BSA ROCKET 3 starter motor

[Poole]

Hi all, I hope someone can help. please see below

I have fitted an electric starter to my A75R pretty painful right Knee and left hip has pushed me this way, I have fitted a Triumph T160V starter assembly with a new Starter motor and have fitted a Lucas type 22 ra relay ( I have changed this for a modern type also), the starter is wired correctly and turns the engine over but it will not start consistently, but will start on the Kick start with no problem the bike is running on a MK IV Boyer ignition with 6 Volt coils, looking online it seems the problem is the starter is pulling volts below the working capacity of the MK IV Boyer when cranking the bike on the starter the battery voltage drops to around 9.7 volts but I have fitted a separate battery supply to the Boyer and the problem still persist, I worked for Exide for many years as there Technical Manager so I know my way around batteries, I have a 140 CCA 9AH new Yuasa battery, I can squeeze in a 175CCA 14.5 Ah MB10U battery but I have also tried car battery 640 CCA 60Ah with no difference all batteries test good, again online people are saying that the Tri Spark system can resolve this but as I am not sure of what the problem actually is I do not want to spend a load of cash to find the problem persists, others online say changing the 6V coils to 4V coils and keep the current MK 4 Boyer may resolve the problem but I have no experience with 4 Volt coils, as stated above the bike kick starts no problem, (it just leaves me with a swollen Knee) but will also intermittently start on the electric start, I have no exhausted my knowledge, I hope someone can help, I just do not want to stop riding my Rocket 3.

Regards

John

[idie]

As you already know, you have a large voltage drop. So much so you are starving the system. Check earth's also find what is drawing off all the current. I would suspect the starter motor. Otherwise go to 4 volt coils and a ballasted system like cars used to have.

[Novocastrian]

I know you're well down the road with this, but the Madigan starter spins the motor like a top compared to the Lucas starter..... and I would guess draws a lot less current.  But that is a guess. My R3 really spins with the Madigan starter whereas my mate's R3 with Lucas starter sounds like it's struggling....

[iansoady]

I have had effectively the same problem with the similar starter on my Norton Electra. After much wailing and gnashing of teeth, I have tried various solutions. Much advice has been along the lines of "they never work, use the kickstart" which I'm afraid doesn't cut it. I too have Boyer Mk 4; on the advice of BB I tried 6 volt coils etc to no avail.

Finally I came to a similar analysis as you and I believe I now have a workable solution. In short, although BB say 10 volts is enough to fire the ignition, I believe the voltage is too low for a decent spark. So what I've done is to add another small 12v battery which only supplies the BB black box. It's brought into operation via a relay switched by the ignition switch, and charged via a voltage sensitive relay of they type usually used to charge motorhome leisure batteries.

I don't know if you can get at it but here is what I've built.

NOC forum

It was starting first push of the button every day through the back end of the summer till I put it away for the winter. There are various other subsequent threads elaborating (and describing further issues) on the same forum. If you don't have access let me know and I'll send you some text - or post it here.

[rhyatt]

have you done a "volts drop test" between the battery Pos terminal and the solenoid and then the other side of the solenoid to the actual starter terminal and finally directly across the solenoid terminals themselves.

and then the neg side from the battery neg terminal to the stages of the earth (battery to frame and frame to engine>
basically working through each leg of the voltage paths and seeing where you are losing the voltages

(don't forget to disconnect the ignition when doing all these cranking based tests - you don't want it to actually start)

[Rog1]

have you done a "volts drop test" between the battery Pos terminal and the solenoid and then the other side of the solenoid to the actual starter terminal and finally directly across the solenoid terminals themselves.

and then the neg side from the battery neg terminal to the stages of the earth (battery to frame and frame to engine>
basically working through each leg of the voltage paths and seeing where you are losing the voltages

(don't forget to disconnect the ignition when doing all these cranking based tests - you don't want it to actually start)

I was once asked about a bored and stroked, tuned up Harley that was not starting on the button. All became clear when I asked if the starter cables were getting warm, "Yes!" they replied, and a change to thicker cables solved the problem.

