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LC4 Alternator tips

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Recently my Duke 1 decided that its alternator rotor magnets needed to be in a thousand pieces. I thought I should share a couple of things I learnt and wish I had found searching the web before I started.

1. You won't get a spark with a bad alternator. The CDi unit is powered from the battery and is fed two phases from the alternator. I assumed the two phases were there so it has some chance of starting with a flat battery but for whatever reason if the alternator is bad or disconnected the CDi will not spark.

2. A KTM shop told me the rotors were ever so reliable and any failure would be due to excessive crank end float. I had read that early Dukes had a habit of destroying magnets and didn't really believe the shop. The original rotor has (had) 4 magnets glued inside. The magnets are the dark grey ferrite type which would shatter with the tap of a hammer. The replacement rotor I got appears to have a single hoop magnet made from something less fragile.

3. The rotor puller special tool for a Suzuki GSX-R 600 or 750 is a perfect fit for the LC4.

4. The bike is an Austrian model with twin 35W headlights which are permanently on. Well permanently until it blows the lamps which in my experience seems to be every 2 or 3 days. I investigated a little and one of the causes is they are running on nearly 15 volts. I know it changed on later models. The alternator regulator box directly feeds the headlights, brake lights, fan and then charges the battery through a diode. Everything else is powered from the battery. The Regulator box has to output enough to fully charge the battery plus at least 0.7v for the diode. I measured a shade under 15v and that's what the headlights run on less a bit of loss in the wiring. I think I am going to wire them through a diode to drop it down a bit.

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