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I have a 99’ ZL440 with 6,000 miles and the rod bearing disintegrated on the crank side. I’m going to rebuild it for my son. What should I look for so it will not happen again?
There is a vacuum hose that attaches to the crank case and I don’t remember removing it could that of caused it?
 

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I have a 99’ ZL440 with 6,000 miles and the rod bearing disintegrated on the crank side. I’m going to rebuild it for my son. What should I look for so it will not happen again?
There is a vacuum hose that attaches to the crank case and I don’t remember removing it could that of caused it?[/b]

Well that vacuum hose is the impulse line. Without it hooked up I don;t see how the sled would run. It send an impulse to the fuel pump to pump fuel. Unless it came undone, adn casued the sled to lean out? Make sure you hook that up or you will pull that thing forever to no start.
 

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The most likely causes of a rod bearing failure are likely either lack of oil or rust. That isn't many miles for a crank bearing so I can't imagine the bearing simply failing unless it was faulty somehow. Lots of possibles for lack of oil or rust though.
 

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I have a 99’ ZL440 with 6,000 miles and the rod bearing disintegrated on the crank side. I’m going to rebuild it for my son. What should I look for so it will not happen again?
There is a vacuum hose that attaches to the crank case and I don’t remember removing it could that of caused it?[/b]
Replace the bearings with new and keep on riding it. There is nothing you can do, other than good maintenance, to prevent a crank from grenading. At this point all the bearings are suspect, so do it right and start with all new.
 

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Catastrophic rod big end failure is usually due to too much side clearance at the rod bearing. The harmonic vibration at high RPM causes the rod to either snap the I-Beam or explode the cages.
 

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Catastrophic rod big end failure is usually due to too much side clearance at the rod bearing. The harmonic vibration at high RPM causes the rod to either snap the I-Beam or explode the cages.[/b]
... and it makes a huge mess. I can atest to that based on the pile of crap that was left in the place my engine was at the start of the day, one day a while ago. I'd post a picture, but that feature does not work for me anymore, sinse the last forum upgrade. I just get a never ending "Initializing Attachments" message.
 

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Catastrophic rod big end failure is usually due to too much side clearance at the rod bearing. The harmonic vibration at high RPM causes the rod to either snap the I-Beam or explode the cages.[/b]

What causes too much side clearance at the rod bearing?

I just lost a rod bearing on a low mileage 800 twin that I am 90% sure did not have a rust issue. It failed after I slowed down from a long pull on a lake. Luckily it happened at a very low RPM and I was able to limit the damage to the crank itself.

If it had been the mag side I would have guess coolant contamination since the head gasket had started leaking not long before.
 

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What causes too much side clearance at the rod bearing?

I just lost a rod bearing on a low mileage 800 twin that I am 90% sure did not have a rust issue. It failed after I slowed down from a long pull on a lake. Luckily it happened at a very low RPM and I was able to limit the damage to the crank itself.

If it had been the mag side I would have guess coolant contamination since the head gasket had started leaking not long before.[/b]
Too much big end side clearance could have been a poor crank build (not common though), Bent connecting rod (caused by water or coolant ingestion), Wear due to foreign matter or snow ingestion. The big end rod bearing is first to be lubed / cooled by incoming mixture... unfortunately whatever is carried by that mixture the rod bearing sees too.
 

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Too much big end side clearance could have been a poor crank build (not common though), Bent connecting rod (caused by water or coolant ingestion), Wear due to foreign matter or snow ingestion. The big end rod bearing is first to be lubed / cooled by incoming mixture... unfortunately whatever is carried by that mixture the rod bearing sees too.[/b]

Well I know it was not snow ingestion since I was on a lake at the time. The oil line to the cylinder intake had oil in it and was connected. Based on the gas I used and the amount of oil required it was using oil at approx a 50:1 ratio.

I will take a look in the air box and reeds for any clues of contamination. I will have more clues once I tear down the top end on the other side.

Thanks again
 

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Too much big end side clearance could have been a poor crank build (not common though), Bent connecting rod (caused by water or coolant ingestion), Wear due to foreign matter or snow ingestion. The big end rod bearing is first to be lubed / cooled by incoming mixture... unfortunately whatever is carried by that mixture the rod bearing sees too.[/b]

Is it possible not enough big end clearance that became an issue after a long pull? Based on my mearurements the PTO end has a little less clearance than the mag end and certainly less clearance than the brand new crank I received from Northern Crank which is a new factory unit that Northern Crank went through to make sure it was true. I am thinking it might have taken a little more heat after I let off the throttle from a long pull and grew just enough to stick. I never noticed any issues with it until I started getting back on the throttle again at low speed. Then the knocking and rattleing started. Usually I burp the thottle a bunch after a long pull but I did not do that this time since I was trying to slow down enough to cross a ridge someone had plowed on the lake.

Other than clearance I cannot find any issue why this went out. I would be interested to hear any comments though.

thanks in advance.
 

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A lot of factors go into a lower rod bearing failure, lack of oil or "garbage" dime store oil, rusty pitted bearings from poor summer storage prep.

Normally its not the bearing that fails, it's the metal cage that keeps all the "marbles" in place cracks and then all the "marbles" fall out causing the failure.
 

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A lot of factors go into a lower rod bearing failure, lack of oil or "garbage" dime store oil, rusty pitted bearings from poor summer storage prep.

Normally its not the bearing that fails, it's the metal cage that keeps all the "marbles" in place cracks and then all the "marbles" fall out causing the failure.[/b]

Thanks for the info - The motor has always been fogged and stored in a dry place over the summer since I had it. Before I it came to me it was supposedly a spare from the cat race dept so who know what really happened to it then. The rest of the motor and bearings all looked good. Oh well sometimes you just never know. Maybe John from Northern Crank will have some idea when he gets it in to look at it.

Thanks all for the help/input.
 
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