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 Post subject: piston rework 420 Kuda
PostPosted: Wed Feb 23, 2011 8:55 pm 
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Joined: Sat Jun 30, 2007 7:45 am
Posts: 1040
Location: hole above ground
this is work done to yz490 piston for kuda fl350 race Engine
shorten bottom skirt and cut intake window

just copied old piston

Speed


Attachments:
File comment: cutting skirt down to match old piston
DSCN4004.jpg
DSCN4004.jpg [ 396 KiB | Viewed 2856 times ]
DSCN4005.jpg
DSCN4005.jpg [ 374.51 KiB | Viewed 2856 times ]
File comment: checking height of each
DSCN4006.jpg
DSCN4006.jpg [ 404.52 KiB | Viewed 2856 times ]
File comment: yep there the same pin slides in both
DSCN4008.jpg
DSCN4008.jpg [ 388.16 KiB | Viewed 2856 times ]
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PostPosted: Wed Feb 23, 2011 8:56 pm 
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Joined: Sat Jun 30, 2007 7:45 am
Posts: 1040
Location: hole above ground
cutting window on intake side



SpeedChaser :-)


Attachments:
DSCN4009.jpg
DSCN4009.jpg [ 451.39 KiB | Viewed 2855 times ]
DSCN4010.jpg
DSCN4010.jpg [ 507.93 KiB | Viewed 2855 times ]
DSCN4011.jpg
DSCN4011.jpg [ 384.66 KiB | Viewed 2855 times ]
File comment: .422 x 1.140 with top cut at 21mm from the center of wrist pin
DSCN4012.jpg
DSCN4012.jpg [ 357.58 KiB | Viewed 2855 times ]
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PostPosted: Wed Feb 23, 2011 9:42 pm 
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Joined: Mon Dec 15, 2003 2:40 pm
Posts: 22512
Location: Chicago
Sweet, is their any material you can remove from the sides to lighten the pistons?


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PostPosted: Thu Feb 24, 2011 12:28 pm 
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Joined: Wed Jan 14, 2004 8:45 pm
Posts: 2243
Here are some pics of the spare piston that came with the 400 stuff. Some are ready to use, some need skirt work n a window. You can see the longer skirt on the one side of the YZ490 piston. Now, what the factory did to keep the "balance" of the pison on the rod was move the wrist pin hole off center. When we remove part of the long skirt(to keep it from bottoming out in the 350 bottom end, 350s shorter rod), it becomes heavier on one side. I ran it like that for a while in my Leckich but after about a year, it started pinching the alum wall onto the ring/ring groove(sticking ring)...had to open it back up. Kinda worried about the weight unbalance at high rpms. The next piston I cut the skirt off of, I tried to figure the rough amount of material removed then remove that much from the other (arched) side. That was 3 years plus ago and so far no issues...knock on wood. I will be pulling the Leckich Engine soon for another inspection...and probably swap in a Briggs setup to try some trial runs.

Just thought you may want to know about the balance/wristpin issue and what I am trying to compensate for it. Any other ideas are appreciated.

Gary


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PostPosted: Thu Feb 24, 2011 12:30 pm 
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Joined: Wed Jan 14, 2004 8:45 pm
Posts: 2243
oops, pics...derrrrrrrrrrrrr


Attachments:
pistons 490.jpg
pistons 490.jpg [ 109.77 KiB | Viewed 2836 times ]
pistons 2.jpg
pistons 2.jpg [ 118.01 KiB | Viewed 2836 times ]
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PostPosted: Thu Feb 24, 2011 5:19 pm 
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Joined: Sat Jun 30, 2007 7:45 am
Posts: 1040
Location: hole above ground
Nuke Em wrote:
Here are some pics of the spare piston that came with the 400 stuff. Some are ready to use, some need skirt work n a window. You can see the longer skirt on the one side of the YZ490 piston. Now, what the factory did to keep the "balance" of the pison on the rod was move the wrist pin hole off center. When we remove part of the long skirt(to keep it from bottoming out in the 350 bottom end, 350s shorter rod), it becomes heavier on one side. I ran it like that for a while in my Leckich but after about a year, it started pinching the alum wall onto the ring/ring groove(sticking ring)...had to open it back up. Kinda worried about the weight unbalance at high rpms. The next piston I cut the skirt off of, I tried to figure the rough amount of material removed then remove that much from the other (arched) side. That was 3 years plus ago and so far no issues...knock on wood. I will be pulling the Leckich Engine soon for another inspection...and probably swap in a Briggs setup to try some trial runs.

Just thought you may want to know about the balance/wrist pin issue and what I am trying to compensate for it. Any other ideas are appreciated.

Gary


you know you got me thinking and I measured the piston up and the wrist pin is in the center of the piston
so was there another reason for the longer skirt on one side ?

confused speedchaser :-)


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PostPosted: Thu Feb 24, 2011 10:31 pm 
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Joined: Fri Jan 12, 2007 2:17 pm
Posts: 3620
Location: Wichita ks
Nukem/Speed could be a couple of reasons as far as the pin offset/skirt it has an effect on the wrist pin bearing, big end bearing, rod and crank bearings. It allows the crank to roll as it reaches TDC (Top Dead Center) instead of slaming to a stop and then starting up again adding vertical load to the crank train. It provides more of a rotational motion at TDC (Top Dead Center). Depending on the offset the skirt will have more wear from the added force (slap)on that side. The side it rolles to will need more skirt surface area. Also the exhaust port side skirt will need to maitain ex port clouser when At TDC (Top Dead Center). If you raise the skirt to far it will expose the ex port. With the piston in the jug set at the approate deck turn it upside down and check. I alway mark this so as I clean up and match ports I do not take the EX down to far. Just a couple of thoughts.


Attachments:
Piston positions at port timing.JPG [84.29 KiB]
Downloaded 98 times
Old piston incylinder for check and lay out..JPG [91.44 KiB]
Downloaded 98 times
Setting limits with the piston used.JPG [100.82 KiB]
Downloaded 98 times
New intake layout.JPG [112.47 KiB]
Downloaded 98 times
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PostPosted: Fri Feb 25, 2011 8:29 pm 
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Joined: Sat Dec 11, 2010 11:07 am
Posts: 421
Location: Cheyenne, Wyoming
Nuke Em wrote:
oops, pics...derrrrrrrrrrrrr

Old mans losing it :-)


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PostPosted: Fri Feb 25, 2011 10:48 pm 
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Joined: Wed Jan 14, 2004 8:45 pm
Posts: 2243
I just checked these new pistons, all the wrist pins holes are centered. I may be losing my mind or remembering a different project combo. Hate this getting old crap. lol I need to get to my garage in Cheyenne and find my notes on the Leckich 420 setup.

Sorry for the confusion, my bad. Nice job on the explaination Adnoh. Like the pics too.


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PostPosted: Sun Feb 27, 2011 5:32 pm 
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Joined: Fri Jan 12, 2007 2:17 pm
Posts: 3620
Location: Wichita ks
Thanks Nukem, Here is a pdf of some #s using piston pin offsets. You can see how they relate to skirt postion when cutting piston to fit alternate applications as well as changing port timing and cyliner volumes.


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