06 450 Broken engine case - advise needed

Hey guys, I have an 06 yz450 with 34 hours on it. I replaced the oem chain after the first ride with a DID chain, then replaced the oem sprockets at about 20 hours with Primary Drive sprockets.

I was out for the second time this season at a MX practice and had a minor disaster:

285534819_gRnsc-L.jpg

285532767_SmBzd-L.jpg

The chain snapped and went into the case after landing a smaller double as normal and coasting into the corner at the very end of the day. I was actually on my last laps before heading to the truck, I was only out there to pace my buddy over one of the jumps.

So I have found the cases sold as a set on most yamaha oem parts stores online for about $520. There is a guy offering them on ebay for the 06-07 for $265. Sucks, but I guess it's not horrendous pricing.

Can anyone shed some light on the process of tearing the motor apart and rebuilding? What am I going to need for additional parts/gaskets? Recomendation for a good shop manual? Is there anything that should be replaced with only 34 hours on the motor? Any tricky steps that I need to watch out for?

I did have a good day and did all the jumps for a change and took some pictures:

286727436_kbuXW-L.jpg Me

286726356_T4xQH-L-1.jpg

Nate

New at crotchrocket.com is just over $400 with shipping. I ordered a set yesterday for my '04. I normally buy at oem.thumpertalk, but they wanted $35 more, so I figured I would try another source once.

If you haven't split cases before, watch the rockymountain videos on youtube. I also used post-its to map out all the steps in the manual. The book is good at getting it apart, but not clear on putting it all back together.

Good luck.

When exactly did the chain break?

Im going to guess that the chain broke on the landing of the double (didn't case it or bottom out). I just coasted into the following corner about 15ft and when I went to get on the gas again I noticed the free rev, kicked the shifter and free reved again. looked down and my left boot was oily & smoking and hit the kill switch.

Ill check the wheel alignment and make sure nothing came loose tommorrow when I get to the garage to wash the bike and start taking it apart.

Hey guys, I have an 06 yz450 with 34 hours on it. I replaced the oem chain after the first ride with a DID chain, then replaced the oem sprockets at about 20 hours with Primary Drive sprockets.

I was out for the second time this season at a MX practice and had a minor disaster:

285534819_gRnsc-L.jpg

285532767_SmBzd-L.jpg

The chain snapped and went into the case after landing a smaller double as normal and coasting into the corner at the very end of the day. I was actually on my last laps before heading to the truck, I was only out there to let my buddy pace me over one of the jumps.

So I have found the cases sold as a set on most yamaha oem parts stores online for about $520. There is a guy offering them on ebay for the 06-07 for $265. Sucks, but I guess it's not horrendous pricing.

Can anyone shed some light on the process of tearing the motor apart and rebuilding? What am I going to need for additional parts/gaskets? Recomendation for a good shop manual? Is there anything that should be replaced with only 34 hours on the motor? Any tricky steps that I need to watch out for?

I did have a good day and did all the jumps for a change and took some pictures:

286727436_kbuXW-L.jpg Me

286726356_T4xQH-L-1.jpg

Nate

What track were those pictures taken at? I live in Delaware & always looking for a different place to ride.

correct me if im wrong, but dont you have to buy both main cases as a set because they are machined to match?

correct me if im wrong, but dont you have to buy both main cases as a set because they are machined to match?
You are correct, but that's what the quoted prices are for.

The track was Irish Valley MX in PA. www.irishvalleymx.com is the website

wow man thats ruff. a guy that i knew had the same thing happen to him he slaped some jb weld on ithahaha

You are correct, but that's what the quoted prices are for.

so does this mean that we can't use another piece of crankcase that are sold from ebay? even though it's the same year.

I had a similar problem with my chain which split my case open and ended up costing me mucho $. You'll need the 2 case pieces sold as a set to replace it.

You need to change the cases as a set becuase they are likely cast as a single "block" then cut into 2 halfs. So if the cut down the center is not exactly the same between two sets of cases, when you mix and match them you can get different clearances for the bearings.

For a bike that is this new and everything else on it being in mint shape, I don't want to rig it in any way. Id rather spend more now, fix it correctly, and know it was done right.

I had to go through the same thing on my '03 when it was only a few months old. My chain didn't break but it did fall off when a small rock got in just the right place. Same result. It was my first time taking apart a 4-banger but I had plenty of experience with replacing gears and such in 2-smokes.

At any rate the biggest difficulty was in recovering the bearings out of the used cases. It would have been much easier to buy new ones but that's a lot of bearings I'm just too damn cheap. You really need special tools to remove the bearings without destroying them. I didn't want to buy those either. What I had to do was totally destroy the used cases by cutting the bearing out of the pockets. That was a real pain in the butt and then I had to spend a lot of time making sure they were completely clean before installing them in the new cases. :eek:

Maybe someone else can give you some tips in getting the bearing out? I sure hope so.

Have fun.:p

--KT--

The cases are made as two separate parts, up to the point where the major shaft bores are cut. During that operation, they are bolted together.

The only bearing that is hard to remove is the left side main shaft bearing, fro which you can use most any blind bearing puller. It helps to heat the case to 250 in an oven, too. However, that bearing is also the one of most likely of all to fail. IMO, if you do this much work on the bike, you should replace all of the bearings for the crank, balancer, and trans at the same time. The shift cam bearings experience far less wear, and can be reused if they appear in good condition.

Put a new cam chain in too :eek:

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