daverclasper Posted October 24, 2019 Report Share Posted October 24, 2019 (edited) Hi. Can't find much about this online/my books, so attempted this a bit blindly. With my multi meter set at 200 in the ohms range (no continuity buzzer on meter), I am getting a reading of 0.5, with negative probe to block and pos probe to pos battery post. Is this about right and is this the way to do it please. Thanks, Dave Edited October 24, 2019 by daverclasper Link to comment Share on other sites More sharing options...
Pete Lewis Posted October 24, 2019 Report Share Posted October 24, 2019 i would turn it up to a higher range , youre looking for a high resistance i think , on the other hand stop worrying , if it starts sleep well Pete Link to comment Share on other sites More sharing options...
Clive Posted October 24, 2019 Report Share Posted October 24, 2019 No, earth test should be neg battery terminal to block. If you are going positive terminal to block, it is a dead short... To accurately test low resistance, you will need something a bit more expensive in tgd way if a meter. My recently purchased Megger tester is very accurate down to fractions of an ohm, and calibrated. But cost is "substantial" I wouldn't Worry, a decent earth lead from battery to block with clean connections will be fine. Link to comment Share on other sites More sharing options...
Pete Lewis Posted October 24, 2019 Report Share Posted October 24, 2019 good spot Clive missed daves +ve post Im sure his Vitesse is Neg earth Pete Link to comment Share on other sites More sharing options...
daverclasper Posted October 24, 2019 Author Report Share Posted October 24, 2019 Thanks. sorry, wrote than down wrong ,doh. I did do it to battery earth. Dave Link to comment Share on other sites More sharing options...
RogerH Posted October 24, 2019 Report Share Posted October 24, 2019 Hi Folks, the standard earthing on my 4A is battery Neg to body then chassis to engine. This means that that must be some mystical contact between body and chassis. Therefore I also fit a battery neg to engine block. Roger Link to comment Share on other sites More sharing options...
dougbgt6 Posted October 24, 2019 Report Share Posted October 24, 2019 Uh.....I would use the lowest range you have, 0.5 ohms is quite high, this may be down to your meter, but this result suggests your earth strap has 0.5 ohm resistance. V= IR, 0.5 ohms carrying 10 amps, say, means a 5 volt voltage drop! Short circuit the earth strap with a jump lead and retest? Doug Link to comment Share on other sites More sharing options...
KevinR Posted October 24, 2019 Report Share Posted October 24, 2019 To do the test properly you need an earth bond continuity meter with Kelvin probes. With a test current of 10amps you should be getting a resistance of about 1 milli Ohm. Link to comment Share on other sites More sharing options...
Nigel Clark Posted October 24, 2019 Report Share Posted October 24, 2019 11 minutes ago, KevinR said: To do the test properly you need an earth bond continuity meter with Kelvin probes. With a test current of 10amps you should be getting a resistance of about 1 milli Ohm. Exactly... The resistanceoff a properly functioning earth strap is a tiny fraction of an ohm. A regular multimeter cannot measure it. If a regular multimeter shows a measurable resistance in the engine earth circuit, there is a problem. Nigel Link to comment Share on other sites More sharing options...
dougbgt6 Posted October 24, 2019 Report Share Posted October 24, 2019 Come on guys! This is not rocket science, do the jump lead test, if it’s different it’s the earth strap! Doug Link to comment Share on other sites More sharing options...
Clive Posted October 25, 2019 Report Share Posted October 25, 2019 The point is a normal multimeter is just not accurate for low resistances. Doug, in practical terms checking if the starter works better with a jump lead as an extra earth strap is a perfectly good check. Link to comment Share on other sites More sharing options...
Peter Truman Posted October 25, 2019 Report Share Posted October 25, 2019 its amazing over 55 years how things get basterised by PO, my daughters Mk2 Spit which we got in 2001 always started OK and had no issues it had been converted to neg earth sometime in its history, after about 5yrs I decided to pull the engine and undertake a minor reco, bearings, rings, oil pump, timing chain & sprockets & head rebuild, when putting the engine back in I had an Eureka moment where's the engine earth, THERE WAS'T ONE! the engine had been earthing by the choke cable!! I fitted a MkIV set up Battery earth to body around the back of the battery box earthing to the body near coil bracket which as a one piece cable extended to the engine bellhousing bolt, I also fitted a Vitesse style engine to chassis earth strap plus a second body to bellhousing strap on the drivers side "belt and braces" well I had a stack of 9in 1in wide long woven style straps surplus from the refit of a 4MW very large metro water transfer pump where each pump had over 300 straps. The 4 river pumps pulled 20MW on startup enough to dim the lights in local outer metro townships!! Someone had stuffed the auto restart program they were supposed to restart with a 20min delay between each pump!. Depending on the storage res level (0 to 80mts) the 4 pumps could push 1000,000,000 litres per day (1000 MLD.) bit bigger than a Spit engine. Peter T 1 Link to comment Share on other sites More sharing options...
dougbgt6 Posted October 25, 2019 Report Share Posted October 25, 2019 Clive, Mine is accurate 😄 I have an Avo8 and a Fluke to compare it with. I’ve had a number of cheap multimeters but never one 0.5 ohms out on a continuity test. Doug Link to comment Share on other sites More sharing options...
Clive Posted October 25, 2019 Report Share Posted October 25, 2019 Quality meters will be fine, but cheap meters (I own some, expensive or cheap all break the same when dropped/trodden on/run over) just don't seem to cope with very low resistance. But maybe my cheap meters are too cheap... Then again, for an earth lead, 0.5ohm is very significant. I guess a starter motor impedance is about 0.1 ohms (ballpark, 100A at 10V allowing for voltage drop) a 0.5ohm earth lead would restrict current down to 20amps! (or 24 as you wouldn't get the same voltage drop) but the starter would not be turning. But this is all irrelevant. I have never even considered checking earth paths on a car, just use a decent earth strap and job done. Link to comment Share on other sites More sharing options...
RogerH Posted October 25, 2019 Report Share Posted October 25, 2019 Look for paint and corrosion under the earth strap contacts. Roger Link to comment Share on other sites More sharing options...
Pete Lewis Posted October 25, 2019 Report Share Posted October 25, 2019 talking earths we earth bonded everything with a dedicated cable from rear lamps both body tubs , chassis and all bonnet back to the battery saves a lot of rusty volt drops Pete Link to comment Share on other sites More sharing options...
SpitFire6 Posted November 9, 2019 Report Share Posted November 9, 2019 Hi, You can spend a bit of money on a four-wire low Ohm meter. You could save money and buy one that uses your cheap multimeters display. Why spend a lot of money. Why bother? You are worried about potential volt drops? Measure them. Without the engine running and all loads on, measure the volt drop across the earth strap without actually touching the earth strap so that you are measuring any non-perfect connection points. Non cranking < 0.3 Volts? It would be nice. During cranking, I would love 0.5 volts. You could measure the volt drop on +ve or -ve cables. Meter polarity makes no difference. Put the leads any way round you are only interested in the number. I have a milliohm to millivolt 4 wire module you are welcome to borrow. You could measure any voltage present between the coolant in the radiator to ground/earth to see if you have any internal corrosion going on. Cheers, Iain. Link to comment Share on other sites More sharing options...
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