Topic: When cam journals start failing, what eventually happens?

[Tugboat]

You run a motor with bad cam journals and eventually......??

[iron_worker]

The excess oil clearance from worn journals won't allow the top end to properly build pressure which will actually affect pressure to the entire system (top and bottom end). The oil pump doesn't create pressure. The oil pump simply creates a certain flow that is proportional to engine speed and the tight clearances and passages within an engine that the oil must work it's way through create a resistance to the flow. This resistance to flow is what creates the engine oiling pressure. If you have one bad cam bearing then a lot of the flow will tend to go there since it is the path of least resistance ... and will begin to starve other parts of your engine.

http://forums.sohc4.net/index.php?topic=52413.0

So essentially, if it gets bad enough you'll drop the entire system pressure and possibly damage your top and bottom end. You will also probably start sending a lot of metal particulate through your engine which will mostly be caught by the filter but not all and it also likes to block up oil pickup screens.

And also, your oil pump picks up all the junk that's in your oil *before* it's filtered ...

Sooooo.... if you know you have a worn cam bearing I wouldn't run it unless you're prepared to potentially cook the whole thing.

IW

[mcswny]

You run a motor with bad cam journals and eventually......??

oof, you getting nervous about tomorrow?

[Tugboat]

I am indeed. If it breaks, it breaks. I'm just trying to be safe you know?

[MCRider]

I am indeed. If it breaks, it breaks. I'm just trying to be safe you know?

Never seen or heard of a wear failure. Or wear so bad it caused a failure, elsewhere, though anythings possible.

Usually they get starved for oil from debris lodged in the oiling jets. Then they wear a different way, get real hot and seize. Usually one side or the other, and the cam snaps in half. Really.

[mcswny]

I am indeed. If it breaks, it breaks. I'm just trying to be safe you know?

regardless, let us know how it goes!

[dlhoulton]

This is what could possibly happen:

[MCRider]

DL: Did that happen from a slow deterioration of the journal with otherwise good oil supply and pressure, or was it a catstrophic failure from lack of oil?
Looks pretty dry.

[dlhoulton]

My guess was from a lack of oil. When I took it apart I found out that the PO had put the cylinder gasket on wrong, blocking oil supply/return on 3 and 4. Which also caused wear to cam chain and guide.

[MCRider]

My guess was from a lack of oil. When I took it apart I found out that the PO had put the cylinder gasket on wrong, blocking oil supply/return on 3 and 4. Which also caused wear to cam chain and guide.

That's what it looked like.

I should add to this conversation, and my remarks, that not only have I never seen one die (cam beariiings or otherwise) of natural causes, but rather oil starvation, the starvation has always been caused by someone rooting around in the engine, leaving behind a cause like your gasket, or silicone gasket sealer chipis breaking off and clogging the holes, etc.

I've never seen one die that hadn't been opened and tinkered with. OCICBW, but it would be a rare fluke.

[seanbarney41]

I recently had a 750f3 cam end up looking very similar to dhoulton's.  It was caused by a plugged oil jet,  so not any kind of normal wear, and failed completely in under an hour of run time.  Engine was stuck from sitting when I got it.  When it failed, the cam was bouncing around so much that it lost all valve clearance on two cylinders and had no compression.  Surprisingly, after resetting valve clearances, the engine started and ran good but made some VERY bad noises.  I will get pics uploaded soon.  They look very similar to dHoulton's.

[thirsty 1]

This is what could possibly happen:

In full on surfer talk... Dude. that is gnarly.

[HondaMan]

If the bearings are smooth, but loose, and the oil is coming, they run fine. At worst, a lateral vibration MIGHT happen at continuous high RPM, like racing, which accelerates the wear somewhat. But on the street, running at normal engine speeds, these engines run fine with up to .012" of clearance in these bearings, as they get a flood of oil pushed in from the bottom behind, and roll it up and over the top, to spread it out before it goes under load in the front-bottom of the rotation. I haven't seen any yet with more than .012" in a running engine, but since the design only requires the cam actually stay in place while it pours oil on top of it, it's not a very stressed system. 

[MCRider]

"In full on surfer talk... Dude. that is gnarly. "

True. Mine, (hapened to me) and 2 others I have seen were much less destructive. Other than discoloration of the parts from heat, all that could be seen was that the cam was sheared in half near the sprocket. Pretty clean break. Mine ran perfectly fine on 2 cylinders, sort of like one set of points was gone. But it was the wrong pair of cylinders.  And yes, I had been in it and used hardening silicone gasket sealer. Mea culpa.   

[Tugboat]

Awesome advice guys, and is why I posted this here. To be honest: this is our 76 XL250 that I'm talking about. If y'all don't know, I'm competing in an event to put as many miles on a bike whose total cost doesn't exceed $500, in 24 hours. 13 hours from now I'll be on it, buzzing down the highway at a respectable 60mph. Long saga, all thoroughly documented on the Other Bikes forum if ya wanna know more. Long story short: cams look pretty bad and the bits in my filter and condition of my oil indicates journal wear. Metal is non-ferrous. Full tuneup done, oil changes planned ~every 300mi, running 20/50. As it stands our plan is to just get into the power band in 5th gear (~60 mph, unsure of rpm no tach) and keep it there to hopefully reduce engine stress. Our goal is to just keep it running the whole time -we don't care about actual mileage or speed. What I'm wanting to avoid is any kind of catastrophic failure that would result in some sort of rear wheel lockup,thus this thread.

[dave500]

the oil restrictors help maintain bottom end pressure,the pressure wont drop much if at all with worn cam bearings.

[Don R]

give it heck and don't think about it.

[seanbarney41]

I don't think there is much chance of a rear wheel lockup.

[MCRider]

Awesome advice guys, and is why I posted this here. To be honest: this is our 76 XL250 that I'm talking about. If y'all don't know, I'm competing in an event to put as many miles on a bike whose total cost doesn't exceed $500, in 24 hours. 13 hours from now I'll be on it, buzzing down the highway at a respectable 60mph. Long saga, all thoroughly documented on the Other Bikes forum if ya wanna know more. Long story short: cams look pretty bad and the bits in my filter and condition of my oil indicates journal wear. Metal is non-ferrous. Full tuneup done, oil changes planned ~every 300mi, running 20/50. As it stands our plan is to just get into the power band in 5th gear (~60 mph, unsure of rpm no tach) and keep it there to hopefully reduce engine stress. Our goal is to just keep it running the whole time -we don't care about actual mileage or speed. What I'm wanting to avoid is any kind of catastrophic failure that would result in some sort of rear wheel lockup,thus this thread.

What a great bike to do that on. Good luck.

IIRC the XL250 is a ball bearing crank and doesn't hold ANY oil pressure in the bottom end, contrast to the CB. Its all splash affair. The pump squirts oil to the top. Keep it clean and 20W-50 and you should be OK.  (Oh duh, I see that's the plan.)

Agreed, rear wheel lock up unlikely. Just be aware and keep 2 fingers on the clutch.