Changing a timing chain. Part#1

AG200 bent inletDoes this AG200 inlet valve look a bit wonky to you? It should…it’s been smacked by a piston! This is what WILL happen if you neglect your timing chain. It’s all easily preventable though and the bike tells you when it needs changing. The diagnosis and remedy is all pretty straight forward. Lets have a look at what’s involved.

First the diagnosis…does the timing chain need changing in your AG? There are a few components in the AG200 engine that, in my opinion, are marginal and can wear out quickly if neglected. The timing chain is one of them. It was upgraded to a stronger assembly on some of its sister engines and that suggests to me that it was borderline, and Yamaha knew it. Consequently, I tend to be overly cautious of its maintenance and replacement regimes and as with most engine components, oil changes are its biggest life-extender.

So replacement time is pretty simple; if you can hear the chain rattling around in your engine (preferably when its running!), it needs replacing. That’s how I roll with the timing chain in the AG200 anyway. The chain can be had for $20 and with an oil change and a few gaskets you’re looking at around $50 or less for this preventive maintenance. That’s a lot cheaper than leaving it until it spits the dummy! If you have a second hand bike that has missed a lot of owner love then you can keep an eye/ear on it and replace it if it’s noisy. Once you know its been renewed keep fresh, quality oil in the engine and it will repay you with good reliability.

If you neglect oil change intervals and ignore the AG200 timing chaindeath rattle coming from within the engine, eventually the chain stretches and the tensioner will not be able to do it’s job of keeping the chain on the sprockets. Before it finally chucks the teddy in the dirt, in an act of defiance the timing chain will slap around, grinding into the inner walls of the head and cylinder (see pic at right), showering the engine internals with alloy swarf before finally flinging off and causing grief proportional to the RPM you’re doing at the time.  If left to these extremes, it will cause issues down the track by spreading metal around the engine. The 3GX is a tough old lump, but no engine likes metal in it even if it’s soft metal.

Please, please, pleeeease don’t think you can extend the tensioner shaft! Yes, a lot of people on-line say you can extend the “service life” of the timing chain by adding some length to the tensioner shaft that puts the pressure on the chain guide. You can buy a new chain for less than $20 and one, maybe two gaskets and the head or cylinder doesn’t need to come off to do the replacement. Why would you bodge it up like this? When the chain starts to rattle, its worn out. All it does now is start to wear the timing gears which are not listed as a replacement part on the crank end. So if you wreck this gear you wreck the crank. Don’t be a hack, spend the 20 bucks!

OK, so lets get into it…this is what you’ll need;

TOOLS; 8mm hex socket (or Philips for the older bikes), flat blade screwdriver for timing/flywheel bolt covers, 17mm socket, extension and square drive for the flywheel bolt, Flywheel puller (M16 x 1.2mm), Flywheel holder.

PARTS; 104 link timing chain, stator cover gasket, timing chain tensioner gasket, oil.

Kick your bike in the guts (Aussie speak for start it up!) and warm it up (you haven’t let the timing chain fling off have you?!), shut it down and drain the oil out. A general service is a good time as any to do this timing chain job so clean the filter and dispose of the oil. When you’re done, stick the drain cap and filter cover back on and nip them up.

WAIT!!! Stop! Sorry to be so dramatic…but before we go any further, when you do change your oil, check your oil filter and mesh strainer for any signs of black plastic chunks. If there is any black rubbish in there I’d say your timing chain tensioners have gone brittle and are starting to fall apart. This is a sign of pretty serious neglect though so it’s not that common to see. If you do see it then you wont be able to do this job without taking the top end off to replace the tensioners which I will cover in an up-coming blog. Its not that common to see but I thought I’d mention it at this point in the disassembly.

OK, the tensioners are fine and we can continue with the chain swap. Every major (or even minor) maintenance job on a motorcycle should start with a good clean. Not only paying attention to the areas that will be worked on, but the whole bike really. Pull off the tank and seat and scrub it all up. Rubbish likes to accumulate up under the tank around the wiring looms and on top of the head and just loves to fall down into your opened up motor!

