[DaveTheCanuck]

I ordered the JT +1 sprocket last week from Amazon. Reading the reviews in this thread, I really can't wait for it to come in now. I might not have a chance to test it out until spring at this point though

1st gear is definitely all but useless on the 300.

 

[ionized]

I don't like the idea of having to tap on the sprocket to get it to fit the larger CS of the 300 and would prefer to wait for the correct part to come out from vendors. I would think that front sprockets are designed to have free play on the counter shaft for a reason and I would prefer it to have its wiggle room like it should. That is just my opinion of course.

 

[old3]

It should be a tighter fit, if it rocks it will hammer the splines and can destroy the shaft. Hammering it on is an exaggeration, it needs to be tapped but it fits and is the correct size.

 

[Patto'sNinja]

Can a mod be done to the rear sprocket to perform the same fucntion as adding one to the front?

 

[socalmike]

I'm guessing so, at least close. Not sure how far back the wheel can go to take up the slack though. Old3 will probably know.

~mike

 

[ionized]

Can a mod be done to the rear sprocket to perform the same fucntion as adding one to the front?

Yes but it is much easier to change the front sprocket. I changed both front and rear on my 250 in order to get the ratio I wanted, but on the 300 changing just the front +1 sounds perfect.

 

[ionized]

It should be a tighter fit, if it rocks it will hammer the splines and can destroy the shaft. Hammering it on is an exaggeration, it needs to be tapped but it fits and is the correct size.

Maybe it is a different CS than what I am used to on the pre-gen 250. On that bike the front sprocket is purposely able to wiggle laterally, not front to rear in the splines, but side to side to allow a slight amount of chain drift. Maybe I'm being paranoid but I thought I read that the 300 spline is a larger diameter than the 250, hence my concern with using one meant for the 250.

 

[ghost3772]

I don't like the idea of having to tap on the sprocket to get it to fit the larger CS of the 300 and would prefer to wait for the correct part to come out from vendors. I would think that front sprockets are designed to have free play on the counter shaft for a reason and I would prefer it to have its wiggle room like it should. That is just my opinion of course.

its not tapping it on hard.. its just fitting snug, thats all, its not a BANG BANG!!! kind of tap..

 

[old3]

Can a mod be done to the rear sprocket to perform the same fucntion as adding one to the front?

Adding +1 CS is roughly equal to -2/3 on the rear sprocket. I didn't look any further for alternate rears as I now find it perfect. On my KTM SE950 I ran -1 and + 5 for dualsporting and off road racing. My 950 SMR I had a -2 front CS. I like low gearing with good snap. For me to gear taller was not a normal direction but this ratio just flat out works on the 300.

The speedo correction was just a bonus too, I'd run this gearing if it made the speedo read even worse!

 

[old3]

Maybe it is a different CS than what I am used to on the pre-gen 250. On that bike the front sprocket is purposely able to wiggle laterally, not front to rear in the splines, but side to side to allow a slight amount of chain drift. Maybe I'm being paranoid but I thought I read that the 300 spline is a larger diameter than the 250, hence my concern with using one meant for the 250.

I think you are overthinking this. The chain will drift slightly across the teeth of the sprocket. If the sprocket is moving around on the shaft it will have excessive wear at that point where it is allowed to move. If the chain is moving the sprocket side to side there are other issues that need correction IMO, like alignment of the wheel or a bent rear sprocket/wheel/axle/countershaft.

I've replaced hundreds of sprockets and am comfortable stating the 250 sprocket is an exact replacement for the 300.

 

[jaybo]

+1 tooth on front is closer to -4 on back. Im glad that the 250 sprocket fits the front. I found an aluminum rear for the 250 and wanted to swap out the 300's steel rear with about 3-4 less teeth but the front will be cheaper and easier to swap. Since the 300 allready has 3 less teeth stock on back than the 250 it may be hard to find a rear that is 4 more teeth smaller still

 

[ionized]

I found an aluminum rear...

Probably best to avoid aluminum sprockets all together if you want any longevity from them.

Okay old3 I'll take a look @ that part number. I might already have it in my bin if it's the same as pre gen 250s. I was going to wait and swap a +1 @ same time as full exhaust and fuel mapper but maybe not since that won't be until January.

 

[rodcar125]

old3, you used the jtf516.15 sprocket right?

 

[jaybo]

correction, on this bike it would be 3:1. On my dirtbikes that run around 12-13 front and 50-52 rear it is 4:1

 

[bigwood212]

JTF1539
This is the one I ordered. It's my understanding this one is the correct one. The 516 also fits because the difference is only like 1.2 mm of back spacing and I think the 516 has holes in it

 

[old3]

Scratch that! pn # jtf516.15, I sw the package in the bin in the garage.

This is what I used, nearing 2k miles now. Had it on for most of that. Working great.

 

[cruizin]

Top speed in each gear at the rev limiter;

1st=37 MPH
2nd=57
3rd=72
4th=88
5th=?
6th=?

man why are you still posting on this forum???

remember what happens at 88.8 Mph???

 

[old3]

Thats why I stop at 88!

 

[ghost3772]

man why are you still posting on this forum???

remember what happens at 88.8 Mph???

HUH? whats this even mean??? lol maybe this just went over my head.. i've had my bike up to 95 mph... no prob!!!

 

[socalmike]

Movie reference...