Author Topic: Stroker Wrist Pin Placement  (Read 1980 times)

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Offline jlmccuan

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Stroker Wrist Pin Placement
« on: October 25, 2012, 10:22:55 PM »
Just trying to get some "been there, done that" advice.  I'm building a stroker motor whis is pretty much at the ragged edge in a few areas.  My question is "What would be the ideal wrist pin position with the crank at BDC"  My thinking is that if the wrist pin is at the bottom of the cylinder or below, the only thing keeping the piston from wedging and cocking in the bore is the rings.  But, how far can you push this.  Max revs 7,000 rpm.  Please make your recommendations and a summary of why.  Maybe there is something I can do with the block to work as a guide for the piston skirt which extends out the bottom of the stroke.
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Offline wobblywalrus

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Re: Stroker Wrist Pin Placement
« Reply #1 on: October 25, 2012, 11:22:56 PM »
Jim, installing longer sleeves might be a solution.  Just make sure the connecting rods do not hit the bottoms of the sleeves during mid stroke and the flywheel weights don't wack them.   

Offline jlmccuan

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Re: Stroker Wrist Pin Placement
« Reply #2 on: October 26, 2012, 09:08:15 PM »
Does anyone have a range of typical successful engines' dimensions for wrist pin to bottom of cylinder?
Rabid Snail Racing

Offline JimL

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Re: Stroker Wrist Pin Placement
« Reply #3 on: October 26, 2012, 11:13:19 PM »
You can have the wrist pin located behind the rings, except top ring, to keep rod length.  One method, if you only move behind the oil ring, is a simple bridge.  To position behind the oil ring and number 2 ring requires a tight fitting aluminum insert (with lands), using a shorter wrist pin.  Number 2 ring is a busy guy, moving and blocking  heat, it needs to be able to do its job.

Your piston maker can also squeeze the compression ring a little higher on the piston, but it shortens the life, and has very little strength during detonation.  I still have one out of my first drag bike, that has nearly all the pieces of that high-mount top ring, neatly embedded in the dome in a pretty starburst pattern....like a flower, lovely!

Keep all the rod length you possibly can.
JimL