Which piston?

[morbidelli17]

Looks like the bike is leaking oil past the rings. I'm going to go ahead and take the opportunity to drop in an 11:1 piston (and a solid balancer shaft gear). I have a stock con rod, and want to keep the stock displacement. Suggestions on piston manufacturer/kit? Thanks - M

[basser23]

check with Barkers Exhaust or Trinity racing...many were using JE

[basser23]

I checked Trinity Racing's site, they carry both Weisco and JE, The 10.75 cr JE is about $190, the Weisco is $141,both om 100mm and oversize.Good cam selection too....
Barkers didnt have 660 pistons that I could find...

[Bill Jurgenson]

I have used both, and prefer the Wiseco which I have installed in many engines in several varieties.
you will need:
part Nº.4737M10050

i.e. 100,5Ø 11:1

[morbidelli17]

Thanks for the info. Does the 100.5 mm (0.020) piston require a rebore or can I get by with a simple hone?

[Bill Jurgenson]

need a rebore.
If you think your sleeve is good enuf to jst be honed, you can go for the 100mm piston of course.
4737M10000
normally they are not. I was assuming normal wear and thus oversize.
Or skip the oversize and go directly to 101Ø for a few more CCs.
4737M10100

[morbidelli17]

Thanks. Mechanic says the cylinder is in good shape, rings are just worn. So I'll grab the stock size. Thanks again - M

[morbidelli17]

After thinking about Bill's suggestion and doing a bit more research, it is affordable and possible to do the bore job in the time before the next race. So I've gone for the 11:1 100.50 mm piston kit. Replacing the exhaust valves as well. Will keep y'all posted, and thanks for the advice, all.

p.s. Tex: I'm thinking about trying the single-disc setup for the race at the end of April at Willow Springs. On this bike, you'll only touch the brake lever twice a lap, and not very hard either time. Will let you know.

p.s. I'll be selling the MZ Skorpion wheels and front fork and brake assembly. The whole thing - caliper, master, steel line, levers. If anyone wants them, PM me and make me an offer. Don't forget you'll be taking care of shipping ...

[Bill Jurgenson]

why are you replacing the valves?
I have never ever had to replace original Yamaha valves due to wear. Bent or otherwise damaged due for instance to timing chain breakage is another matter but the the guides are shot as well.
And there is no advantage to larger valves in this particular cylinder head. Many have been there/doneit and it is a waste of time and money. In fact it can be detrimental. The valves are large enuf and the quality is the best there is. Regrinding the seats to maximize orifice and reduce seating area is probably necessary and porting is obviously necessary. Both of these are things only people with real hands-on experience with this cylinder head should untertake. The good old amuricun bigger is better has no place here at all. that can and does work with big 2-valve pushrod engines but it cannot be transfered to to cylinder heads like this one.
There are alternatives to the OEM valves such as from GS Valves but these are neither cheaper (I know; I use them in the 4-valves engine) nor easier to get.
On the intake sind one could be tempted to use the titanium valves from the last Raptor and one should set the center valve about 2mm deeper. In as much as RPM has never been a problem for me, revving the race engine to 9500 and even my street engine to nearly 9, I have not been tempted.

[morbidelli17]

The exhaust valves appear to be bent slightly. And there are indications that they have touched the piston lightly at some point in the past. Remember, I've never had this motor apart other than removing the head, and God knows how much wear is on it. So since the motor is apart anyway (and man, how much money has that phrase cost me in the past!) I'll put in a couple of new ones. I am going with stock size, stock valves. You are right, I saw no reason to go bigger.

It is funny, the bigger-is-better mentality that you mentioned. Part of the reason I'm going with the .5 mm overbore is that using an overbore was far easier than trying to find a stock size piston. Part of the American mindset - and it's a shame, because that means most people will never experience the joy of racing an MZ Skorpion.

[edfmaniac]

Enough bashing Americans already. I love small displacement motorcycles. So much so that it's a fault. I'm a very large guy and always get made fun of riding the smaller bikes, but I love them. Even when it comes to custom Harleys, if I ever get a chance to own one, it will be the Indian Larry style of old school minimalist chopper. Bigger isn't always better, but it is most of the time, just ask the citizens of Europe when it comes to being able to defend yourself.

Oh no he didn't!!!

[edfmaniac]

For the record, I live in Austin and embrace the more efficient European style of living. Just try moving over here and convincing anyone to get on a train or bus. You may as well ask them to kiss a homeless street person. Only time and the inevitable decline in global oil output will convince Americans to change their ways. It's coming though, it's coming.

[morbidelli17]

I'm born and raised and live in Southern California. I lust after the smaller bikes that get sold everywhere in the world but manus won't even bring them here. And I just shake my head at the new riders I talk to all the time who insist that they'll get bored on anything smaller than a 1000. Jesus, I had a ZX-10R out at Buttonwillow Raceway Park in November, and I never got the thing out of third gear. 145 mph was fast enough.

Irrelevant but true story: I rode an endurance race last year - first time I'd ever raced a 1000. It had a reversed shift pattern - I did not discover this until about five seconds before I jumped on the bike for my stint. I did the whole session in third gear.

And we won.

[DAVID THOMPSON]

where i live in the usa the rednecks call any thing under 500cc a moped
dave

[edfmaniac]

I wished that I had a GoPro when I was driving around on town on my XT225. I'm 5'10" and 300lbs and you'd have thought that I was trained gorilla from the looks that I'd get. On more than one occasion, a car full of Asian folks almost got in a wreck trying to snap some pictures of me.