Author Topic: Points gap question  (Read 572 times)

Offline UncleD

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Points gap question
« on: 08.12. 2018 08:17 »
1958 Super Rocket with K2F magneto.

I am in the intiial stages of checking the timing for the first time (new procedure to me). Timing cover is off; magneto lock nut is loosened.

As I rotate the real wheel in 4th gear, maximum open points gap measures .012 on the right cylinder (bottom of the magneto) but 2.0 on the left cylinder (top of the magneto).  Shouldn't these be similar (nothing's perfect).  Is this a sign of warped internals?  Can it be accommodated or is a new magneto required?

Interestingly the right cylinder plug runs black sooty but the left is good. 

I suspect that the timing is out just by looking at the points movement in relation to piston travel.

Northern Territory, Australia

Offline UncleD

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Re: Points gap question
« Reply #1 on: 08.12. 2018 08:45 »
..answering myself a bit...(or possibly just confusing myself / everybody.

The bike starts (not easily but that could just be my lack of familiarity with it) and runs reasonably well (comparing it with my fully reconditioned A65)...if something were majors wrong, this would be unlikely and my experience says that most problems are simple.

I'm thinking the huge difference in point gaps might be due to the cam ring being out of position?  Is this possible?

Can anyone point me to some relatively simple information (preferably with pictures) on adjustments to the points, cam rings etc?  It's clear to me that there is a lot of adjustment required in this bike's timing.

This is all new to me so please excuse my musing.

Northern Territory, Australia

Online JulianS

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Re: Points gap question
« Reply #2 on: 08.12. 2018 09:13 »
Variation in points gap can be more than a cam ring issue.

There is often a difference between gaps.

Lucas put a tolerence of 3 thou gap variation.

There is a lot mechanically going on in a magneto.

The points assembly retaining screw needs to be straight and the right one for your points assembly. The taper in the shaft and on the points assembly needs to be good, Sometimes substituting a different complete points assembly will give you closer gaps.

The bearing housings and cam ring housing need to be square and concentric.

The armature needs to be true.

The bearing inners need to be square on the shaft (it is easy to damage the brass shaft wen dring on the bearing inner) and the bearing outers need to be square in the insulators and the housings. Sometimes, on assembly, the insulator is damaged allowing the outer to sit off centre.

The bearings need to be shimmed properly.

Online duTch

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Re: Points gap question
« Reply #3 on: 08.12. 2018 09:26 »

 
Quote
...... maximum open points gap measures .012 on the right cylinder (bottom of the magneto) but 2.0 on the left cylinder (top of the magneto)..........

 I guess that's another typo ?

 As Julian said, (apparently) common to have variation (Lucas claim is just to cover their butts)...If there's any slop in the camring as was mine, I packed it out with strips of tin-foil, which worked ok until I had another issue....(variation 0.012"-0.016")
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Offline Swarfcut

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Re: Points gap question
« Reply #4 on: 08.12. 2018 09:42 »

  Julian has covered more than I could ever have anticipated!

   Quick check......see if there is any wobble on the points retaining bolt as the engine is running, indicating a bent bolt/ and also that the points fit into the armature shaft taper with no rock. These factors will affect the relationship of the cam ring and the points heel.

 Swarfy.

Offline UncleD

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Re: Points gap question
« Reply #5 on: 08.12. 2018 10:06 »
No, not a typo, those were the feeler gauge measures of the two gaps. 

I will check again tomorrow, looking for any movement.  I will remove the centre retaining bolt and make sure it's straight.

Will the fact that the locking screw (in the timng case) is loosened make a difference /allow movement or wobble?

Northern Territory, Australia

Online JulianS

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Re: Points gap question
« Reply #6 on: 08.12. 2018 11:16 »
I would suspect the spark timing between cylinders to be quite a bit out with such a variation in points gap. 1 degree at magneto = 2 degrees at crankshaft.

Most mags are a few degrees out between cylinders.

Below an exploded K2F. The insulators parts 28 and 43.

Offline Swarfcut

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Re: Points gap question
« Reply #7 on: 08.12. 2018 11:58 »
UncleD....Can you describe what you mean by "The locking screw in the timing case". This makes no sense to me. If you mean the scabby bolt holding the ATD in place, this has no effect on the points.

 The magneto can be fitted with either of two types of contact breaker.    Early type with a brass backing plate. This type comes in two different configurations for clockwise or anticlockwise rotation. This has a long retaining bolt with a taper under the head. The later type of contact breaker is of steel construction and can be assembled for either clockwise or anticlockwise rotation. Has a shorter retaining bolt with no taper but a more snug fit into the points plate. This is the one in Julian's post above.  Disregard the information about the distributor clamp plate, that is not about magnetos.

 These bolts are specific to the contact breaker fitted.  Fitting the longer early bolt to a later steel contact breaker risks damage to the coil in the armature, as it will enter deeper into the armature shaft. So check your bolt is correct for the points plate.

  As a general rule, the cam pivot should lead ahead of the cam heel, so here again is a possibility of incorrect contact breaker application or assembly. Julian's picture above shows the later points, with the magneto  set up for clockwise rotation of the points. As an added confusion, magneto rotation type is classed from the driven end. So you have an anti-clockwise magneto (as defined), but in use the points rotate clockwise as viewed when working. Note the gap between the cam ring and the points spring blade. One of the quirks of this later design of contact breaker is that the points can be earthed if the blade touches the cam ring, miss-firing is a sign. The earlier type does not exhibit this behaviour and you often come across them with nicely marked spring blades, but still running fine and polishing the cam.

 Welcome to the Wonderful World of the Prince of Darkness.

  Swarfy.

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Re: Points gap question
« Reply #8 on: 08.12. 2018 14:02 »
The earlier type does not exhibit this behaviour and you often come across them with nicely marked spring blades, but still running fine and polishing the cam.

