Top End rebuild question - Yamaha Raptor Forum
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post #1 of 3 (permalink) Old 06-09-2019, 01:41 PM Thread Starter
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Join Date: Jun 2019
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Top End rebuild question

This post might be a little premature due to the fact have not taken it apart to see the exact problem but appreciate any feedback. I recently purchased a 05 Raptor which has had a ton of mods. The person I bought it from didn't know a lot of the details. He said it had a big bore kit and cam that's all he really knew about what was done to the engine. Noticed it had some noise in the top end. To me sounded like piston slap and it was smoking pretty good was hoping it would last threw the summer and get it freshened over the winter. No such luck. Last night it gave up. Nosed over in high gear wide open throttle and died. Pretty sure it burnt the piston. My main question is who makes the best quality top end kits. I have built auto racing engines all my life but I am new to ATV engines so my knowledge is limited but I think I'm going to do the rebuild myself as long as its only the top end I'm not sure I would be comfortable splitting the case. I also am the type of person that thinks you get what you pay for so I'm not looking for the cheapest parts but best quality at a reasonable price. Thanks in advance for any feedback and will post more when I have a better idea of the damage.
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post #2 of 3 (permalink) Old 06-09-2019, 04:19 PM
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Join Date: May 2012
Location: Northern Colorado
Posts: 7,663
Welcome to the forum,

Without knowing exactly what size piston you currently have, best bet would be to open it up and check the size prior to ordering new piston and rings. CP Pistons seem to be the choice throughout this site.

[U]2006 raptor 700

DMC Force 4's, FCI W/box, Dynatek Fusion,
CP 11:1 piston, BaMotorsports porting, HC3
RacersEdge +3TB
YFZ 450 fronts & reworked rear by JOGACA
Trailtech 1 1/8 xbar w/vapor dash & Vapor installed
ODI Rogue grips & ASV pro pack levers
Fastway steering stabilizer
68HP 49TQ

PM me if you need service manuals
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post #3 of 3 (permalink) Old 06-12-2019, 07:15 PM Thread Starter
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Join Date: Jun 2019
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Ok got it tore apart. Piston is scored also damaged the cylinder and the piston pin was seized. Did discover it had been bored but was not a 686 big bore it was only bored to 100.5. But it did have a wiseco 11:1 piston in it. The person I bought it from said he ran it on regular pump gas. In the automotive world that kind of compression will eat a motor on pump gas so Im thinking that could have been the cause. Any input on that would be helpful. Now I have a question about the rod bearing. The rod has no play end to end but has about 1/8 inch of play side to side. Is this excessive and a sign that the rod bearing is about gone? Don't want to fix the top end just to have bottom end to come apart soon after.
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