Author Topic: A10 RGS Replica  (Read 606 times)

Online Triton Thrasher

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Re: A10 RGS Replica
« Reply #15 on: 15.09. 2020 10:50 »
Sparking apparently healthily and blue outside the cylinder but not under compression in the cylinder is usually an HT problem.

Dirty or cracked magneto slip ring or pickups, duff plugs or leads, inadvisedly resistive suppressor plug caps

Offline Swarfcut

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Re: A10 RGS Replica
« Reply #16 on: 15.09. 2020 10:53 »
 They are high compression pistons, raised crown type. Ratio is above standard A10 of 7.25:1  Other ratios available were 8.3, 8.26 on Super Rocket and 8.75 for Spitfire Scrambler. All  work with the 357 Cam.

 Try the suggested timing piston height. With a manual mag you can retard easily if the motor turns out too far advanced for today's fuels, and yes more of a chance of a runner with fresh fuel, not that stuff from the lawnmower.  Once we have sparks of sorts in the right place, we're in with a chance. Whether they are good sparks is another matter.

 If the compression is poor, we may have to dig a little deeper, but see how you go for now.

 Additional point.

 Make yourself a nice saddle washer for the dynamo strap, otherwise looks a pretty clean build. Don't forget the cork washer on the dynamo/crankcase joint, and give the dynamo chain some grease in that sealed cavity.

 Cheers

 Swarfy.

Offline r3sc

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Re: A10 RGS Replica
« Reply #17 on: 15.09. 2020 11:16 »
Hi,

The HT leads are brand new as are the plugs and caps. Both are non resistor type.

The engine has had every seal and gasket replaced including the corks for breather and dynamo.

Fuel is brand new super unleaded.

Dynamo chain has been well greased and adjusted correctly.

The magneto is an area of concern. I built it up from parts from two different old magnetos as I needed to convert from auto advance to manual advance. It didn’t have the auto advance gear assembly with it anyway!

It all tested out correctly and I cleaned the slip ring and fitted new carbon brushes to everything with new lead connector assemblies etc but I do worry if it’s ok under compression pressure.

I can’t wait to get back down there to look at it and I think I’ll start with all your suggestions and then move on to valve timing.

Its all good fun!

Great input from you guys for sure!👍🏻👍🏻

Offline a10rgs

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Re: A10 RGS Replica
« Reply #18 on: 16.09. 2020 07:34 »
Hi,

have you tried to swap the plug leads? Put the left lead on the right plug and vice versa! Maybe that helps!

Regards
Uwe

Offline Radlan2

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Re: A10 RGS Replica
« Reply #19 on: 16.09. 2020 15:04 »
Hi R3sc
     I had a similar problem starting a new build, not so much as a phut, re checked ignition, thought it has to be valve timing, it turned out to be ignition timing. From that experience if I had similar probs again I would try over advancing it, say 7/16" just to get a response which will tell you your mag is sparking, also you do have copper core plugs? Champion N3's they make a difference. I have never had hint of pre-ignition and am not completely sold on the adjustment for modern petrol for these bikes. If you have a larger engine sprocket it makes it harder to get a good swing...
         P.S Always handy to have a fire extinguisher/celebration beer close by.
      Best of luck
               Chris

Offline r3sc

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Re: A10 RGS Replica
« Reply #20 on: 16.09. 2020 19:30 »
Hi Guys,

Yes, I’ve tried swapping the leads with no joy.

The plugs in the bike are brand new NGK items but at the moment I can’t remember the number.

I’ll try advancing the timing a little, especially as it would be easy to do.

One thing that bothering me is with the magneto.

I tried to identify which lead belonged to which cam opening of the points so I put one end my multimeter  in the end of one of the plug caps and the other end on the centre screw in the magneto. When I turned the engine over, the multimeter indicated continuity when the points were opened by the top cam. When I put the multimeter into the end of the other plug cap and turned the engine over I didn’t get any continuity in any position of rotation. This would surely indicate no continuity between the slip ring and the second plug cap?

However, I do get a healthy blue spark on both plugs when laid on the head.

AND, I’m pretty sure a would get some indication of a fire even if one cylinder only had a spark.

Am I thinking this through correctly??

Regards.

Online Triton Thrasher

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Re: A10 RGS Replica
« Reply #21 on: 16.09. 2020 21:31 »
You don’t need a meter for this.

When the points are just opening on one of the cam ring ramps, the brass segment on the slip ring is visible in one of the holes that the HT pickups fit into.

