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View Full Version : Changing sprocket! please help!



Cayman911
1st June 2007, 14:55
ok i changed the engine to a A115, and the front sprocket wasnt right so my chain blew off, lol. so now i got new chain and front sprocket but have no idea how to changed it.
any help?

kinger
1st June 2007, 15:42
Sprocket cover off, chain still in place.
Stick it in gear, have a mate hold the back brake on.
Bend back tab washer, and release torque on the sprocket nut.
Take tension off the chain by shifting the back wheel forward, undo nut, release chain, remove old sprocket and tab washer, fit new, and reverse the process to fit the new one.
(Worth fitting a new tab washer when you do it, so get hold of one before you start.)
Are you akay with the chain links?

Gadgit
5th June 2007, 19:38
It's not the same as a big bike sorry.. for starters no gearbox...
There are three different types of sprocket 1 has a nut on the rear and is keyed into the hub-remove nut and hit sprocket out with punch 2 is screwed into hub and normaly locktyte added- heat up back of sprocket and unscrew. 3 is splined and is like number 1 to remove... best way I have found is buy a new clutch hub with the right size sprocket fitted and it only $10 more .. the bearings dont last long anyhow

zooter
6th June 2007, 21:49
I was wondering how lomg it would take for someone who actually has a clue about pocketbikes to pipe up, but I hope the poster can understand because I don't have a clue what you're trying to say!

Gadgit
6th June 2007, 22:36
Haha yea ya got to own one and have taken one apart a few times to know what I am talking about.... I'm not good with words when it comes to describing stuff....more hands on

zooter
6th June 2007, 23:19
Yeah Gadgit, methinks the poster is the "not much experience taking stuff apart" camp. Care to take another stab at it?

I've pulled a few things apart in my time so I'll maybe get the discussion going while waiting for the Loui Vutton to kick off:

Presumably the sprocket is located on the rear of the clutch drum and the nut is on the end of the crankshaft? That's the simplest arrangement I can envisiage.

That being the case you need to stop the crankshaft from turning.

Otherwise the nut is just holding the sprocket onto the clutch drum and you need it to stop turning. Post some pics or links to the stuff you bought and all will become clear.

Cayman911
7th June 2007, 08:03
yeah, im the kind that isnt born with mechanical skills haha. nor do i have all the right tools. so im kinda hopeless.

the whole problem was that the new engine i bought had a different sprocket to my chain. so i got sent a new sprocket and chain but a new problem is that the sprocket is actualy welded to the casing in the new engine. so newmanz told me i should take the whole sprocket/clutch casing from my old engine and put it in my new engine. but that just kills the point of getting a new engine with better quality pieces. he said he'd have some new casings arrive for him so i dont know if i should wait or do something.
queenstreet motor cycles was goign to charge me $50 to change the casings..

Cayman911
7th June 2007, 09:33
This is the one that needs replacing, and the sprocket is welded to the casing for some stupid reason. :
http://img505.imageshack.us/img505/3695/dsc02238rh9.jpg
http://img299.imageshack.us/img299/4299/dsc02239aq2.jpg

this is new sprocket and chain:
http://img50.imageshack.us/img50/8986/dsc02241wa2.jpg

this is the old engine sprocket and chain. i need put this case on the new engine apparently.
http://img50.imageshack.us/img50/9573/dsc02240dt5.jpg

zooter
7th June 2007, 21:36
I very much doubt the sprocket of the new engine is welded to anything. You need some Allen wrenches for starters. Presumably you aready own a socket set? If not you do now. You're just about covered for the tools with what you're saving not getting Colemans on the case.

With the clutch unit off the engine it should be pretty clear what to attack next, or else just post some more pics.

Be careful how tight you try to do things back up as the steel allen bolts will strip out the alloy engine case pretty easily. A torque wrench is a good investment.

Gadgit
9th June 2007, 09:31
Ok easy fix... remove the 4 10mm bolts holding the clutch drum housing from both engines .. and swap them over they should be the same size housings... There is a special tool to remove the sprockets your one just screws out but will be locktited in, heres the tool http://www.xminimoto.co.nz/tools.htm

Cayman911
15th June 2007, 16:53
ok i just took the sprocket plus the casing from my old engine and replaced the new one cause the sprocket was actualy welded in the new engine so that is fixed. now i just need to go to the shop and shorten my chain. =) until something else breaks lol. wont be long with pocket bikes

newmanz
19th June 2007, 11:24
Yes the sprocket had been spot welded on for some crazy reason only known by the assembler at the factory. Perhaps they ran out of lock tight !!!!

I have ordered in some standard clutch bells to remedy this problem and will gladly ship one free to you for the inconvenience caused. Hope you got the free chain and other parts I sent you. Let me know how it goes.

Also for future reference, most sprockets come off by lightly heating with a blow torch to loosen the lock tight then twist off in a clockwise turn (as most sprockets have an oppisite thread pattern).. You can check your thread pattern by screwing in your new sprocket from underneath the old one....

Do not turn the wrong way or you will snap off your old sprocket... I have seen this done many many times. Good luck, and call me if you need any more help....

zooter
19th June 2007, 13:41
No wonder they need locktiting.

