ReX
TY 4 Stroke God
rehm70 said:I have a feeling the problems with failure are attributed to Yamaha's horrible engineering decision for the reverse system.
My Doo was much. more simple as far as the chaincase goes, and when I trued my Apex drivers, and took the cover off of the chaincase, I was appalled at the conglomeration of crap in there!!
I believe with all of those extra pieces, the whole case runs hotter, then burns the seal out and lubrication is lost.
I also understand the breakage when the brakes are applied hard. Because there is so much slop in the HEAVY gears Yammy uses, the chain/gears can't take the stress from throttle to full brake and they lunch.
This is unacceptable for a machine that is otherwise engineered very well.
My friend had his case cover off of his Mach Z, and there isn't even a chain tensioner in the thing!!
There is no doubt in my mind that the Mach's drivetrain is far more efficient than our Yammies and explains why (among other reasons)a well tuned Mach will dust our behinds.
I guess I can take one negative to owning a baddass Apex..................
I couldn't disagree more with some of your statements.
Prior to Skidoo coming out with spinning the engine backwards for reverse, all manufacturers were using mechanical, geared reverse systems. Yamaha's system is the most reliable and best mechanical system out there. Yes Yamaha uses some extra parts, but the extra bearing in the cover keeps the gears running true even under extreme loads and the extra bearings in the reverse system keep everything running smoothly.
I will agree with you that the current Skidoo and Polaris chaincases are much simpler (and possibly more durable because of this), but when you have a 4-stroke that can't be spun backwards you need a mechanical reverse system.
The problem with Yamaha's chaincase IMO started in 2006 when they switched to magnesium. To the best of my knowledge all prior years, their chaincases were bulletproof (if you changed the oil per the schedule).
Magnesium, while being lighter than aluminum, doesn't conduct heat as well as aluminum. This means the heat can't get out as fast and it runs hotter. The bigger and real problem is in the magnesium casting process they somehow messed up the geometry for the seal relative to the cover. I carefully measured the seal interface on an 05 chaincase and an 06 chaincase and discovered with at least these particular cases, the seal had about 0.080" less surface in contact with the flat surface in the cover and the outside of the seal didn't get pushed up tight against the outer lip on the cover (again about an 0.080" gap). The updated 07 cover fixes this by provided the best interface with the seal, but the outer retaining lip is still a little loose compared to the 05 cover (which shouldn't really matter).
So the problem is the chaincase sometimes leaks due to a combination of the reduced seal interface and the increase in temperature (which softens the seal when you run the sled hard). Over time and many high temperature heat cycles, the seal sometimes slowly walks inwards until it lets the oil leak out. After the oil leaks out, the chain overheats and fails. Note that not all sleds are suffering this fate (probably a fairly small percentage overall).
As long as the case doesn't leak and you run a quality gear oil, these things are still very reliable (even though the magnesium doesn't cool as well). The ultimate in reliability would be to run an 05 aluminum chaincase, but I very much doubt anyone will have trouble once they get the updated 07 cover on their 06/07.
