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YZF1000R-SPRINT · Test Rider

Hey up guys.

So I've been thinking about my project, I'm definitely going to get a 1040 big bore kit for my engine but I've been thinking.

I've seen new pistons for the Thunderace 1040 and these seem to retail at approx. £650+

Now I have found another bike, its a 2001 YZ250F with 5 valves and the same bore (77mm) as a 1040 thunderace big bore kit, I can buy a brand new piston for this bike for about £90, 90x4= £360 which is more than half the price of the £650+ kit advertised.

The thunderace has a stroke of 56mm the YZ250F has a stroke of 53.6

My question is

Would a piston from a 2001 YZ250F fit a rebored (1040) Thunderace barrel

I have found a 2nd hand piston on ebay for £10 so bidding on that to see if it does

Any thoughts?

creedxup · Parts department

If the gudgeon pin (wrist pin) is the same diameter, the width of the cutout for the the con-rod is the same, the distance between the gudgeon pin and top of the piston, the shape of the top of the piston and the cutouts for the valves on the crown of the piston are the same then you’ll be fine unibrow

You also get the rings and new gudgeon pins in the 1040 kit, do you get those with your £90 YZ250F pistons?

You’re also supposed to get a head gasket in the big bore kit (although I didn’t with the 1070 kit), so you’ll have to add that to your cost, I think a genuine Yamaha one (which you can use) is about £60.
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1992 RU midnight blue, Wiseco 1070, 6 speed, r1 calipers, ducati discs , 157 bhp crank, Ohlins shock

creedxup · Parts department

Just seen this, you’ll have to add import duty, usually calculated and added at checkout (15% I think), but still a lot cheaper and easier that fudging something from another bike.

The item no is 233899584103

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1992 RU midnight blue, Wiseco 1070, 6 speed, r1 calipers, ducati discs , 157 bhp crank, Ohlins shock

nuggitt · Moderator

Try sending of Kurt Boehringer a PM. He could maybe help out with it. He sends me stuff every now and again. 👍
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Bit of advice. Buy a good bed and a good pair of shoes, because if you aren't in one you'll be in the other.

YZF1000R-SPRINT · Test Rider

Hmm, a few options to consider.
I'll do some measuring when I get the used yzf250f piston and see if everything is the same