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Author Topic: 1982 CB750F... The resto-not  (Read 33488 times)

Offline pidjones

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Re: 1982 CB750F... The resto-not
« Reply #380 on: Mar 04, 2019, 16:39:06 »
Ok, think about it. The engines spin near 10 k. Do you think they want the cable spinning 40k RPM?
"Love 'em all.... Let God sort 'em out!"

Offline Jimbonaut

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Re: 1982 CB750F... The resto-not
« Reply #381 on: Mar 04, 2019, 16:41:59 »
Ok, think about it. The engines spin near 10 k. Do you think they want the cable spinning 40k RPM?
Sorry mate, mind expanding on that? 

Feel like I should know what you're talking about but, don't.

4:1?  1:4?  Both are options apparently, as i said.
« Last Edit: Mar 04, 2019, 16:51:07 by The Jimbonaut »
"I'm telling you Donnie, nuthin' but nuthin' but right"

Offline advCo

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Re: 1982 CB750F... The resto-not
« Reply #382 on: Mar 04, 2019, 16:50:41 »
I believe that a 4:1 ratio means for every 4 revolutions of the engine, the tacho cable or whatever gears inside the tacho that register the RPMs would do one revolution. So if you're doing 8k RPM, the cable is spinning 2k times per minute.

In a 1:4 ratio, the cable would be turning 4 times for every 1 revolution on the engine. So at 8k RPM your cable would be spinning 32k times per minute.

Offline Jimbonaut

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Re: 1982 CB750F... The resto-not
« Reply #383 on: Mar 04, 2019, 16:54:29 »
Ok, thanks for that explanation.  Still none the wiser though as to which ratio I need for the bike - some sites say 1:4, others 4:1.  Pidjones - I'm thinking about it, just utterly non-plussed.
« Last Edit: Mar 04, 2019, 17:01:56 by The Jimbonaut »
"I'm telling you Donnie, nuthin' but nuthin' but right"

Offline teazer

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Re: 1982 CB750F... The resto-not
« Reply #384 on: Mar 04, 2019, 18:28:41 »
Are we sure that any tacho runs faster than engine speed?  That makes no sense.  I suspect that 1:4 means one tacho cable revolution per engine revolution and 4:1 means 4 engine revolutions per tacho revolution.  The same thing.

Offline Jimbonaut

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Re: 1982 CB750F... The resto-not
« Reply #385 on: Mar 04, 2019, 18:34:05 »
Are we sure that any tacho runs faster than engine speed?  That makes no sense.  I suspect that 1:4 means one tacho cable revolution per engine revolution and 4:1 means 4 engine revolutions per tacho revolution.  The same thing.
Yeah, it's crazy pills time.  What's thrown me is that I bought a 1:4 tach from Dime City for another DOHC Honda (they list all their tachs 1:2, 1:4, 1:7 etc etc), and yet I contacted the seller of the Triumph repro tach (in the image a few posts ago) that told me it was a 4:1 ratio, and that 4:1 and 1:4 were not the same thing.  He told me the tach would not work on my bike for that reason.

WTF?
"I'm telling you Donnie, nuthin' but nuthin' but right"

Offline advCo

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Re: 1982 CB750F... The resto-not
« Reply #386 on: Mar 04, 2019, 20:31:22 »
Yeah, it's crazy pills time.  What's thrown me is that I bought a 1:4 tach from Dime City for another DOHC Honda (they list all their tachs 1:2, 1:4, 1:7 etc etc), and yet I contacted the seller of the Triumph repro tach (in the image a few posts ago) that told me it was a 4:1 ratio, and that 4:1 and 1:4 were not the same thing.  He told me the tach would not work on my bike for that reason.

WTF?

I think you need to buy and test them both so we can figure this out once and for all   ;D

Offline Jimbonaut

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Re: 1982 CB750F... The resto-not
« Reply #387 on: Mar 04, 2019, 20:39:56 »
I think you need to buy and test them both so we can figure this out once and for all   ;D
That.  Then maybe I can finally answer the question pidjones keeps asking me  ::)
"I'm telling you Donnie, nuthin' but nuthin' but right"

Offline irk miller

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Re: 1982 CB750F... The resto-not
« Reply #388 on: Mar 04, 2019, 21:15:53 »
Or get a Speedhut and it won't matter.

Offline canyoncarver

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Re: 1982 CB750F... The resto-not
« Reply #389 on: Mar 04, 2019, 21:25:18 »
Or get a Speedhut and it won't matter.

See, that's what I was thinking.