How do I tell difference between these bikes?

Hello all new guy here and have an interesting question. I have a new to me YZ which one I hope you can tell me. The title says 2000 in one area and 2005 in another the nomenclature is MX480. I see a non-stock cylinder in there and gent I bought it from says a big bore was put on. My guess is it's an 05 YZ450 with a big bore to a 480. Is there any way to confirm this visually? Thanks.

The tenth character of the VIN will tell you the year of the frame. "Y" is 2000, "1" is 2001, and so on. "5" would be an '05.

The engine can best be identified as to its generation by looking at the left side. Post a picture using the "more reply options" button.

I see a Y so that answers a couple of questions. Here's a pic tell me what you think please.

20140413_090131.jpg

That's a 426.  The giveaway is the left crankcase cover and the red hot start knob on the carb.  A 450 has a smaller flywheel cover and the hot start is operated from the handlebar. 

Sweet thanks as far as the cylinder could they have replaced it with stock or could it be true they put a big bore on it? Last question and thank you first off you seem to be the YZ4XX master. I know 0 about the history of this motor. It starts good and no weird sounds but what should I be planning on replaceing with out knowing the condition of the motor?

It could be a number of things.  It is a cylinder for use on the 400/426  engines. That can be seen by the use of inverted studs on the outside of the chain tunnel.  The 450 uses bolts in from the top.

 

Yamaha cylinders are marked on the front below the exhaust  with the engine size they're made for.  Other people like Athena made big bore cylinders, but most of them put their name on them.

 

There's no way to know what you should be planning to replace, at this point, without opening it up and having a look.  If you wanted, you could plan on a top end job (piston, rings, wrist pin, clips, timing chain), which would freshen up the engine and give you a look at it at the same time.  You wouldn't be able to order parts ahead until you found out what size it is.

 

Replacing the timing chain is something that should be done periodically for maintenance.  Yearly is pretty common. Doing that along with a clearance check is a good idea on a new-to-you bike in any case.

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