Top end rebuild - Yamaha YFZ450 Forum : YFZ450, YFZ450R, YFZ450X Forums
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post #1 of 2 (permalink) Old 08-05-2011, 11:32 AM Thread Starter
Join Date: Feb 2011
Location: Fayetteville, Arkansas
Posts: 39
Lightbulb Top end rebuild

Alright I have a yfz 2004. The piston locked up and snapped the connecting rod about two months ago. I have been slowly rebuilding everything. I have completed installing a new crank and crank bearings (hot rods heavy duty crank and hot rods bearings). I have cleaned what i hope to be all the little shavings out of the bottom cases and plan on putting the clutch and all the covers back together tomorrow evening. I picked up my head monday from the machine shop. I had 5 new titanium valvues and all new springs put in the head. When the connecting rod snapped the piston scared a place in the head and he also grinded it down and refinished it. One of the value guides were cracked as well and had to be fixed. So basically he completely over hauled the head. Now I am to the step of installing the new factory cyclinder and a high compression piston. I have heard that there are specific ways you have to tighten the bolts when installing the top end. I am just looking for the do it yourselfers out there that have gathered tips over the years. This is the first motor that I have built and could use any tips. SMALL AND BIG!! Everything is much appreciated! Thanks for taking the time!

2004 yfz 450-XC
Full Skids
HD Hot rods Crank
High Comp Wiesco Piston
Adjustable axle
2005 yfz 450-XC
WR Crank
Works Big Bore
Ported and polish head
Stage 3 exhaust hot cam
Works Pro series shocks
Plus 1.5 a-arms
Adjustable axle
Flexx Bars
Full Skids
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post #2 of 2 (permalink) Old 08-05-2011, 04:19 PM
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Join Date: Nov 2008
Location: bc/alberta
Posts: 1,819
If you do a search on here there's service manuals an follow the sequence and torque specs and you shouldn't have an issue.
Make sure cylinder and head are free of oil on the gasket surface, put moly grease on the threads of the bolts,

04 YFZ. WR crank, MMAD 14.25 piston, CW 98mm, KW ss Valves, KW spring, Velocity head, YZF cams, GYTR Kickstart, Dyna FS, Nology coil, Rossier exhaust, Tusk clutch, FCI intake, Boyesen quickshot R&D fuel screw .
Elka triple rate front & back, Houser +2 arms, +1 swinger & +2 stem, G-force axle, Streamline lines, wave rotors, AC nerfs, IMS pegs, douglas beadlocks, MXR6 tires, Pro taper bars, ASV levers, Gibson stablizer, MP twist.
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