Misc: Ignition ATD

[Chris Launders]

For 30 years I've been running my Norvin with a standard ATD driving just a cam with twin points, first twin plugged but latterly single plugs and I've never been really happy with the way it runs, I've had 34mm Amal Mk2s and Mikuni VM34s on it but still never been able to get it to run happily.

It has occurred to me the standard ATD just driving a set of points will not be giving a suitable advance operation, probably advancing too soon and even fluctuating at certain revs.

What does anyone think, I do now have a good magneto I can fit which obviously the ATD is suited to.

I also have enough bits including manifolds for either a pair of 32mm Amal Mk1s or 30mm Mk2s, but one thing at a time.

Chris

 

[timetraveller]

Chris, I am a fan of the stroboscopic timing lights. You can see if the ignition timing is hunting or not straight away. Problem with a Vin is that you have to set up a system to run the engine, fit a timing disc into the big end quill and still get oil to the big end. Trevor Southwell, (ClevTrev on here) designed such a system years ago. I still have one somewhere or possibly someone nearer you still has one.

 

[greg brillus]

Possible, but remember countless thousands of distributors don't have the drag factor you are thinking due to the magneto armature. Could be the actual timing of points opening may not be right for both cylinders.......It will be something like that I'm guessing.......There are many other instances that could cause same.......I've seen valves not seat fully due to the inspection caps just holding the valve off its seat.......a leaking inlet manifold on one cylinder........Guides out of alignment and valves not sealing correctly.......When you say it does not run happily, what are the symptoms........

 

[Chris Launders]

Chris, I am a fan of the stroboscopic timing lights. You can see if the ignition timing is hunting or not straight away. Problem with a Vin is that you have to set up a system to run the engine, fit a timing disc into the big end quill and still get oil to the big end. Trevor Southwell, (ClevTrev on here) designed such a system years ago. I still have one somewhere or possibly someone nearer you still has one.

Not a problem for me as I have an open belt primary, but unfortunately no strobe (I can borrow one)

 

[Chris Launders]

Possible, but remember countless thousands of distributors don't have the drag factor you are thinking due to the magneto armature. Could be the actual timing of points opening may not be right for both cylinders.......It will be something like that I'm guessing.......There are many other instances that could cause same.......I've seen valves not seat fully due to the inspection caps just holding the valve off its seat.......a leaking inlet manifold on one cylinder........Guides out of alignment and valves not sealing correctly.......When you say it does not run happily, what are the symptoms........

Currently I have got it ticking over nicely and pulls away really good but has developed a vibration around 2.500 -3000rpm, it has always been erratic in this area but since changing from a Manx tank/seat with rear sets to a standard Norton tank/seat/ footrests seems much worse (though why that should make a difference I don't know) I think it's more obvious as I'm riding it steadier but it's rubbish compared to my "standard" twin with a BTH and 32mm Mk1s

 

[greg brillus]

developed a vibration........could be the rear chain too tight.......something out of sync.......are both slides the same cutaway.......Perhaps the flywheels have shifted.........having the engine mounted in a full loop frame they will behave different to a Vincent........Cranks should be nearer to 60% bal factor when housed in a frame.

 

[Chris Launders]

I had the engine built and balanced by Maughan's for this bike and I've allowed for it's foibles, (no cush in the drive train at all) the crank shouldn't have shifted it's not been used hard enough. The back chain could be a thing but it's now up on the bench so I'll get it off it's wheels and check.

 

[greg brillus]

Sounds good.......start looking for something loose then, and/or something moving or cracked......Engine mounts head stays, something changed......

 

[Chris Launders]

Sounds good.......start looking for something loose then, and/or something moving or cracked......Engine mounts head stays, something changed......

That still doesn't answer my question about the performance of a standard ATD driving just a cam rather than a magneto.

 

[Simon Dinsdale]

That still doesn't answer my question about the performance of a standard ATD driving just a cam rather than a magneto.

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