Offline r3sc

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Re: A10 RGS Replica
« Reply #22 on: 16.09. 2020 22:27 »
Hi,

Yes, I realise that but it would be extremely difficult to get the screws out which hold the pickups without taking the magneto off the engine.

I thought there would be some logic involved in simply testing with the multimeter.

Are all the rotors and slip rings the same on the K2F magneto’s or are there slip rings for single cylinder bikes and twin cylinder bikes?

I’m sorry if this is a stupid question but I don’t have sufficient experience of this device.

Regards.

Online Triton Thrasher

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Re: A10 RGS Replica
« Reply #23 on: 16.09. 2020 23:37 »
Single cyl magnetos have a continuous brass ring around the base of the slip ring.

Can you not get one pickup off?

Offline chaterlea25

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Re: A10 RGS Replica
« Reply #24 on: 16.09. 2020 23:44 »
Hi
Cam rings are different from single to twin, Auto and manual ? ( Groily ? )
You said you made up the mag form different parts?
This could easily be an issue? are the points/ rotor the correct rotation?
Is it a Brass or steel points rotor?
Check from the plug lead  to magneto body for resistance of about 4k ohms when the slipring is inline with that pickup  (points opening) It should be the same for the other side 180 degrees later
Place both plugs on their leads side by side on the engine, get an assistant to kick the engine over
The plugs should fie alternately , If you see both plugs sparking at the same time the slipring is faulty
Both plugs will spark in the air but not under compression

John
1961 Super Rocket
1963 RGS (ongoing)

Online Triton Thrasher

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Re: A10 RGS Replica
« Reply #25 on: 17.09. 2020 00:10 »
I seriously doubt that both plugs sparking simultaneously will ever be seen.

Offline Swarfcut

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Re: A10 RGS Replica
« Reply #26 on: 17.09. 2020 08:38 »
AahThree....At this stage of the game I reckon checking the magneto is the next step. At least it's simpler than a major engine rebuild.

 So whizz it off, get those screw on pickups off, and have a look at the slip ring. For a twin, the contact  is a single descrete brass segment. Single cylinder maggys have a continuous all the way round type, as mentioned earlier by TT.  ChaterleaJohn's test is measuring the HT part of the armature, any difference in reading points to a problem between the slip ring and the plug cap.

 Remove the points plate. Your cam ring should have two distinct cam ramps, run your finger round, find one and mark the position on the housing. Temporarily replace the points and rotate the magneto anticlockwise from the drive end, watch for the points heel approaching the marked cam. When the points break, look at the slip ring, the segment will be in view down one of the pick up holes. This pick up is for the cylinder on its  firing stroke.

 Regarding the points, both clockwise and anticlockwise types are used, depending on the magneto variant and machine application. The K2F on the A10 is classed as anticlockwise. This refers to the normal rotation when viewed from the drive end. The confusion comes as when running, the armature and points rotate clockwise.

 So, are the points correct?  Early brass points mounting is either clock or anti-clock. The way to tell is that when rotating, the pivot "leads" the heel, so the points preceede the pivot, followed by the heel. The  two assemblies are mirror images, so often confused.

 The later steel backed type were designed to suit both clock and anti-clock applications. The component parts used here are the same for either rotation but as the backplate is symmetrical they can be assembled either way. If you have this type, use the above rule to ensure correct assembly.

 While the magneto is off, you can use the published data and test procedures to make sure all within is as it should be. Recommended resources are Brightspark Magnetos and Priory Magnetos. The Magneto Guys have an interesting website, more directed to classic cars, but nevertheless full of good stuff.

 Apologies if all this is old news to you, but re-reading from the start we could be closer now to getting a runner.

Swarfy.

Offline chaterlea25

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Re: A10 RGS Replica
« Reply #27 on: 17.09. 2020 09:48 »
Hi All,
TT, there has been a lot of crap sliprings about in recent times
They absorb carbon from the brushes so to speak, resulting in the HT trying to fire both plugs at once
I have come across at least a half dozen cases

John
1961 Super Rocket
1963 RGS (ongoing)

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Re: A10 RGS Replica
« Reply #28 on: 17.09. 2020 09:53 »
On the various points arising ref the mag  . . . my ha'penceworth  . . .
The cam lobe that is about 4 or 5 o'clock looking at the points end-on always fires the HT pick-up on your right - the rear, gearbox side, one.  The points will be at about 10 o'clock when the heel opens them on that lobe.
The lobe at 10 o'clock-ish fires the front one.
Which plug lead you connect to which pick-up doesn't matter at all as long as you know which cyl is on compression when you set things up. I always have the rear pick-up to the rh plug on my bikes, many prefer the left.

