HELP/ADVICE NEEDED CON ROD FAILURE
Posted December 22, 2001 - 06:16 PM
I tore down the engine yesterday to find the conrod has failed just below the small end. It has gouged out the cylinder, destroyed the piston and on splitting the cases I have found 4th gear (input and output) shattered on a couple of teeth, a shift fork rod has also come loose causing the lugs for the rod in both cases to break off. I imagine this would mean both cases are now junk.
On further inspection the crank around the big end area has gone blue either side of the big end crank pin.
My question is, what does anyone think has happened. What has failed first and what the hell should I do. Repair or New Engine.
Just for info, I don't race the bike, It is regularly serviced and looked after extremely well. It hasn't got many miles on it also. Has anyone heard of this happening?
Posted December 22, 2001 - 11:09 PM
Posted December 23, 2001 - 02:33 AM
Didn't you do a rebuild this past year?
I recall some input from you pertaining to bent shift forks, gears, ect.
I have that ticking noise inside the left side cover right at the C.S./sprocket, so I'm planning to have a look this Winter to see if I can figure out what's happening.
Also, I think I better replace the CB key - was there ever a confirmed material / source for the harder stuff?
I have an '02 - very low hours.
Posted December 23, 2001 - 05:18 AM
A blued crank points to severe overheating of that part of the metal. I would not think that this is normal for this motor. The only thing that I can think of which would allow that part of the crank to get so hot is lack of lubrication. Bad gas or lean jetting can contribute to overheating in general, and maybe even blueing of the wrist pin and top of the connecting rod, but for the buttom end I would guess that lack of lubrication would be the most likely cause. Maybe the next step would be to look closely at the oil system and see if you can find anything wrong. I'm not a pro mechanic so hopefully someone who is can provide more info on this.
Posted December 23, 2001 - 02:06 PM
Posted December 23, 2001 - 05:29 PM
4th gear tooth snapped off during hard shift or landing, piece of gear takes out shift fork causing this to snap off lugs from cases, all debris some how fouls oiling system overheating big end and ultimately whole con rod overheats and fails at weakest section (just below big end). Result - BANG. Any other suggestions.
I just don't want to put it all back together and do it again.
And yeah the Hayabusa is incredible, for any of you guys that haven't ridden one I strongly recommend it, even if you hate road bikes just try one.
Posted December 23, 2001 - 07:03 PM
Posted December 24, 2001 - 05:27 AM
Here is my theory on your bike...while under a great load, a transmission gear broke. Just enough debris got between gears to cause the engine to ubruptly stop turning, and snap goes the rod. At 10,000 rpm it would not take much.
As for the rebuild, I was advised by everyone I talked to to go with 2001 or 2002 parts(crank, rod, piston, cylinder, head, valvetrain, ect...). At the desert races around here, fast guys on 2001's were still breaking transmissions. I decided to scrap it and bought a KTM 520 instead . It (the YZ) still sits in my garage in full desert trim.
Talk to the fine folks at Montclair Yamaha, I'll bet no team had more experience blowing up YZF's than they do. When I mentioned my bike blowing up on this board, many questioned my mechanic. After speaking to Montclair Yamaha, and Yamaha themselves I question the design.
Posted December 24, 2001 - 05:39 AM
The cases should be able to be heli-arced. I'd definitely go with a rebuild instead of a new motor.
Two other options you need to think about. A 426 rod has a 1mm bigger diameter than a 400. The rods are interchangeable. Since the cylinder needs to be repaired, a big bore kit would be a feasable option at this time. A 2mm overbire is known as the 420 kit (416cc actual) and makes a big improvement in overall power. If you go with teh 426 rod, you can go with a new 426 cylinder and piston (bolts right on a 400 bottom end). And a 3rd option would be boring the 426 cylinder 2mm and making it a 450 (444cc actual). This is what I did with my WR 400 and it is similar to driving a V8 powered Pinto. Incredible boost of power from idle on up. It is then a *race fuel only* motor but, like Toyota says, "oh, what a feeling!!!"
