Starter Motor / Solenoid Strip Down (Startis Interuptus part 2)

Already done the direct fused wire from the starter relay to the battery because of an episode of startis interuptus a couple of years back.

Well lately the fuse in this circuit has blown a few times so we have the sequel, Startis Interuptus 2. I decided to strip the motor and solenoid to clean and re-grease the gears in the starter and to give the solenoid a bit of a shine up. I think it may be due to dirt that the fuse is blowing! I have an electronic version of a technical bulletin from MG on how to do the job, but I don't know how to post it DUH, I took a few photos that may be of help to anyone that wants to know what the guts of the starter looks like.

First I pulled the main fuse & disconnect the battery, then pulled the motor and blew (make sure to wear dust mask) out as much clutch dust as I could from both sides of flywheel housing. {before someone says it the red thing is not the top of my finger}

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Then marked the body of the starter and solenoid before stripping,
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Cleaned everything(WD40 or similar) and blew with compressed air
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Everything greased and ready for assembly (I didn't grease the solenoid plunger just a drop of WD40)
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All back together again and no parts left over, you don't need to take the armature out of its housing or you could have a problem putting back the spring loaded brushes (just blow out with compressed air)
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I put it back in the bike and started it a few times, seemed nice and smooth. Only time will tell if it fixes the fuse blowing problem  Hope this is some help to someone,

Neat. Well documented. Well done.

Pete

Thanks GC
These posts greatly help us amateur mechanics out here when and if needed into the future.
Would be good if this was popped into the archive.
Have a great day

Guzzi Cat,
I had the same symptom of a blown fuse and the stater motor no worky and started a thread looking for a source for a new starter.  I had time and curiosity so I pulled the starter apart (though not as far as you) and found nothing suspicious.  It wasn't even dirty due to low miles.  After cleaning the commutator, I put it back together and it worked but I have no idea what was wrong.

Several things to note however.  The blown fuse was the one labeled B in the workshop manual schematic.  The key to the schematic calls it the "Start-up relay".  The diagram for the fuse block says fuse B has the "ignition relay" and fuse D has the "start-up relay coil".  I think the fuse block diagram is wrong.  This had me looking for a blown fuse in the wrong fuse block position at first.  I replaced the blown fuse and it blew again so it wasn't a one time event and a close look at the blown fuses revealed they weren't cracked but blasted open with a lot of current by their burned appearance and wide gap of vaporized metal.

Back to my initial trouble shooting.  I was sure that the solenoid coil was shorted to the frame when I measured it with a good meter (Fluke 189).  That was before I did some internet searches and found a schematic sketch of these automotive style solenoids.  Note that this diagram is simplified and does not show the ECU, the fuses, or the relay.  It's for a car but the solenoid wiring is the same.

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As you can see there are two coils, one pull in and one holding.  They both have low resistance and are in parallel so the total resistance is less than the lowest resistance of either one (half the resistance if they are both the same).  The pull in coil gets its return through the motor windings and is shorted out when the power contacts are energized.  The hold in coil returns directly through the frame.  After reassembling the starter I repeated the measurement of the solenoid coil terminal to the frame and got the same very low resistance (less than 1 ohm).  This proved to be normal as the starter worked when I then pushed the starter button.  I also tested the starter motor on the bench before I reassembled and measured the hold in current to be 6 amps.  This means a total circuit impedance of about 2 ohms if they haven't repealed ohms law.

I have looked of course for exposed or damaged wiring.  I don't know if I can trust it but have operated the starter dozens of times with no problems.  I believe if it happened again on the road I would put the spare 30A fuse in to get me home. A dead short would pop a 30A fuse as surely as a 15A fuse if it didn't fuse a small wire first.  Worth a try if you are stuck on the road.  Possibly the 15A fuse is under rated though it doesn't seem likely.  There is some reason but I don't know what it is right now.

cheers,
tod

fishbulb wrote:

Guzzi Cat,
I had the same symptom of a blown fuse and the stater motor no worky and started a thread looking for a source for a new starter.  I had time and curiosity so I pulled the starter apart (though not as far as you) and found nothing suspicious.  It wasn't even dirty due to low miles.  After cleaning the commutator, I put it back together and it worked but I have no idea what was wrong.

Several things to note however.  The blown fuse was the one labeled B in the workshop manual schematic.  The key to the schematic calls it the "Start-up relay".  The diagram for the fuse block says fuse B has the "ignition relay" and fuse D has the "start-up relay coil".  I think the fuse block diagram is wrong.  This had me looking for a blown fuse in the wrong fuse block position at first.  I replaced the blown fuse and it blew again so it wasn't a one time event and a close look at the blown fuses revealed they weren't cracked but blasted open with a lot of current by their burned appearance and wide gap of vaporized metal.

