There could be a variety of issues at play here, so it would be good to hear what the mechanic says happened to it.
1)There could be an oil starvation problem from some sort of blockage.
2)The big end of the con-rod, which is supposed to be hardened to serve as the outer bearing race, might have not been hardened enough, and eventually wore out.
3) The big end bearing rollers might have had hardness issues too. If not hard enough, they will also wear out.
4) The clearance from race to rollers in the big end bearing assembly may have been set too wide, causing eventual failure. These roller bearings need very tight clearances, that are very precisely set at assembly time.
5) The crankpin itself might have been soft on the surface, causing accelerated wear.
6)The engine may have been assembled with the crank too far out of true, and the resulting vibrations and misalignments may have eventually caused the bearing failures.
7)There may have been some kind of abrasive grit from somewhere that got in the oil and didn't get trapped by the filter, or maybe there was an oil break-down problem from heat or something.
If it is apart for a big end bearing job, you definitely want to put new main bearings in the engine too. Quality ones of known source that are for sure not counterfeits.
The problem with the crank assembly that your mechanic mentioned does seem to have some basis in fact. The varying degrees of "true-ness" of the crank from one Bullet to the next does seem to be evident. These bikes are not inherently bad vibrators. They can be very smooth, if the crank is trued well. So, I hypothesize that if you have a Bullet which is doing a lot of vibrating, and your engine mount bolts and head steady are tight, then you likely have a "less than optimally trued crank", and may expect some future bearing issues at a shorter time than other Bullets might see.
Regarding the big end issues, it has been occasionally seen in the AVL(which shares the same basic crank construction) that some of the con-rod big ends were not hard enough to serve as the bearing race, and they crapped out early. Sometimes the crankpin showed the lack of hardness problem, instead. Sometimes the race-to-roller clearance was not right. This is a known issue with AVL, so it's possible that it might also occasionally be seen in the UCE as a carry-over of the crank production methods.
Another thing that the UCE crank shares with the AVL crank is the method of construction and truing during production. You can only buy the whole crank/rod/bearing assembly as a complete set. They build them that way. I don't want to get into why they build them that way.
Topic: Big end gone bad ! (Read 32130 times)