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V8Astro

04 YZ450 piston choice

5 posts in this topic

I'm gathering parts for my YZ supermoto bike. I got a WR 5-spd and stage 2 Hot Cams so far. I want to keep stock displacement and stock compression

What's the preferred piston for these? I've been using Vertex in my KTM's. Not sure what the innernets suggests for the YZ

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Stock piston is very good if you are not compression. Track or street? I had an 04 with hot cams and porting with a CP 14:1. Was faaaast.

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A lot of people don't realize that the stock YZ450F piston is a high quality forged part. If you want to retain the stock compression ratio, there is no piston that I'm aware of that beats the durability and value of the standard replacement genuine Yamaha piston.  And by durability, one thing I'm considering is the durability of the ring seal. 

 

I did not replace the rings or piston in my '06 until it hit the 300 hour mark (roughly).  I'm a desert racer, so the engine gets used a little less hard, but only a little, and the races are over two hours long.  I'm an old desert racer, too, so figure that.  Nevertheless, the bike went 8 seasons of racing and just running around for fun without loosing a seriously significant amount of compression, and I only really tore it down to do a gear ratio swap. 

 

As it turns out, it was high time; the piston was dragging on the bore in between the rings and the skirt tips were showing wear.  That means it was loose in the bore to the point that it was tipping that much.  The ring lands are never supposed to contact the bore because wear at the edges of the grooves tends to pinch the rings so they can't float on the bore walls right.  240 hours would have been a smarter time, but no harm came from it, the bore cleaned up well within specs, the engine was still sealing at 92% under pressure, and never rattled (any more than it ever did).

 

Yamaha in general, and the YZF engine family in particular have a reputation for reliability that can't be faked.  Regardless how good the design is, you can't pull that off by using junk for parts.  OEM parts are always one of the best choices you can make unless you're building for really big power, and they aren't a bad staring point then.

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Thanks for the info. It's all street use. Might get my lazy butt to the track one day...

The crank timing sprocket is all chewed up. I read hit or miss opinions on aftermarket cranks so I bought an OE unit. For another $100 I won't have to worry

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