SQ4 Mk2 starting issues

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Gui.dorey
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Re: SQ4 Mk2 starting issues

Postby Gui.dorey » Sun Apr 12, 2020 5:28 pm

Dean Mitchell wrote:Could it be a starting technique problem. I was shown by a good friend how to start my one, like he does with his one. On with the fuel , full choke, su carb, leave ignition off, two or three kicks, then half choke, ignition on , a little throttle and it would start fine.
Dean.

That’s how my MKI starts. Every time. Two, three kicks tops depending on the weather.

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paul.jameson
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Re: SQ4 Mk2 starting issues

Postby paul.jameson » Tue Apr 14, 2020 8:52 pm

The Mk II with SU carb is usually very, very easy to start. One thing which can upset this is a sticking dashpot. Try taking off the air cleaner, putting your finger down the inlet tract and seeing if the slide will move up and down totally freely. Do this with the choke off so there is no danger of a badly centred jet fouling the needle. If the slide does not move utterly smoothly, take the dashpot off and clean everything. Polish the inside of the dashpot with nothing harsher than Brasso. Try again. If it is still not completely smooth, try rotating the dashpot by 180 degrees as the clearances are tiny and sometimes the carb body has warped slightly so that the dashpot top only fits one way.

Another likely cause of trouble is the points cam on top of the distributor shaft. Try rocking it. You sometimes get wear in the distributor shaft bushes inside the main distributor body which you can cure but more common is wear between the points cam on top of the shaft and the shaft itself. This you can't cure easily, except by converting to electronic ignition which overcomes the problem. You may also get wear in the advance - retard mechanism which upsets things.
Paul Jameson
36 4G, 37 VH, 54 KH(A), 75 Healey 1000/4, 52/53 ex ISDT KHA (project).
Former Machine Registrar & Archivist, General Secretary and Single Spares Organiser (over a 25 year period).
Now Archivist once more - but not Machine Registrar.

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berniejones
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Re: SQ4 Mk2 starting issues

Postby berniejones » Wed Apr 15, 2020 9:03 am

Many thanks again for your thoughts and replies. I'll check the dashpot again although I have spent some time checking that it moves freely during the rebuild so probably not that. There is quite a lot of rotary slack in the rotor arm. Some of this might be worn springs - I'm ordering a new set shortly - but it sounds like most of this is backlash in the driving gears. I suspect this isn't an issue provided that the timing is done with the the slack taken out in the driving direction.

I am tempted by an electronic ignition option but so far I seem to remember that the only options that eliminate the points and mechanical A/R require a 12V conversion?

Cheers,
Bernie
'56 SQ4
'52 BSA M21
'56 BSA M21 combination
'61 Dommie 99
'64 B40 SS90
'65 A50CC project
AOMCC# 4631

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paul.jameson
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Re: SQ4 Mk2 starting issues

Postby paul.jameson » Wed Apr 15, 2020 8:49 pm

I know Geoff Brown is running a 6 volt conversion on his S/A Square with Mk II engine but I also know that the conversion cost more than the brand new distributor complete with electronic ignition on my Healey. On the other hand, Geoff's system is easy to time and mine is an absolute swine but having set it, the results so far are excellent.
Paul Jameson
36 4G, 37 VH, 54 KH(A), 75 Healey 1000/4, 52/53 ex ISDT KHA (project).
Former Machine Registrar & Archivist, General Secretary and Single Spares Organiser (over a 25 year period).
Now Archivist once more - but not Machine Registrar.

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Re: SQ4 Mk2 starting issues

Postby Gui.dorey » Thu Apr 16, 2020 11:33 am

You can also look up Thorspark ignitions. They have a 6V kit I believe. I’m using one with 12V and am very happy with it. Very easy to assemble and set up.

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Re: SQ4 Mk2 starting issues

Postby berniejones » Thu Apr 16, 2020 12:08 pm

I'm now wondering about modifying a system designed for twins. By either using four trigger coils on one rotor plate - a mod to the circuitry - or two boards mounted back-to-back and rotationally offset by 90 degrees I could then machine a standard rotor to fit on the distributor shaft and enclose the assembly inside the standard distributor housing (need to confirm dimensions).

This would probably need two control units, each triggered by one of the stators, and running a wasted-spark ignition through a pair of dual ouput coils.
Reconnecting the four coils together and triggering a single control unit might also work but I'd need advice from the manufacturers there.

I'd have to provide a 12V supply to the system but can probably get a solid state step-up circuit that will allow me to continue with the 6V components that I've only recently bought and installed for the rest of the electrics.

