The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: r3sc on 14.09. 2020 21:13

Title: A10 RGS Replica
Post by: r3sc on 14.09. 2020 21:13
Hi All,

I’m brand new to this forum so be gentle with me and be aware that my knowledge and experience with the British marques is still somewhat limited.

Anyway, it’s a bit of a story so if you’re sitting comfortably, I’ll begin.

About a year ago a good friend of mine decided he wanted a nice RGS replica, so without mentioning it to me he went out and paid a considerable amount of money for what can only be described as a very, very poor kit of badly selected parts which came in several large boxes and crates.

The quality of the parts left a lot to be desired and I was a little apprehensive when he asked me to build the engine but I went for it and built the engine using the parts provided and many more purchased on the way.

Anyway, I gave the completed engine back to him a number of months ago and left it with him to fit it into the frame along with all the running gear.

The process of getting it ready for commissioning was slow due to Covid but I finally went to get the engine running last week for the first time. Guess what? It won’t start!☹️

So, here’s a list of things that I’ve done.

1, At the time of rebuilding the engine I totally rebuilt the magneto and I have a healthy spark on both leads. The magneto has manual cable advance.
2, Totally stripped, ultrasonically cleaned and rebuilt the carb with new Amal parts where required.
3, The engine block is a thick base cast iron item which was honed and fitted with new Hepolite piston rings, gaps checked, all good.
4, Cylinder head is aluminium and is fitted with all new BSA valves, lapped in and checked with petrol, all good.
5, The crankcase/bottom end is allegedly a rebuilt unit and does look to be in good shape. It is fitted with the 67-357 spitfire cam.

So, I have good spark timed at full advance of 3/8”, the carb is a fresh rebuild, valve clearances are all set to correct specification and despite all that with hours of kicking, not even a glimmer of a fire.

I’ve exchanged the leads, tried it on easy start and double checked the ignition timing with no joy.

The only thing I can think of now is valve timing.

The engine number is DA10R 12*** and I know it has the 357 cam in it as I’ve seen the number on the end. The timing gears are crank- 22T, cam- 44T and idler- 49T and when I set it all up all the marks were aligned.

I seem to have good compression and good vacuum on the induction stroke but the only thing I can think of is that it’s not quite happening in the right place.

Main questions-
A, Are the valve timing figures for this cam 51, 68, 78 and 37?

B, If I fit my degree wheel to this motor and set the valve clearances to 0.0020”, do the timing figures relate to the valve just starting to open/close or is it when they are fully opened or closed?

C, Are there any different combinations of timing gears as the ones that are fitted to the engine could be the wrong ones as they were loose in a bag.

D, Am I missing something obvious? Is my lack of experience with British iron shining through?

Another annoying issue he has is that the gearbox, which is stamped with the RRT2 designation provides for the kickstart leaning forward towards the front end dramatically and this makes it very difficult to kick, but that’s another post!

Anyway, I hope you guys aren’t fed up of me already and that you can give me some pointers relating to the above.

Many thanks in advance.👍🏻
Title: Re: A10 RGS Replica
Post by: Triton Thrasher on 14.09. 2020 21:46
Did you try some petrol in through the spark plug holes?

Did you try starting it fully advanced?  That’s where the strong sparks are.

51, 68, 78, 37 means inlet just starts to open 51 degrees before TDC at the end of the exhaust stroke and just closes 68 degrees after BDC during the compression stroke.  Exhaust just starts to open 78 degrees before BDC during the power stroke and just closes 37 degrees after TDC at the start of the intake stroke. 

I don’t know whether 51, 68, 78 and 37 are correct, but that’s what they mean.
Title: Re: A10 RGS Replica
Post by: r3sc on 14.09. 2020 21:53

Yes, I tried fuel down the plug holes and directly into the throat of the carb and I have to say, never at any time did the plugs look wet.

If I put my hand over the inlet tract with the carb off it does try to suck my hand in but no fuel seems to be getting to the motor. I’ve even checked if there had been a bung of rag left in the inlet but nothing.

I tried with full advance, no advance and every position in between and never even had a single puff or hint of a fire.

I’m stumped so now looking at the valve timing.

