has necesitated moving the timing towards 35-34 BTDC and speaking to Roy Price shortly before he died he was thinking (or actually was reducing?) the throw of his mecanism to allow for this.
personally I think measuring the throw of the ATD is the first step. if we think 4*deg BTD is a kick start figure then a throw of 15 degrees should be in the ball park
* alter to taste

Roy Price did reduce the later ATD's he made from 17 degrees to 15 degrees as that is what I got from him. This allows 30 degrees advance at the crank so you can set full retard to 4 deg BTDC for easy starting and it results with 34 full advance BTDC which works fine with the current rubbish fuel available for the last 30,000 plus miles.

 

[LoneStar]

The argument for reducing maximum advance with current fuel necessarily rests on the claim that it burns more quickly than that sold decades ago. Is there any actual evidence of this?

 

[oexing]

We lot on the continent are quite unfamiliar with ATDs in the drive gear. Typically this device is on the breaker end of a mag or distributor where it will not do much damage on timing stops like breaking ears off the Lucas type. Seems to me same effect like broken gears in Altons or triplex chains from the unspeakable ESA on the crank. All throttle blipping will hit stops in the ATD with force as there is a wide range from retard to advance till the drive gear can spin up the mass of the rotor. So when thinking about mag or coil ignition I´d rather have a distributor with ATD on breaker end on the Vincent as the old Lucas mag is not nice anyway to elder people when no electric leg has been added already.

Vic

 

[vibrac]

The argument for reducing maximum advance with current fuel necessarily rests on the claim that it burns more quickly than that sold decades ago. Is there any actual evidence of this?

You really should get on a dyno sometime its an hour well spent

 

[greg brillus]

If the ATD was advancing quickly then the engine would readily "Ping" and very audible at that.......If the return springs are doing their job then the unit should be fine......In any case, I'm not sure what a supposed vibration has to do with poor running.......regardless of who built the crank/engine if the running characteristics have changed then something has caused it......unless it was like it from the beginning.