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<  Performance issues  ~  Gear Box Problems...

pedro750
Posted: Mon Feb 16, 2009 3:25 pm Reply with quote
Member Member
Joined: 16 Jan 2006 Posts: 48 Location: Italy
Dear friends, I need help about gearbox.
On my "750" I've a big problem: when power arives at 5500 rpm 4° gear slips out... This's a drama! I can't use all the 4° gear. So I decided to open the engine and I've found the 4° disaster... Rounded dogs. I've to check forks but I think that they aren't in good conditions...
So, I have 3 or 4 engine in my box and I want to know if its possible use an F1 engine’s gearbox on a K1's engine, from the shop manual I've sow that F1 has:
- Primary reduction is different. (Shorter than K1)
- 1°, 2° and 3°: have the same ratio.
- 4°: have a different ratio. (Shorter than K1)
- 5°: have a different ratio. (Longer than K1)
The clutch box are compatible?
The transmission mainshaft and countershaft are compatible?
The bearings are compatible?
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Voxonda
Posted: Mon Feb 16, 2009 7:29 pm Reply with quote
Member Member
Joined: 01 Nov 2006 Posts: 42 Location: The Netherlands
Hey pedro,

Must say I've never interchanged gearboxes, but IMHO think it allright to do so. Like you have seen, you're gears are somewhat different in ratio, but that is not a problem.

Good luck and keep us informed, please.

Cheers, Rob
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Satanic Mechanic
Posted: Tue Feb 17, 2009 7:19 pm Reply with quote
Moderator Moderator
Joined: 04 Sep 2005 Posts: 309 Location: Munich, Germany
As long as you change the complete gearbox, you should be allright. The final drive shaft may be different, then you will have to use the old one (which should not be a problem). The clutches are interchangeable. It should be pretty much straightforward.

All the best,
Axl
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pedro750
Posted: Wed Feb 18, 2009 9:11 am Reply with quote
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Joined: 16 Jan 2006 Posts: 48 Location: Italy
Thanks at all. In this w-e I'll work on it and I'll try to post some pictures.

Kind regards at all!
Pedro
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fang
Posted: Thu Feb 19, 2009 6:07 pm Reply with quote
Junior member Junior member
Joined: 19 Oct 2005 Posts: 23 Location: Austin, Texas, USA
Another option is to get the gears "back cut." The do this on many race engines -- they put a slight positive angle on the gear dogs so that the gears lock together more strongly. This costs about to back cut a set of gears and many machine shops will do it.
-fang
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pedro750
Posted: Fri Feb 20, 2009 9:03 am Reply with quote
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Joined: 16 Jan 2006 Posts: 48 Location: Italy
fang wrote:
Another option is to get the gears "back cut." The do this on many race engines -- they put a slight positive angle on the gear dogs so that the gears lock together more strongly. This costs about to back cut a set of gears and many machine shops will do it.
-fang


This's an option that I'm studing and probably I'll do by myself...
Today I'll return at home and I'll start to see various gearbox that I've at home, I'll do measurament adn I'll decide. So I'll try to back cut.
I'll try to post some photos too.
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fang
Posted: Fri Feb 20, 2009 7:17 pm Reply with quote
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Joined: 19 Oct 2005 Posts: 23 Location: Austin, Texas, USA
I think it is very doable at home by a skilled craftsman. The trick is consistency. You want the exact same angle and the exact same amount of metal removed from each gear dog. If you set up a rig to do it, you can do it right. Most people only back-cut the dogs, but some will do the leading/front edge too for engine braking as well as acceleration.
Here is a random pic I saw on the internet:

I'm sure you will research before you start cutting!

Best of luck to you!
-fang
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pedro750
Posted: Tue Feb 24, 2009 3:05 pm Reply with quote
Member Member
Joined: 16 Jan 2006 Posts: 48 Location: Italy
Thanks Fang,
yes did a lot of reserch and the most intrasting answer about back cut I've found on SOHC4.com
I can work with lang for a good cut
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pedro750
Posted: Wed Mar 11, 2009 12:12 pm Reply with quote
Member Member
Joined: 16 Jan 2006 Posts: 48 Location: Italy
So,
the situation is this:
I've cheked all engins I've and I fund that the gearbox from SS (F1) is different from the standard specifications:
The primary reduction, 1° gear, 2°gear, 3° gear, 5° gear are the same if comparated with K1 gears-ratio.
The only diference is the 4° :
- 1.097 K1,
- 1.133 F1,
and final reduction:
- 1.097 K1,
- 1.133 F1.

So I'll follow this combination:
I'll replace all the K1's gear box with F1's gearbox but I'll mantain the K1's reduction (more shorter than the F1).

The F1's gearbox has 20000 km and is in very good conditions, the dogs are good, so 90% I'll don't undercut them. I'll use all F1's parts about gearing system.

Stay tuned Wink
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