what caused this engine failure?
Posted September 14, 2010 - 03:41 AM
Posted September 14, 2010 - 05:10 AM
Posted September 14, 2010 - 05:14 AM
there was oil in the head, cant see if there was oil in the crank.
Im going to assume overrevved,
Posted September 14, 2010 - 05:15 AM
Posted September 14, 2010 - 07:46 AM
Thats a bummer.
Posted September 14, 2010 - 09:35 AM
We have one pin boss in place, one torn off. The small end is till on the rod, and there's that cute little wear mark outside of the clip groove on the broken pin boss...
You dropped a circlip, most likely because it wasn't installed correctly. The pin slides out until there's only one side of the pin boss holding it, and the combination of the doubled up load and the rocking strain breaks the piston.
Posted September 14, 2010 - 09:49 AM
There is no such issue with the YZ450 motorcycle engines. That was a problem that the quad engines had for a time. When the oil spray nozzle was added to the '07 YZ/WR engine, it was done for piston crown cooling, but people wrongly concluded it was for the oiling problem the quad had.
It looks like the cause is the oiling issue on the 03-06 450s.
Posted September 15, 2010 - 01:46 AM
The oiling theory makes sense now.
Posted September 15, 2010 - 02:00 AM
"04 and 05's used a flat circlip too hold the gudgeon pin in place, 06 and onwards use a round circlip the reason is that apparently the gudgeon pin would push againest the flat circlip in the older models and eventually unseat the circlip, eventually the gudgeon pin would move out of place and cause this sort of damage. the round circlip in the newer models is actually forced deeper into the retaining grove when pressure is applied too it.
You are lucky your conrod didnt do more damage."
Posted September 15, 2010 - 08:55 AM
There are two mistakes that can be made when installing the flat, "TruArc" type snap rings:
- All such rings have a right and wrong side. One side will be very flat clear to the edge, with sharp, square corners, and the other will have a more rounded, stamped look. The flatter side must always be placed so that it bears the holding load, and in the case of the piston pin, that means the rings must be installed flat side out, against the groove.
- The rings should be oriented with the gap between the ends facing straight up. At extremes of RPM, it is actually possible for the inertia generated by changing directions to flex the clip enough to lift free of the groove and potentially dislodge it. Orienting the clip as above minimizes the effect as much as possible.
It's also possible for the pin to rotate the clip into a disadvantageous position (2), but if the clip is installed right side out (1), that should be much less likely.
A third, less common, but serious mistake is using the wrong clip for the piston. Never use a wire ring in a piston cut for snap rings, or vice-versa.
Posted October 05, 2010 - 05:36 PM