Title: Re: A10 RGS Replica
Post by: Triton Thrasher on 14.09. 2020 22:44
You didn’t time the ignition to 3/8” after TDC or do it rotating the engine backwards?

Such things do happen!

Blocked exhaust?
Title: Re: A10 RGS Replica
Post by: berger on 14.09. 2020 22:47
I would take the rocker covers off and get a piston tdc on firing to see what's happening , put it on centre stand or block it up if it hasn't got one and use 4th gear and turn the back wheel forward and backwards checking for tappet clearance at tdc when points should then be well on the cam and fully open
Title: Re: A10 RGS Replica
Post by: trevinoz on 14.09. 2020 22:50
Those figures for the valve timing are correct.
As to timing gears, the early long stroke gears are the same but with timing marks in different positions.
Check that the pilot circuit in the carby is clear, the engine won't start usually or will start after tickling and cut out quickly.
Your magneto may have a strong spark in the open but may not fire a plug under compression.
Good luck.
Title: Re: A10 RGS Replica
Post by: Swarfcut on 14.09. 2020 22:52
The earlier Longstroke A7 uses timing gears which are identical in dimension and teeth numbers to your  later A series, but differ in the position of the timing marks. Search the Forum "Longstroke Timing Gears." So yes, remote possibility of wrong parts.

 Other possible ignition wise is that there is an error in the way the timing has been set, eg after top dead centre instead of before. With the piston coming up on compression to the specified position, either by degree disc or measurement, set the magneto to full advance with the points just breaking. Hold everything still and fit the magneto drive gear.  Look down the pick up hole, the slip ring brass segment seen will be for the pick up and lead to that cylinder on compression.

 Plenty on the Forum about pre -start preparation for new build engines, particularly ensuring the oil is circulating.

  Before taking it apart, a first try, put some oil down the plug holes and give it a good kick session to lubricate the bores, seal the rings and circulate oil to the crank bearings. Plugs in, magneto end cap off to avoid any unintended magneto earthing and a good dose of "Start Yer Bast**d"  If it fires, turn your attention to the fuel system. If not, a compression test will tell if the rings are working, modern Hepolites have been reported as not quite cutting the mustard.

  Depending on construction the kickstart quadrant can be moved round on the splines. Possible with pressed on construction, brazed up variants no chance.


Title: Re: A10 RGS Replica
Post by: Triton Thrasher on 14.09. 2020 22:54
And re-check the ignition timing in case it slipped.
Title: Re: A10 RGS Replica
Post by: trevinoz on 14.09. 2020 22:59
I wouldn't be pouring much oil down the plug hole, probably none. It may seal the rings temporarily but won't help with bedding them in, more harm than good.
Title: Re: A10 RGS Replica
Post by: RichardL on 15.09. 2020 04:29
I think it may have been mentioned earlier that your points may be slipping when tightening  the magneto pinion driving nut. Once you've rotated the points to just open at 3/8" BTDC (or, maybe 11/32), you need to sneak up on tightening the nut while applying enough back pressure on the points carrier to prevent it from slipping due to the tightening. Once you've tightened the nut, you need to check the timing again. Assuming you are using fag paper between the points, insert the fag paper with the piston about 1 1/2" BTDC, now turn the engine over with the rear wheel or with a socket on the cush-drive nut just until the fag paper releases. Now, remeasure BTDC. As you are a newcomer to the process, I'd be very impressed (or embarrassed, recalling my own learning curve) if you got this right within about the first ten tries.

Here's an extra trick, attach an electrical clip lead to the fag paper and let the weight of the lead pull the fag paper out when the points open. Here's another trick, wedge a piece of pink eraser between the points carrier and the cam ring to create friction that prevents the points "bumper" (uuhh, don't know what else to call it) from running back down the slope of the cam ring.

Can't really say that this the cause of your grief (the bike not starting, not the grief of reading my ideas), but I hope it's useful, regardless. Also, as my Brit friends say, I hope this isn't teaching gramma  to suck eggs.

Richard L.   
Title: Re: A10 RGS Replica
Post by: KiwiGF on 15.09. 2020 05:10

Yes, I tried fuel down the plug holes and directly into the throat of the carb and I have to say, never at any time did the plugs look wet.

