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Rev counter link up
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1935Hillman



Joined: 06 Apr 2010
Posts: 257
Location: Hampshire

PostPosted: Fri Jul 01, 2016 12:34 pm    Post subject: Rev counter link up Reply with quote

I am still trying to get my little brain round my rev counter link up. I have fitted a Lucas dynamo with rev counter take off at the blunt end and need to connect it to my rev counter.
The crank and dynamo pulleys are both the same 4" diameter which means that the ratio between these pulleys is 1:1 and the take of at the back of the dynamo is turning at the same rate as the crank i.e. engine revs.
The rev counter is a 3" Smiths type marked 2-1 which I assume is the gearing in the gauge itself.
My question is this: Do I simply need to hook up the dynamo with the rev counter and the gauge will read correctly or do I need a gear off the back of the dynamo to gear it 1:2 which will then be converted back at the gauge which is rated 2:1 ?
Help please
Many thanks,
Tim
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peter scott



Joined: 18 Dec 2007
Posts: 6177
Location: Edinburgh

PostPosted: Fri Jul 01, 2016 2:35 pm    Post subject: Reply with quote

Hi Tim,

Take advice from these folk:
http://www.speedograph-richfield.com/html/minature_gearbox.html

Peter
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1939 SS Jaguar 2 litre saloon
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1935Hillman



Joined: 06 Apr 2010
Posts: 257
Location: Hampshire

PostPosted: Fri Jul 01, 2016 10:39 pm    Post subject: Reply with quote

Hi Peter,

Thanks for your reply. I had already asked them but their specialist is away for a few weeks and I was just doing some homework in the meantime !
Terribly impatient !!
Any opinions that might help me understand in the meantime would be very welcome still Shocked
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MVPeters



Joined: 28 Aug 2008
Posts: 679
Location: Northern MA, USA

PostPosted: Sun Jul 03, 2016 12:24 am    Post subject: Reply with quote

Can you hook up the bits & bobs you do have & see what the rev-counter says?
If you assume the idle speed is, what, 7 or 800 rpm? see if the rev-counter is similar. (A dwell meter could be used to see the actual idle speed if you have or could borrow one).
If it's half, or double, that, it will tell you what you need to add or remove. I don't think you can damage anything by trying this.
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2002 Mini Cooper 'S'
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jp928



Joined: 07 Jun 2016
Posts: 247
Location: Australia

PostPosted: Sun Jul 03, 2016 9:09 am    Post subject: Reply with quote

Absent anything else that can count revs, if you make one big white mark on your fan belt and hold a fluro lamp over it, the white mark will be stationery at 3000rpm; with 2 equally spaced (preferable but not mandatory) white marks, at 1500rpm - should be able to do this with an idle adjustment? This assumes your AC power is 50cycle, which I think is true for UK. For USA the rpm would be 3600 and 1800.

You can probably get an app for a smart phone that can do optical rev counting.

jp
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1935Hillman



Joined: 06 Apr 2010
Posts: 257
Location: Hampshire

PostPosted: Sun Jul 03, 2016 12:55 pm    Post subject: Reply with quote

Both very good suggestions. I must admit I was thinking of 'just trying it to see what revs the gauge showed at idle and then gently increasing the revs.
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47Jag



Joined: 26 Jun 2008
Posts: 1470
Location: Bothwell, Scotland

PostPosted: Sun Jul 03, 2016 1:25 pm    Post subject: Reply with quote

Tim,

The fact that the Rev counter has 2:1 on it suggests to me that it should be camshaft driven.

Art
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