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Yamaha Telling if you have a stroker or big bore kit

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I am wondering if anyone know how you can tell if you have an aftermarket piston configuration or a bigger stroke on your movement. I bought the quad from a person who says that there is no internal engine work but this yfz 450 runs like no other I have ever riden before. Please let me know if anyone has any ideas on how I can figure this out. Thanks alot everyone and talk to you soon.

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It would be very difficult to find out if a motor has been modified without pulling the head off. You may be able to get a dial indicator down the spark plug hole to measure the stroke ( stock stroke is 62 mm ; stock bore is 95 mm ). If you have access to a bore scope, you may be able to read markings on the top of the piston to see if it is original or aftermarket. IMO if it runs great, leave it alone and just ride!:thumbsup:

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I am not sure where to even start looking for marks. It does however ride awesome. I am going to take a closer look. What would an oem marking look like. Forgive me I am ignorant on this subject. I have had problems with the intake cam jumping the timing chain and it bent all my intake valves. No assembly lube on the cam after reshimm. I know ignorant. Anyway I have fixed all that and had the head off and was just curious that maybe the piston had longer travel that I wasn't aware of and that was the reason it bent the valves. But I know why as mentioned above. There were heat seize marks on the center cam journal and it basically locked up and stopped as the engine kept spinning. I did have a mechanic look at the piston head and rod and crank and all is fine though. No cracks warping damage what so ever. He even went as far as to put a head on that was off his quad to make sure everything was still in order and it ran great. I have sense built a new head ported and polished with kibble white valves and springs and hotcams intake. Figured that it was a good excuse to spend the money. Thanks for the help talk to you soon

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I have not seen any marks on the piston at all. Where would they be at. The only reason I think so is because this quad runs with so much more power than even my buddies 08 yfz with the same basic mods. Maybe its because its mine. lol. Well I had a mechanic look at it at the local repair shop and he said that he wasn't sure either. If I figure anything out I will let you know and thanks for the help. Its greatly appreciated

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Ballplerstud. On the contrary it was torqued to much I believe and that is what cause the galling and heat marks on the center cam journal, if I can get a couple of pic I will upload them and you all can look. I through the cam away cause I got a hotcam and th valves were toast. Had to get a new head

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Well all the money and sweat were worth it by far. It runs great and better than before. I will definetly be doing this on all of my other quads I purchase in the future. Thanks for all the help talk to you all soon.

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