Poole, is the starter motor not turning very quickly? If so and the cables are getting warm, thicker cables are at the very least part of the solution.

[Poole]

Thank you all for your input, it has given me a few new things to look at.

[iansoady]

I actually did the voltage tests as described on my Electra. With a fully charged 9Ah, 120CCA battery I was seeing 12.7 volts at the BB box with no load and between 10.2 and 10.4 with the starter operating. I just don't believe this is enough to reliably operate the BB system. As suggested by Rog1 I have 10 sqmm cables for both supply and engine earth (very important and often overlooked).

It's also worth checking the starter motor itself - I believe the R3/Trident use the same basic motor as the Electra. Inside the brush end cover there should be a fibre insulating ring preventing shorting bwteen the brush leads and the casing. Some previous owner of my bike had replaced this with PVC tape resulting in, initially a partial short but eventually a complete short. This made the cables very hot!

Oddly enough, as I was trying different things, I tried the BB v3 black box that came with the bike originally and it worked perfectly well with my auxiliary battery setup. But then so it should being supplied as it is with a full 12.7 volts. You can waste a lot of money and time trying different things.......

[rhyatt]

As a yardstick on volts drop tests , you should not see any more than 0.5 v maximum at any section of the tests along each path.
When one breaks the actual test down , there are loads of segments , for example ---
Take the + side,
1)Battery lug itself to cable terminal.
2)Crimp to conductor
3)conductor to other end crimp
4)crimp to component fixing

The solenoid itself , one can go directly across the 2 heavy posts themselves and hopefully not see any more than 0.5v max on the meter.

It's surprising how much total volt drop is accumulated along each conductor.

Many modern cars ecus will not function below 10.5v and a few below 11v.
Given that the standing voltage of average 12.5v doesn't give a lot of leeway before a vehicle won't fire.

All these tests must be done when the vehicle is actually cranking ie working hard.
It must not start for this test

[iansoady]

I don't think that voltage drop as describedis the problem here. It's the fact that the starter takes so much power that it drops the available voltage for the BB box below what it needs. Even with perfect conductors you'd get the same effect. Hence my use of an additional battery. Not a conventional solution I grant you but it works.

BB say their Mk 4 box works down to 10 volts but I'm afraid I don't believe that. I do wonder whether using a conventional Kettering system with points might actually be better here although of course that then raises issues of accurate and consistent timing etc.

[Poole]

Hi Iansoady

I have re-looked and checked all points from above, and all seems OK, so I set a car battery to power the starter and a separate 9ah bike battery to power the Boyer both being charged with separate battery optimizers, The R3 has started on the button all day today, so it seems it is the Boyer Mk 4, I guess now I must decide how I move forward, I downloaded you sketch, I think the diode is a Schottky barrier diode do you have the spec? I have looked on line for a Voltage sensitive relay the standard seems to be 12V 140A is this the type you used, at this moment the biggest issue is where to fit an Auxiliary battery, but I have moved forward a good pace, I would like to thank all for input.

[iansoady]

I have a slightly better sketch here: rather than using a diode I've fitted a voltage sensitive relay (split charge relay) which kicks in at about 13.5 volts. As it's negative earth I've had to use it to drive a relay. I got this one from my local electrical supplier:

https://www.almsolutions.co.uk/battery-products/split-charge-relays/automatic-vsr-dual-split-charge-relay-30a

I do not believe that the BB unit is fit for purpose with an electric start machine.

[Poole]

Iansoady, thank you for the information and diagram, I will try this, again thank you for all you help. Regards John

[iansoady]

Just for information, this is the auxiliary battery I fitted. It doesn't need to be huge as it's only driving the ignition and is being charged as soon as the engine is running. It fitted in the toolbox of the Electra (the main battery is between the toolbox and oil tank).

https://www.tayna.co.uk/industrial-batteries/numax/lsla4-5-12/

[limeyrob]

Would it be possible to put a DC to DC voltage booster in parallel to supply the BB unit? Connected to the starter feed so its only live when cranking? These are small-ish and cheap so you could experiment.  You could set it for 10v input 12.5 output.