XR600 top end questions

Discussion in 'Thumpers' started by mothsmear, Feb 19, 2010.

  1. mothsmear

    mothsmear n00b

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    I rode in the Rock Hound Rally here in Ontario last summer, and about 5 minutes before the end of the ride I started to hear noise in the top end. The camshaft and rocker arms are toast. What could be the cause of this? I don't understand why it would overheat like it did. Everything was gone over and checked before the ride. When the bottom banjo bolt is loosened and the bike is kicked over oil comes out real fast, but when doing the same with the top bolt it seems like a lot less comes out. I took a spare oil line, cut the middle out, welded two hose barbs on and have a piece of braided stainless hose to put in. I was planning on opening up the banjo bolts but have been reading on here that it might not be a good idea. It was actually suggested to me by a bike mechanic who said they open up the lines to the top end on harley's. I realize changing things are going against a long track record with these bikes, I just don't want to replace the cam and rocker arms and have it happen again.
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  2. Ghost_Mutant

    Ghost_Mutant looking for bionics

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    I don't suppose you have a photo to show us what toast is?

    One of my parts RFVC XR500s had a 'toasted' head. I just checked my collection of photos and can't find one of this head to show you right now. But if I get a chance, I'll dig it out of the attic and take one to post.

    This head has a melted center cam support and ruined cam. The rockers are probably bad since they are highly discolored. It also showed signs of oil ingestion into the combustion chamber, but I don't know how this damage happened. It's just a cheap parts bike after all. Previous owner just wanted it gone.

    But like you, I wanted to understand what happened to cause this so that I could avoid the same situation.

    My best guess is oil starvation due to twisting the oil supply line at the bottom of the frame tube/oil tank. But that didn't explain the carbon buildup on everything from the piston on up. It's still a mystery to me.
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  3. kdxkawboy

    kdxkawboy Mr. NVKLRGirl

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    Journal bearings ride on an oil wedge - can read all about it hear. When the wedge breaks down the bearing looses its lubrication and you get catastrophic failure. The wedge will break down for one of two reasons: insufficient oil flow, insufficient oil pressure. This can be caused by either low oil level, a worn out oil pump, blocked oil line, or the clearances in the bearing exceed service limits.

    While not familiar with the inner workings of of the XR, if you are getting strong oil flow by kicking the beast over you more than likely have a gear driven oil pump - meaning you have two gears that mesh and the meshing action pumps the oil. This is a common design for oil pumps because it is stone reliable, wears for ever and provides pressure at low rpms, like at start up. I don't think its a flow thing, you loose a half pound of pressure for each foot of rise so the low flow at the top is more than likely result of low pressure when just kicking the engine over. Check the oil line to make sure it did not have any blockage. Was your oil low? Since the camshaft is toast, more than likely you can't do a post mortem to check clearances, but with a well worn engine this could be the likely suspect.
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  4. uranys

    uranys Been here awhile

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    After rebuilding my xrl, I couldn't get it to pump oil up to the head. I finally took the oil pump back apart and found I had one of the parts in backwords. Since your problem sounds similar, I'd guess it's either the pump or the supply to it. Have you checked the strainer bolt at the bottom of the down tube? If you haven't, I'd bet that it's partially clogged and restricting flow, which ultimately caused your top end starvation.
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  5. GodSilla

    GodSilla I did that.

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    Just a thought, some motors rely on oil volume for lubrication (old Kawasaki Z900's, for instance) while others rely on pressure (old K series Honda 4's, for example). Common problem with the old Honda 4's used to be that if an owner didn't do regular servicing and let the oil get dirty, it would block the little jets in the head that distribute the oil under pressure, resulting in starvation and camshaft seizures, failed rockers, etc.

    I'd be soaking everything in a strong solvent, then blasting clean with compressed air or high-pressure fluid.
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  6. uranys

    uranys Been here awhile

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    Yeah, the xr650l & xr600r are a high volume low pressure setup. The point I was trying to make in my earlier post is that it doesn't take much to cause problems. In my experience, the strainer bolt in the downtube catches a lot of crap, I check it at least every third oil change.

    I'm against opening up the banjo bolts and increasing the diameter of the feed tube because the way it's set up, if you send more oil to the top end, your sending less to the bottom end.

    There is also a strainer screen on the bottom of the engine that's accessible by removing the clutch cover, but in my experience it rarely has anything on it.
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  7. mothsmear

    mothsmear n00b

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    I took a few pictures but it's hard to see the damage with my crappy camera. The two exhaust rocker arms are worn concave big time, and the camshaft has flat spots worn into it. I don't think the oil level was the cause of it, as I just changed the oil a few days before the ride, and when I drained the oil about 2L came out.
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  8. katbeanz

    katbeanz earthbound misfit, I

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    I've read there's an oil seal inside the clutch cover that mates up with the oil pump. If it get's bad it starves the top end of oil. I've looked at parts fiche but can't seem to find it. My xrl wet sumps like a mofo, you can barely get the dipstick unscrewed before it drains back to the crankcase. :scratch
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  9. mcma111

    mcma111 Long timer

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    [​IMG]



