Sprocket question...lower cruising RPMs?

[thielb]

Driving an 82 xs400j maxim to work everyday this summer. The bike handles highway speeds well enough i guess for what it is, I bought it to save some gas $$. My old man use to be a real big bike guy and has ridden lots of bikes. He's real stubborn and opinionated though so I tend not to take everything he says 100% . In this case I have to agree with him though. This bike really could've used a sixth gear. Cruising around at 60 65 this thing sounds like a loud cry for help. I understand these are higher reving bikes but i sure wouldnt mind a little more comfort at highway speeds. Just recently I caught a post in the " what'd you do today" thread about swapping a sprocket. A reply quickly followed explaining that it would drop rpms by 500 or so. Could one of you experienced gearheads please explain the sprocket swap and what difference it makes both good and bad? If its not a serious pain and actually provides a more comfortable cruising rev, I would look into it. Thanks for the help guys

 

[bcware]

A smaller front sprocket and/or a larger rear sprocket will tend to increase acceleration at the cost of top speed. The most extreme example is a stunt motorcycle; these utilize giant over-sized rear sprockets and as a result they wheelie very easily but will struggle to maintain legal speeds.

Conversely a larger front sprocket and/or a smaller rear sprocket will tend to increase top speed at the cost of acceleration. This is the swap you're interested in if you want to lower the engine rpms at a given speed.

Decreasing the size of the front sprocket will probably increase the wear on the chain.

I have not done the swap myself, but it has been discussed over time. Some of the guys/gals on here can probably chime in with their opinion and whether or not they are happy with the results. My impression was that the results were worth the swap for those that wanted a more relaxed ride on the highway.

 

[markjs]

Slap a 17 on front, I just did. I am a BIG dude and that thing accelerates OK, it did take a hit I can feel, if you weigh less it probably would be barely noticeable, but it revs so much smoother at highways speed, will be the best 20 you spend on that bike. Better yet, find a Seca engine and slap it in there! Then you got your sixth gear and you can play with sprockets too!

 

[thielb]

thanks for the help. Markjs, was that a relatively easy swap you pulled off? I'm flying through the manuals looking for drive sprocket access unsuccessfully but I'll have to take a closer look when I have the time I suppose. Run into any serious issues when getting in at that sprocket?

 

[markjs]

Yeah the sprocket cover screws can be easy to strip. If you don't have Japanese screwdrivers, I suggest replacing them with allen bolts if they give you trouble. Other than that fighting with the back tired to get the chain tension right is the only tedious part and that is really nothing. All in all, piece of cake. (Might be well to invest in an impact driver if you don't have one for those case screws.)

 

[thielb]

thanks for the help mark, definitely going to check that out when I get home to my bike in a couple weeks. Easy enough part to find?

 

[Scorpio1963]

Even having the 6th gear on the sohc engine my bike builds up very high rpms at hiway speeds.Im also thinking of a sproket change also.

 

[Lou Ranger]

thanks for the help mark, definitely going to check that out when I get home to my bike in a couple weeks. Easy enough part to find?

The sprocket was easy to find. I chose to order it from the local M-C accessory shop in town. A little more than on-line, but no shipping costs and he would take it back if it wasn't right. Plus, I think we should try and keep our neighbours in business when overall cost and convenience nets out about the same.
It cost $23 and I chose to buy an impact driver instead of allen-key bolts. The original Phillips heads may not look as pretty, but this way I have a useful tool (which I've used extensively since) and the original bolts work just fine. Pounding the JIS tips on the impact driver into the soft aluminum head actually fixed them up pretty well.

You may enjoy this thread. It covers all the issues - sohc and dohc ratios & revs, getting the covers off, installation, impact on the chain, how not to install the front sprocket backwards (at least one person inherited a PO's backwards installation) and the results of comparative runs I did with the 16T and then the 17T. Great fun.

http://www.xs400.com/forum/showthread.php?t=7592&page=2
​

 

[thielb]

That thread is great, thanks Lou.
http://www.ebay.com/itm/JT-Front-Sprocket-17T-Yamaha-XS400-Maxim-1982-1983-/390576206631?pt=Motorcycles_Parts_Accessories&hash=item5af027f327&vxp=mtr
thats the right part i believe?

 

[16VGTIDave]

Looks right to me.

 

[Lou Ranger]

That thread is great, thanks Lou.
http://www.ebay.com/itm/JT-Front-Sp...Parts_Accessories&hash=item5af027f327&vxp=mtr
thats the right part i believe?

The number is probably right but the one in their picture is definitely NOT the one you want. It only has 14 teeth and the pattern for the centre spline is totally different.
This is why I bought from the local shop - if he ordered the wrong one for me, he would have to take it back with no re-stocking or return shipping charge. $23 including taxes.

 

[thielb]

thanks Lou, just found that exact sprocket on amazon for $14 so I think I'm gunna pull the trigger
http://www.amazon.com/JT-Sprockets-JTF571-17-Steel-Sprocket/dp/B001AVQM3W#productDetails

 

[Lou Ranger]

thanks Lou, just found that exact sprocket on amazon for $14 so I think I'm gunna pull the trigger
http://www.amazon.com/JT-Sprockets-JTF571-17-Steel-Sprocket/dp/B001AVQM3W#productDetails

That's the one - like in the sketch.