M1tch's SV650 kart project

My mate is a custom fabricator who works on both exhausts for bikes and race cars (including some SV650s!) he also has solidworks, so I should be able to check out the stress points on the chassis, it will be cross braced with extra support plus the extra support the engine will give when thats bolted in.

I will check out what the other higher power karts like Gixxerkarts use with regards to sprockets to use, I will have to change both front and rear sprockets due to the standard sprocket not yielding a very good top speed - although I could get a custom rear sprocket and use the OEM front sprocket etc.

This will be a long project, it will take me a while to work out all the details and get the parts together, the kart has front disk brakes which will help with braking, I will also try and keep the OEM top speed/gear ratio the same as on the bike to ensure that the engine isn't overgeared.

Ok, I am just working out the sprockets, the tyre circumference is 35.5", if I were to use the OEM sprockets - 15 on the front and 45 on the rear, my top speed in 6th would be 57mph lol

Listed below are the issues I face with getting the gearing to work correctly on this kart:

The tyres are much smaller
Kart rear sprockets are between 60 and 95 teeth
Front sprockets are 10 or 11 teeth (usually)
Kart chain is a different sort - uses a 219 chain rather than a 525 on the SV
The kart rear axle is 50mm (rear sprocket carrier shown below)
Front sprocket on the engine has limited space around it

Rear sprocket carrier:



So, with that in mind I had to think of ways to either:

Swap the front sprocket on the engine with a kart sized sprocket, run a kart chain and rear sprocket

Swap the rear sprocket on the kart to fit a bike sprocket and run a bike chain

I had through to perhaps extend the shaft from the engine so I could fit a kart sprocket onto it to then go to the rear kart sprocket but I think I have now found a solution.

The rear sprocket carrier on a kart is attached with pressure fittings onto a keyway on the axle, I was thinking about trying to fit a custom sprocket onto the OEM carrier to make it work, but then thought...why don't I just use the keyway on the axle for the sprocket to attach onto?

I know that you can get plus or minus teeth on the OEM front sprocket ie you can get between 12 to 18 teeth to replace to gear up or down the bike for races for acceleration or top end. This got me thinking with what I could do with the front sprocket.

I am thinking of buying another front sprocket with a few extra teeth, then increase the centre bore and cut a keyway into it. The sprocket will be reinforced by means of some extra material on each side - which will help centre it exactly on the rear axle.

I have found with a 1:1 ratio ie OEM 15T to OEM 15T the top speed would be 170mph in 6th lol although it wouldn't ever get there, so I had a look at what other ratios I could use, it seems that the top end of the bikes gearing allows around 123mph in 6th @ 9000rpm, im going to aim for around that figure as I know the engine can pull that gearing as its OEM.

I found the following:

Front 15T, rear 18T = 142mph
Front 12T, rear 18T = 113mph
Front 18T, rear 12T = 255mph - LOL

Then I found:

Front 12T, rear 15T = 135mph
Front 14T, rear 18T = 132mph
Front 13T, rear 17T = 130mph

Those are the closest I can get to around stock top end still be within 'OEM' upgraded sprockets, if I can find a 12T front sprocket it would mean I would only need to buy 1 sprocket instead of 2, bonus lol I do need to double check if there is enough material I can remove from the OEM front sprocket though to be able to get the 50mm centre, I think as OEM its 25mm centre bore, I would just need another 12.5mms of material to make it a 50mm centrebore, so it should be do-able? It will be strenghtened as well, although it might not sit that far off the rear axle, at least I don't need to worry about ground clearance lol

Ah ha! Just found a 12T 525 sprocket:

http://www.ebay.co.uk/itm/RENTHAL-FR...item2c5b741d87

I have seen that people are converting to 520 pitch chain, is there any reason for this?

Only a minor update, I don't have much space in the garage at the moment, I have started to polish up a set of front alloys though, I might repaint the centres black to give some contast, I do have a pair of all black front alloys already which is why I cleaned and polished up the spare set.

Before



After



Theres are the rims I am planning on running on the rear - massive rear dish

[embee]

You can get taperlock sprockets with various chain pitch, shaft diameter etc such as these for example . You need the other half of the taperlock too (the bush to fit the shaft).

(Edit - looking at the ranges it might well be that a bush for a 50mm shaft means the smallest sprocket might be too many teeth for what you're after, but something like 18/26 looks possibly viable. Another edit - looks like those are 530 sprockets, thickness 9.5mm or so, but you get the idea of what's available)

I know it makes sprocket changes a little more time consuming, but you probably won't need to change the rear one that often. Industrial chain isn't rated for auto/bike use, but the sprockets should be OK. Don't be tempted to use industrial chain, use bike spec chain.

