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SippinOnTheOrangeJuice

What should I know when swapping cases? 06-09 YZ450F

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Hey everyone,

 

Just picked up a super clean, very low hour '07 YZ450 that has a cracked case. Low hours like under 50. I have a fellow TT member breaking down a bottom end right now to sell me the cases and what I am wondering is what should I replace while I am in there? I know clutch is good and valves are still in spec, piston has to be good with the amount of hours. Do I need to replace piston rings because it was torn down? I know I will need a full gasket set but is there anything else? I have the abillity and tools to complete the job just looking for some helpful insight on what I need to check out or look for while it's torn down. Thanks for any responses and tips.

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Look for a way to get the chain to stop clashing with cases. Your the 4th person this year I have heard of needing to have a 06-09 yamaha 450 re-cased due to broken cases from(what looks like in your pic) chain damage. Your the first person I have seen that is going to actually try to fix the bike. 

 

Only tip I have is that the cases are matched to each other so you need a set of both left and right side. replacing the broken one only is not recommended. 

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Look for a way to get the chain to stop clashing with cases. Your the 4th person this year I have heard of needing to have a 06-09 yamaha 450 re-cased due to broken cases from(what looks like in your pic) chain damage. Your the first person I have seen that is going to actually try to fix the bike. 

 

Only tip I have is that the cases are matched to each other so you need a set of both left and right side. replacing the broken one only is not recommended. 

Yeah I bought the bike off craigslist for $1500 just for something to do. I do know that you need a complete set of cases and that is why I am going used, new is around $750. The only thing I can think is a nice aftermarket case saver, obviously the stock one isn't doing it's job. The bike ran fine with the case cracked just leaked oil, I test rode it to check that the gears still shifted smooth. I was going to try to re weld the broken area but after cleaning off his JB weld job there was a decent sized chunk missing, I don't like half assed stuff so that is why I am just going to swap cases.

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The way to keep the chain from breaking the cases is to stop breaking chains.  If you run a good, premium chain, and actually replace it when it becomes worn beyond specs, periodically inspect the master link clip, etc., you simply won't have the problem.

 

Far too many people will either run the chain too tight (because the spec'd setting "looks" loose, or to get rid of the slap at low RPM loaded, and/or will run a chain well beyond it's specified wear limit, and end up tossing the chain, which will inevitably get wadded up between the sprocket and case and all that horsepower.   Of course it breaks the case.

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The way to keep the chain from breaking the cases is to stop breaking chains.  If you run a good, premium chain, and actually replace it when it becomes worn beyond specs, periodically inspect the master link clip, etc., you simply won't have the problem.

 

Far too many people will either run the chain too tight (because the spec'd setting "looks" loose, or to get rid of the slap at low RPM loaded, and/or will run a chain well beyond it's specified wear limit, and end up tossing the chain, which will inevitably get wadded up between the sprocket and case and all that horsepower.   Of course it breaks the case.

 

Yeah like I said I bought it that way, he told me it was the master link that came apart. Anyways, Gray, you seem to be the Yamaha master tech around here. Any helpful insight on waht I am about to attempt?  Thanks.

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Not really.  It should be just as simple as replacing with new OEM.   The parts fiche at Yamaha calls out the specific contents of the gasket sets.  They DON'T contain all the seals you might need for the job, like the crankshaft oil seal in the right crankcase cover, so look that over.  As far as bearings, obviously the best course is all brand new ones, but that adds up big by the time you get all of them.  Check them and use your own judgment. 

 

New rings, of course. 

 

As far as welding the old cases, that's a bigger deal on YZF's than many others because there is an oil passage running through that part of the case that needs to be re-drilled, etc., after such work, so things are more complicated.

 

The stock "case saver" isn't a case saver, it's a chain guide, intended to keep the chain from "overshooting" the front sprocket at speed while the top run of chain is slack due to deceleration.  Any of the aftermarket "savers" that don't bear against the back of the flywheel housing won't help very much, anyway, and as I said before, the best case saver is a good chain, properly maintained.

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