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2t bottom end questions?

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Im new to this whole 2stroke thing and have a few questions about bottom ends.

-The lower rod bearing is fairly simple to figure out while doing top ends but..

-How often should the bottom end specifically the main bearings be overhauled?

-What are the signs the main bearings are on there way out?

-What are the signs the main bearings are shot?

-Typically can a crank be re-used

-What kinda catastrophic failures can the main bearings cause?

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-Whenever the bearing is out of spec

-Any play when you push and pull on the connecting rod,increasing noise,roughness when you turn the crank with the rod.

-You can re-use the crank as long as the seal journals are in good shape

-Big end catastrophic failure is rare, there are plenty of signs before it is toast.

Check it when you do a top end.

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I have had the bottom end catastrophically fail once on my bike, there were no symptoms and them bam it locked up. But that was because the water pump failed and it over heated and that causes the ring in the bearing to break and all the balls bunched up in the bearing.

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Im new to this whole 2stroke thing and have a few questions about bottom ends.

-The lower rod bearing is fairly simple to figure out while doing top ends but..

-How often should the bottom end specifically the main bearings be overhauled?

-What are the signs the main bearings are on there way out?

-What are the signs the main bearings are shot?

-Typically can a crank be re-used

-What kinda catastrophic failures can the main bearings cause?

Main bearings are roller bearings (rolling-element) and don't give much evidence of failure, other than being grumbly when you spin 'em. I don't think main bearings have a 'routine' replacement schedule. But, you inspect 'em (listen / feel) when you do a top-end and decide then. You can also, if you have a good feel for this sort of thing, try to determine if they have any 'up-and-down' play. They should have minimal play - ie, less than 0.001"

Lower rod bearing is also a rolling element bearing (needle bearing, typically) and it's checked the same way - grab the rod and see if you can detect any up-and-down movement.

Otherwise, lower rod bearing is 'officially' checked dimensionally vs. the journal, but this requires the crankshaft be pressed apart, checked, then pressed precisely and accurately back together - not something for the home mechanic.

As mentioned, the crank can be reused as long as the rod journal, main journals, and the area where the seals ride are all good.

What kinda failures can main bearings cause??? Use your imagination! What can happen if a roller bearing seizes?

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