Relay Modification Version 2

[Adrian M]

I have an R400 with a magnetron starter and had been experiencing the K click intermittently. I had tried everything I could think of! I did Myles’s MFRU relay modification, I replaced the solenoid with a new one, I heat wrapped the starter and solenoid, I heat wrapped the primaries, I heat wrapped the starter feed and solenoid actuation circuit. I was still getting the K click so I started to investigate the issue.

 

I ran a fly lead from the solenoid activation circuit and when I got the K click I touched the end of the fly lead on the positive battery terminal and this would start the engine. This demonstrated that the problem was with the solenoid activation circuit rather than the solenoid it’s self.

 

I then spent a few hours with the help of my father and a multimeter checking all the connections and resistances. We couldn’t find anything in particular that would cause the voltage to drop enough by the time it reached solenoid. We tried bypassing the FIA cut out switch to make sure it wasn’t this and this didn’t cure the problem.

 

Then my dad tested the solenoid off the car and found that by connecting it to a battery and increasing the length of wire he didn’t have to increase it much (or add much resistance) to make it fail. This demonstrated that the solenoid needed as close to 12v as possible to actuate.

 

So what he suggested was fitting a heavy duty (100 amp) relay as close to the starter as possible and taking a feed from the positive of the starter motor and using this to actuate the solenoid it should ensure that there was minimal resistance. The actuation of the relay would be done by the original solenoid feed. Also by taking the feed from the starter it would ensure it was on the correct side of the FIA cut out.

 

Here are a few images (sorry for the quality - phone cam);

 

Here are the parts I used.

 

Here is the starter.

 

Here is the relay.

 

I haven’t had a chance to test it fully but so far it has worked fine on hot starts. I’ll report back with any findings soon. Fingers crossed!

 

Ade

[Tony Whitley]

I did something similar a couple of years ago but from the + terminal of the battery. It's the wrong side of the cut-off but I don't compete so that's not a problem. It's started every time.

[Paul Richards]

Adrian

I think I beat you to this one.

Over 5 years and not one single problem.See:-

http://www.blatchat.com/T.asp?id=16555

 

Paul Richards

Area Representative - L.A.D.S. (Lancashire and District Sevens)

www.lads7.co.uk

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