Repairing and Servicing a Rist Horn

At a recent Auto-jumble I was lucky to find a Rist horn complete and in working order but rather rusty and dented, needing refurbishment. Tests proved that the horn worked well but in order to return it to its original condition I decided to strip it completely and to repaint it. What I learnt during this exercise may be of interest to other Austin Seven owners.

On stripping the horn I found that it consisted of five main constituent parts, the Trumpet (1), the electromagnetic mechanism on mounting plate (2), a spring steel diaphragm (3) and the end cover (4) and mounting bracket.

rist h 4

When stripping I found I had to be careful with the fibre insulating washers on the horn mounting bracket and the terminal mounting assembly and in fact in the end I resorted to making new ones. The whole horn is held together with through 4BA screw and nut system to clamp the trumpet body, diaphragm and electromagnetic assembly together.

The electromechanical assembly was checked out visually and the contact points carefully cleaned with 320 wet/dry paper.

The other metal components were paint stripped, rotary wire brushed and treated with Jenolite. All dents in the trumpet and end cover were easily tapped out and then, owing to the heavily corrosion pitted surface, spray painted with high build primer prior to satin finish black.

During assembly it was important to remake three gaskets which sandwich between the horn body, diaphragm and electromagnetic mechanism mounting plate ( see diagram ) These were made from 0.030” thick paper gasket and this dimension is important to maintain the correct distance between the actuating pin of the magnetic mechanism against the spring steel diaphragm which gives the Rist its characteristic sound.

rist h 2

Owing to the corroded nature of the original screw fixings I replaced then with new 4BA nuts and screws supplied by Surplus Supplies [see parts source]. It was remarkable that they could supply exact replacements down to screw head profile and the square dished self locking nuts.

It is important to ensure that the 6v supply terminals are well insulated from contact with the horn assembly and that the 4 horn mounting bracket screws are insulated from the horn with fibre washers and rubber sleeving Test for continuity with a test meter before finally linking up to 6v supply.

rist h 3

Operation of the horn may initially give a muted sound due to the actuating pin being out of adjustment with the diaphragm owing to dimensional deviation of the assembly or compression of the gaskets etc. There is a locknut and adjustment screw on the top of the magnetic actuating mechanism. [See Photo above] This will need only slight adjustment to give the plunger suitable clearance to vibrate against the diaphragm. Experimentation will achieve the best setting for optimum sound.

The final detail is to fit a new Rist badge to the horn trumpet and the whole assembly looks and sounds as it did 75 years ago when first delivered to Longbridge.

Parts Source

6 off 4BA Screws 3/4” long
   3 off 4BA Screws 3/8” long
   9 off 4BA square self locking nut

Surplus Supplies, Rosengarth,
   Mill Lane, Caunton, Nr Newark
   Notts NG23 6AJ. UK
   Tel: +44 (0)1636 636735

3 x paper gaskets 0.030” thick

Normal Gasket material

Hi-build primer
   Black satin paint finish
   Jenolite Rust Converter

Motor accessory shop

Rist reproduction badge
   Red Fibre strip for terminal insulation

Seven Workshop



This article, written by Steve Baldwin, originally appeared in CA7C Seven Focus in Dec 2002 pp 16-18.