We have a section that we need to pay particular attention to with this procedure – the front sprocket area. If we don’t get this area nice and clean before we remove the stator/flywheel cover, all the rubbish that will be in behind there will try its best to get inside the motor. So turn your attention to the front sprocket cover. Remove the gear shift lever by removing the 10mm hex head bolt and sliding the lever off it’s spline. Remove the two Philips screws holding the rubber cover to the plastic sprocket cover. Two more bolts are required to remove the front sprocket cover.

DSC_0045You will now have access to the front sprocket area to get it as clean as you can. Take your time and actually, if you have a pressure washer, now is the time to put it to good use. Otherwise, pry out as much rubbish as you can with a pick or screwdriver and finish off with de-greaser and a stiff brush. Removing the drive chain and front sprocket will make this job even easier. The pic. at left shows a partially disassembled bike but it will give you an idea on how clean it should be. The wiring in the photo is also relevant as we get into the job.

top timing gear cover Remove the two bolts that hold the top timing gear coverStator cover. Early bikes had Philips screws while newer bikes stepped up to 8mm hex heads. When the bolts are removed you can take off the cover and view the top timing gear. Next job is to remove the two inspection caps on the stator cover. The small upper one is to give you visual access to the timing marks on the flywheel while the larger, lower one allows you to get access to the flywheel bolt so you can rotate the crankshaft.

Timing markRemove the spark plug and insert your square drive socket into the flywheel bolt hole and rotate the crank so the timing marks line up. The flywheel mark can be seen at left and you can see the other one in the above photo of the top timing gear. The mark on the gear should line up with the pointer cast into the head right at the top of the gear housing. You don’t have to get too pedantic with it all at this point, the reason I do this first is to get any tension off the valve assembly so when you start undoing bits it wont fly off everywhere because the cam is sitting up on a compressed valve spring.

I would now take the opportunity to loosen off the top cam gear bolt. Use your square drive socket to hold the flywheel steady while you get another 17mm socket or spanner onto the bolt holding the top gear to the cam. Get it loose and leave it alone for now, we will come back to it.

Now the eight stator cover screws (for later, electric start bikes) can be DSC_0041removed and a light tap on the cover with a soft faced hammer might be needed to jar the cover free from an old, hard gasket. Once you have the case loosened off, have a look at the wiring going to the stator cover and work out if you want to disconnect the connectors from the loom or have something handy for the cover to sit on close to the bike while you are poking around on the engine. I like to disconnect the wiring and remove the cover completely from the workspace but it’s up to you. Take note of the neutral switch wire which also needs to be removed, shown at right of this paragraph.

Be aware that there will feel like there is resistance when you pull on the cover because of the magnets in the flywheel trying to hang on to the steel coil formers of the stator. Just be careful especially if you have left the wiring attached. Also take note of the two locating dowels in upper and lower rear screws of the case. These dowels like to fall out and go missing at times! Download the manual and check out the (p. 121, ref. 4) diagrams if this is all getting confusing.

DSC_0031When the cover is off you will see the flywheel…which now has to come off. But before we do this we need to remove the starter idler assembly as shown here at left. Remove the aluminium washer in front of the gear (just behind my finger and thumb in the pic) and slide out the shaft and you can then remove the idler gear. Now we can remove the flywheel. This is a really easy job for me because I have a cordless impact gun! Getting flywheels off used to be a real chore when I was a kid. Getting the nut/bolt off was hard enough and then removing the flywheel without a puller was always an adventure! Doing things to engines that make me shudder now!