    Katbeanz,

    Your referring to item #13 and 19
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  10. katbeanz

    katbeanz earthbound misfit, I

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    Thanks! :thumb Too bad the L thread is so full of crap and the ignore button works only when you log in. :dunno
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  11. kdxkawboy

    kdxkawboy Mr. NVKLRGirl

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    Do you have flat spots on the cam lobes with the follower on the rocker arms (were the rocker arm contacts the cam shaft) worn concave? If so would want to definitely see pictures, no matter how bad you camera is. How do the cam shaft journals look? If the journals look ok, but the cam shaft lobes have flat spots then I don't think you had an oil delivery problem. It sounds like you just have a well worn engine.
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  12. Ghost_Mutant

    Ghost_Mutant looking for bionics

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    Ok, here are some photos of the bad 84 XR500 RFVC head from the parts bike. It's been cleaned up some and is now a teaching aid for my kids :wink:

    I'm still thinking oil starvation due to twisted supply line. Can anyone confirm this?

    Bad head and cam
    [​IMG]

    Cam with worn center:
    [​IMG]

    Close up of head, note burned out valve stem seals on exhaust
    [​IMG]

    Cam placed in head

    [​IMG]


    So, is your XR600 head damage similar to this?
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  13. mothsmear

    mothsmear n00b

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    No, my damage is more on the rocker arms. Here's the clearest picture I could get. The arm on the left is the worst, and the lobe on the camshaft that contacts that one has a flat spot on it. The valves were checked often and before my final ride on it, so all that damage was done in one day. It was ridden for about 8 hours straight or so.



    http://i1002.photobucket.com/albums/af148/mothsmear/xr600/bike004.jpg?t=1266805972
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  14. uranys

    uranys Been here awhile

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    From the pics, it doesn't look like a starvation issue to me. The center journal almost always gets nuked before everything else.

    Any chance you goofed on the adjustment? Not having enough lash can cause damage like that.
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  15. mcma111

    mcma111 Long timer

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    Actually the rockers and cam usually get the worst of it as the cam is supported on either end by nice big roller bearings. My XR600 lost a rocker arm/cam lobe at the end of a day's riding once and I don't have an explaination as to why. The next time it ate the cam was right after an oil service and I guess that the oil cavitated and never got flow to the top end.
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  16. XRider

    XRider Almost Lifelike

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    The cam shaft in that picture was running with no clearance between it and the rocker arms. You can tell by the way the lobes are black all the way around. The back side of the lobe should lose contact with the rocker arm if it is adjusted properly. The back side of the lobe is also were the oil hole is so if the rocker never lifts off the cam it won't oil properly. Normaly at TDC compression stroke all the spring tension from the valves is off the cam, this allows the tiney bit of clearance on the center cam journal to open up and get a fresh splash of oil. The cam in the photo always had spring tension on it so it started to over heat and catastrophic failer was next. First the aluminum center journal will go and the rockers were next. And all from not having properly adjusted valves.

    This may not be why your 600 ate the valve train but I'm sure that's what happend to the 500 in the pic.

    A few questions about the 600, is the top end stock? You're not running a stage 1 Hot Cam are you? Are you using stock valve springs?
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  17. Ghost_Mutant

    Ghost_Mutant looking for bionics

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    If you don't mind, I have a few more questions regarding your explanation above which I had not heard before.

    Those oil holes in the cam are uncovered for most of the cam's rotation anyway. But you are saying that any oil that comes out (for say 3/4 of a cam revolution) is not going to lube the rockers due to the fact that the rockers are always in contact with the lobes?

    I had always thought that the top end was just splash lubricated where the oil coming out of the cam's oil holes filled up the dish surrounding the cam on the top of the head. I think the cam acts like a centrifuge and throws the oil out the holes.

    Doesn't the oil just pool up on the right side (left side of my photo) of the head near the sprocket bearing? Somehow the oil then finds it's way into the hollow portion of the cam shaft and then get thrown out the little oil holes to lube everything else.

    It's a heck of way to get oil to the other side of the cam. That roller bearing on the far end of the cam seems a long ways away from the oil source.

    What about the rocker pivots? Doesn't both the primary and secondary pivots points get splash lubricated?

    Seems like this is the real weak link in the XR engine design. Hmmmmm

    Sorry for the thread hijack. We still need to figure out what happened to mothsmear's XR600.
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  18. XRider

    XRider Almost Lifelike

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    The 600 (and 500) top end is splash lubricated but if the rockers never lift off the cam then the oil film under the rocker gets wiped off. Same with the center cam journal, with spring tension always pushing it down and the oil not being under pressure inside the cam, it soon runs dry.

    It all works pretty good so long as you service your motor.
    #18
  19. Ghost_Mutant

    Ghost_Mutant looking for bionics

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    That I do not doubt. My main (not the parts bike) 84 XR500 had it's original piston and head still running when I took it apart last year to start the current rebuild. So unlike my parts XR500s, it was better cared for by it's previous owners.

    Thank you for the explanation, it does make sense.

    Perhaps an Archimedes screw inside the cam would get the oil to the other side with a little pressure to help :D
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  20. XRider

    XRider Almost Lifelike

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    I kind of like the screw inside the cam idea. It won't get you any pressure but it would move some oil.
    #20