super duty wrist pins

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wistech · #1 Post by **wistech** » Sat Sep 26, 2009 3:59 pm

One of the worst failure an engine can have is a snapped wrist pin. We have all heard the horror stories of of the WWE /ATK pistons and there sad history of short timers disease. I think its obvious the cup design with the wide bridged space is whats causing the issues . There is only one way to try to control piston flex and that is with a stronger wrist pin. I knew it was suicide to install the paper thin garbage stock wrist pins so we went with a thicker CP wrist pin . I tapered the ends to keep the weight down as much as possible and that seemed to work pretty good. I think in engine running low horsepower they would hold up for quite a few years but since all of mine are well over 50 horse it has become an issue again. Although I will never run the cup design pistons again maybe this will help out for those who are on the edge of the inevitable fatigue failure inherent in the design. As you can see by the pics the wrist pins in these pistons are spinning around and moving like mad.
The two one the left are the atk pins and the one on the right is the thicker CP .

wistech · #2 Post by **wistech** » Sat Sep 26, 2009 4:42 pm

Since they are breaking in the middle I am trying out a new .200" thick pin that will be taper bored from the ends to lighten them up. Hopefully this will be the cats meow for the hard hitting nitrous as well. i am gong to drop the rev limiters down as well as stress is increased much more above 10,000 rpm.

Kuma · #3 Post by **Kuma** » Sun Sep 27, 2009 12:09 am

QUOTE (Wistech @ Sep 26 2009, 09:42 AM) <{POST_SNAPBACK}>

Since they are breaking in the middle I am trying out a new .200" thick pin that will be taper bored from the ends to lighten them up. Hopefully this will be the cats meow for the hard hitting nitrous as well. i am gong to drop the rev limiters down as well as stress is increased much more above 10,000 rpm.

Why can the 2 strokes get away with thinner lighter wrist pins? is it because the same HP is has twice the powre strokes so the load is actually 1/2?

Kuma · #4 Post by **Kuma** » Sun Sep 27, 2009 12:09 am

does anyone have a titanium wrist pin? must be plenty tough

cannondale27 · #5 Post by **cannondale27** » Sun Sep 27, 2009 2:09 am

Titaunium flexes too much. 2strokes can get away with it because the skirts are so long on the pistons they offer support the wristpin is lacking.

fast moto · #6 Post by **fast moto** » Thu Oct 15, 2009 10:40 pm

Aperaceparts makes some tool steel wrist pins they claim are pretty strong. http://aperaceparts.com/wristpins.html Do you guys think the ones for cp pistons would be just as strong as the ones Tim sells but lighter?

wistech · #7 Post by **wistech** » Thu Oct 15, 2009 10:48 pm

Funny you should mention them. They are the guys I have turned to for the prototype pins. Kuma's assement on the wrist pins is correct. The other thing that comes into play with our engines is stress buildup as rpms increase. Hard to believe but most 4 strokes have to move more mass at much higher rpms than the 2 strokes ever did. Our pistons are the same size as you would find in a standard v8. Just think what it would take to spool your small block chevy up to 10,000, 11,000 + rpm. This is where our little single runs all the time.

fast moto · #8 Post by **fast moto** » Fri Oct 16, 2009 1:34 am

So do you think the ape wristpins would work well with the Cannondale cp pistons?

peterock · #9 Post by **peterock** » Fri Oct 16, 2009 2:11 am

I guess I have to ask how many wristpins have actually failed. Talking about cp and the stockers?

cannondale27 · #10 Post by **cannondale27** » Fri Oct 16, 2009 3:52 am

You need to remember that many of these wristpin failures were on the junk pistons that Wade had designed.Yes CP made them but they are his design.I believe they were so bad that Timbo gave them away and threw the rest in garbage.Nothing like the CP's Timbo sells.If any of Timbos CP's had wristpin failures I cant think of any.Stockers either.