Gearing for a Chainsaw engine

[Crabapple]

Sorry about not putting much info and ideas in my post last time.
Here is what it should have said...



I am debating weather to put the clutch on the motor. (make a clutch housing and put a sprocket on it to make it work.)
like this

Or make a sprocket fit the engine, and then put the clutch on the jack shaft, like this

There are problems with both of the options.

OPTION1
I will have to make a housing for the clutch, and attache a sprocket to it, which may be difficult.
If i burn up this clutch, i probbaly wont be able to use this chainsaw for its actual use of cutting wood any more.


OPTION2
I will need to buy a left hand tap with the right pitch and thread, then find a sprocket with no hole in it, drill a hole in it dead center, then tap the hole. I may also need to make a spacer to get it far enough away from the engine for clearance. Making the spacer would be no problem, i can get help using the lathe at work.
I will also have to buy a whole new clutch (no big deal only $20-$30)
If i cant find a sprocket with no hole, or not the corect sized hole in the middle, i may have to make an adaptor, which will make the system more likley to fail, and definently sketch.



ANY ideas or comments appreciated!



P.S.
And i think that i will run it at about 8,000 RPM, because i dont know how well it will do under load and at 10,000 RPM, so 8,000 RPM it is ok?

P.P.S.
I am getting a set of old racing hubs and a racing axel for free or verry little $$ HU-RA

 

[RobertD]

step it down to max of around 4000 at the end.

So, if the engine makes 8000 tops...

2:1 will give you 4000 tops at the clutch, and then 6:1 will give you about normal go kart speeds at the rear tire.

or, 3:1 will give you 2666 at the clutch, just enough to make it engage.

So, shoot for 2:1 or 2.5:1 or so is what i think.

 

[Crabapple]

So a 10 tooth on the Engine, 20 tooth on the jackshaft, then a clutch with a 10 tooth on it, and a sprocket with a 40 tooth on the axel?
Will that get me correct gearing ratios?

Could you also explain the gearing concept? Like how to calculate what sprocket is needed in what place.
Just so that i can set up my own gear ratios in the future.

 

[RobertD]

Well, sprockets in different sizes are used to increase, or decrease the gear ratio. The gear ratio is the relationship between the sizes of the sprockets. So a 10 and a 20 give you 2:1 difference. That will slow the speed down by half.

Basically, for your setup, you're aiming to get the RPM's in the working neighborhood of the clutch, which begins working at 2200 RPM.

And you don't want too much RPM on the clutch, because then you won't get any power. These engines make power at high RPM, so you need the engine spinning really fast, but at the clutch for it to be slower so the clutch works.

Of course, if you had a clutch that locked up at 6000 instead of 2200, then you wouldn't need all this jackshaft stuff, get it? Let us know what still isn't clear -- it's a complicated subject no doubt.

 

[Crabapple]

So if i have 8,000 rpm on the engine, and i put a 10 tooth on the engie. Then i put a 20 tooth on the jackshaft, and have the clutch on the other side of the jackshaft, i should be ok.

What about gearing for the rear wheel?
Would i then use regurlar gokart gearing.

Like a 13 on the clutch, and a 20 on the axel.