Relocate 750 Starter Relay

S

Simon Yates

Senior member
In order to move the offside side cover inboard I am considering relocating the  starter relay on my '69 750.  Has anyone done this and have any pictures?
Since it arrived I have inverted the relay for better access to the terminals, but it still sticks out a long way.
 

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Why the horn there Red? just neatness? muffled by the panel,or is it very loud, must say the pair of Fiamms upfront on the SF without the relay there are super loud,more than my car!
 
because mounting the horn there cleans up the front of the bike and the owner of this machine is after that clean tidy look, he is not after a standard look at all
he supplied me with a photo of a 750 that he found on the internet showing a pretty neat stripped down 750 and that is what we are building him
horn is loud enough, no issues there

 
Horns are overrated. Haven't had one for 35 years - you tend to concentrate more on defensive riding. Sometimes it would be nice to blast someone with the Fiamms, but these days I'm only fitting them for roadworthy certs.
 
I love my horn, so much the rubber cover on it in the car has torn from whacking it so hard. Must be a Sydney traffic thing, hardly a trip goes by without a massive horn session, bike or car.
 
I too try to ride defensively, but there's always some deaf/dumb/blind cunt out there that doesn't give a shit who he/she is about to kill.  But they do wake up when the twin air horns come into action! :D  Don't use them very often, but very glad I have them.

piet
 
The metal cased item that Ernesto identified is obsolete.  Wolfgang was offering refurbished items some time ago.  The plastic cased replacement used on RGS (& 500s?) is Bosch part no. 0332002160.  Or you could use a BMW item - Bosch 0332002161

The Bosch item ain't cheap and quality may not be what it was - http://www.laverdaforum.com/forum/index.php/topic,96286

Cheapest source I found last week was
https://www.amazon.co.uk/gp/product/B004Z0W24I/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1
 
I would not fit a starter relay to a 750 twin if its contacts are rated below 150A. Other way there may be a danger to burn the contacts closed on certain conditions. The old mini has similar relay to the original. Those at least should be available.

Also the cables should be at least as thick as the originals. A littlebit thicker can be used as well.
 
Current rating is a function of time, amongst other things.  Because the starter is only operated briefly, it's quite OK to use a relay that isn't rated to carry the current continuously.  If the 75A contacts weld together then you've got a serious starter motor problem to fix. 
In fact it's not a bad idea to take the starter apart once in a while to clean the crap out; check the brushes, clean up the commutator and lube the bearings!  I must do that sometime  :-[
 
It is very likely to weld 75A (original rating) contacts on BMW K100 if you have low battery charge. And the power of the starter motor is about half than on Lav 750 twins.

The amperage rating for a relay is the largest current it can trustable switch off. It can carry higher short term currents if the contacts remain closed during them. Also switching on is easier situation for relay contacts and that current can be larger.

 
MotoJouni said:
Also the cables should be at least as thick as the originals. A littlebit thicker can be used as well.
Click to expand...

Yes, the original cables are a bit marginal in size. I put thicker cables on my Jota and there was a noticeable improvement in engine cranking speed.

Note: If you're going to upgrade the starter cables, you need to do all of them in the starting circuit. Battery positive terminal to starter relay,
starter relay to starter motor,
earth cable from engine to frame (esp on an RGS with rubber mounted engine),
earth cable between frame and battery negative terminal.
 
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