ET: Engine (Twin) Seeking Ignition Suggestions For Twin - Can't Get The ATD Fitted

[Speedtwin]

Very interesting point on the gap.
I have been told that my gap is to big at fag box folded over thick factory setting.
I am tightening down here on in.
Al

 

[Keith Martin]

Since you are switching from Lucas magneto to BTH and back we have seen the Allen head bolt supplied with the BTH to replace one of the studs be too long and foul the fibre gear if used with the Lucas magneto but not on the BTH mag.

 

[oexing]

I remember early reports when electronic ignitions were new, on old gear the engines did not like the very short sparks from CDI types. With less than perfect mixture they were not well suited to ignite the mixture. So a means was to have wider spark gaps for a longer spark . Extra high tension was no problem to achieve but the longer spark duration from the capacitor-coil system plus breaker could not be had from CDI . So for me I want a spark I can hear loud and clear, not something that is barely visible to the naked eye - high tension or not. When that crack is not loud enough I do not have much faith in its stored energy.
As to stuck flyweights in the Lucas ATD, possibly a misconception:
The ATD is the driving component for the armature, so when you move these flyweights they are supposed to drive/move the armature at same time. BUT in two positions of the armature it will be locked by magnetic forces. So you will feel resistance in flyweights when you move them as you try to shift the armature from the magnet locked position. When you turn the engine over the flyweights will most likely return to retarded with ease - hopefully, unless the components are really stuck somehow.
The ATD on the drive end is not great I believe, quite some forces on it from rotor mass and all. Better go for ATDs on the breaker end that just deal with the breaker cam. So then a distributor is the best way for the Vincent twins I think, to go with coil ignition and its fat sparks. You can do an electronic mod on these for binning the breaker, at low costs without the magnetic complications.

Vic

 

[CarlHungness]

I think Carl is chasing shadows (if you will excuse the pun) surely two of the problems that have been suggested are extremely easy to check and either confirm your suspicions, or rule out completely, if the ATD is slipping on the taper, then once set at say 34 degrees advance, kick the engine over a few times, and then check it again, if it has moved it would immediately be apparent, the same goes for cams slipping on camshafts.

BT-H magnetos do not throw off big fat blue sparks, but they certainly work, they are not just made for Vincents, but all the British Bikes that used Lucas type magnetos, if they did not work I am certain they would have been exposed as charlatans a long time ago, I have been very happy with my BT-Hs barely perceptible sparks for the past 18 years, only the condensers let me down once.

Vincents will run very well, even when in appalling mechanical condition, as I can testify as recently as last year at the Far Far North Rally, front big end disintegrated, thrown debris up into the front cylinder bore taking the piston and liner with it, and it was running very well indeed, two up.

I think the most likely outcome will be a fuel problem, but I think I would have given up long ago, and sought the help of a second pair of eyes and hands.

And in reply to Hugo, I agree with his comments, but having said that, I have lapped, but only with the finest grade paste, and just until you can see that you have full contact of the taper with a fine grey finish, we are not talking lapping in heads and barrels here, or valves.

I hope I have NOT over-lapped, if there is such a term.

 

[CarlHungness]

I

Since you are switching from Lucas magneto to BTH and back we have seen the Allen head bolt supplied with the BTH to replace one of the studs be too long and foul the fibre gear if used with the Lucas magneto but not on the BTH mag.

I used the B-TH from 2003-2023 with a short Allen bolt on the right hand side, the one that is a real
challenge to get in with the long allen wrench/driver, so that's not an issue.

I hesitate to join this discussion as I am no engineer and barely a mechanic. I have been riding Vincents for 60 years, both Comets and a Rapide. In that time, I have had a few problems with ATDs, namely stripped fibre pinions (once notably on a burn up with George Lazenby in Park Lane), sheered advance stop ears and broken springs. I have also had this problem of the ATD stuck at full advance. All my replacement ATDS were second hand and I admit I have never lapped in the tapers on any of them. The ATD in question would stick at full advance whenever it was tightened up on the magneto. I suspected it was binding on the crankcase. I stuck some plasticene on the back side and screwed it on. This quickly showed that it was, in fact, binding on the crankcase. At some time in its previous life the taper had been enthusiastically lapped in on the magneto shaft, probably more than once, thus taking up all the necessary clearance and was therefore useless. Incidentally, although I have never lapped in any of the ATDs, none of the ones that I have used has ever slipped.

