Rhino gets a new battery – 31 Mar 2017

The other week I finally got around to taking Rhino for his MOT (annual road worthiness test). Before I could go I had to charge the battery despite having charged it only a couple of weeks before. There are no parasitic drains on the battery of old bikes like these so I knew that the time had come for replacement. It is worth noting that the old battery was bought in March 2003. I’ve still got the receipt. 14 years ain’t bad. It was a Hawker Odyssey and was much smaller than recommended for an old Guzzi.

The new battery is a Motobatt MBTX30UHD the same as I have fitted to The Fire Bike. This is the correct size at 32Ah but is physically shorter than the original “wet” battery the bike came with.

I had soon extracted the tired old battery and the cage I made to hold it. Next I added two rubber buffers – one each side – to support the new battery. I had bought these during the rebuild but left them off to fit my home made battery cage instead.


I also bought the original style battery straps.



The hook on the longer strap appeared to have been fitted the wrong way up so I changed it. Now it won’t try and “dig in” to the battery.


Having never had these fitted before, I established from a photo in a manual that the longer strap with the hook goes to the back.

the straps locate behind and are then held down by tags. At the rear there is a tag on the frame and the strap is easily snapped in place because it can be pushed past the plastic lower mudguard section.


The front one is more difficult because the plate below the battery, joining the frame to gearbox has to be loosened to get the strap in place. It goes here.


I put a luggage strap around my new battery to make it easier to get in and out.


Then put the battery in place. It is a snug fit between the rubber buffers. Joining the two heavy rubber straps was tough going. I also added a zip tie to the long strap to stop me pulling it apart with my cack-handedness.


According to the parts book there should be a rubber bung in the middle of the long strap but it doesn’t seem necessary.

I ended up using diagonally opposite cable terminals as these just seemed easiest. I like the way these batteries have these connection options. My lifting strap was tightened so that it can’t move about but can be slackened to give me a hand hold if I need to lift the (heavy) battery out.




Too many volts! – 11 Mar 2017

I’ve mentioned before that, over the last few months, the voltage warning light on The Fire Bike has been “playing about”. I fitted this soon after getting the bike so that I will know if the charging system develops a fault and can do something before I get stranded with a flat battery. I have said that the light had flashed red on one occasion indicating low voltage. Well more recently it was flashing alternate green and red which indicates an over-voltage (more than 15.2V). It may be that this was what was happening the first time but I just couldn’t see the green colour in the sunlight. Anyway, an over-voltage is to be avoided because it will soon kill the battery.

My bike has a Magneti Marelli dynamo and mechanical control box. The original fitment. I consulted with my friends on the Guzziriders forum as there is a thread there about fitting a solid state control box/voltage regulator sold as a replacement for an old Fiat. Someone had bought one from Teo Lammers but they are currently out of stock. It’s here. I decided to see if I could find one at a classic Fiat specialist here in the UK and managed to get one from Motobambino. I thought the price was good and it arrived inside 24 hours.


There was some discussion on the forum about the current rating of the solid state regulator. The original mechanical box was rated at 25A and this replacement at 16A. The dynamo is also 25A. So far as I can tell, a 16A regulator with a 25A dynamo will work fine but, the output (current draw) is limited to the 16A of the regulator. I’ve done some searching and it looks like the Fiats had a 230W charging system as opposed to the Guzzi’s 300W. However the two systems seem to have had their ratings worked out differently.
– Fiat – 14.5V x 16A = 232W.
– Guzzi – 12V x 25A = 300W.

The lowered capacity of the system could cause issues on an original police bike running radio, siren, blue lights and other stuff but, should be fine for my “civilianised” one. I’ve used a “worst case scenario” of 12V x 16A which gives a maximum system capacity of 192W. I think my maximum constant draw is about;
– Lights (bike) – 75W
– Lights (trailer) – 10W
This leaves plenty for the ignition circuit. The intermittent draw from starter, indicators, horn and the like can be disregarded. I might have to think again if I add heated grips or stuff like that.

Changing the control box.

I removed the battery and, before I did anything else, photographed the original mechanical box in situ and made a note of all the connections.



I disconnected the wires and undid the nuts securing the box to its bracket but I couldn’t shift it! The two bolts were too tight in the mountings and appeared to need to be unscrewed from the back. To get to the first bolt I removed the nuts and bolts securing the left hand tool box which released the mounting bracket for the control box on that side.


I then realised that I didn’t actually need to take the tool boxes right off. I could just remove the top fixing.


This done you have access to the back of the bracket. Here the bracket is fully floating and the old Marelli box has been removed.


The mountings for the box weren’t threaded. Just tight and the screws had to be wound out.

Here are the two control boxes for comparison.


The mounting holes are at the correct centres but needed to be drilled out. There was also an earth/ground terminal on the original. I found this area could be drilled to accept a terminal while still clearing the mounting bracket.



Being a mechanical device, the old box had mountings to protect it from vibration. These are not removable.


I don’t think these are strictly necessary for the solid state replacement but I punched some bigger holes in some rubber washers and used them to mount the plate. You’ll notice that I filed all the corners off that plate. Twas flippin’ sharp.



You can see in the photos that the wiring connections were in the same order as on the original. I had to do some checking in my manuals to make sure this was the case as the terminology on the two boxes was (of course) not the same.
– Marelli box.              “D+ 61”  – “DF”      – “51 B”.
– Replacement box.   “51”        – “67”       – “30 +12V”.
– Guzzi manual says. “D+/51” – “DF/67” – “30/B+”.
This is the illustration from the V7 workshop manual which explains things.

Marelli Regulator Unit

With everything back together again the bike was restarted. All seemed good then it stalled. Once I’d turned the fuel on all was well!

Today I’ve been out for a test ride. Just the 20 miles up the A487 to Aberystwyth for coffee and cake on the sea front then back home. I have to say that the new regulator is an improvement. The strange messages given by my voltage light have stopped. Not only that, the light turns green (signifying normal charging) at lower engine revs than before. This means I don’t have to change down to keep it “in the green” and can potter about in a lower gear.

I have had a look inside the old control box which is clean with no obvious faults. Interesting.