Back to my initial trouble shooting.  I was sure that the solenoid coil was shorted to the frame when I measured it with a good meter (Fluke 189).  That was before I did some internet searches and found a schematic sketch of these automotive style solenoids.  Note that this diagram is simplified and does not show the ECU, the fuses, or the relay.  It's for a car but the solenoid wiring is the same.

[You must be registered and logged in to see this image.]

As you can see there are two coils, one pull in and one holding.  They both have low resistance and are in parallel so the total resistance is less than the lowest resistance of either one (half the resistance if they are both the same).  The pull in coil gets its return through the motor windings and is shorted out when the power contacts are energized.  The hold in coil returns directly through the frame.  After reassembling the starter I repeated the measurement of the solenoid coil terminal to the frame and got the same very low resistance (less than 1 ohm).  This proved to be normal as the starter worked when I then pushed the starter button.  I also tested the starter motor on the bench before I reassembled and measured the hold in current to be 6 amps.  This means a total circuit impedance of about 2 ohms if they haven't repealed ohms law.

I have looked of course for exposed or damaged wiring.  I don't know if I can trust it but have operated the starter dozens of times with no problems.  I believe if it happened again on the road I would put the spare 30A fuse in to get me home. A dead short would pop a 30A fuse as surely as a 15A fuse if it didn't fuse a small wire first.  Worth a try if you are stuck on the road.  Possibly the 15A fuse is under rated though it doesn't seem likely.  There is some reason but I don't know what it is right now.

cheers,
tod

Cheers Tod for the input, I think that the problem is caused once in a while by the solenoid switch not moving quick enough or the solenoid sticking just a little but enough to overload the circuit. It could be the solenoid plunger sticking or the linkage gear not being greased enough between the the solenoid fork and the sliding gear mechanism. ( maybe even lack of grease from new in your case).

My inital problem a few years back was that fuse (B) blew so I wired the starter relay direct from the battery and installed a 15 amp fuse between battery and relay which was fine for a long time. But now that 15 amp fuse between battery and relay has blown a few times but bike always started when I changed the fuse with a new 15 amp.

I will wait for a while to see if it is fixed by the clean and grease up that I gave it before delving any further. Always try the obvious first

Cheers,
Larry,

Larry,
I think you are right.  A sticky mechanism could draw the load current for longer than the fuse can take.  A fuse is a thermal device and has a blow curve which shows when it will open depending on both current magnitude and duration.  That is why a temporary fix would be to put a 30A fuse in.

I looked at the other loads on that fuse and they did not seem  likely culprits.  All are lights I believe.

I also looked at the gauge of wire and measured its resistance from the relay to the solenoid and it was quite adequate.  I did this also for the ECU ground wire.  I suspect that bypassing or replacing this wire will not fix anything which is why the problem returned.  If others have this problem, I would try the 30A fuse at least temporarily (if you are not comfortable leaving the larger fuse in).  If that works, it wasn't the wire.

Nice to have this discussion.  Best forum I've encountered with the experts we have.

tod

edit:
one other point to be clear.  A high resistance or open circuit wire could not draw more current, only less or none so bypassing that wire with a new wire would not be a fix if the fuse blew from high current.

fishbulb wrote:

edit:
one other point to be clear.  A high resistance or open circuit wire could not draw more current, only less or none so bypassing that wire with a new wire would not be a fix if the fuse blew from high current.

Ye Tod, I remember that the reason I done the direct wire from the battery to starter relay is because it has been a known guzzi problem for years that some current may be lost through the original circuit which takes a long route through ignition switch etc and as connections get older there may not be enough amps to open the starter relay. You are correct in pointing out that the B fuse blowing is a separate problem,  which I think is due to the possible sticking solenoid mechanism that we discussed and is now blowing the fuse in the new battery to starter relay circuit.
I still think it is a good idea to wire directly to the battery as many people here have done as preventive maintenance. A lot of people have been left stranded by both of these problems, relay not opening and I think sticking solenoid.
Cheers,

Where in Kilkenny are you Cat?

We're in Oghterard tonight. No idea where we'll be tomorrow?

Pete

Pete Roper wrote:

Where in Kilkenny are you Cat?

We're in Oghterard tonight. No idea where we'll be tomorrow?

Pete

Pete, I am in the Thomastown / Inistioge area of Kilkenny.

I am actually in Castlebar, Co. Mayo at the moment for work and will be back home tomorrow afternoon. I will pm you my mobile number if you need any info just give me a call,

Kilkenny city is well worth a visit if you get the chance, nice old Castle and places to have a look at (pubs too)

Larry

Pete
If you pass thru Fethard ( Co Tipperary) my Mum was brought up up in Stokes hotel which used to be in corner of main square. I think you'll still be able to get a pint somewhere in town..,
Conor