So , the guys are cutting their top cases for full skirted pistons .

Q1 : what will the new pistons be ?

Q2 : If the piston skirts are cut , what is the benefit of cutting the top case ?

I have new barrels now with new cast pistons and will be installing them soon , after they have been ported .
I had a problem with my earlier 300 barrels being nicasiled and scoring after 5 mins of running - waiting to hear if i did a mistake or the nicasil was a bad job .

Thanks , Neal

Hey bro,

Both top and bottom cases need some material removing with a rotary tool to clear the skirts of unmodified pistons.

The new forged pistons will be made by Wiseco, hopefully. I'm sure when they appear, Tyga will still sell them with the skirts trimmed so they can retain their 'bolt on' convenience for most online customers. But you have the option of asking Matt to send full skirted pistons with just the two holes drilled for the exhaust bridge if you want to cut your cases as i have done.

So if you keep using pistons with the skirts cut, there's no reason to modify the cases.

But I'm hoping that with equal, full length skirts on either side of the wrist pin, the piston will be better balanced as it moves up and down and won't rock in the bore as much - if indeed that was the reason for my skirts cracking earlier in the year.

I also noticed the two cooling holes are smaller in my new cast pistons compared to the originals i got with my 300 kit 5 or 6 years ago. That's perhaps a refinement that's come about more recently.
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Last edited by Hermit on Thu Jan 05, 2012 8:40 am; edited 1 time in total

Thanks mate ,

the balance issue is a factor to consider .

My two stroke man says that Wossner are very good , Lets hold thumbs !

My bottom end is coming apart for a flush out. I am skilled with a Dremel so plan to mod the cases to take full length piston skirts too.

Q1) Andy/Matt, can you please post here for me (and others for future reference) the details involved in grinding the NSR250 crank case to fit the full length piston skirt of the 300cc kit?

Q2) If/when the forged pistons arrive, will we have the option of full length skirts for us with modified cases?

Thanks
Phil

Q1/ i'll put the photos and details up on this thread, i have a couple pics from Matt himself and some of my own.

Q2/There probably won't be an option on the website but what i did with my lastest cast pistons was email Matt directly and ask him for full length skirts (but still keeping the two cooling holes) he then tells you to order the 300 top end rebuild kits (also includes wrist pins, rings, bearings etc) as normal on the Tyga site but to put a note in the text box that comes up when you choose the shipping type saying; "Please send full skirted pistons, ask Matt for details".

This then flags the order to the packers at Tyga and they'll go ask Matt what to do and he'll hand them the special full skirted jobs for your order.
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The Wiseco pistons are in production, although not completed yet. I had to jump through all sorts of hoops to get them done, even as far as speaking to the machine programmer and sweet talking him to convince the big cheese that the programming is not a big issue.

These new Wiseco's are basically the same spec as previous but with a coated skirt.

The Wossner's are in process. After some mailing back and worth we've agreed on the design and they're hopefully getting the forgings sorted out. When they're done and tested we'll possibly stop the Wiseco's or offer a choice. We'll see. They'll be twin ring, just like the cast and Wisceco's and will be coated on the skirt.

Once we've got this all sorted I'll probably stop the cast pistons. They're not the best, so I'd rather not sell them. They're just the best of the OEM pistons I could find that worked for the 300.

The bridge cooling holes are now reduced in size. One reason is that I found that the smaller holes work just as well. There's less chance of piston fatigue too.

The Wiseco's are not supplied with the holes drilled (they don't do that for some reason), but I will drill them as matter of course.

The Wossner's will also be drilled.

If you need full length skirts just do as Hermit says and make a note in the comments on the order.

Concerning the case mods required. It just a bit of grinding, well within most people's capabilities. You could use a half round file if you could be bothered.

The pictures I have are not exactly pretty but they do show you where needs to be cut. Mail me directly if you want the pics.

Thank you Matt, good to hear the ball is rolling.
Email on the way.

Any chance of posting the photo's

I don't have photos, but if you fit a full-length piston to the rod and turn the crank down towards BDC, it will be immediately apparent where you need to grind. It's not a lot that needs to be taken off.

It's the front (exhaust side) of the case on both cylinders that needs attention.
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Here are Matt's pics;





Put a lubed piston in one of your bores and sit it in its normal assembled postion on the crankcase half you are working on. Move the piston down until it catches on the crank case then simply start grinding/filing in that area until the piston slides all the way down to where bottom dead centre would be if the engine were all assembled and that's it really. Matt says chamfer all sharp edges that you make with your filing/dremeling.

For the bottom case you can still sit a barrel (with piston inside) on the two remaining studs and slide the piston down to see where it catches. You dont need to take much off to get full clearance - as you'll see yourself.

I took alot of time afterwards to banish all trace of swarf and aluminium dust from all engine surfaces.
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Thanks for the pics !

Is that a pencil grinder

That bottom case looks strangely familiar!
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Andy.
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Please keep all responses to Forum posts on the Forum so that others may benefit.

Please DO NOT PM me for technical advice. My time is precious, and you will probably receive a faster response on the Forum anyway.

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You have that motor in bits yet Phil?

Guess I'll be bringing a dremel over soon

Andy wrote:That bottom case looks strangely familiar!

Funny that!

Yes, that's the latest technology in Japanese pencil grinders. As you can see, it also marks in permanent blue. Amazing.

What spark plugs are you using in your 300? I need to find a set
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