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Discussion Starter #1
In theory, on our engines, would it be possible to have a 72mm crank with a 6mm shorter rods?....couldnt you keep the pistons you have with this instead of having special ones made?...or is there some reason no one has done it...

I've been pondering this for a while...:confused::confused:
 

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First off this is only speculation as I don't know the clearances and tolerances of these engines but my intial thoughts would be the area of concern would be the longer throw of the crank would bring the piston lower down in the cylinder lining on the downward stroke, coupled with this if you had an even shorter rod it would be lower still, maybe too low? I don't know!
 

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It doesn't work like that.

If you stroke +6 in reality the pin is only moved 3mm. It raises the piston 3mm and lowers the piston 3mm.

You could if you get the swing weight of the crank undercut as it will never make the pass at BDC.piston would hit the crank. pin is too low

Now you are changing the piston rod angle which will also put additional side load.

Easier way is to run a spacerplate under the lower jug, but then the piston skirt gets exposed more. and you need longer chains.

John
 

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Discussion Starter #4
I thought about the side load on the piston and dont think that would be a problem...thats one of the reasons I thought about doing it this way...if the piston and cylinder ever start rubbing it would be easier and quicker to get a new standard 88 or 89 mm piston and bore the cylinder...didnt think about the swing weight though...I would think machining it down would be benificial..less rotating weight...I would also have to lose weight on the opposite side of the crank of course but as long as it would hold I think it would be great!....I was just wanting something outside the box...a PP&P 875 stroker.:D

Yall let me know if I'm stupid..Im going to the machine shop today to talk with them in 2 hours...
 

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When you add stroke, you have to add weight, My stroker crank is undercut, and has Mallory slug added to the bottom for counterbalance.

I run the stock length Falicon rods, shorter piston w raised pin, and balanced and undercut crank falicon crank.

this is a 950cc setup. 947cc actually. my own JE 92mm pistons and my own custom 71.25 stroke crank for the added trough clearance.



you can see how they undercut the crank. I use the long rods and it was even a problem with hitting BDC even with the custom pistons.

If you want a 72mm crank I have one. It spun a bearing and needs the journal repaired, it's already stroked to 72mm. easy fix for someone that wants a cheap stroker crank.

John
 

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What's up Cole? That little ol 800 not enough for ya anymore? Or are you just trying to keep ahead of Chance and me?
 

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Discussion Starter #7
The 800 is plenty...:eek:I quit trying to play keep up when I got layed off...and Its a good thing because me and Chance would have a hell of a time blowing money to one up our bikes...(we might play when the railroad calls me back though):D:D

sent ya a pm John...
 
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