These days with the correct tools, this job is a snap. With a puller flywheel & pullerand a rattle gun, I don’t even require holding the flywheel with the removal procedure. Releasing the retaining bolt and flywheel from the crank are both quick and easy compared to trying to do it with spanners or square drive tools. At right is a picture of an example of a set-up you could use if you don’t have a rattle gun. It shows a holder and the flywheel puller installed ready to pop off the flywheel. There are a few variations of flywheel holder tools and this photo is kindly supplied via “SpudRider” over at China Riders Forum and is showing the procedure on his Zongshen GY-2 which has a very similar engine to the AG200. How you get the flywheel off is ultimately up to you. Buy, beg or borrow the correct tools to do the job or you will have to resort to bashing things which normally never ends well!

OK, so you got the flywheel off. Check the manual again (p.123) to see what you need to keep track of. There is a woodruff key (ref.4) that may or may not dislodge from the crank and a washer or shim (ref.6) that sits behind the flywheel that may or may not stay on the crank. Watch what happens to these items. Also try and keep the whole flywheel/starter clutch assembly together if you can. Bits can go everywhere if they come apart…its no big deal, its easy to reassemble but if you slide it all off as one unit then it makes it all easier.

DSC_0007Put the flywheel/starter clutch assembly aside and you should be looking at the pic at left. Note that the washer that sits behind the flywheel is still on the crank and the woodruff key has been removed from the crank in this photo.

Lets turn our attention to the timing chain tensioner. First DSC_0042thing to do is loosen the 10mm bolt on the centre post. Don’t remove it, just loosen it for now. Now remove the two Allen bolts at the top and bottom and remove the DSC_0010tensioner from the cylinder. You will feel the pressure that the tensioner exerts on the chain as you loosen the two Allen bolts.

Remove the timing chain tensioner assembly and you will have a nice slack timing chain that you can slip off the top timing gear and let drop down the engine to the crank shaft and lower timing gear. DSC_0013The top timing gear can be removed to help facilitate this – or not. Sometimes the chain will be loose enough that it will lift off the side of the gear and you can just let it drop down to the the crank and remove it.

That’s the removal part done. True to form it was getting a bit long so I will break it up into two parts; removal and reassembly. My only other suggestion before signing off is to jam some rags into the engine cases and clean the gasket surfaces on the engine side and stator cover ready for reassembly.

Keep an eye out for part two…



7 thoughts on “Changing a timing chain. Part#1

  1. This is just what I needed. I am starting to get what sounds like a chain rattle on startup with my 6 volt kick start model. I wonder if the chain for the TW 200 model (available in the US) is the same part#?

    Keep it coming!



    1. Hi Pitt
      Just went and checked…I have a parts listing for an ’06 TW – 94580-41104, the same as the AG200 right back to ’84. If you want to go for a manufacturers (DID) part number, it’s DID25SH 104L. You can get these on Ebay for around $20 last time I looked. When I mentioned in the post that the sister motors were stronger, they went with the “standard” or “silent” (I like to call them spur) type of chain and not the roller chain of the AG200 and TW200. You cant miss the difference, totally different design. My description of “stronger” might be up for debate too! I’ll cover this in part 2

  2. Hey there,
    Just wondering how you are getting on with Part #2 of the Timing chain repair? Part 1 was awesomely helpful. Hopeing part 2 is not far off?

  3. Great site !!
    Also keen to see part 2.
    Could you tell me when the camchain sprocket is lined up correctly – where should the alignment on the flywheel be ? I seem to possibly have a valve timing issue – but do not necessarily ant to pull the flywheel off at this stage if I can help it.

    1. Hi Mark
      I have most of the writing done but need to take some decent snaps of the whole procedure. Maybe I’ll just post up the info and add photos as I get them. The timing procedure is in the manuals I have posted up if you want to take a look there, very little has to come apart, just remove the top timing gear cover and the inspection caps on the flywheel cover.

      1. Hi AGman. Downloaded the manual which was very helpful in a lot of areas but it does not show me which mark on the flywheel ( the T or somewhere in the H) should line up when the timing sprocket mark is lined up with some it’s mark. Unless I missed it somehow ?

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