Z320 Posted September 19, 2020 Report Share Posted September 19, 2020 Good morning at all, I have a short question about the earth cable on the left side of the engine: on my TR4A it is bolted under one of the two bolts of the cross tube of the frame? It is not bolted on the car shell where the earth cable of the battery is bolted on.... Is this correct? Ciao, Marco Quote Link to post Share on other sites
RogerH Posted September 19, 2020 Report Share Posted September 19, 2020 Hi Marco, that is correct. Engine to chassis and battery to body. In my mind this is an error How do you guarantee a chassis to body connection. So I add another earth cable from engine to battery. Roger Quote Link to post Share on other sites
keith1948 Posted September 19, 2020 Report Share Posted September 19, 2020 Hi Marco On my 4A looking down at the cross tube mine is not bolted onto the cross tube bolt. Look down at the end of the left of the cross tube and approximately 1 inch (2.5cm) to the right of the top bolt of the cross tube and then 1 inch down is where it is bolted onto the chassis. However I agree with Roger that it would make more sense to connect to the body but then again on my car it has worked ok for last 55 years. You could run an extra bit of earth cable from the engine to the body or chassis to body to be sure. Keith p.s. Hi Roger hope you are well Quote Link to post Share on other sites
Geko Posted September 19, 2020 Report Share Posted September 19, 2020 17 bolts chassis to body should be good enough earthing no ? Quote Link to post Share on other sites
RogerH Posted September 19, 2020 Report Share Posted September 19, 2020 Hi Steph, it would appear that after 50+ years you are right. However if you look at the mechanics - the body is painted (an insulator) it is separated from the chassis by rubber pads (insulator). The bolts and washers connect through to the chassis. So there is a possibility that the body could remain insulated from the chassis. I accept that it is very unlikely. I also appreciate that there are a number of other connections that are not insulated etc. What is the cost in putting in another earth strap to make it right in an engineering sense. Using the TRiumph logic, aircraft would be falling out of the sky left, right and centre. Roger Quote Link to post Share on other sites
Motorsport Mickey Posted September 19, 2020 Report Share Posted September 19, 2020 44 minutes ago, Geko said: 17 bolts chassis to body should be good enough earthing no ? Another logic failure I’m afraid Steph. There have been a number of owners ( myself included) who’ve found their choke cable becoming hot when it acts like an earth point. As Roger says too easy for the 17 attachment points to become insulated, a direct earth prevents any guessing games... it just works. Mick Richards Quote Link to post Share on other sites
john.r.davies Posted September 19, 2020 Report Share Posted September 19, 2020 (edited) In small chassis Triumphs, the symptom of a hot choke cable after starting is quite well known! They were the last in the industry to have a separate body and chassis, and used the same "technology" as Triumph had for so long. But the poor conduction between the two, possibly made worse by years, corrosion, or forgetful DPOs who didn't re-install the engine earth cable, left the choke cable as the only earthing connection between the two. I have a length of starter cable between the battery earthing point and the engine block. JOhn Drat! And Double Drat! Mickey got in first! But let it stand. Edited September 19, 2020 by john.r.davies Quote Link to post Share on other sites
ianc Posted September 19, 2020 Report Share Posted September 19, 2020 When one engages the starter, a high current should flow from the battery to the motor and from the motor back to the other terminal on the battery. Every extra amount of resistance (ohms) in that circuit will diminish the power to the motor. Far better to ensure the best possible path (least resistance) from battery to motor and from motor back to the battery, as suggested above. Same principle applies to lights - I recall that in the 50s and 60s many cars, including TRs, displayed some interesting symptoms when trafficators, side and brake lights were supposed to be operating. I had a number of letters on the subject when I was Tech Ed in the early days. The well-rusted metal and/or filler in the vicinity of the lamp housing(s) did not conduct very well! Ian Cornish Quote Link to post Share on other sites
Z320 Posted September 19, 2020 Author Report Share Posted September 19, 2020 (edited) Hi Roger, thank you for that, this was also my idea and I thought it was a mistake of a previous owner. This engineers in these days have been young and careless? But I have no worry because on my 4A is a second earth cable direct from the upper bolt of the starter to the car body. This could be not correct but not wrong? Ciao, Marco Edited September 19, 2020 by Z320 Quote Link to post Share on other sites
Rob Salisbury Posted September 19, 2020 Report Share Posted September 19, 2020 Hi Marco, Like it when I first got the car back in '69, my engine /body earth has always been attached to the front diagonal tube (Moss CHAS7) via the body mount bolt that runs through the body and through the diag. tube so body and chassis are earthed together (star washer gripping through the body paint). Cheers Rob Quote Link to post Share on other sites
Z320 Posted September 20, 2020 Author Report Share Posted September 20, 2020 Reason why I realized this could be wrong and asked: a previous owner fitted a flat wire litz, the end soldered and drilled. Under the load of the bolt the tin becames soft and "flowed" away, so I found this bolt of the cross tube not tight. This made me doubt about using a wire litz under a bolt that has to bear forces AND about the position, even when I swap over to a cable with a crimped brass or copper end. Ciao, Marco Quote Link to post Share on other sites
rcreweread Posted September 20, 2020 Report Share Posted September 20, 2020 (edited) My solution was to buy an earth lead from a modern motor factors ( they do lots of sizes and lengths) and attach it to the body mounting point next to the battery, in addition to the battery earth lead, using star washers between the two, and then attach the other end to a nearby bolt/nut on the gearbox bellhousing - has worked fine for many years and is hardly noticeable, I still kept the earth lead from the chassis turret to the block by the timing chain cover. Simple and cheap as chips! Cheers Rich Edited September 20, 2020 by rcreweread clarification Quote Link to post Share on other sites
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