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Sept 29, 2007 20:21:31 GMT
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I've resurrected a bit of a dash mod that I started doing some time ago. Basically I've grafted in a rev counter where my old instruments are, and am putting an oil pressure / water temp gauge somewhere else. I have a couple of questions... Is there any way to modify a rev counter that's for a V8 to work on a 4-cyl? The one I'm fitting (or planning to) is from a V8 Rover P6. Also, the Smiths temp gauge I have doesn't seem to have any electrical connectors. There's a brass sensor type thing linked to a wire cable covered in a coil winding. It doesn't look like it should carry a current - perhaps it does though! Baffling. Any light that can be shed on these little conundrums would be great!
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Sept 29, 2007 20:26:06 GMT
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No easy way (that I know of) to make an 8 cyl rev counter work a 4 cyl car except put up with it reading half of what it should. Less of a problem than the other way round cos you won't exceed the redline! The coil thingy is a thermocouple, like you get on sprites, midgets and MGB's, its an entirely mechanical gague, expansion of the metal inside the cable moves the pointer. (they are usually broken though)
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To get a standard A40 this low, you'd have to dig a hole to put it in
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Sept 29, 2007 20:33:01 GMT
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Thanks for that , I couldn't figure out if it'd read half or double... but half is OK I reckon, I can live with that. And it'll make it easier if I go V8 at a later date. And the mechanical temp gauge... hmm, maybe that's more trouble than it's worth... it's new old stock by the looks, so it should be functioning. I'll have to look into things before fitting that I think.
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Sept 29, 2007 20:51:47 GMT
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the rev counter question sound to me you need some kind of resistor as on after market types have a 4/6/8 switch on the back which after looking in the back of mine seems to be a 1k resistor for the 4 cylinder switch try maplins 50 p each
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Sept 29, 2007 21:05:11 GMT
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the rev counter question sound to me you need some kind of resistor as on after market types have a 4/6/8 switch on the back which after looking in the back of mine seems to be a 1k resistor for the 4 cylinder switch try maplins 50 p each thats only for aftermarket ones, not OE. the pins on the back just switch the counter frequency to match no of cyls. To do this to the rover counter would mean taking it apart, figuring the circuit out and changing it to alter the frequency to half of its current value. Not a 50p maplins job, i'm afraid.
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To get a standard A40 this low, you'd have to dig a hole to put it in
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Sept 29, 2007 23:07:13 GMT
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Hmm, I might have a poke around the rev counter to see if there's anything. I did some reading on the subject and to be honest anything electronic makes my head explode so it didn't really sink in! I suppose I should really just get an appropriate rev counter really, but I'll have a mess with this one first.
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Sept 29, 2007 23:41:09 GMT
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A guy on another forum i use looked into modding rev counters as you need. iirc it involved some very complicated (Complicated for me anyway, I get confused by anything trickier than a relay) circuitry....proper pcb`s and microchips and stuff, to double or half or whatever the number of pulses to the counter. I believe www.picbits.com is his website. Maybe worth having a look there.
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1986 Panda 4x4. 1990 Metro Sport. 1999 Ford Escort estate.
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Sept 30, 2007 15:43:47 GMT
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it should be fairly simple really, a logic gate can be configured to produce a pulse on both a rising edge and falling edge, so every time the engine sends a pulse the logic would generate one for the 'on' and one for the 'off' again - giving twice the frequency, exactly what a v8 rev counter is expecting.
Can do the same the other way too, with a flipflop wired in a certain way.
The problem would be making sure everything works on 12v, as most logic ICs are happy at 5v and tend to explode and smell bad at 12v.
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Never trust a man Who names himself Trevor. Or one day you might find He's not a real drug dealer.
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Sept 30, 2007 16:31:30 GMT
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Benzboy
Check the temp gauge in boiling water to see whether it actually works before you install it. It should the be fitted in the waterway somewhere, with a suitable thread tapped in or possibly tee it off the other temp gauge.
Hope that helps.
Cheers Roland
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23 T Bucket..46 Chevy Truck..63 Chevy Panel Van..89 GMC Crew Cab Pick Up..96 Honda Legend..96 Jaguar Executive..3Number later than 2000
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Sept 30, 2007 16:47:41 GMT
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Paint over the dial and re position the numbers.
Wont work if its backlit though.
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Sept 30, 2007 18:07:10 GMT
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don't know if it will be an issue but most older rev counters don't run of 12 volts as the coils are generally ballasted so you would need to have the correct voltage for the rev counter in question to work
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Dez
Club Retro Rides Member
And I won't sit down. And I won't shut up. And most of all I will not grow up.
Posts: 11,784
Club RR Member Number: 34
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Sept 30, 2007 18:13:33 GMT
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is it jsut me, or does anyone else think that fitting smiths gauges instead of VDO is a serious downgrade? id do some searching in the scrappy and egay and pick up some much more compatable vdo stuff.
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Sept 30, 2007 18:48:05 GMT
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1986 Panda 4x4. 1990 Metro Sport. 1999 Ford Escort estate.
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Sept 30, 2007 18:53:55 GMT
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Cheers fellas. I think if I was to chuck any money at gizmos to convert the signal, I might as well get a different gauge. The P6 one was just kicking about - I tend to just use stuff I find lying around and this sort of fitted the bill (or so I thought ) I'm inclined to agree Dez, it'd be better to get some VDO kit. Maybe I'll go back to the drawing board on this and punt this one on.
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