If I put my hand over the inlet tract with the carb off it does try to suck my hand in but no fuel seems to be getting to the motor. I’ve even checked if there had been a bung of rag left in the inlet but nothing.

I tried with full advance, no advance and every position in between and never even had a single puff or hint of a fire.

I’m stumped so now looking at the valve timing.


Does the carb flood properly when you “tickle” it? (I am assuming you know the normal starting procedure)

If the carb floods and you have spark this should result in it firing at least (but keeping it going after firing is another part of the puzzle)

Title: Re: A10 RGS Replica
Post by: Swarfcut on 15.09. 2020 08:38
 Trev. Good point there, not too much oil, just enough to produce decent compression. But to be honest I'd worry more about getting it to fire and run.

 AAHThree.     Its back to basics, mechanical, ignition, fuel. Easy fix if you work through it in a methodical manner. We've all been down this road, I reckon Richard has pointed the way. When fitting the magneto drive gear, make sure the tapers are dry, push it on and then give it a  very light tap to hold the two tapers together. Then hold things still and sneak up on that retaining bolt. Yes, it is a case of being very lucky to get it right first time.



Title: Re: A10 RGS Replica
Post by: r3sc on 15.09. 2020 08:56
Hi Guys,

Many thanks for all your input. I’ll try to answer all your queries in turn.

When I rebuilt the engine all internal components including bores etc did get a liberal coating of oil so I’m happy they are well lubricated.

Yes, when I tickle the carb there is flooding and all looks to be ok. The carb did spend at least an hour in the ultrasonic cleaning tank at time of rebuild and I’ve re stripped it and double checked for any blockages.

I’ve checked and double checked the timing. I’ve turned the motor over using the back wheel in 4th gear until it’s at TDC then turned it backwards and measured the downstroke at 3/8”. Then pushed the timing gear onto the magneto shaft just as the points were about to open. I’ve been very careful about tightening the magneto nut over the square section spring washer to ensure it doesn’t turn during tightening. I’ve since double checked this a number of times.

Exhaust system is brand new.

In my head, if any of these things were wrong I would at least get a fart or a backfire, but there’s nothing. No sign of life at all.

After using easy start down the throat of the carb, still nothing so I think that eliminates fuel.

The Unknown’s for me are as mentioned, a break down of the magneto output under compression pressure or valve timing and at the moment my money is on valve timing.

Sadly I can’t get access to the bike for a couple of weeks as my mate is on holiday but I want to be fully armed with options for when he gets back.

Once again, thanks for the input, everything is welcome!

Title: Re: A10 RGS Replica
Post by: Swarfcut on 15.09. 2020 09:28
AAHThree. The way you set the timing position may be significant. Rotating the engine forward means the timing gears are moving under load and backlash is eliminated. Try rotating forward, finger over the plug hole to feel the compression build, insert your measuring stick and stop when the marks show the piston correctly positioned. Now turn the timing gears backwards by turning the cam drive gear to ensure the gear train is loaded as in normal running. Set the mag at full advance, points breaking, and fit the drive gear.

 Late model piston height, A10 SR (GA frame prefix, so assume 357 cam) is given as 13/32" BTDC.

Title: Re: A10 RGS Replica
Post by: r3sc on 15.09. 2020 10:17
Hi Swarfy,

Thanks for that. I’ll certainly try that ASAP.

With regards to pistons, I’m not sure what they are but I think they are oversize. The cam is definitely the 357 item.

I’ve included an image of the pistons prior to ringing and fitting of the barrel and wondered if you could comment as to whether they are the right ones in terms of compression ratio to suit the 357 cam and the timing figure you suggested?


Title: Re: A10 RGS Replica
Post by: Triton Thrasher 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
Title: Re: A10 RGS Replica
Post by: Swarfcut 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.


Title: Re: A10 RGS Replica
Post by: r3sc on 15.09. 2020 11:16

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!👍🏻👍🏻
Title: Re: A10 RGS Replica
Post by: a10rgs on 16.09. 2020 07:34

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

Title: Re: A10 RGS Replica
Post by: Radlan2 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
Title: Re: A10 RGS Replica
Post by: r3sc 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??

Title: Re: A10 RGS Replica
Post by: Triton Thrasher 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.
Title: Re: A10 RGS Replica
Post by: r3sc on 16.09. 2020 22:27

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.