I DID vigorously lap the ATD to the Lucas shaft and hope I didn't over do it. I just ordered a brand new ATD for
250 Pounds sterling plus extreme postage cost to the US. NOW I have the Lucas Workshop Instructions printed out thanks to a fellow member on this forum. Here's the quote that has set me on my ear:
NOTE: When refitting or replacing an auto-advance unit do not press the unit right home on the armature driving taper, but allow the retaining bolt to do this as it is tightened. In this way the danger of locking the retaining bolt before the auto advance- unit is fully engaged on the taper, or of accidentally engaging the extractor left hand thread with the retaining bolt will be avoided. The italics are mine. I don't know how I learned it, or where I read it,
but (lately) I have been setting the unit with a socket. That won't happen again. Now my only fear is my lapping of the old ATD to the shaft may have decreased/changed the taper on the mag and all I can hope is the new unit goes
on and matches the taper, etc. I'll have the unit by the end of next week.

 

[CarlHungness]

I think Carl is chasing shadows (if you will excuse the pun) surely two of the problems that have been suggested are extremely easy to check and either confirm your suspicions, or rule out completely, if the ATD is slipping on the taper, then once set at say 34 degrees advance, kick the engine over a few times, and then check it again, if it has moved it would immediately be apparent, the same goes for cams slipping on camshafts.

BT-H magnetos do not throw off big fat blue sparks, but they certainly work, they are not just made for Vincents, but all the British Bikes that used Lucas type magnetos, if they did not work I am certain they would have been exposed as charlatans a long time ago, I have been very happy with my BT-Hs barely perceptible sparks for the past 18 years, only the condensers let me down once.

Vincents will run very well, even when in appalling mechanical condition, as I can testify as recently as last year at the Far Far North Rally, front big end disintegrated, thrown debris up into the front cylinder bore taking the piston and liner with it, and it was running very well indeed, two up.

I think the most likely outcome will be a fuel problem, but I think I would have given up long ago, and sought the help of a second pair of eyes and hands.

And in reply to Hugo, I agree with his comments, but having said that, I have lapped, but only with the finest grade paste, and just until you can see that you have full contact of the taper with a fine grey finish, we are not talking lapping in heads and barrels here, or valves.

I did give up long ago and sought help from journeyman Vincent rebuilder Glen Bewley whom I've known for decades. We know that we've both studied Vincenteering and have read all of the same literature. The difference is Glen has taken his knowledge to the highest level, become a proficient machinist in things Vincent oriented. He has basically said, "You KNOW what to do Carl, think! Thus each time he's given me a suggestion I've slightly raised his ire because I've said, "I've done that." He has shown extreme patience with me, given me a few hundred dollars of his time and all he has gotten back is aggravation which I've transmitted to him. When something comes out of Glen's shop, it's as it ought to be. I am actually pretty happy to hear that others have experienced the fiddle with the ATD problem. I THINK I got it installed OK first time as the bike fired and ran for 60 seconds, and then it quit. It sounded normal. Thus the reasonable thing for me to think is, get the mag-ATD fitted and Bob's your uncle.

 

[CarlHungness]

One other B-TH point you dont need a large plug gap
A quote from the B-TH web site
N.B A local Dyno expert who has tuned many race winning vintage machines has found that a plug gap as low as 0.007" (Seven thousandths of an inch) does not reduce the power output registered on the dynamomete.

Great stuff, seven thousandths! As mentioned I popped for an extra few bucks and sent my B-TH back to the factory to let them check it out. If it's OK, I'm screwed. If I can't start it with the old B-TH and the new Lucas (new ATD and rebuilt
Lucas) I'm going to put the machine on a trailer and deliver it to Glen Bewley, if he'll take it. He'll give me his
usual rant of, "You know what to do," and maybe I'll just start crying and he'll take pity on me. This has been one
fun circumstance, but it's getting in the way of me learning my new discipline of panel beating, welding aluminum
with oxy and TIG and stretching and shrinking metal/aluminum.