TT's bit 'o brass should be visible in the appropriate pick-up hole when the points start to open - if you can get them off. If the screws on the pick-ups don't have hex heads for a spanner, as they should (as well as slots for a scrooge), it can be darn difficult. They are a fiddle at the best of times on the bike. The threads are also a bit feeble - so careful with the weaponry, as it's not a simple fix when they are stripped. They are often damaged, sometimes fubarred - and there isn't a lot of metal for a 3BA thread insert.

There are 3 basic sliprings for Lucas mags with rotating coils. 360° brass for singles and 4+ cylinder mags with distributors, and twin types with a single segment about 90° of the circumference. Where precisely the segment is embedded in the plastic depends on the rotation of the magneto (or on which end of the armature the slipring is fixed). The camring position is different according to rotation - that is why the brass has to be in a different spot, but 90% of Brit parallel twins are Anti-Clockwise drive and use K2Fs. Exceptions are some few Royal Oilfields, and I think maybe Douglas and another 'minor' marque I can't recall off the top of my head.. Vincents are all clockwise drive. Exactly the same variations are to be found with BTH or other marques, depending on rotation and internal construction.

While there are some dodgy sliprings out there, most that are fitted by repairers of these things are of decent quality and UK-made - the problem with carbonisation of the thing, if it's a decent one, is usually soft brushes (see posts numerous on here!)

Camrings are different for manual and fixed, but only in the sense that manual ones have to be notched for the movement of the ring, and for the plunger that moves it. Fixed ones just have one notch, a small one. If the ring is badly positioned with ref to the armature, it might account for weak sparks if retarded, or no sparks if over-advanced. The points want to open JUST after the 'flip' of the armature, at full advance. If making notches - extreme care needed - and going at it willy-nilly will lead to woe.  However, the rings are symmetrical on a 360° twin so in the worst case - if there's a problem - it can be rotated 180° and new notches put where notches need to be.

Resistances - the low tension coil has a resistace of about 0.55 or 0.6 ohms typically. Because that is pretty tiny, you'll not be able easily to tell when points are open or shut using a battery and bulb. You can measure the low tension R by sticking a meter across the points with them open. A low tension failure, other than a broken wire problem very occasionally at the condenser end, is very rare.

A meter from a plug lead to the mag body should show the resistance of the HT coil, about 5000 ohms typically, when the HT brush attached to that HT cable is 'on the brass'. Ie for about 90° of the rotation of the magneto only. When off the brass - nothing shows. That 5000-odd should show up whatever part of the mag you touch.

If there is no HT resistance reading at any position of the mag, then one of 2 things has happened. Either the connection of the coil to the slipring is bad (it often can be after a mag has been taken apart, it's not a great design), or, more likely, there's a break in the HT winding. A small break won't stop the thing sparking on the bench, and quite often it will run the engine for a goodly while. Until arcing makes the break too long for the spark to hop across it plus then fire the plug.
Any loss of HT continuity needs to be looked into - because a call to the breakdown service, or to a mate with a van, is only a gnat's cock away.

Coming back to the total failure to fart or bang, it does seem possible that the mag isn't sparking under load, because even if the timing weren't that close to right, or the camring were off its optimal position, you'd expect a bang now and then. I'd see whether the spark in free air can jump a decent 1/4 inch at kickstart speed by holding a bared HT cable that distance away from the head or whatever. Sparking a 20thou plug gap in plain air is not a good enough indicator unfortunately. But of course, could be valve timing, or a carb thing, or summat else altogether. Tis a process of elimination!
Bill

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Re: A10 RGS Replica
« Reply #29 on: 17.09. 2020 11:18 »
Hi All,
TT, there has been a lot of crap sliprings about in recent times
They absorb carbon from the brushes so to speak, resulting in the HT trying to fire both plugs at once
I have come across at least a half dozen cases

John

I just mean that an adventitious conduction path around the slip ring from one pickup to the other is still only going to make one plug spark: the plug with a smaller gap if the plugs are in the open air.

If the plugs are in place in the cylinder head, the plug that is not under compression will spark.

I’ve had this happen while riding the bike.  It’s one of those “magneto madness” faults, because it starts with very very low conductivity that has no effect at small throttle openings (meaning low cylinder pressure).