Bad Crank Bearing?

[plattey]

So the old xs has started making some loud noises while I was riding it down the road. I thought it was the valvetrain and camchain so I tightened them up as per the forums. The noise persisted though. Took out the screwdriver and listened to it while it ran at idle and poked around until I stuck the screwdriver in front of the engine below the oil feed tube where the cases split. It sounded horrible, kinda like a tire does when it gets a flatspot. Is that sound coming from a bad crank bearing or a worn camchain guide?

 

[jayel]

have you checked the sump filter? bad guide will leave plastic and alloy debris bearing will leave magnetic (steel) flakes

 

[PHeller]

I had a CB400F that I feared had a bad bearing.

Sold it for $100 less than I bought it for, and about a $300 loss.

New owner split it apart, bearings were fine.

Cam chain guide/tensioner was trashed.

In the end I was fine with my decision because it will cost him more than $300 just to put it back together with a new guide and tensioner and gaskets, and I used the money of the sale to buy a running xs650 with a excellent spare engine.

 

[plattey]

I checked the right side case filter quick and there was a mixture of steel and brown something....could be plastic but more steel than anything else. But the front camchain guide was replaced when the bike had around 5k on it. Is the rear camchain tensioner made of steel and plastic? I've got too much into this bike to get ride of it now. It's also my first bike as well. I drained the oil and I'll check the sump screen once I have time from homework and classes to do so.

 

[Patches]

I checked the right side case filter and there was a mixture of steel and brown something....could be plastic. But the front camchain guide was replaced when the bike had around 5k on it. Is the rear camchain tensioner made of steel and plastic? I've got too much into this bike to get ride of it now. It's also my first bike as well.

I would say you need to find out for yourself. These motors are easy to rebuild and by the sounds of things you are AT LEAST going to need to pull the top end off which just requires some basic tools.
The steel may be from a cam tensioner gone bad. It's is plastic and steel. We can speculate all day long but in the end it sounds like you're gonna have to pull that bitch and check it out.

 

[plattey]

Ah wonderful!!!!! Patches, thank you for the info on the cam tensioner! Another question, while the motor's out of the frame, the crank should probably be taken out and have the bearings checked right? If a bad one is found, where can the roller bearings be located and purchased? I looked on Mikesxs and I could only find the ball bearing one.

 

[jayel]

what year are you dealing with anyway? doesn't hurt to put that info in your profile or signature

 

[plattey]

It's an '82....i'll put that in right away.

 

[plattey]

I checked the sump filter and it was clean, no debris in it but only steel filings stuck to the two magnets.....it's ready to come out of the bike. Hopefully this weekend.

 

[plattey]

I took the cylinder head off and peaked inside. The front and rear guides are in great shape. I'll have to split the cases soon and have a look see.

 

[plattey]

Split the cases and checked the 3 roller bearings and the ball bearing. They all look great! I checked the connecting rods and the left one's a loosey goosey. The big end side clearance is .559 mm, stock is around .4mm and the connecting rod, at tdc, can be moved back and forth probably over an 1/8th inch parallel to the crank axis. Will a bad big end make a loud clunking noise when the engine is idling? Also, what size of a press can handle pressing the crank apart?