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Old 02-19-2010, 08:01 PM   #1
mothsmear OP
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XR600 top end questions

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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Old 02-19-2010, 08:42 PM   #2
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A photo would help

Quote:
Originally Posted by mothsmear
The camshaft and rocker arms are toast.
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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Old 02-19-2010, 10:16 PM   #3
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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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Old 02-20-2010, 09:00 AM   #4
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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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Old 02-20-2010, 02:38 PM   #5
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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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Old 02-20-2010, 04:14 PM   #6
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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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Old 02-20-2010, 04:52 PM   #7
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Quote:
Originally Posted by Ghost_Mutant
I don't suppose you have a photo to show us what toast is?
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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Old 02-20-2010, 05:45 PM   #8
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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.
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Old 02-20-2010, 05:59 PM   #9
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Katbeanz,

Your referring to item #13 and 19
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Old 02-20-2010, 06:09 PM   #10
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Thanks! Too bad the L thread is so full of crap and the ignore button works only when you log in.
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Old 02-20-2010, 06:37 PM   #11
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Quote:
Originally Posted by mothsmear
The two exhaust rocker arms are worn concave big time, and the camshaft has flat spots worn into it.
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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Old 02-21-2010, 05:09 PM   #12
Ghost_Mutant
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Quote:
Originally Posted by Ghost_Mutant
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.
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

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

Bad head and cam


Cam with worn center:


Close up of head, note burned out valve stem seals on exhaust


Cam placed in head




So, is your XR600 head damage similar to this?
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Old 02-21-2010, 06:38 PM   #13
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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/...g?t=1266805972
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Old 02-21-2010, 07:59 PM   #14
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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.

Quote:
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.
Any chance you goofed on the adjustment? Not having enough lash can cause damage like that.
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Old 02-21-2010, 08:20 PM   #15
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Cam

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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