Greetings for the new year folks, hope you all had a good festive break and the new year is a big one for you…even if we are 3 months into it already!
I thought we would start the year off with a bit of a tip for your basic AG200 overhaul. I say “basic” because there is really nothing too bad going on here. When I had a shed full of these things and old trade-ins and barn-finds seemed to follow me home weekly (daily?!), this was my standard engine overhaul kit that I used to keep in stock.
I found that the AG200s lasted somewhere between 15000 to 20000kms with zero maintenance. And 80% of the AGs I fixed that were from farms pretty much had zero maintenance. Oh, they might of had the free first service but after that – nothing. They would ride it until it self destructed! So what I have listed here is the standard top-end rebuild kit that you would have to put through the engine when it got to this point.
Now you might look at the list I have down below and say WTF! Why so many bits AGman? Well, you have to put things into context. It may be hard for someone coming from a different background to get their head around everything I have listed here, I get it. But we are not talking about an engine that has had periodic servicing done here…its had NOTHING for 20000km. And not normal 20000kms either. No airfilter cleaning, probably a clogged oil filter that at least has restricted oil flow. No cleaning so there is probably baked mud in the cylinder/head cooling fins…its a train wreck!
Here is the thing you need to remember most; anything rubber must be replaced. The biggest issue with leaving oil in an engine for this long is that it turns into an evil destructive sludge. If the inner cases look like they have been painted in varnish then the oil has been in for way too long and the chemicals that build up in it destroys rubber and I suspect doesn’t do a whole lot of good for gaskets either.
As for the parts themselves, you can get after-market gasket kits but I have never really liked them. I prefer the Yamaha originals. The timing chain can be sourced after-market, RK is a good brand. Everything else I would go with Yamaha. Lets have a look…
From this exploded view we will require part 6, 8, 13, and 2×17.
From this view we will need 2, 3 and 4
From below – 2×6 and 12.
From below – 2, 7 and 9.
From below – 7 and 11.
And finally, from below – 9 and maybe 2×11 (see text).
To sum up:
1NU-11181-00 GASKET, CYLINDER HEAD 1
93210-57634 O-RING x 2
5LB-11351-00 GASKET, CYLINDER
5H0-12119-00 SEAL, VALVE STEM x 2
93210-09165 AA5 O-RING
4BE-15451-03 GASKET, CRANKCASE COVER 1
94580-41104 CHAIN (DID25SH 104L)
4FM-1 2213-00 GASKET, TENSIONER CASE
15A-11603-00 PISTON RING SET (STD)
93450-17044 CIRCLIP x 2 (if you need to remove the piston to clean it)
There are assumptions and additions here; The two valve guide seals are needed because most AGs at this stage have been pretty fumy and there will be lots of carbon in the combustion chamber and the exhaust port. you really should pull the valves out to help with this clean-up and inspect the valve faces. I would strongly recommend a grind to clean up the faces – they will probably need it. So if the valves come out, you will need the valve guide seals.
I have covered mostly consumables here. There are lots of parts that need to be checked as well; are the cam chain tension guides going brittle? How does the cam look? Rockers? Valve clearance adjusting screws? Valves? Was the base gasket leaking? How do the cases look where they join up at the cylinder base? Lots to cover in a later tutorial…
The rubber parts that go in between the cylinder/base and cylinder/head are critical. Re-use the old ones at your peril! Take a look at the three radial seals on the engine as well – counter-shaft, gearlever and kickstart. If one is weeping replace them all because they will be going hard and failing soon.
Don’t be tempted to replace the o-rings listed here with generic bearing shop stuff – all rubber is not created equal. These need to resist oil and elevated heat. Unless you know where to source these o-rings from, go with Yamaha.
Obviously the part number of the piston rings will depend on the oversize of your engine but I doubt anyone would bother boring an AG200 up to the next oversize. If the piston and cylinder is worn out on one of these bikes then the rest of it will be rubble! Check anyway, and while you are there measure, or get someone with the equipment to measure your piston and cylinder to see if they are within specs.
Hopefully I will be able to do a tutorial this year to show the fitment and little tips and tricks of putting all these bits together. Don’t hold your breath though! 🙂