Skorpion sport cup rebuild

[edfmaniac]

Granted, we have our opinions. But I think .5mm is quite expected between the expansion from room temperature to full operating temperature and the extreme forces created when the piston reverses directions 8k times per minute. And I checked piston rock on mine before assembly. With the cylinder bored to piston manufacturers specs, there was definitely room for the piston to rock .5 out at the edge.

Then again, the aluminum cylinder may expand more than the rod, increasing the squish band at full temp. Haven't really looked into that.

[twinlinemoto]

Hey again!

The rebuild has been tedious, but I am almost finished! My head to piston clearance is 0.7mm, piston to valve clearance is the same. Unfortunately, I noticed I am getting a case of coil bind on the intake valve springs at max lift. I backed off the adjusters and checked how much clearance I need and its about 3mm! It appears this motor no longer has the valve springs I know it used to. Any recommendations?

[DAVID THOMPSON]

mixed up parts boxes maybe

[twinlinemoto]

Well, I finally got it going last week!
I Installed the motor, upgraded the brakes to brembo master cylinders and calipers, new tires and chain, new turn signals. I did 2 heat cycles on the motor and checked for leaks, then went straight to the dyno for testing! It did pretty well, though I was hoping for a bit more. Next time I will certainly lighten the crankshaft. Below is a picture of my two dyno runs. The short run is with the stock cdi box (7200 rev limit), the long one is with the ignitech sparker box using Bill J's mild advance curve with a 9k rev limit. It made just a little less power, but the curve is much smoother and less violent on the piston!

After I knew it was solid, I took it for a "spirited" 200 mile ride in the mountains with some friends. The bike handles better than I remembered, the new tires and brakes are awesome! I had a fun and well matched race with a suzuki SV650 and a Ducati pantah 650.

[edfmaniac]

That's respectable. Glad to hear you were successful. Now swap those wheels out and you'll be pulling further away from those riding partners in every corner. It's one of the biggest performance improvements you can do besides engine work. Better acceleration, better braking and less gryo effect when whipping the bike around in tight corners. Then again, if you don't have a lathe, making the wheel spacers and axle parts for different wheels can get stupid expensive.

[twinlinemoto]

Haha thanks edfmaniac! I was faster than both of those bikes, but had trouble with a ZRX1100, haha. I could line up every corner I wanted, but he had the grunt to pull away from me just as I could get a wheel in front of him!
My headache now is getting the accelerator pump dialed in and the oil tank to stop leaking. I do have a lathe, but I am out of money and have 2 other bike projects in the works, so the wheels will have to wait. What models exactly and I looking to use the wheels from? SZR only?

[edfmaniac]

I can only speak about the SZR swap since that's all I have experience with, but I think you can fit KTM 690SMC wheels. I've seen some Marchesini's on a Skorpion.

[dandywarhol]

Hey again!

The rebuild has been tedious, but I am almost finished! My head to piston clearance is 0.7mm, piston to valve clearance is the same. Unfortunately, I noticed I am getting a case of coil bind on the intake valve springs at max lift. I backed off the adjusters and checked how much clearance I need and its about 3mm! It appears this motor no longer has the valve springs I know it used to. Any recommendations?

Good to hear you have it running, I'm just starting to build a 105mm oversize engine with stock stroke and a Carillo rod and a Hotcam Stage 3.
How did you sort your valve spring bind problem? Did you have to modify/shorten the centre intake guide for the X2 cam?

Cheers

[silver]

I recently fitted Aprilia RS125 wheels for a saving of 4.5kg. I have also fitted ZX6R forks for full adjustability. Just a bit fiddly with the spacers, but I kept the speedo drive hub. Had to turn the back wheel, but getting good chain run wasn't too difficult.
All the best, Dave.
PS the Aprilia wheels are same size as originals. Also made by Grimeca.