big bore yzf set-up

[SFO]

Rich, super thanks for the hook up.
I have the 97mm piston kit ala Gore/Rohrich for my 426.
I sent my cams to falicon for the vernier sprockets, and have my piston on the rotary table to pull some of the weight out of it.
Is there an advantage to the weisco untapered wrist pin? Or can I machine the taper into it?
I am going to set up the squish with the cylinder .010" under the deck, the cometic gasket sets up around .040" right?
The hone finish that us chrome is using now looks 100% better than a few years ago. It is obvious they got some new equipment.
Should I machine the head surface or do you recommend the oem volume. I don't have a burret(sp?) to check the volume.
Thanks again for your help Rich, This is getting interesting...:)

 

[Jonny426]

SFO, I'm glad to see the large 426 coming together. I am curious about your connecting rod issues,did Yamaha step up or were you forced to make repairs yourself? I'd also like to know where you end up with the cam timing, because the 22.5 deg. spread between YZ+WR's is hard for me to swallow. I like the power( much more linear ) but a lobe center change that radical reeks of compromise. Keep us posted! Jonny 426

 

[Rich Rohrich]

Originally posted by SFO
Rich, super thanks for the hook up.
I have the 97mm piston kit ala Gore/Rohrich for my 426.
I sent my cams to falicon for the vernier sprockets, and have my piston on the rotary table to pull some of the weight out of it.
Is there an advantage to the weisco untapered wrist pin? Or can I machine the taper into it?

Bill - The pin is fairly heavy at 74grams (98 YZF 400 pin weighs 63gm) but you might want to calculate the loads before you go hacking away at that thing :)
For reference:
97mm Wiseco : 293 gm
Piston pin : 74gm
clips :~ 1gm
Ring package: 29gm
Total package 397gm

94mm Wiseco total package : 348gm
92mm OEM total package : 342gm

Originally posted by SFO

I am going to set up the squish with the cylinder .010" under the deck, the cometic gasket sets up around .040" right?

Compressed the Cometic head gasket should be .033" - .035" . I set my 97mm up at .012" deck and a .033" compressed gasket for a .045" total squish.

Originally posted by SFO

Should I machine the head surface or do you recommend the oem volume. I don't have a burret(sp?) to check the volume.

My uncut 98 400 cylinder head volume (with OEM steel valves) was 21.2cc and the valve cutouts on the piston crown on the 97mm piston measured out at 5cc.
With some smoothing of the transitions on the piston crown I ended up with a total clearance volume of 34.64cc (about 13.8:1 CR) . That should give you a rough starting point to work from.

Originally posted by SFO

Thanks again for your help Rich, This is getting interesting...:)

No problem. Glad to help. I'll be interested to hear your impressions once you get it buttoned up.

 

[Thump]

FWIW, Eric did the big bore to my 99 400 now a 417 and Rich built it for me because I am a moron when it come to this stuff. All I know it that when I put the engine back in it ripped. Rich and Eric, thanks for all that you have done. My bike is a near perfect as I can imagine.

 

[SFO]

Re: Re: big bore yzf set-up

Johny 426, I didn't pursue the rod galling.
The oe wrist pin took the blunt of it, and I ball honed the small end to an "acceptable" finish.
I was running golden spectro because it made the bike shift the best, I am considering changing to Yamalube or Mobil 1.
I am also going to order an Arrow pipe and see how it looks. The pictures show it with a long silencer. I will have to adapt a spark arrestor to it. A full Ti/carbon fiber set-up is around 400-450.
I have to also research the local race gas situation, and post my options to make the right fuel choice.
If anyone has race gas awareness in the Bay area I would appreciate it.



QUOTE]Originally posted by Rich Rohrich


Bill - The pin is fairly heavy at 74grams (98 YZF 400 pin weighs 63gm) but you might want to calculate the loads before you go hacking away at that thing :)


Hacking away? My poor hubris! Rich thinks I am a hack now...
Nobody feels the pain but me.javascript:smilie(':eek:')


As far as the piston crown...
When you smoothed the transitions, did you radius the cutouts more? Man, I love the smooth edge of the piston, ie no valve pockets in the squish for detonation to hang out and breach the ring pack...


Thanks again Rich, when I get the cams back I will do the "fixture".
I would like to be able to put an indicator on both the outer and the inner intakes at the same time and see whats happening the inner and outer relationship.

 

[Rich Rohrich]

Re: Re: Re: big bore yzf set-up

Originally posted by SFO
Hacking away? My poor hubris! Rich thinks I am a hack now...
Nobody feels the pain but me.javascript:smilie(':eek:')

You know what I meant. :)

Originally posted by SFO
As far as the piston crown...
When you smoothed the transitions, did you radius the cutouts more?

Basically. I attempted to minimize the disruptive effect the cutouts would have on mixture motion in the chamber .
If you look at your original piston you'll see areas where combustion sort of stagnates, and what you can do to try and wake it up in certain areas. I tried a couple of new things in the combustion chamber my 97mm engine but it will take some time before I can tell if it had a positive effect.

 

[SFO]

STAGNATION....

Basically. I attempted to minimize the disruptive effect the cutouts would have on mixture motion in the chamber .
If you look at your original piston you'll see areas where combustion sort of stagnates, and what you can do to try and wake it up in certain areas. I tried a couple of new things in the combustion chamber my 97mm engine but it will take some time before I can tell if it had a positive effect.

The witness of combustion stagnation is the carbon deposit?
Rich, this notion of combustion/flame front motion/control is a bit new to me.
What would you regard as a optimum burn? What are you reading as a witness mark of the combustion motion? Is it the carbon deposit?
What have you changed in your chamber to create a more "complete?" motion?
Crisp jetting on race gas won't leave much in the way of deposits will it? Is that why it will take a while to determine if you are successful?
My oe piston had the bulk of its deposits shaped like a horse shoe, with the open end at the center intake valve.
so many motors to build, so little time!