IamCornholio
19th June 2007, 22:21
Yes the sprocket had been spot welded on for some crazy reason only known by the assembler at the factory. Perhaps they ran out of lock tight !!!!

....


I have a couple of bells that have 'welded' pinions. They are trash IMO...

The reason that many are spot welded such as this is to prevent the pinion from 'unscrewing' itself on deceleration. Some racers even go so far as to do their own spotweld when there was not one before to help prevent this from happening...

I have had spot welded pinions 'unscrew' on me in the past and tear up other parts in the process. It CAN still happen even with a small weld... :yes:

I use the Permatex red threadlocker (strong) to install all replacement pinions now as it will not come loose, sets up in @ 30minutes, and can be removed later by heating to @ 500degrees or so. :scooter:

As for pinion removal, I use a real deal pinion wrench as they are very cheap to buy but you can also grab the pinion with a 'Gatorgrip Socket' I believe it is called. I do not suggest using vicegrips as you could damage the teeth.

If anyone needs to see pics for clarification, Just ask and I'll post them up here... :rockon:


IamCornholio

IamCornholio
20th June 2007, 12:22
Pertaining to the direction of the threads on the pinion (front sprocket) commonly found on cagliari type bikes and the removal and installation of new pinions + the use of 'spotwelds' on pinions to secure them in place...
:sherlock:



The reason that pinions are threaded the way that they are is soas that as you are accelerating it will not come loose... If you will carefully notice the threads on the pinion as you rotate it in a 'clockwise' manner (same as when accelerating) they go in the opposite direction as the pinion rotation... This causes the pinion to become 'tighter' as one accelerates and this is a very GOOD thing. :yes:

Many racers like to add 'extra insurance' by 'tack welding' their pinions in place after assembly... :cry: This WILL work on most lame ass 'stock' engines, but when you have an engine capable of actually 'launching' when you want it to and then 'stopping on a dime' when you decide... This weld CAN and WILL break and the pinion may 'unscrew' as you are decelerating and the forces of drag push the pinion in the opposite direction...

Pics below... :yes:



Many guys will look at these pictures and see a broken ass part that needs to go in the garbage. :(

'Cornholio' sees a few good circlips, bearings, outer clutch housing, and a barely used 78mm drum which CAN be cleaned up/retapped for a new pinon, and used again with NO issues at all... Only thing I lost here was a pinion and some time... :yes:



IamCornholio (Lord of the Harvest - Master of the Catbox)

IamCornholio
20th June 2007, 12:42
Pertaining to the direction of the threads on the pinion (front sprocket) commonly found on cagliari type bikes and the removal and installation of new pinions + the use of 'spotwelds' on pinions to secure them in place... :headbang:


Pictures below are the only things one will NEED to remove and install a front sprocket on a 'cag'... (less the oven of course :cool:)

A screwdriver to lock the assembly in place, a sprocket wrench for 'unscrewing' the pinion, and some Permatex 'red', threadlocker to make sure it does NOT come out...



The oven is ONLY needed to ease with the removal of bearings and such and to help 'loosen' the bond that the Permatex will make if one is trying to remove the pinion... (It takes 500deg to loosen the seal here) This WILL make SURE that the pinion does not come loose when it is not wanted and will set-up fairly quickly IMHO... :yes:




IamCornholio (and I really hope this helps someone using the 'search' button someday as that IS all I was trying to do here...)

Gadgit
25th June 2007, 18:16
Hay there CornHolio
I dont use thred locker because it makes it harder to remove the sprocket when you break one or want to change gear ratio... the engine spins in the direction that tightens the sprocket up so no way the sprocket is going to undo it's self while racing.. well I'v never had one come out in the 3 years I have been racing anyhow.

IamCornholio
28th June 2007, 11:54
Hay there CornHolio
I dont use thred locker because it makes it harder to remove the sprocket when you break one or want to change gear ratio... the engine spins in the direction that tightens the sprocket up so no way the sprocket is going to undo it's self while racing.. well I'v never had one come out in the 3 years I have been racing anyhow.

The threadlocker can be loosened either by heating the entire assembly in the oven for a few minutes at 500deg or by using a small 'pentorch' directly on the threaded pinion for a few seconds or so... :yes:

You are absolutely correct about the pinion getting tighter as you accelerate friend. Most pinions that 'unscrew' do so on deceleration. All it takes is a single bad bearing to cause enough drag to break even a welded pinion on a 'wound-up' engine when one lets off the gas...

I am very slow with building engines for our bike but they tend to have good power when finished and most parts that can't 'hold up' generally fail quickly... :innocent:

Here is a pic of the pinion that 'unscrewed' on me. I have other friends on other sites that have experienced this as well. It CAN happen if one is not careful with their maintenance and pre-ride 'checks'... :shit:



If any of this helped you with your pocketbike... That was a good thing IMO...



IamCornholio

newmanz
1st August 2007, 23:46
Ok, I am lazy and in the past have just replaced the whole clutch bell with sprocket already installed. I have had clutch bells with factory threadlock glue that was impossible to remove without using a torch to heat it up and most times this heat passed straight into the bearings and stuffed them.

For the price, a sprocket tool is a nice friend. I think for the first time you ever change the front sprocket it really is a bit of hit and miss,especially if you have not read up on thread directions... after that, because you have done the job yourself, its always easier.