So what does a lower bearing sound like when it's going out?

[zrx24]

And what exactly is going on when a bearing is on the brink of failure?

I've heard of a spun bearing, and have seen the results of that. Where a bearing seizes and starts spinning in the housing or on the rod.

I've heard talk of bearings starting to "knock" when they develop a problem. What actually causes that knocking sound? Is it the result of slop that has developed in the bearing?

What is it that actually causes a bearing to seize? Is it simply heat that causes the parts to expand to the point they actually weld together?

[SteddyTeddy]

Most start to knock if you catch them soon enough at lower speeds. The knock is the slop in the bearing. If its bad enough then its also from the piston smaking into the head. If a bearing seizes its usually from lack of oil and or high speed runs causing massive heat from metal on metal contact.

[zrx24]

Have you run across my other "noise" thread by chance?

http://www.zrxoa.org/forums/showthre...ighlight=sound

[SteddyTeddy]

Been out of town and busy with other issues. Just saw the vid and it doesn't sound good. Tear into it till you find it! A good oil pressure test would give you an idea if its a bearing or not.

[Hogan]

bummer man - hope it aint a bearing - best of luck w/that

from listening to the other vid I was hoping it was some tensioner or ? not too involved ..

[zrx24]

A good oil pressure test would give you an idea if its a bearing or not.

How does checking the oil pressure allow one to determine that a bearing is bad?

[KWICK]

How does checking the oil pressure allow one to determine that a bearing is bad?

If one or more bearings have an issue, the oil pressure will be low.

[zrx24]

If one or more bearings have an issue, the oil pressure will be low.

How does that work?

Having a hard time making the connection here.

Please excuse my ignorance on this topic. Never performed or had exposure to this type of analysis before.

[Ca Pete]

If one or more bearings have an issue, the oil pressure will be low.

Are you allowed to answer questions like this without Perko's permission?

[zrx24]

Ok, this shed some light on the topic.

http://www.youfixcars.com/oil-pressure-testing.html

[eddie lane]

how many miles have you logged on the engine since first noticing the new noise? if it's a bearing going out, it will go from noticeable to a definite rod knock in 100 miles or less. there will be NO doubt.

[Copyguy]

One test for bottom-end bearing problems that I recall is to lightly accelerate in 2nd or 3rd gear, not too fast - like 40 mph or so, thereby loading the bearing, then quickly back off the throttle to unload the bearing (knocking should go away), then as quickly roll it back on again. If the bearing's going bad, there'll be slack that'll be taken up on the re-roll-on and you'll hear it as a pronounced knock. At least that's the theory. I've not actually had reason to do the test.

[green12]

The crank is XXX diameter. The bore that it rides in is XXX diameter. The bearing in in between. It is XXX thickness. Result is about .002 or so clearance. More or less.0015 on a rod maybe. The crank doesn't ride on the bearing. Oil is pumped in between. As the bearing wears the clearance increases. The "gap that the oil has to fill is greater and the oil "leaks" out. Results in more volume so the pressure drops. 2 things: The crank can now wallow in the bore that may have .005 clearance or the lower oil pressure makes the oil film easier to "push away" . Crank rides on the bearing with less oil film. The oil also pulls heat away. Without the film heat builds up. Bearing galls to the crank and can spin with the crank. Then the bore in the rod or block get FUBAR.

[green12]

Also a loose bearing can be bad enough that the piston travels past it's normal range and hit the head.

[KWICK]

How does that work?

Having a hard time making the connection here.

Please excuse my ignorance on this topic. Never performed or had exposure to this type of analysis before.

Pretend you are blowing thru a straw.

If you keep your fingertip over the end, you'll get some resistance and a bit of air pressure built up.

Remove your fingertip and there will be no pressure.

Oil systems work the same way. Make one of the rod bearings have a 1/4 inch slop and there will be no buildup of oil pressure at the bearing.
Plain bearing cranks work on the accumulation of oil pressure at each bearing. Loose pressure in one, and the oil will take the path of least resistance and will exit thru the bad bearing and the pressure will drop on the remaining ones, and soon another will go bad....

It's early, it's a simple explanation...there may be holes in it...

[KWICK]

Are you allowed to answer questions like this without Perko's permission?

...my bad...

[sillyhillbilly]

How does checking the oil pressure allow one to determine that a bearing is bad?

bad bearing = loss of metal= metal in oil=oil gap between crank and rod bearing to be larger= large space that oil leaks out of= loss of total friction of oil system = more flow but lower oil pressure from max flow of oil pump being exceeded because of leak at loose bearing
seriously look for metal filings in the oil, it will look like the metallic swirl in bowling balls.

