Timing Chain Replacement - Also Do Piston??

Here's the Background:

2006 YZ450F - I'm the second Owner. Bike has probably 50-70 Hours. I've put 40 hours on it and I would guess the previous owner had not more than 20. Bike has run well and except for the usual engine noises nothing out of the ordinary. Valves were checked / adjusted (were withing spec but at the limit) when I first picked up the bike and haven't moved since.

I figured it was time to do some maintenance on the motor and decided to start with the Timing Chain and Tensioner (Cheap Insurance). Once I started digging into the engine I thought - Why not just pull the top end and take a peek. I wanted to get a good baseline on all the important parts.

When I pulled the cylinder and piston it all looks really good (I think). There is some carbon build-up on the piston and head but no scapes on Piston or cylinder (I can still see the crosshatching on the cylinder).

So my questions are:

Do I just put the old piston and rings back in?

Do I use the same Piston and use new Rings?

Should I bite the bullet since it's all apart and put a new Piston / Rings in while I have it all apart?

I ride mostly recreational wiht a few Desert races thrown in for fun - If I do go with a new piston any reason to do anything other that OEM?

Since the Valves haven't moved at all do I need to worry about them right now?

Here are the pics:

Piston Top:


Intake Skirt:


Exhaust Skirt:


Piston Bottom:








If it was mine, and my budget was in better shape, I'd replace it, but otherwise, I'd rerun that one and not give it a thought. Use a new pin and clips, new rings, and hone the cylinder. There's no harm in replacing that piston, so do it if it makes you feel better, or if you're racing it hard on a weekly basis. Buit I see no compelling reason worry about it.



I guess it depends on how much money you want to spend. If you're not going to replace the piston, at minimum I would measure the piston and cylinder bore. If either is out of spec then they obviously need to be replaced.

If the they are within spec you could just put it all back together but rings are only $25 from TT store so that would be my bottom line.

If you have the money to spare I would replace the piston as well. An OEM piston kit isn't that expensive. The piston is roughly $120 the wrist pin a hair over $10 Don't forget new circlips, there a whopping 20 cents a piece.

You already need new gaskets which are about $26 for the pair.

I am doing all that to mine right now. I went ahead and bought valve springs and seals also... My total bill was only $191 tax and all.... Since it's nasty out here. I stripped her down to the frame and going to grease everything and put back together....A little piece of mind for me. Plus nothing like rolling a freshly greased bike.

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