Yup indeed.
Because the earlier brass type had the fixed point connected to low tension live via the centre screw and the sprung point earthed by the screw on the tail of the spring blade.  So kissing the camring doesn't kill the sparks - but it can cause spring breakage in the end if severe enough.
With the 'low inertia' later steel type, the opening point is live via the screw and the fixed one is earthed. So if the spring kisses, bye bye sparks  . . .
That said, if you test-run the same magneto with the two different types of cb assembly, you'll very often find the steel one will give sparks that match the Lucas test specs at fractionally lower rpm, owing to slightly snappier opening. So one step forward and one step back - and no doubt the steel jobbie pleased the corporate beancounters as it's cheap and cheerful.
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Online RichardL

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Re: Points gap question
« Reply #9 on: 08.12. 2018 15:15 »
Can we get claricication regarding what "2.0" means (see the photo of feeler gauges). (Photo sized with Android app "Snapseed" set to export 1920 px.)

Others have decribed the various possibilities for gap asymetry. Here are a  couple of examples. In my own case, rotating the cam-ring housing 180 derees cured a substantial asymetry. In a10gf's case, shimming the insulated bearing race cured it. Here is s link to his excellent work on this: https://www.a7a10.net/forum/index.php?topic=1375.msg9862#msg9862

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Offline UncleD

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Re: Points gap question
« Reply #10 on: 08.12. 2018 20:39 »
Thanks all,

Swarfy...I have a brass backing plate / clockwise rotation at the points.

Yes, the timing locking bolt is the scabby bolt holding the ATD in place.

I'm not sure of the terminology (cam pivot /cam heel) but the points seem set up in the same configuration for clockwise rotating points compared with other photos.

RichardL,
I will check again the feeler gauge readings (as you have rightfully entered some doubt in my mind), but if you asked me now I'd say .012" and .020" ...but it's now 5am the morning after so I'm making no bets about my memory....it was late and we are in the 'build up'...very hot, sweaty so I could have thought/written anything (including 2.0").

The bike is runnng reasonably well notwithstanding the colour difference in the plug (right cylinder /timing side is blacker with soot). The only quirk that inhibits riding is difficult starting and when idling it will give a woman's fart (Pffft) out of the carb and stall after about 10 seconds.  I tend to think this is a carb tuning issue perhaps exacerbated by poor timing.

I'm making allowances for an old and unfamiliar bike but my initial impressions after getting her to start is that she runs strongly.  In terms of starting, she seems to need priming but floods easily but as I said I put this down to some carby fine tuning perhaps combined with timing that is slightly out.  I can caused her to pink under load but in general running there is no sign of this and the plugs do not suggest a lean burn.  The carb is a 389 monobloc (310 Main, 106 needle, 25 pilot)

For some reason the computer has accepted a photo that yesterday was too big (trick must be to load the photos earlier before the "No" lady starts work.  This photo is the points at the lesser of the two openings (0.012")...I'm thinking this is the left cylinder (as it is closer to the bottom HT lead which runs to that cylinder)...faulty logic?

Northern Territory, Australia

Offline UncleD

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Re: Points gap question
« Reply #11 on: 08.12. 2018 20:52 »
This is the wider of the two openings

Northern Territory, Australia

Offline Swarfcut

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Re: Points gap question
« Reply #12 on: 08.12. 2018 22:56 »
UncleD....Your magneto has the later screw on cap, so I would expect it to be a later unit and have the later steel points as in Julian's post. Your points are the early type and may be fitted with the later retaining bolt (no taper under the bolt head). If so this is incorrect for your points, allowing a slight sideways movement from centre as the bolt is tightened.

  Easy to check, undo the bolt, have a look and maybe wiggle the points off with some needle nosed pliers. They locate on a small keyway, so you cannot upset the timing as they will go back in the same place. The points pivot will be self evident, the heel of the points arm is the hard plastic brown bit that bears on the cam. Your points look correct for the direction of rotation.  The bolt should have a taper to match the one in the points plate.

  The scabby bolt on the Auto Advance Unit (ATD) is supposed to break the taper as it is unscrewed from the magneto armature but is rarely successful, and more violent methods have to be used. Yours looks like a standard bolt crudely modified to drive the Tacho gear. Make sure it is tight before start up, otherwise the ATD will move on the smooth armature taper and the set timing will be lost.

  On a twin cylinder maggy, the pick up slip ring is not continuous, and the cylinder which fires will be the one with the brass contact strip under the pick up brush when the points break. Easy to check, set the maggy to fire, remove the rearmost pickup and look down the hole with a small mirror.

Swarfy.
 

Offline UncleD

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Re: Points gap question
« Reply #13 on: 09.12. 2018 00:15 »
The bolt is tapered and straight.

I remeasured the gaps and this time got 0.19" and 0.06"!  I took these measurement as the heel? rode up onto the cam ring ramp (ie the whole heel was on the ramp).  I was careful not to force the points open with the gauge which may explain the new numbers...either way, still a sizeable difference.

I had an initial tug at the points (with bolt removed)...unsurprisingly they didn't want to move!  Any tips?


Northern Territory, Australia

Offline UncleD

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Re: Points gap question
« Reply #14 on: 09.12. 2018 02:17 »
Righto, please excuse the previous wobbly figures!

I slowly and carefully measured the points gaps...moving and measuring in tiny increments as the heel moved across the two ramps.  The maximum gaps I measured were 0.10 and 0.20". With both of these readings there was a slight stick of the gauge.  If you were after smooth feeler gauge movement across the gaps you would say 0.09 and 0.19"

So tell me docs, how bad is it?  Can she saved or do I join Berger at the pub?

Northern Territory, Australia