SFO

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Feb 16, 2001
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Pardon me, PJ

I stand corrected concerning your gender and will not make that assumption again.
But if girl is the alternative to man I would perhaps choose woman instead.
I am again assuming that you are older than twelve.
It is not my intention to berate or condecend to you. My best friends are women and I apologize if I offended you.

Concerning rod ratio, I never considered piston side thrust issues to be an aspect of the debit side of poor rod ratio #'s.
This is interesting...
I have been schooled to consider the exteded time at tdc with more favorable rod ratios, along with leverage.
This leverage thing you can also achieve with offset boring something honda did on the f2, putting the centerline of the bore ahead of perpendicular to the crank centerline creating more leverage on the power stroke.
You could also do this with an aftermarket cylinder, huh Rich?
 
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Rich Rohrich

Moderator / BioHazard
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Jul 27, 1999
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PJ - What I want to know is how Powroll uses a shorter piston to make up for the stroke change? The pin bore is nearly into the oil ring pack on the standard YZF piston so moving the pin bore would require a serious movement of the ring package. Are you moving the the pin bore and the ring pack or reducing the crown height of the piston?

And on the subject of changing the stroke in conjunction with altering the rod ratio what are you guys doing with the cam timing on these stroker kits to account fore these changes?

Inquiring minds and all :)
 

DualSportr

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Aug 22, 2000
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Rich,

We're chopping the top off the piston. We decreased the pin to deck height that way insead of moving the pin upwards in the piston.

The total stroke is only 2mm over stock, so the change in deck ht is slightly less that 1mm (.010" for you american inch dudes!). In fact, the deck ht on the stock piston would work, but it's too close for comfort -- we know how the m/x'ers like to rev these things!

As far as changing the cam timing to match the decreased dwell time, we leave that up to the customer. Some of them like the way the stock cam setup works with the stroker, but most like us to mess with cam timing slightly to smooth out power at lower rpm. Forgive me for not being specific about what's done - It's Sunday and I've got brain fade! E-mail me at work and I'll tell you exactly which cam, which way :)
 

DualSportr

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Aug 22, 2000
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It is not my intention to berate or condecend to you.

I know that. I didn't bring it up to make you feel bad. I normally don't say anything, but I don't like to mislead people either. Don't worry, you'll never offend me! I have a thick skin! I answer to chick, girl, lady, woman, or in the case of some of my southern customers "little lady". Doesn't bug me -- it's HOW they say it that matters! Some of my best customers call me Sweetheart, and they mean it. Makes me smile.

I have been schooled to consider the exteded time at tdc with more favorable rod ratios, along with leverage.

Agreed, but Yamaha and the YZF showed us that by using a very short rod, we could make a four stroke behave more like a two stroke. Dwell time is cool for producing more torque and horsepower, it just takes the engine longer to do it.

This leverage thing you can also achieve with offset boring something honda did on the f2, putting the centerline of the bore ahead of perpendicular to the crank centerline creating more leverage on the power stroke.

Measure a stock or good quality aftermarket (JE, Arias, Ross) piston. Measure from the pin to the front of the piston skirt. Now go to the back. You'll find that the piston will normally be shorter in the front than the back. This is why you get a smokin' beast if you put a piston in backwards :)
 

Shaw520

Damn Yankees
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May 14, 2000
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Wow ,....this Chick knows her sh....., I mean stuff!

(Chick was first on your list) >shrugging shoulders<
 

DualSportr

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Aug 22, 2000
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Thanks Shaw. I love my job, I love riding, and I really enjoy learning how things work. I'm very lucky to have a boss who knows his sh.. and he's been nice enough to pass a tiny bit of that knowledge on to me.
 

SFO

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Feb 16, 2001
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For the record, 1mm=.03937"
.040" off of the top of the piston is not dramatic considering I will have to cut my cylinder that much to get my squish to .040".
Thanks for telling us where you get your stroker clearance from...
I had an old boss who said tell the people everything you know...
Cause in the end they still aren't you...
It has been fun getting to know you PJ.
Bill
 

JasonJ

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Jun 15, 2001
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Heheh, he said squish agian, heheheh, anyway, was it Honda or Yamaha that was using oval cylinders in in-line 4 bikes a few years ago? Hey Dual Sport, Stop tearin YZs up to make fast quads! Tell em if they want to go fast to give up the lounge cair and by their own! On second thought, it is making for a good supply of cheap parts, but it still hurts to think of it, its as bad as the micro sprinters buying up all the 2 smoke 250s from the bone yards for little go carst :( .
 

DualSportr

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Aug 22, 2000
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OMIGOSH! Bill -- I can't believe I typed that - Doh! Even after reading your post, I couldn't believe I'd be that dumb, had to go back and read it for myself. Gulp! Talk about a blonde moment! Sorry.

Yup - 1mm = .040. .25mm = .010" Guess I'll have to go back to metric grade school. I'm an idiot!

JasonJ, Honda did that oval bore thingy on a 400-4, I think -- I'm sure someone can tell you all the specs. I've only seen one once, a long time ago. Very different.

Yea, it's kinda sick to see a bran-spankin new YZF 426 in our shop, and know it's being used as a "parts bike". Fortunately, it's out of the range of most quad rider's budgets.

I will admit tho - I do also ride quads (dunes and snow) -- hey, quit throwing stuff!! -- and I've never ridden anything else nearly as fun as the 426 conversion. It hauls patotie! Quicker by far than most Banshees I've ridden, and it handles like a Honda 250R.
 

DualSportr

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Aug 22, 2000
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Rich is going to have a heart attack when he sees the "Q" word being discussed here.

Yea, I know. I'll bare my back and be ready for 10 lashings with a whip made from slices of old inner tubes.

I forgot about the DRN "don't ask, don't tell" policy regarding those of us who swing both ways!
 

JasonJ

Member
Jun 15, 2001
1,150
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I was wondering why all the quad guys were looking at me out of the corner of thier goggles when we were sitting around watching hill climbs. Then one of the guys on a QuadZilla told me shocking stories of canabolism.:eek: I felt their eyes undressing my bike! I felt so violated! At least none of them had the nerve to ask me if I wanted to sell my engine! I know they would buy the motor in a heartbeat, I have seen them spend 3500 bucks on brand new Banshee's before even taking off the trailer. They are sick, I just can not condone the hacking of brand new beautyful bikes for quad raceing. I cant belive that if this mod is so hot for quads that Yamaha has not given them what they want. Is the raptor overkill or something? Why do they continure to ravage our YZFs and WRs? WHY, WHIIIIIIIIIIIIIYYYYYYYYY,sob, sob, sniffle :( .
 

DualSportr

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Aug 22, 2000
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Doug, why not lose the ALL CAPS, kay?

Different companies set up the cams at different degrees of change for different uses. Valve clearance would never change with just cam timing changes. Valve clearance only changes with lift/duration changes.

Why do you want to know? It appears you don't own a YZF. I'm sorry, but it just seem weird that someone who doesn't even own a dirt bike would be interested in this.
 
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