In a post a while back I wrote that given that I couldn't take the horn to pieces to clean the points and that as it worked, I would just go ahead and fit it. The trouble is once I'd wired it up, pressing the button had no effect. It just didn't work. I had it on the bench, checking the resistance of the coil with the multimeter and driving it with a bench top power supply but it was having none of it. It would have to come apart.
The difficulty with these horns is that the armature is retained in the diaphragm by a nut which is extremely tight. It's very difficult to remove, mainly because it's shallow and you have to be careful to hold the diaphragm to avoid it getting damaged. The way I resolved this was to make a wooden clamp that I could put in the big vice and hold the fragile diaphragm against the body of the horn whilst undoing the nut with a closely fitting tube spanner. With a 400 mm tommy bar, which I bent, it eventually came undone.
So that's the horn in bits. Once you've loosened the centre armature nut, you can remove the diaphragm leaving the armature in place. With the diaphragm off, you can slide the armature out from underneath the points assembly and that is about all the dismantling that you will need to do.
The point spring is very strong and it's helpful to use a jewellers screwdriver inserted between the moving point and the fixed point such that you can get a small sliver of wet and dry paper between the contacts to clean them.
Clean all the rust off with the wire wheel and Emery cloth. It's impossible to set the horn up properly if there is still rust on the body and inside the diaphragm and you won't be able to tighten the armature adequately if the nut is still stiff and rusty.
When you reassemble it, if you align these slots in the armature with the peg on the outside of the horn body you will have the armature in the correct relationship with the points assembly. When you have it in the right position you can tighten the nut up again using the same clamping mechanism that you used to undo it.
By the way, that peg is important. You'll note that the diaphragm has an inclined slot which engages with the peg? Well, the diaphragm can be rotated such that the slot causes the diaphragm to move up and down in relation to the body of the horn. This is how the armature air gap is set on these later HF1441 horns. The earlier Altette horns use a big grub screw and a nut on the back of the body for the same purpose. The diaphragm is held in place after setting with a clamping ring around the outside.
The easiest way to test the deflection of the diaphragm is to set the horn up on the bike with a magnetic DTI base sitting on some suitable surface, in this case the pillion footrest mount which on a PRF framed Ariel is quite flat. To test the deflection, back out the horn adjustment screw fully so that the points will not open when the push button is operated. Don't forget to undo the lock nut before you attempt to move the points screw.
When you press the horn button with the screw all the way out, you will hear the diaphragm deflect with a click. If you don't hear anything it's likely that the deflection is insufficient or non-existent so use your hand to increase the deflection of the diaphragm by turning the whole diaphragm anticlockwise slightly.
According to the Lucas instructions the deflection is supposed to be 11 to 13 thousandths of an inch.
When you've got the deflection correct, you can replace the clamping ring to hold the diaphragm in position. Then it's time to adjust the horn points setting: undo the locking ring and adjust the points using a small screwdriver. Turning the screw clockwise opens the points further for each deflection of the diaphragm.
You have to fiddle a bit with this screw to get the tone you want. Don't be afraid to turn it half a turn each way or more if necessary and test the horn each time until you get a tone that's consistent and doesn't sound like a dying parrot. When you fit the tone ring you'll hear it change substantially.
When you're happy with the sound you're getting from your rebuilt horn, don't forget to do up the locking ring, put the tone ring on and do up the acorn nut. I made this tool to turn the locking ring:
While waiting for bits for the QR50, I took the opportunity to refinish the horn for the Huntmaster. It tests OK in that it pulls a current and deflects the diaphragm, so some adjustment will have it working.
Lucas catalogues are very useful. This is catalogue 716A, section F - six pages of horns and horn pushes. The application page tells you which part number you should have:
In the case of my 1958 Huntmaster, it's a HF1441 model horn, part number 70048. The spares list tells us a bit about it:
It's black, and looks like this:
So, I had the correct horn (bought from eBay I think - it was missing from the kit) and all I needed to do was strip it and give it a coat of paint.
First up was the various bits of bracket:
It’s good to clean the points in these horns, but this nut is usually very tight and it retains the diaphragm to around the moving point. I had it soaking in Plus-Gas for a few days but I couldn't shift it:
Since the horn worked I gave up and cleaned the old paint off with emery tape.
I painted it with the usual U-Pol etch primer and gloss black. I know the tone disc is supposed to be black, as is the nut, but it looks nice like this:
Back in January, before I started work on the crankshafts and before my little Grandchildren laid us out with those pre-school viruses they love to share, I was assembling the toolbox and some bits around it. I wrote about it here.
Workshop time for bikes often occurs as a distraction from something domestic you are supposed to be doing but have become tired of - or maybe I have a short attention span; so it was that yesterday found me building shelves for my off-grid battery bank and making a horn bracket while the glue dried.
You'll recall that I have a toolbox which may be too early for my FH. The bottom bracket looks like this
Ariel do not list a separate horn bracket for 1958 and here's why - the horn bolts directly to the toolbox tab as shown in MickD's picture below. As you can see, I don't have those holes on my toolbox! The swinging arm toolbox carried a -54 part number through to the end of four stroke production, so I must have an earlier incarnation of the same part, designed to be used with an Altette and not the Lucas HF1441 horn used in 1958.
I needed to make an intermediate bracket, or modify my toolbox. I have the correct Lucas HF1441, which I think came from eBay. It has a right angle bracket, retained to the multi-leaf horn bracket with two 2BA hex head screws:
As always with any sheet metal work, we mock up the required part in cardboard and test it for fit:
Then, with some Dykem marking blue we can lay it out on a bit of 4mm sheet. It's hard to see with the lighting, but I have punched witness marks around the perimeter of the part to help me see the shape during the filing & linishing that will happen later:
Cut out commences with the hacksaw, and carries on with files and the linisher - a very useful tool that I acquired recently.
The holes were actually drilled while the part was still square - so that it could be clamped securely in the machine vice on the drill press:
Test fit - good to go to paint I think, though it's very close to the upturn on the toolbox bracket. I'll need to deal with that as the toolbox may get powder coated.
Last night included a bit of dry building activity around the toolbox, regulator and horn. I added the primary case and the clutch cover to understand the space and fastener requirements.
The toolbox hangs from one of the seat mountings using a bolt passing up through the top of the box, through the seat mounting and into the seat - all quite straightforward.
The other fixing point is this tab, beneath the toolbox which allows the toolbox to bolt to a mounting on the frame. This tab is shared with the horn.
Here's a puzzle: Ariel do not list a separate horn bracket for 1958 and here's why - the horn bolts directly to the toolbox tab as shown in MickD's picture below. I don't have those holes on my toolbox! The swinging arm toolbox carried a -54 part number through to the end of four stroke production, so I must have an earlier incarnation of the same part, designed to be used with an Altette and not the Lucas HF1441 horn used in 1958.
I will have to make an intermediate bracket, or modify my toolbox.
Post script, April 2019: This bracket was made here.
My Lucas HF1441 horn, for the FH.
Here's a Lucas voltage regulator fitted in position behind the toolbox - but this is the 40W MCR1 regulator, smaller than the correct RB108.
Here are two views of the large void from above:
And behind, complete with an up the nostril shot. Sorry about that.
