This blown engine thing makes me need to have a rant. It is a long time pet peeve for me.
Lunchbag didn't really do anything "wrong" to make this happen to him. This falls, in large percentage, on the previous owner.
How so?
Once upon a time..., just maybe 5 short years ago, this was a common story here on this forum. I'm sure that some of the early members all recall reading plenty of this stuff happening. In fact, when I first joined here, it was the general consensus that 500 Bullets couldn't be successfully modded, and only fools would waste their time and money in such folly. And there were plenty of stories just like this one to reinforce that idea.
This happened largely due to general lack of knowledge, and partly due to penny-pinching, and there was enough of those things going on with both the purveyors and customers to make this result approach epidemic proportions among modders. The customers did not know enough about these engines to know the weak points, and didn't want to spend much money on a "cheap bike". The parts makers knew this, and wanted to make sales, so they sold the parts to the customers as if the customers knew what to do. Crank rebuilds or racing cranks were made available, but that was more than the neophyte wanted to spend, and nobody really gave them stern warning that these bottom ends will grenade like this, if stressed much over the stock power and rpm level.
So, the fuse was lit. Install race parts on weak bottom ends, by neophyte owners who had never done anything like this before. Little or no tech support available.
On top of that, corners were cut on parts manufacture, to try to keep prices lower and still make money, and nowhere was this more evident than with the heavy pistons. The stock cast 500 low-compression piston was already too heavy(514g with pin) and the 500 had a record of failures related to this, compared to the 350 which had a much lighter piston. So then, the speed parts makers came out with forged oversize 535 pistons with high compression domes on them which weighed somewhere north of 550g, and some over 600g. This was because it costs money to lighten pistons by machine work, and so it wasn't done, in order to save cost. The result was much more reciprocating stress on a bottom end which was already prone to failing under normal stress with a piston about 2 ounces lighter. And higher heat and compression loads to boot. Another nail in the coffin.
But no, we ain't even done yet
These heavy pistons have design issues which made them more prone to detonation. And they had design issues that made them more prone to seize. And no tuning instructions were available as to how to run these pistons in terms of setting compression or timing or anything. So, detonate and seize, they did! But, not to worry, after they did, they could go back and buy another one just like it, and repeat the performance again, because nobody knew why it was happening. I know of one guy who went through 4 of them prior to me coming along with the answers.
The con rod failure usually happens when the piston seizes. It can happen on over-rev too, but breaking after piston seizure is most common. So, the seizure is typically the precipitating factor in its demise. The overly heavy piston, usually after higher revving over some time, associated with the rider's desire to taste some of that performance he paid for, causes some repeated stress and fatigue in the con rod alloy. Heat also reduces the tensile strength in most aluminum alloys. So it's already weakened, and it wasn't strong to start with. Then, the detonation starts up because the compression was usually set too high because the owner had no idea that even needed to be done, and just installed it "as is", and used standard ignition timing and God-knows-what carb tuning, and probably still in the cast iron barrel. So of course, the thing is very precarious at the very least, and is probably regularly detonating all over the place. But one day, the owner decides to open up the throttle a little more than usual at lower rpms, for maybe pulling a hill, or maybe feeling so grunt in the lower rpms, and BANG! That detonation really heats up the piston fast and it seizes hard in the bore and snaps that pathetic little con rod in half, and the busted end flails around along with the crankshaft, poking holes through the crankcase as it goes.
This isn't even getting into the other probability that the heavy piston and detonation forces were also in the process of wiping out all the main bearings and big-end bearing along the way, which might even happen before the seizure happens. That might even be considered a saving grace, because at least you didn't lose the whole engine in the process.
So this is a long way of saying that these engines need improved bottom ends for power modding, and it also is a very good idea even if you are not power modding, because they are so VERY weak inside there.
With the stuff that previous owner did, even though he may have thought he was "doing good", he created a time bomb that ended up blowing up later. It is not caused by "modding", it is caused by not knowing what is proper to do when modding. This is a very big distinction.
Now, after I came along here, most of you know that I made a very big effort to try to help people understand what they were doing wrong, and how to make it right. I made it clear that they needed to spend the money on a good bottom end, and that it was not something that could be "skipped". I taught people to set compression, made very lightweight pistons, explained cam timing, gave tuning instructions, and worked with people neay 24/7 to try to turn this debacle around, and get the boat back on course. It's all in the archives here.
Topic: Sprag Clutch replacement on 2005 Bullet 500 Military (Read 9447 times)