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Teeth missing on front sprocket, should I replace front, rear and chain?

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Hello fellow riders and racers, I'm newly registered to Thumper Talk, but always reading different forums on here. Anyway I ran into a problem the other day with my 2006 yz125, as I was cleaning it I happened to notice 3-4 teeth missing off of my front sprocket. Obviously not good, I'm assuming a rock got stuck up in there when I was riding last(thankfully the chain didn't get thrown). That being said, the chain and rear sprocket look pretty dang good to me since they haven't been rode much, so this leads me to the question of, can I just replace the front sprocket and ride on, or should I replace them all together? Also if I do just go about changing the front sprocket, what is the easiest way as I've never had to change one before, but I'm not scared to get my hands dirty and save a little money at the same time lol. Any help will me MUCH appreciated since I don't want to mess the ole yami up, thanks again!

 

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Yes replace as a set. 

Buy a chain break and crimp tool.

Split the old chain to remove it. Then both sprockets....obviously have to remove the rear wheel and the counter shaft sprocket guard.

Use blue loctite on the rear sprocket bolts when putting it back together. 

Install new chain with chain tool is recommended,  but you can just use a master link if you want to. If you do choose to go the master link route,  put the clip on so the closed end is facing the direction of travel the chain turns.

Aka with the chain master link on top of the swingarm, the closed end is towards the front of the bike.

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I’ve never seen teeth break off a good sprocket, a picture would help. How many hours is “haven’t been rode much”? I always replace all three as a set although it is possible to replace just the front sprocket. Lock up rear wheel, bend tab, loosen nut, remove master link, roll chain off, remove sprocket. New sprocket and reverse order.

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I’ve never seen teeth break off a good sprocket, a picture would help. How many hours is “haven’t been rode much”? I always replace all three as a set although it is possible to replace just the front sprocket. Lock up rear wheel, bend tab, loosen nut, remove master link, roll chain off, remove sprocket. New sprocket and reverse order.

I figured I would get mixed replies, and tbh I’m trying to do this the most cost effective way, so if I can just replace front for now that’d be great lol. I’m gonna try attaching photos, but bare with me as it is my first time using this forum.

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HOLY &%$#@!ING SHIT!!

 

Both of those sprockets are EXTREMELY WORN OUT!! The chain will be too after rolling through those sprocket teeth.

 

Go look at what new sprockets look like.  I STRONGLY suggest that you find a service manual and read it.

 

INCREDIBLE!

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Agreed with above statement. All 3 are trash. Once you receive the new parts, compare. You will be amazed at the difference. Your lucky you haven't thrown the chain and done some serious damage. 

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Its the chain that wears the teeth on the sprocket.  As the chain wears, the center to center distance on the chain increases causing the chain to ride higher on the sprockets and sliding back down into the bottom of the teeth as it rotates.  That's where the wear comes from.

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I figured I would get mixed replies, and tbh I’m trying to do this the most cost effective way, so if I can just replace front for now that’d be great lol.

Sorry dude, that stuff is just all worn out. A new front sprocket would only get you one ride. Time to replace all three as a set i’m afraid.
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well I’m very glad I came to you guys, no one in my family is MX savvy so I have to rely on the internet. I just thought the teeth were supposed to be longer, but now I see they’re supposed to be thicker, hence probably more strong as well. Guess my moto IQ is lower then I thought but you learn something new everyday lol thank y’all again for all the replies. I’m gonna try and order a set this week and change them out so I will keep y’all updated on how that goes since I haven’t had to do it before. Hopefully I can make it to the track Saturday

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I was in your shoes for a long time, always got my money out of tires, chain and sprocket‘s. You are smart to replace yours now. Can’t believe they can’t make sprockets to last more than 15 years, The one on the bike I use for rippin lumber now!IMG_1577.JPGIMG_1572.JPG

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Posted (edited)

Any further you would have thought your clutch was slipping. That would have been a great topic starter. :lol:

As members have said, replace as a set. I prefer RMATV, and none O-ring. Just get a roller chain as the 125 likes to spin. 

You can buy as a set, or mix match, and still come in at 80-100 bucks depending on a steel rear, or aluminum Primary Gear stuff (pretty good quality). 

Edited by 2 STROKE YZ DOC
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I already said it before,  but even more so after seeing those pics....replace all three. That procket will make a good paper weight for your desk.

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I was in your shoes for a long time, always got my money out of tires, chain and sprocket‘s. You are smart to replace yours now. Can’t believe they can’t make sprockets to last more than 15 years, The one on the bike I use for rippin lumber now!IMG_1577.thumb.JPG.b29a934c0c3cf48a2d643f1caea43b54.JPGIMG_1572.thumb.JPG.dc4a56dc362af8bd6634bc662c518eab.JPG

Dang I thought my front one was bad 🤣, the one in the first pic you posted is real torn up lol. But anyway, it all doesn’t seem too hard to change out, everyone’s directions were pretty clear so I think I can figure it out when I get the parts. The only thing confusing me is, how do you go about bending the little tab back on the front sprocket? Is there a special tool or trick?

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Strewdriver, chisel, anything to get under it to get it started. They are soft.

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Let's be clear that it is not necessary to replace all three as a set (even though the OP's sprockets are toast).  

For example, if you run steel sprockets front and rear, the rear will last much longer than the front, so you can usually greatly extend the life of your drive line by replacing the front sprocket when it starts to show significant wear.  By the time the second front sprocket is worn, the chain and rear sprocket are probably also worn out.  

Another good example to consider is the iron man rear sprockets,  Those things will last a really long time.  Mine still looked when I sold the bike it was on, and it had outlasted two o-ring chains and numerous front sprockets.

With experience you will learn to judge the wear on the individual components of your drive line.  

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I agree the OPs equipment is heavily worn and should have been replaced awhile back.  Generally the life of a chain/sprocket set depends on the materials, the maintenance, the power of the bike and the rider's habits.  A brand new heavy steel final drive can be worn out quickly by a very powerful bike that is ridden hard, even if it's kept clean.  I am not a racer so I always use steel rear sprockets and try to keep the set reasonably clean.  Also I do enjoy wide open bursts, but not all the time... in certain sections of single track I just putt along at low throttle and keep the momentum going to carry me through.  So my final drive stuff tends to last a long time.  I know racers like to save weight everywhere they can, but a critical part such as rear sprocket really needs maximum durability.  My $0.02

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1 hour ago, rpt50 said:

Let's be clear that it is not necessary to replace all three as a set (even though the OP's sprockets are toast).  

For example, if you run steel sprockets front and rear, the rear will last much longer than the front, so you can usually greatly extend the life of your drive line by replacing the front sprocket when it starts to show significant wear.  By the time the second front sprocket is worn, the chain and rear sprocket are probably also worn out.  

Another good example to consider is the iron man rear sprockets,  Those things will last a really long time.  Mine still looked when I sold the bike it was on, and it had outlasted two o-ring chains and numerous front sprockets.

With experience you will learn to judge the wear on the individual components of your drive line.  

This. For the life of me i dont understand why so many here replace everything based on the highest wear item.  I typically run 2 quality  CS sprockets per set. 

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