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 Post subject: Re: Revcounter drive ratio
PostPosted: Sun Dec 18, 2011 2:28 pm 
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Joined: Wed Apr 27, 2011 4:56 pm
Posts: 79
I have to write this down somewhere before I forget how I've done it...here is as good a place as any!

I decided to strip an old '93 900SS tacho to see what i can do with it. I have searched online for previous similar attempts by others.

The bezel is quite hard to get off, but can be levered and stretched a little around the circumference, carefully using a screwdriver. Might not look too tidy when I put it back together, but that should not be too much of a problem as the instrument will be pressed into a foam surround when on the bike! I guess I will use a bit of silicone around it as well to maintain its waterproofing.

The innards come out very easily complete, just the two screw on the back to undo. There are two methods described online for removing the needle, pull off with watchmakers tools, or it unscrews anti clockwise...well the needle on the 900SS veglia instrument (also the 600SS, 750SS and the late F1 will be the same methinks!) doesnt unscrew, it comes off if you hold the bell rigid inside, then twist and pull slightly! however this does loosen the needle a little bit so I guess a blob of superglue on the drivepin when I stick it all back together might be in order.

To explain the 'bell' bit.... the cable drive rotates a magnet, this sits in a 'bell' housing which then drives a springloaded needle drive pin...as the magnet rotates it pulls the bell housing around, turning the needle. As the revs are decresed again the spring returns the bell housing back towards its original off position!


Now all I need to do is get a new face made up and substitute it for the original. I dont know about starting at 2000 RPM as the race ones seem to do. I notice the race needles rest against a pin when the engine is turned off. I guess this is held at the 2000 rev mark instead of zero revs, and the 0-2000 revs are not shown on the face!


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 Post subject: Re: Revcounter drive ratio
PostPosted: Sun Dec 18, 2011 7:17 pm 
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Joined: Thu Oct 14, 2010 11:23 am
Posts: 1074
So, the question remains, how do all those TT2s and TT1s get by using the Veglia 4:1 race tach for the bevels and singles? Seems they would have had tach worm gears for a 5:1 tach of some type. Is there a 17/7 set of tach gears for the heads?


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 Post subject: Re: Revcounter drive ratio
PostPosted: Sun Dec 18, 2011 10:43 pm 
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Joined: Fri Nov 18, 2011 7:18 am
Posts: 116
Images: 5
Yes, 618F1 I was wondering that as well, I want to use one of the replica Tachs myself for my TT2 racebike. Can it be done?

Corsa.


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 Post subject: Re: Revcounter drive ratio
PostPosted: Mon Dec 19, 2011 2:44 am 
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Joined: Sun Nov 07, 2010 10:54 pm
Posts: 425
Location: Brisbane
Corsa, where are you? In Oz?
If so you could get the tach re calibrated at Lionell Otto's in Brisvegas, or there is a place in Melbourne I believe.
Also Rod at Cutgrafix can make different face decals for gauges. (if that helps)
Graeme


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 Post subject: Re: Revcounter drive ratio
PostPosted: Mon Dec 19, 2011 4:49 am 
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Joined: Fri Nov 18, 2011 7:18 am
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Graeme,
I'm in the Latrobe Valley in Vic, about 1and a half hrs from Phillip Island and about the same from Melbourne.
I'll look into getting one of the Replica tachs working with a TT2.
Lee.


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 Post subject: Re: Revcounter drive ratio
PostPosted: Thu Dec 22, 2011 6:08 am 
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Joined: Wed Apr 27, 2011 4:56 pm
Posts: 79
So according to Steves Parts number list there are various rev counter drives for various Ducati models...and it would seem that the standard 'replica' Veglia race rev counter is a 1:4 for bevels and singles only.

There are a fair few race rev counters both original and replica for sale on ebay..and quite a few differences between them!

Most are marked as 1:4 and one is even on the ex Adamo bike that was on ebay this summer gone!


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 Post subject: Re: Revcounter drive ratio
PostPosted: Mon Dec 26, 2011 7:26 am 
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Posts: 79
I have been pondering this question a fair deal... and I am not an engineer so perhaps someone with a sharper mind can help me out.

Most of the pictures that I have posted are marked as having a 1:4 gear ratio (on eBay). This I take it means the rev-counter drive gear which takes its reading from the camshaft revoultions.

One would then assume that if most of these instruments have a 1:4 gearing... then they should have the same increment scale shown on the instrument face! regardless of whether they start at 2000, 3000 or more revs and regardless of the highest number of revolutions shown. Shouldnt that be true with the same gearing and presumably the same instrument size (80mm I think!)?

So why should there be a different increment scale? would that mean that there are different strength springs which actually turn the needle? or a different diameter bell housing which tightens the spring which turns the needle? If so wouldnt this mean that the ratio is different?

Most confusing! And presumably people Like Louis Saif have fitted the Original (and replica) Veglia race rev-counters (also presumably all 1:4 ratio) to the TT bikes that they have built (both original and replica) without adverse problems??????

And if you fitted a 1:4 when it should be a 1:5 or a 1:6 how much out are you going to be on the instrument when the engine is running?


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 Post subject: Re: Revcounter drive ratio
PostPosted: Mon Dec 26, 2011 9:15 pm 
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Joined: Fri Nov 18, 2011 7:18 am
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Great questions!! I wondered the same thing myself!!!
Looking forward to someone on here giving us the answers.
Corsa.


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 Post subject: Re: Revcounter drive ratio
PostPosted: Fri Jan 20, 2012 3:09 am 
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Joined: Wed Apr 27, 2011 4:56 pm
Posts: 79
Problem solved... I made my own! (well I didnt make it... I got someone else to make the instrument face... I just put it all together!)


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