Now usually my luck is absolutely trash, however this weekend we packed up the camper and drove 2 hours to the race weekend at Utica-Rome speedway in Vernon NY. During my second practice session on Saturday I heard this weird slapping sound inside the engine of my RM-Z 450. Initially I thought it sounded a bit like chain slap but the chain tension was where I normally have it. I pulled the oil filter and didn't see any metal and made sure the oil lever was topped off. Missed the 3rd session while playing with jetting on the kids bike, go out for the fourth and final session and don't hear it until the very end of the 15 minute group
Sunday morning rolls around and decided to skip practice but never heard anything while warming the bike up on the stand. Go out for my first moto of +25 B and instantly hear the noise again. By the end of the moto it's more coarse and swear it was substantially down on power so just idled through the last lap. Decided to play it safe and not risk it locking up on me mid flight so I sat out the second moto
Today I tore it down bit by bit trying to be as least evasive as possible. I had every intention of doing the timing chain and piston this winter but just need it to hold together another 4 races. At this point the bike has 100ish hours on it and the CP piston has a solid 88 of those. I found a 3/8"x1/8" chunk of steel inside the stator cover and a chunk just slightly larger than a sliver in the magnetic screen behind the 3rd drain plug. Finally I had to break down and split the bottom end and surely enough I found the issue. Fortunately the crank and case seem perfectly intact. Even more miraculously I happen to have a timing chain, crank bearings and complete gasket set sitting here for the bike
Just wanted everyone's thoughts if they've ever seen the cage break inside a crank bearing before? The bearing still spins perfectly in your hands and none of the balls are missing, but it certainly makes sense that it was making the noise I was hearing
You were seconds away from that thing letting go! Good thing you shut it down in time. It’s rare, but I have seen cages break before. In a four stroke, it’s even more rare as the lubrication is more than in a two stroke. The majority of broken bearing cages I’ve seen were two strokes that say for years with crappy ethanol gas. It starts with a whirling sound and ends up growling, then letting go. Glad you caught it in time!
So before I toss this back together, I figured I would do some die hard detective work first to try to figure out what caused this. 120ish hours on a 450 is nothing for the crank bearings so I'm trying to figure out what caused this. When the bike had approximately 12 hours on it, the connecting rod bearing went bad and Suzuki told me to shit in my hat. I ended up sending the crank to Crank Works and had a new pro X rod thrown on it. While it was there. I asked about having a balanced to the CP piston that I intended on running and they said that the weight shouldn't be off enough for it to make a difference.
I never weighed the piston before but I was able to find the OEM piston that came out of the bike and with the rings, wrist pin, and circlips the OEM piston weighed 321 g. I just weighed the CP and it weighs 356 g in the same fashion. Is that wheat difference enough to cause the extreme vibration I've always felt after putting the bike back together? I noticed that the bike had a vibration but honestly hardly wrote it prior to the rod going bad so I just figured it was normal. It's to the point where I actually replaced the rubber bar mounts with a softer derometer set and a set of aftermarket motor mounts, both of which helped the issue some. Could this imbalance from the 35 g weight difference been enough to kill this bearing?
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