Not quite the same league but I once fitted a Honda C70 into a kart for a customer who wanted a "quiet" kart for his lad so it didn't annoy the neighbours too much (a big driveway!). I used one of these taperlock sprockets on the rear axle for the same gearing reasons as you describe.

As an aside, on the chain tensioning business I'd definitely use a fixed idler sprocket, and fit it on the "slack" run, not the tight run. You can probably find sprockets with centre bearings off the shelf, just need to fabricate an arm and adjuster (in fact on the same site there's these idlers )

[yorkie_chris]

Aye, the SV engine makes considerable engine braking, which will mean all the slack goes to the other side and the tensioner gets pushed to the opposite side of it's adjustment.

There will be a large force on it from this tension. It's enough to slide the rear tyre on the bike so you should make sure the mounting of 3rd sprocket has considerable strength to it.


On the other hand, a bit of chain slack is acceptable on the SV. At full extension 25mm or more. Easily enough to set the engine in place for say 20mm of slack and that'll do. Too much slack will cause the gearshifting to go all to pot too.


IMO don't go down to 12t on the front. I think it will give you problems, like the teeth falling off, especially if you don't have a cush drive at rear. Find a way to fit a smaller one at the back and go up to 15/16 at the front.

Thanks for all this help guys! I wouldn't know where to start with finding that sort of sprocket which is why I tried to keep it OEM sizes as I know those fit etc. I am guessing I would need to change both the front and rear sprockets to the new chain size, how much space is there for me to run a larger front sprocket? I won't be doing many miles on the kart, so its more of a case of getting something that fits and it probably won't need to be replaced for a loooong time.

I could go with a custom 525 sprocket meaning that I would be able to use bike chain, I could get 2 of those ie a 33/40 and just buy 2 off the shelf from there and increase the centre bore on one?

http://www.moto-racing.co.uk/item--B...Sprockets.html
http://www.moto-racing.co.uk/item--Y...Sprockets.html

I will measure the distance of where the chain will be vs the rear sprocket - there might be a shorter lenght of chain so there might not be a massive amount of slack in the chain, are you suggesting I run the tensioner under the chain or on top of the chain?

Update on the engine - its out of the donor bike and will get some photos when they are sent over - im getting it from a bike breaker who is giving me EVERYTHING needed for the engine to run outside of the bike (ie carbs, injection, radiator etc) which is a cheaper option than me buying a used bare engine and then spending loads on getting it running lol

[yorkie_chris]

Buy streetfighters mag and have a look in the back, there are ads for custom sprocket makers for the stunt crowd.

Tensioner under the chain, personally I don't think you should need one.


You can definitely get 16t in there, probably more. Front sprockets are not expensive just to give it a go though.

Well I need as few teeth on the front as possible otherwise the top speed is massivly reduce due to the smaller tyre size

eg:

16t front / 33t rear = 79mph
15t front / 33t rear = 74mph

Looks like I can have up to a 17 tooth front sprocket but thats only 83mph @ 9000rpm

What chain pitch is a 525 chain? Is it 5/8"?

It seems that a BSA gearbox sprocket is 5/8" X 3/8" meaning that it will take a 530 chain - would mean I can run a 18t rear sprocket if I changed the front sprocket to a 530 chain sprocket?

http://www.ebay.co.uk/itm/BSA-A7-A10...item2567a341e0

Or this 19t Norton sprocket

http://www.ebay.co.uk/itm/Norton-Gea...item20c021239c

Im taking the sprocket info from here:

http://www.gizmology.net/sprockets.htm

Hmm would a 530 chain be ok on a 525 front sprocket and a 530 rear sprocket? They look identical apart from the 525 front sprocket being slightly narrower by 0.059" - I know if you change an SV to a 520 sprocket you have to do the same on the rear are they are narrower, would it be ok to run a slightly wider 530 chain on a 525 sprocket?

It looks like you can get 530 Suzuki front sprockets anyway, so I could convert to 530 sprockets and chains and be done with it lol

[yorkie_chris]

That doesn't make sense, the front sprocket wants to be as big as possible for top speed.

I can't use the OEM rear sprocket though due to the wheel size difference, the OEM 15T/45T gives me 54mph, I will be changing both sprockets so the OEM ratio is the same/close for the different size wheel, the rolling circumference of the OEM wheel is 77", the Kart circumference is 34". I do agree that with a larger front sprocket it does increase the top speed, but only to 61mph with a 17T/45T, im planning to drop the number of teeth on the rear and run more teeth/the same teeth on the front.

I have found that with the Gixxerkarts they are using around 15T/30T but thats for around 81mph, which give a lower top speed than the bike.

Im using gearing commander for this as it has loads of different bike gearboxes you can load and I can see what the top speed is.

http://www.gearingcommander.com/