I'm going to email some of the suppliers and see what they say. Plenty of time on my hands at the moment and it's either tinkering with bikes or painting the bathroom....

Cheers,
Bernie
'56 SQ4
'52 BSA M21
'56 BSA M21 combination
'61 Dommie 99
'64 B40 SS90
'65 A50CC project
AOMCC# 4631

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paul.jameson
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Re: SQ4 Mk2 starting issues

Postby paul.jameson » Thu Apr 16, 2020 9:09 pm

Bernie,

The issue in timing mine is that you really need to do it using a timing light and there is no facility for this on a Square Four unless you do the modification to the coupling gear case which some of the Dutch boys have done. The system on mine will provide a dummy "spark" about 45 degrees wrong if it is left turned on for some time - like the time you need to set the timing statically. I have overcome this by knowing where the spark should occur (courtesy of investigation by the manufacturer) and working from there aiming for a little over advance.

Whilst I am happy to do this on my own bike using my own experience, it is not something I would suggest can be reliably used by anyone. But I do have a spare system available if anyone wants one at £40 inc postage (UK). My new distributor (and system) cost me £130 which to me for a reliable advance retard system seemed like a bargain.
Paul Jameson
36 4G, 37 VH, 54 KH(A), 75 Healey 1000/4, 52/53 ex ISDT KHA (project).
Former Machine Registrar & Archivist, General Secretary and Single Spares Organiser (over a 25 year period).
Now Archivist once more - but not Machine Registrar.

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Re: SQ4 Mk2 starting issues

Postby david.anderson » Fri Apr 17, 2020 12:28 am

Bernie
My distributor was badly worn so I looked at other options. There are many electronic distributors from various cars that can be readily adapted to fit. There is a bit in the knowledgebase about using a Mitsubishi sigma distributor. I picked up a distributor from the wreckers (cant remember from what) turned the body down a little to fit the square and fitted the drive gear. It worked well. However for the sake of originality I then rebuilt the original distributor. New bushes and new advance springs and it was like new. However as I was running 12v it suffered from excessive point burning so I picked up a tfi unit from a ford and wired that in. With the tfi unit the points are a trigger only and do not burn. Dwell is also controlled by the tfi but the advance is by the mechanical distributor. The tfi unit is a high energy ignition which made starting easier and enabled me to open the plug gaps a bit.

Some of the electronic ignition conversions do not have a built in advance and do not use the existing mechanical advance, fixed timing, no thanks.
Also do not forget a couple of drops of light oil in the top of the SU dashpot. Without oil the dashpot will stick which will make starting more difficult and idling poor.
David

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rebushing the dkx4a

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berniejones
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Re: SQ4 Mk2 starting issues

Postby berniejones » Fri Apr 17, 2020 8:11 am

Thanks again all for the tips and your ideas - just thinking my earlier idea through overnight I realise that if I did try it I would need to use two control units rather then trying to trigger one from four coils connected together - otherwise the advance would be wrong. If I've thought it through correctly then a single control unit for each opposite pair of cylinders would give about the right curve whereas in my other idea it would count twice the frequency and over advance. More pondering to do....

Paul, I'd be interested to know more about your system and what I'd need to accomplish something similar - I'll send you a P.M.

I have managed to strobe mine successfully by putting marks on the the front crankshaft bolt and casing after removing the small, round cover on the timing side. The diameter available is limited but I've managed to get an accurate TDC marker on there to use as a datum for a fully advanced mark.

Cheers,
Bernie
'56 SQ4
'52 BSA M21
'56 BSA M21 combination
'61 Dommie 99
'64 B40 SS90
'65 A50CC project
AOMCC# 4631

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berniejones
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Re: SQ4 Mk2 starting issues

Postby berniejones » Sun Apr 19, 2020 10:23 am

I contacted Powerspark and here's their reply:

Hi Bernie - the DK4A distributor we supply (our part number D31PP for the positive earth version) is intended for the Austin 7. It rotates clockwise and will work with 6v or 12v, but the drive gear will be different to your Ariel. It's possible that you can swap the drive gear, however some machine work may be necessary to do this.


As this is a fully solid-state solution I think I might give it a try - will likely need to machine or bush the shaft and swap the drive gear over from mine, but hopefully that won't be a problem. Paul - do you remember having to do this on your system?

Thanks,
Bernie
'56 SQ4
'52 BSA M21
'56 BSA M21 combination
'61 Dommie 99
'64 B40 SS90
'65 A50CC project
AOMCC# 4631


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