[KWICK]

One test for bottom-end bearing problems that I recall is to lightly accelerate in 2nd or 3rd gear, not too fast - like 40 mph or so, thereby loading the bearing, then quickly back off the throttle to unload the bearing (knocking should go away), then as quickly roll it back on again. If the bearing's going bad, there'll be slack that'll be taken up on the re-roll-on and you'll hear it as a pronounced knock. At least that's the theory. I've not actually had reason to do the test.

Be sure to wear full gear on a ZRX when you do the above.
Often, the time between noise and the rod escaping thru the from of the block can be measured in hundreds of feet, or minutes.

[Ca Pete]

I heard one cluncking at 80 mph, pulled in the clutch and pulled over on the freeway, gone. Opened the engine and #3 bearing was destroyed.

The second, also at 80 mph blew the front of the cases out without any warning. In fact that morning I thought to myself, as I was riding into work, how great the bike felt.

[eddie lane]

I heard one cluncking at 80 mph, pulled in the clutch and pulled over on the freeway, gone. Opened the engine and #3 bearing was destroyed.

The second, also at 80 mph blew the front of the cases out without any warning. In fact that morning I thought to myself, as I was riding into work, how great the bike felt.

can you connect any dot's to either of those failures? like running it low on oil or the bike having run on it's side, previously and relatively recently?

[Ca Pete]

can you connect any dot's to either of those failures? like running it low on oil or the bike having run on it's side, previously and relatively recently?

The first one ran on it's side after I went off the side of the road, went around 2,500 mile later.

The second, bike had been down on it's side 3 times over its life, don't know if it was running or not on its side, went at about 3,500 miles after the last one.

[zrx24]

how many miles have you logged on the engine since first noticing the new noise? if it's a bearing going out, it will go from noticeable to a definite rod knock in 100 miles or less. there will be NO doubt.

Just checked while I was home at lunch. I have about 200 miles on it since noticing this tapping noise.

[KWICK]

Just checked while I was home at lunch. I have about 200 miles on it since noticing this tapping noise.

200 miles?

It's probably a valve shim that fell out rather than the rod...a rod won't last 200 miles.

Where's the sound coming from?

[zrx24]

bad bearing = loss of metal= metal in oil=oil gap between crank and rod bearing to be larger= large space that oil leaks out of= loss of total friction of oil system = more flow but lower oil pressure from max flow of oil pump being exceeded because of leak at loose bearing
seriously look for metal filings in the oil, it will look like the metallic swirl in bowling balls.

Ahhhh! Yes, that is what triggered me to problems with my dirt bike last summer.


I've seen no signs of metal in the oil at all. So that gives me a little comfort at least.

[zrx24]

200 miles?

It's probably a valve shim that fell out rather than the rod...a rod won't last 200 miles.

Where's the sound coming from?

First thing I did when I started hearing the tapping was pull the valve cover and check the valves. All valves were in spec except one, and it was on the loose side. Made the necessary adjustment, buttoned everything back up and still have the tapping.

The ticking sounds like it's coming from the top end. But not certain on that. At times it also sounds like its emanating from the clutch area. That's why in my video I was moving the camera around to try and isolate where the sound was coming from. I'm still leaning toward it being in the top end, right side. Sounds much like the ticking a bad valve makes.

I wonder if maybe a rocker has gone bad.

[KWICK]

Take a long plastic handle screw driver, stick the handle in your ear and probe around...you should be able to find the source.

Really...

[zrx24]

Take a long plastic handle screw driver, stick the handle in your ear and probe around...you should be able to find the source.

Really...

Tried that. Didn't work.

Even tried sticking a long skinny transmission fluid funnel in my ear. That didn't work either.

[KWICK]

Kool, then turn the stereo/mp3/iPod up louder.

[zrx24]

I'm planning to try and get a better idea on the location of the noise when I get the bike back together. Pulled the side cover and starter chain tensioner last weekend thinking I'd have a replacement in the mail this week.

[eddie lane]

does the tick sound like it's a 1:1 ratio with the crank speed or a 1:2 ratio with the cam speed? or maybe it's more like a 6:1 like mine was.
seriously, i can't help but go back to your missing piece of shrapnel. did you ever pull the clutch assembly to inspect the clutch/ crank gears?