Title: Re: A10 RGS Replica
Post by: Triton Thrasher 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?
Title: Re: A10 RGS Replica
Post by: chaterlea25 on 16.09. 2020 23:44
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

Title: Re: A10 RGS Replica
Post by: Triton Thrasher on 17.09. 2020 00:10
I seriously doubt that both plugs sparking simultaneously will ever be seen.
Title: Re: A10 RGS Replica
Post by: Swarfcut 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.

Title: Re: A10 RGS Replica
Post by: chaterlea25 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

Title: Re: A10 RGS Replica
Post by: groily 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!
Title: Re: A10 RGS Replica
Post by: Triton Thrasher 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


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).
Title: Re: A10 RGS Replica
Post by: JulianS on 17.09. 2020 12:28
It can be a real struggle to get the lower pickup out of the K2FC type mag shown in the photo, you need a 4 ba socket for the hex headed screws. Easiest if the ski slope is removed. Space a little tighter if you have a reverse camplate fitted to the gearbox. Also fun to get this one back in.

The top pickup should not be too much of a problem.

Photo shows the orientation of points and cam as fitted to my A10 (also shows an EasyCap fitted)
Title: Re: A10 RGS Replica
Post by: RichardL on 17.09. 2020 12:39
I'm not going to try to rationalize this against visible sparks, long-jumping sparks, sparks that die under compression, sparks that leak through slipping or pickup cracks, correct or incorrect resistances, etc., but, with all this trouble, if the mag is apart for inspection/repair, you should throw in a test for magnetization strength. There are instructions for that test either here on the forum or in Lucas service sheets. Can't point to it right now.

Another thing to do while it's apart is to change from the stock capacitor to a Brightspark EasyCap. Why wonder if your cap is a problem now or in the future?

Richard L.

Ha! Julian posted the photo of the EasyCap almost exactly when I was writing that you should add one.
Title: Re: A10 RGS Replica
Post by: r3sc on 17.09. 2020 13:18
Hi All,

I can’t thank you all enough for the input, it’s fantastic and I can’t wait until I can get back to the bike and implement the suggestions that you’ve all made.

I’m going to take off the magneto firstly and strip it to find out exactly what I have and then move on from there.

Where is the stock capacitor usually located as I don’t remember seeing one when I stripped and rebuilt the mag?!

Where is the best place to buy an Easycap? I’ve never heard of or seen one before.

The other consideration would be to send the entire unit off to have it reconditioned and tested which would eliminate it for sure.

I’ll keep you posted but I can’t get to the bike until W/C 28-9-20.

Once again, many thanks.
Title: Re: A10 RGS Replica
Post by: RichardL on 17.09. 2020 13:57
A few links to Brightspark Magnetos' pages:

This one will show you where to locate the condenser (condenser, capacitor, tomato, tomAHto) while showing how to completely remove it:

This one shows what most of us have done, that is, the easy way:

Here is the EasyCap replacement:

Richard L.
Title: Re: A10 RGS Replica
Post by: Steveba10 on 23.09. 2020 19:57
Interesting thread.
You would think with fuel, compression and a spark something should happen.
I think perhaps the dry spark plug might be the best clue you have.

A couple of quick practical tests I use to start recalcitrant engines follow.

Usually if you place your hand over any carb intake and turn the motor over the strong suction will pull plenty of fuel out of both jet circuits and the return pressure pulse due to the inlet valve closing will give a palm wet with petrol. Not very scientific but a quick and dirty way to draw fuel through and see its presence.
Both my Jags run Webbers and this trick gets them to fire after long periods of inactivity.

Another useful test.
I keep a couple of neon spark plug indicators in tool boxes, if you’ve not seen them they look like extensions to a spark plug fitting between the plug and it’s cap. The body is transparent coloured plastic and within is a neon bulb that will flash bright every time the plug is fired.  This will show whether your plug is sparking under compression or not. A weak flash shows a poor or non-existent spark. If the engine starts it will run happily with the tester in place. Very useful for lawn mowers where the coils seem to die over winter.

Performing both those test usually quickly pinpoint the trouble being either fuel or spark. If both are good then look for something deeper.
Good luck,
mod edit: found neon spark indicator on fleebay