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Reducing piston weight XL500 s

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I have built a couple of motors in my time, the last one I did was a motorised pushbike motor, I extensively ported, balanced / shaved the piston skirt and reduced piston weight, changed port timing.. parts are $10 each for just about everything so plenty of fun to play/experiment/ learn with.

 

I got a 1mm oversize forsetty piston kit and was wondering if I should reduce pistin weight or add more lube holes for the oil rings before installation, who has experience with these? IMAG0554.jpg

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Nice idea, but if you start reducing the piston weight, you could upset the engine balance. But it's a challenge isn't it ! ..... go for it and see what happens. The parts are cheap enough.

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Yes, according to the Honda shop manual for the XL500s the engine balancer system is the same weight as the piston and con-rod. The balance goes down when the piston and con rod go up. Thats a simplification but close enough. So if you take weight off the piston you might have to take weight off the balancers.

Then again some people simply remove the whole balancer system..

 

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Just put balancers back into aa bike which PO had removed. 

 Bike much nicer to use and revved free=er.

     I wouldn't mess with piston or balancer system.

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I still have several of those engines around.   Most of mine ended up with large pistons in them.   What i did try to do with reasonable success was to get the weight of the big ones down to the weight of the original piston and pin.  Running a single compression ring worked pretty well on arias pistons.  Rev'd freer too.  Short life,  but ice and flattrack pistons don't live all that long anyway.  Beefing up the plate that acts as a chain adjuster was a good idea.   Just building it up with the wirefeed was handy,  or you could gusset it.  

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Agree. Keep ng things balanced makes perfect sense,, but to deliberatly un-balance could be a bit daft.

     Any professional race engine builder would balance to keep internal stresses to a minimum.

             OP would be better off going to a higher comp than shagging around with a grinder.

         Standard is only 8.6........

Edited by Muzz67
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our best running xrs made the most overall gains with pistons no more than a mm oversized with compression ratios that were in the 12-1 range.  All of them used cams from megacycle and you needed some of the added static compression numbers just to compensate for the added overlap and duration.  If you ever looked at one of the heads that engine dynamics ported you get an idea of what to do on your own.   Al Baker could build very good ones,  I doubt anyone at that business that kept his name has done one of the early 500's.  

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