Just presenting a couple upgrade options that would make sense right now.
Posted December 24, 2001 - 01:29 PM
Just to answer a few questions I use Mobil 1 15-50 and change without fail every two rides so bad oil shouldn't be an issue.
The conrod has snapped just below the small end. The big end has NOT seized onto the crank pin but the crank is noticeably blue either side of the crank pin (I haven't taken the conrod off yet).
As for all this happening at once, I'm just lucky I guess. After all I wrapped my first Hayabusa around a pole and couldn't even salvage small bolts.
I give the heli-arc a shot, this should save me big $$$$, is is reliable?
MX Tuner - Thanks for giving me some options, I like the 426 idea. In fact I think that would be the go with the bigger rod. Thanks again everyone.
Posted December 24, 2001 - 02:22 PM
Was the cylinder seized or scored?
Could the loose end of the rod have stabbed the transmission and caused that damage?
Got any pictures?
Posted December 24, 2001 - 11:48 PM
The small end wasn't seized or scored. The gudgeon pin was still in good condition however it had broken free from the piston lug (piston lug cracked).
The cyclinder wasn't seized however was badly scored (due to broken rod) I believe by looking at the length of the rod it couldn't reach that far over to the transmission to hit the gears.
Don't have pictures yet but if you think it might help I will go to the shop and take some.
Posted December 27, 2001 - 08:08 PM
yz454 bored and stoked long rod.
Posted December 28, 2001 - 02:09 AM
YZ454, is yours a 97mm bore? 97mm figures to a 444cc, not a 454cc.
Posted December 28, 2001 - 03:50 AM
Originally posted by MX Tuner:
YZ454, is yours a 97mm bore? 97mm figures to a 444cc, not a 454cc.
Posted December 28, 2001 - 07:52 AM
Posted December 28, 2001 - 01:42 PM
Originally posted by hayabusa:
The big end has NOT seized onto the crank pin but the crank is noticeably blue either side of the crank pin (I haven't taken the conrod off yet).
This is an interesting post, I wish I’d seen it sooner. My ’00 had third gear explode, this spit a shift fork into the crank, resulting in a bent rod and damaged crank. It sounds like a slightly more extreme version of the same thing may have happened to you. In my case the rod did not remain lodged under the crank, I could still spin the motor (but not the tranny), but it was easy to see where they got together.
When I got the new crank it already had those same marks you describe on either side of the con rod. Maybe they heat the crank when they press it together at the factory.
My total parts bill was about $1,000. I got a new crank assembly, cases, piston, four gear wheels, the fork, and (almost) every bearing and gasket in the motor. I also went with a 97 mm piston and bored/replated cylinder. I think I paid Eric Gorr like $350 (not included in the above $1,000) for the boring and plating work. You will need all the help you can get to install new bearings in new case halves if you go this route, I used a ten ton press, my torch, & my freezer, and still had a hard time coaxing all the bearings in there.
I also replaced both fourth gears as they had chips on the load-bearing face of each tooth. I thought this was a ’00 issue only, but it sounds like your ’99 has the same problem.
The expensive thing is the crank assembly, I paid $300 for a ’00 part, but remember this includes the rod and bearing (and it is already installed).
Also, Tuner makes a good point about the 426 parts, especially the cylinder. Unlike a two stroke cylinder with its all-important ports a four stroke is just a hole with water jackets, they are only around $250, brand new. Cheaper than boring and plating your 400 cylinder.
Sorry for your misfortune, good luck with the repairs.
Posted December 28, 2001 - 02:03 PM
I am looking at buying 426 parts after the new year so thanks to you guys I might have a better bike after all this S**T.
What do I do with the hot start then if the 426 doesn't have it on the cylinder because I will be running the 400 carb (I imagine).
Posted December 28, 2001 - 02:17 PM
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