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2006 YFZ450
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4 Posts
Discussion Starter · #1 ·
Hey everyone. Been lurking a while but I finally decided to make an account and share this definitely fun, not at all frustrating experience.

I've got a 2006 YFZ450 that had the top end go kaboom on me a few weeks back. Best guess of what happened was an overheat scenario likely caused from a mix of poor cooling flow and lean top end (it's been pretty damn hot here in Utah).

So I decide that since the OEM cylinder is ovaled pretty hard and the piston is definitely shot, might as well go big bore. Bought the Athena 98mm (480cc) kit and a boyensen hi-flow water pump. Everything went pretty smooth on the install. I'm a motorsports mechanic professionally, so I've got all the tools and experience to do this right. I made sure everything was torqued properly, made triple sure cam timing was good to go (cam mod, too), valve clearance, etc. Fire up and start doing the first heat cycle per the service manual and Athena's recommendations (which is to follow Yamaha's engine break-in procedure). Did all that and moved on to carb tuning (which was a large part of me lurking this forum, if I'm being totally honest). Got the pilot circuit figured out, moved on to needle position.

Went to start up with the new needle position fixed and it rolled halfway before I heard a bang. A loud one. Not a backfire or afterburn, either. Something internal. Killed power, popped the spark plug out, popped the crank bolt cover and tried to roll it by hand.

The piston was seized near BDC on the down stroke.

Turns out, I've got a few big and pretty hairline fractures around the bottom of the cylinder and the piston is now scored to hell and back. I've yet to run a dial bore gauge down it but judging by how hard it fought me to get the cylinder off the piston, I'm guessing it warped some sort of way. Piston rings were still fully seated and comfy in their channels on the piston, no broken bits. Valves, cams, and cam chain were all still good to go. No bends, breaks, or otherwise. Made sure coolant was topped off and properly bled and oil was properly replaced and ready to go before the first heat cycle. Soooooooooooo yeah. I'm at a loss on this one. Mentally and financially. I'm not sure what to do about it right now, honestly. Still just kinda trying to process the whole thing before I make any irrational decisions that involve my engine and a healthy amount of thermite. I'm not sure it's even worth trying to reach out to Athena about this since they clearly state in every bit of paperwork that they're not liable for anything that happens after unboxing the parts.

Oh, and for all the carb guys, I got as far as the following
pilot - 45
2 1/2 turns out
NCVQ needle 4th from the top
5000ft elevation, ~90-95 degree summer heat
Other mods include Ron Wood intake and exhaust. They came with the machine when I bought it so I'm not sure how old they are but I don't see the exhaust on their website. Probably an older version of the racing exhaust.

That got my idle figured out, at least. Maybe that'll help someone else who lurks like I do.
 

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959 Posts
That really sucks. I would make sure that your rod bearing does not have any play. I really couldn't see that happening very easy without something moving that shouldn't be.
 

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2006 YFZ450
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4 Posts
Discussion Starter · #4 ·
Rod bearing is fine, though now I'm concerned that whatever happened with the cylinder may have caused issues down the line. I'm currently in talks with my distributor and Athena about what to do, as all signs point to manufacturing defects that slipped past their QC/QA. Since this will likely take a while, I'm probably going to take the time to tear down the bottom end and do a thorough inspection. Might just end up replacing all my bearings and oil seals and stuff while I'm in there anyways. Buddy of mine dropped the idea of going stroker while I'm in there, but that's gonna need some more research before I commit to anything besides just getting the damn thing running again, lol. I've got time. Was really hoping I'd have the carb dialed in and the machine ready to ride for this weekend, but here we are. Just the way she goes sometimes.

However, I do have my YZ450F I can ride for the time being, so there's that. Maybe I'll steal the wife's Grizzly and go romp the hills with that 700cc tank, lol. Not like I'm gonna be building an engine this weekend as of right now.
 

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2006 YFZ450
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4 Posts
Discussion Starter · #5 ·
My apologies if I'm reviving an otherwise dead thread, but I have an update to the situation.

After several long talks with Athena on a one-on-one basis, they more or less told me to kick rocks because "A shop didn't install it". I am "the shop". A Yamaha-certified technician performed the inspection with me and we had both declared everything was good to go prior to the installation. Between the two of us, there is more than 35 combined years of experience, knowledge, and tooling for engine building and performance modification work. No matter. The failure happened anyways and I don't care to try to point fingers about it. This reply is to provide closure and a warning to all who may read it.

I got on the phone with one of my sales reps for the dealer I went through to get the big bore kit. Explained the situation, etc. I ended up having to send the entire kit back and basically sit and wait. Eventually, I got a refund for the kit. Nothing for the additional damages sustained to the engine, but I got my money back at least. They never gave me an update as to what exactly happened. We suspected a manufacturing defect, like a porous cylinder wall, but it's purely speculation. I eventually rerouted my returned money into a Wiseco garage buddy kit with a Cylinder Works jug and Hot Rods water pump rebuild, transmission, and counterbalance bearing kits. If I'm going to split case halves, I might as well make it worth my time and just go all the way at that point, you know?

The engine rebuild was completed tonight. So, the Athena kit definitely caused some minor but salvageable damage to my case halves. The big end connecting rod bearing was definitely pulverized and was now binding about a quarter way through its rotation. Educated minds think the piston seized due to the cracks in the cylinder, which then caused the crankshaft's momentum to plow into that bearing and turn half the bearing into a metal paste. Said metal paste was everywhere, but the oil pickup screen and oil filter did their best to save the oil pump and not clog the oil ports with the larger chunks of shattered bearing rollers.

The crankshaft is definitely ruined either way, so it will be going on my wall of shame. But, the engine is as refreshed as it ever will be again, minus new valve springs and a clutch. Those are coming in the off-season. I decided to stick with OEM spec bore for now, as the situation with Athena has left me weary. I completely understand their perspective and I respect that they stood their ground initially, but they doubled back on that after I returned the big bore kit. I don't know why they changed their minds, but I won't raise a torch about it. Stuff happens when you pin it to win it. I'm just glad the failure happened in the shop and not when I'm sailing across a 60'+ gap or halfway up a sketchy hill climb.

In closing, I want to say again that this is not about bashing Athena or their product. Plenty of people have used their cylinder kits to great effect and I'm not about to try and tarnish that from my little soapbox. This is purely to provide closure to the situation and remind the less experienced that sometimes stuff happens when you least expect it. This is why people will tell you stuff like do your post season inspections and repairs, break in your stuff properly, always tip your bartenders, use quality gas, and wash your damn machine before you take it to a mechanic. Had I thrown a leg over and just sent it, I probably would have had a much worse experience overall. The situation sucked to live through, but now we're here and my engine is damn near ready to rip and tear.

Stay safe out there.
 
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