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crf250x cam bearing failure

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Had problem starting my 250x with bike making a great deal of noise sounding like the cam chain. Took off head cover and cam bearing (on side adjacent to cam chain) was destroyed. The other bearing near decompression lever is fine. Some indication of burns near destroyed bearing. I understand this is very unusual. Bike is 05 250x with faction stainless steel intake valves and stock exhaust valves. Has Athena 280 big bore kit and cylinder/piston/valves/head have 32 hours. Valves clearance was fine 5 hours ago and double checked cam timing and there was adequate oil level. Any ideas . Could this be oil pump problem?

Will post pics later

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Hi, can't help but literally just had the same problem but with the decompressor side bearing.

Mine is an 04 model and just put new piston and inlet valves in. Drizzled oil over cam before start up. Started fine but only ran for s few minutes before not sounding right so took iy apart to ser the bearing had failed. Cam caps and retainer seated properly.

What are your thoughts?

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Yeah photos of the damage would be a good idea, were the lobes damaged and dis colored?

Another question I would have is when the timing chain tensioner was put back on was it retracted or did it get installed with the plunger out and the two bolts then tightened up putting alot of force on the plunger, timing chain and that LS cam bearing?

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If the cam bearing caps, R and L  get switched the oiler hole doesn't lined up but the bike will run. Often the left side bearing will walk out tipping the cam holding the intake open a hair and it won't restart but will turn over  A good thing because it makes you fix it hopefully before oil starvation damage, 

 

Not sayin this was your case, but most valvetrain fails usually occur after someone worked on it.

Edited by highmarker

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TDW

I installed the cam chain tensioner just as you described (the wrong way) because I lost the tool to retract the tensioner. I have had the cam out several times before and used the right technique in the past. Thank you for your help

cam photo 007.JPG

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Thee is a chance you take of the decomp and just replace the bearing.  If the journal isn't too bad, you might get away with slapping the new bearing in, getting it together and being fine.  But, without a pic of the head and the journal for the bearing, I can't tell if it might be salvageable or not.

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I am hoping to just change the bearing as there is no damage to the cam lobes or holder. I have removed the head and it looks fine, I have drained and sieved the oil and found no metal. I don't think any of the bearings came out. Part of the bearing cage was tangled in the bearings and I have pulled it out.

I cannot understand why it has happened. I wondered whether the bearing dried out when the head was off but I drizzled oil all over it before starting. Or has a bit of debris got in the bearing? Does anyone have any thoughts?

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You got me.

 

When you slip and new bearing on I would give it a careful test run.  Put it together, run it for a few minutes, take off the head cover and check everything again just to make sure.  Then get it back to together and keep your fingers crossed.

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TDW

I installed the cam chain tensioner just as you described (the wrong way) because I lost the tool to retract the tensioner. I have had the cam out several times before and used the right technique in the past. Thank you for your helpYou

You dont have to use the special tool, a screwdriver will work fine but its just not quite as easy.

From what I can see in the photo the lobes look ok but looks like the inner race spun and caused some heat discoloration. Unfortunately it looks like its time for a new cam.  

Edited by TDW

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Here is a pic of my failed bearing. Any ideas people?

 

Does the other bearing look good? Hard to say for sure from here what caused it but I think you lucked out if the damage was limited to that cam bearing only!

I would make sure to get all the other metal pieces and ball bearings that came from the damaged bearing accounted for and out of the engine. Looks like when that bearing failed quite a few loose metal pieces were floating around inside there.

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The other bearing is fine. I have just been into my local honda dealer and they think that the cam cap wasn't completely aligned causing the bearing to fail. They are going to order me a new bearing and I'll put it back together.

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Took the head off and my valves are ok. Debris from inner bearing race is in head and left side case. Right side bearing is ok and cam lobes look ok. I dont see any thing in the cylinder and piston looks fine. Looks like cam + cam chain replacement will be all that is needed . Thanks for the help.

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All back together and running fine.

 

Only concern is that after the new valves were fitted and cut the right which was tight has quite a different sized shim to the left. The left is a 185 and the right is a 170. 

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All back together and running fine.

 

Only concern is that after the new valves were fitted and cut the right which was tight has quite a different sized shim to the left. The left is a 185 and the right is a 170.

its common to see a 188 shim size as the original intake shims in an engine that had never had anything done to it yet, 185 is very close. 170 still isnt anywhere near the smallest sized shim which I believe is 120. I dont think you have anything to be concerned about with those two sizes installed and having the correct valve clearance.

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TDW thanks for your guidance.

I had a Drz400 before and rebuilt it when I first got it and then didn't need to do anything afterwards apart from oil changes

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