Author Topic: '81 490 gearbox ratios  (Read 335 times)

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Offline ralph311

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'81 490 gearbox ratios
« on: November 03, 2018, 08:51:42 AM »
Can anyone tell me the difference between the close ratio mx gearbox (RT?) and the wide ratio enduro box (GT?). The ratios for the mx box are easy to find but I can't find any info on the enduro box. Is it an easy job to convert to an mx box? Cheers.

Offline sleepy

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Re: '81 490 gearbox ratios
« Reply #1 on: November 03, 2018, 11:15:12 AM »
The info that I have is that 1st 2nd & 3rd gears are the same number of teeth but 4th & 5th have different numbers of teeth.
The ratios are as follows for the GS 2.985 ,2.175, 1.655, 1.208 & 1.0 MX is 2.71, 1.97, 1.5, 1.2 & 1.0 ( that is 1st up to 5th)
To go to the MX gears you would need the output shaft ,the lay shaft and 4th & 5th gears all of witch are quite hard to find in good condition.
The above figures are from teeth numbers that are hand written in the manual I have so use the info at your own risk.

Offline ralph311

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Re: '81 490 gearbox ratios
« Reply #2 on: November 03, 2018, 01:14:02 PM »
Thanks sleepy. I don't understand tho…stoopid question... if 1,2 & 3 have the same number of teeth why are the ratios different?

Offline sleepy

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Re: '81 490 gearbox ratios
« Reply #3 on: November 03, 2018, 01:38:35 PM »
Good question.
All the gears drive through the 5th gear on the lay shaft to get to the output shaft which in the GS has a different ratio than the MX. Basically means the gap between the gears 1-3 are the same on the GS just all a bit lower, then there is a slightly bigger gap between 3-5.
I personally think the GS ratios are quite ok for MX and not worth the change.

Offline ralph311

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Re: '81 490 gearbox ratios
« Reply #4 on: November 03, 2018, 02:05:32 PM »
Hmmm interesting. 3rd gear is 10% lower on the GS from those numbers, that seems like a lot. 10% on the final drive is going from 56t to 50t to make them similar if I understand it correctly??

Offline sleepy

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Re: '81 490 gearbox ratios
« Reply #5 on: November 03, 2018, 03:47:33 PM »
I just did a calculation and the difference if you had a 13-56 with a MX gearbox and if you went to a 13-51 with a GS gearbox you would end up with 1,2 &3 in close to the same place but then 4th and 5th would be higher and if you had an long enough straight the GS would pull away if your balls were big enough.

Offline ralph311

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Re: '81 490 gearbox ratios
« Reply #6 on: November 03, 2018, 04:10:14 PM »
We have a winner sleepy, all I gots to do is upgrade my balls :-)

I think 14-56 is standard on the mx 490's. Reason 3rd gear in particular interests me is coz that's the trick to a good start with those bikes. For me at least. A lower 3rd could be a significant drawback, four lap races and all. I was even thinking I'd like to try 14-54 with the close ratio box and a strong motor.

14-51 or 14-49 (can u get a 49??) might make for a big gap with the 3rd to 4th shift on the wide box...

Offline sleepy

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Re: '81 490 gearbox ratios
« Reply #7 on: November 03, 2018, 04:34:37 PM »
I have a 81 400 with a GS box and the gap between 3rd and 4th is not an issue on it. I think it has 14-52 as a final drive. May depend a lot on what pipe if fitted as to the power band width. Some of the pipes around make them sign off way to early in my opinion.

Offline KTM47

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Re: '81 490 gearbox ratios
« Reply #8 on: November 06, 2018, 11:30:33 AM »
Can anyone tell me the difference between the close ratio mx gearbox (RT?) and the wide ratio enduro box (GT?). The ratios for the mx box are easy to find but I can't find any info on the enduro box. Is it an easy job to convert to an mx box? Cheers.

Ok you need someone who knows to let you know.

1st, 2nd, 3rd and 4th are the same gears (number of teeth) on both a 490 MX and a 490 GS (enduro).  The difference is the fifth gear and the countershaft gear that the sprocket is on.  So there is three gears that are different. With the GS gears all the gears are slightly higher.  I know because I had a GS 490 and two motors (one in bits) that a guy had used in a Road Race bike.  I changed a GS gearbox to a RT (MX) by swapping the three gears.  The GS also runs the Bosch ignition with a heaver flywheel.

Kevin
MAICOS RULE DESPITE THE FOOLS

1999 KTM 200, 1976/77 KTM 400,1981 Maico 490

Offline sleepy

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Re: '81 490 gearbox ratios
« Reply #9 on: November 06, 2018, 05:45:08 PM »
The info I have came from Noel Harcker you may know him.

It's also quite possible that the ratios changed with different models or production runs. I've noticed quite a difference in gearbox bearing sizes in 490's over a couple of years of production yet they look the same on the outside, except the Mono bikes they have an extra lug under the back of the motor.

Offline ralph311

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Re: '81 490 gearbox ratios
« Reply #10 on: November 06, 2018, 05:59:45 PM »
Well I bought the bike guys and at this point I'm thinking 1) Ride it and see what I think 2) I won't know for sure what's in it until I pull it to bits.

If/when I do have it apart I'll put some info up here.

Offline 80-85 husky

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Re: '81 490 gearbox ratios
« Reply #11 on: November 06, 2018, 08:38:01 PM »
490 goes real well....

Offline Nebo

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Re: '81 490 gearbox ratios
« Reply #12 on: November 08, 2018, 09:39:31 PM »
  Just a few words Re Maico  GS490. A good one should have about 50hp at counter shaft.
 It should pull all most any gearing . How fast do want to go.
  Ride it first  and see  if the gearing suits you. If not try a differant counter shaft and rear sprockets till you come up with a happy medium.

  Just on the Gearbox.  Maico in Late 79 made many changes to the Gearbox and Clutch.
  This was to up grade the Gearbox and Clutch to take the HP of the 490 engine.
   The layshaft for example has 2mm larger shafts at both ends and the bearings used are more heavy duty.
   But also my 81 Mega 2 has the same gearbox upgrades but my 1980 GS 400 does not.
   If you want to know more get a copy of the Maico Service bulitons. They will show you in good detail all
   the changes.

Offline ralph311

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Re: '81 490 gearbox ratios
« Reply #13 on: November 08, 2018, 10:39:49 PM »
Where do you get the service bulletins from Nebo?

Offline Nebo

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Re: '81 490 gearbox ratios
« Reply #14 on: November 10, 2018, 03:24:45 PM »
 
  HI Ralph 311.  All the Information and Manuals can be Download for Free  from the Chippys Maico Web site.  Just click on Manuals.

  There is also information on the Square Barrals and Early Radials.  Some of the information is a bit dated like engine porting and other power upgrades.

  What i mean by that is for example 250 porting and engine mods can done other ways these days than in the Service Bullitins. With High HP gains  .
 
  There is other information supplied by the Maico Factory Called Dealer Support Technical Information. Only given to Dealers Supplyied with Factory Semi Works Bikes.
 
   In that i mean bikes had Magnesium Fork Legs, Fork Crowns, Engine cases and Clutch cover and Differant porting and meany other Mods and Specialfactory Part numbers.

    The information was obtainable from a web site in the US and Germany some years ago for a very sort time. The site can no longer be Found.

    There was even Information on the Works ISDE. 81 GS 490.  My information is Limited.

     Anyway glad to help.