Author Topic: Close Ratio Gearbox  (Read 638 times)

Offline gareth99

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Close Ratio Gearbox
« on: November 10, 2019, 18:29 »
As my Montjuic racing efforts show up the frailty of the engines and my mechanical competence, I now own 3 frames and 5 engines, and am going to build one good race bike and two road bikes over the winter.

As I disassemble all the engines to assess which bits to put in the race bike, I thought it may be useful to show the difference between a standard, and close ratio gearbox.

You can see on the mainshaft (with the clutch basket on it) that there is a very small gear at the far end of the shaft (it has 17 teeth). This is first gear. The close ratio gearbox first gear is much bigger at 21 teeth. You can just see the difference on the lay shaft which has 41 teeth as standard and 37 on the CR version.

Second gear (closest to the Clutch) is 22 teeth on the standard and 24 on the CR, and Third gear (second from the end away from the clutch basket) is 26 teeth standard, 27 CR. All others are the same.
1925 Triumph Model P
1935 Triumph L2/1
1939 Triumph 3HW
1959 MV Agusta Ottantatre
1969 MV Agusta 350B  (race bike)
1979 Laverda Jotarama
1982 Honda CB1100RD
2000 MV Agusta 750 F4 S

Offline F500

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Re: Close Ratio Gearbox
« Reply #1 on: November 11, 2019, 12:20 »
Hi

Before you decide which one you are going to use.

My experience of racing a Formula 500 is that the very long 1st not very usefull on our type of tracks,
it only made it very slow in the start. You will run the bike on high revs and mostly on the upper gears.

Leif

Offline gareth99

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Re: Close Ratio Gearbox
« Reply #2 on: November 11, 2019, 18:53 »
Thanks Leif.

I used the CR gearbox in a bike I brought over from Germany and found it worked well on the smaller (slower) tracks where I could run a big rear sprocket. At places like Darley Moor and Spa it was a waste of time. I reverted back to a normal gearbox for the last two seasons and that was much better.

Decisions, decisions !
1925 Triumph Model P
1935 Triumph L2/1
1939 Triumph 3HW
1959 MV Agusta Ottantatre
1969 MV Agusta 350B  (race bike)
1979 Laverda Jotarama
1982 Honda CB1100RD
2000 MV Agusta 750 F4 S

Offline Andy J

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Re: Close Ratio Gearbox
« Reply #3 on: November 11, 2019, 19:19 »
I agree, a bloody nuisance on short circuits when if you get a bad start no time to catch up the leaders, but Not normally a problem on the IOM TT course Gareth, so perhaps save them for the Classic TT!
An ‘inzane’ number of Zanes (all of which could run)
7 from Breganze (all of which can run)
Several other project bikes
1 x BMW C600 Sport Highline maxi scooter (for comfort and reliability)
1 x Benelli Tre Tornado 900 (cos it should have been the ‘new’ Jota)

Offline hochkoenig

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Re: Close Ratio Gearbox
« Reply #4 on: November 12, 2019, 16:18 »
Maybe this 6 Gearbox can fit the 3Cyl?

Offline Piranha Brother 2

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Re: Close Ratio Gearbox
« Reply #5 on: November 12, 2019, 22:50 »
Not a chance - totally different beasts.
What ... leave it standard??!!

Offline hochkoenig

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Re: Close Ratio Gearbox
« Reply #6 on: November 13, 2019, 12:37 »

Yea, I allways wonder that the 500 of the same Aera was much more developed!
 >:D

Offline Piranha Brother 2

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Re: Close Ratio Gearbox
« Reply #7 on: November 13, 2019, 12:44 »
Yea, I allways wonder that the 500 of the same Aera was much more developed!
 >:D

Being a 500 it did need a 6-speed box. All the bigger models had close ratio options. Four valve heads was the main step ahead.
What ... leave it standard??!!

Offline Paul Marx

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Re: Close Ratio Gearbox
« Reply #8 on: November 13, 2019, 16:21 »
Yea, I allways wonder that the 500 of the same Aera was much more developed!
 >:D

A lot of design solutions on 750s and triples are 50s if not pre war tradition.

Paul

Offline hochkoenig

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Re: Close Ratio Gearbox
« Reply #9 on: November 14, 2019, 11:32 »
Inmagine the Factory would have build a 1000 Triple with 500 Techniqe....
 :o

Offline Paul Marx

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Re: Close Ratio Gearbox
« Reply #10 on: November 14, 2019, 12:24 »
Inmagine the Factory would have build a 1000 Triple with 500 Techniqe....
 :o

It would have gone bust even quicker.

Paul