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sskip75

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Reply with quote  #1 
I have an 08 450 mxr, with a thumper 540 bbk, that I'm replacing the crank on. When the crank went, it took out the cylinder and piston. I've had no problem with this topend set up at all. But i bought it about 5 years ago, and recent reviews of thumper are sketchy at best. I'm trying to figure out if anyone else does a big bore, or if i should take this back to a 525. I'm just trying to make this a stable machine, done searching for more power. Any advice would be appreciated.
TxOutlawRider

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Reply with quote  #2 
I'm going to go waaay against popular opinion here, but I have no problem with Travis at Thumper Racing.  I'm running a motor he built for me and other than some very minor problems (leaky head gasket that surfaced after a few rides- that when I called him he sent another at no charge). 
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2007 Outlaw IRS

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sskip75

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Reply with quote  #3 
I honestly don't have a problem either, my 540 was strong. Parts of the crank took out the cylinder and piston. Absolutely no fault of his. Im just a bit nervous with all ive read lately
TxOutlawRider

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Reply with quote  #4 
Quote:
Originally Posted by sskip75
I honestly don't have a problem either, my 540 was strong. Parts of the crank took out the cylinder and piston. Absolutely no fault of his. Im just a bit nervous with all ive read lately


I understand.  Apparently some people have had some issues, but my experience has been very good.  Over on the KTM Atv website, they seem to favor him. 

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2007 Outlaw IRS

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Rkangel

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Reply with quote  #5 
A factory KTM 525 top end would be the most stable and reliable option, IMO.  You'd still have a horsepower boost over the 450 but also still have the proven factory KTM parts.  Or you could try to find a factory KTM 540 kit, which may be hard or costly to find.

I've seen or heard enough documented cases of problems with aftermarket big bore kits, bad sleeves, out of round cylinders, heat issues, etc..., that I will stick with factory KTM when it comes time to rebuild. 

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2009 Polaris Outlaw IRS
Team Bricktucky

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Reply with quote  #6 
My thumper built Bottom end is still running great, Its been a year of heavy beating on it . I did have one issue with a sleeved cylinder, but I cant complain I got a discount and replacement very fast . However I didn't use that cylinder I installed a oem 525 cylinder and piston.  so I have a thumper 540 kit just sitting here waiting for my mxr 450 to die .
sskip75

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Reply with quote  #7 
I ended up ordering a piston through Thumper, 97+1/4mm, and had cylinder bored. Finally got it all back together, and it is running great
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