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davecampbell

06 head cam oiling problem

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We bought a 2006yz450f basket case and put it back together. It had a exhaust cam seize in the head so we sent the head out and had it repaired and put in a new set of hotcams. After one hour the exhaust cam has seized in the head again! We have blown through all of the oil passageways and can't find a problem. Any ideas as to why the problem is repeating?

Is it possible to buy a high volume oil pump for this motor?

Edited by davecampbell

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We tried rolling the motor over by hand but didn't see any oil coming up to the cam. I just thought since it had to get oil out of the crankcase into the sump then to the oil pump It would probably take a long time that way. I will try tearing the side cover off and check the pumps tomorrow night I guess. Is there another way to check the pump without removing it?

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Ok everything checked out good. Since I have it out I guess I will put in a new oil pump. Should I put in a new rotor assembly too?

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I think I would take out the valves and make sure the cam ran smoothly with the cap on and torqued. Cam cap bolts are 8 ftlbs if I remember correctly.

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Engine dynamics had repaired the cam and we had followed his recommendation that we only torque them to 5 ft lbs instead of the book spec of 8. The head is currently headed back to be machined again and you can be sure we will test to make sure the cams spin freely before reassembly this time. I believe they did last time too but this time we will double and triple check!

There looks like there is a check valve or something right at the base of the cylinder. I would like to know what that is and how to test it because I want no stone unturned this time around.

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Cam cap bolts are 8 ftlbs if I remember correctly.
You remember incorrectly. The specified torque is 86 in/lb or 7.2 ft/lb, and I never run them that tight. I use 75 in/lb. The torque pattern is also critical, as is the practice of torquing in 3 small increments, and it is further extremely important that you never pull the caps down with the bolts. Always seat them by hand.

If the head has been damaged by the seizure, it needs to be repaired again. Likewise, any surface damage to the camshafts must be cleaned up or the cam replaced, and the clearances between the cams and head needs to be checked.

In checking oil passages for flow restrictions, it's always better to use oil in a squeeze bottle or syringe rather than air, because air will flow past significant restrictions without being visibly hindered. I've seen this several times in working with auto transmission valve bodies. There is a check bolt in the head the can be used, but what I would do with this one is to assemble the head onto it minus the cams and the cam chain, and with the spark plug removed, turn the engine until oil is delivered to the head. Remember that in order for this to happen, there must be oil in the "tank" section that feeds the feed pump, and the oil filter well will have to be full.

That brings up one other question in my mind. If the bike has a Ready Racing oil filter cover on it, a black cover with a big "R" on it, the oil filter can be installed backward, and cut off the flow of oil to the entire system. Be sure the filter is in the well with the open end outward. The OEM cover has, or had to start with, a tab that prevents the filter from being reversed, but RR brilliantly omitted that on theirs.

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In checking oil passages for flow restrictions, it's always better to use oil in a squeeze bottle or syringe rather than air, because air will flow past significant restrictions without being visibly hindered. I've seen this several times in working with auto transmission valve bodies. There is a check bolt in the head the can be used, but what I would do with this one is to assemble the head onto it minus the cams and the cam chain, and with the spark plug removed, turn the engine until oil is delivered to the head. Remember that in order for this to happen, there must be oil in the "tank" section that feeds the feed pump, and the oil filter well will have to be full.

I will try that on re-assembly. Do you know what this is?

th_wryz250fparts011.jpg

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If you mean the little gizmo sticking out of the crankcase above the crank, yes. That's spray nozzle to direct oil onto the bottom of the piston crown to help lube the small end and cool the piston.

Need a manual?

NO I guess I just need to READ the manual. I have one but evidently did not search well enough!

THANKS

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NO I guess I just need to READ the manual. I have one but evidently did not search well enough!

THANKS

Everything isn't in it in a lot of detail, sometimes. The whole oil circuit is diagramed out in section 2, though.

You do understand that it's a dry sump system, and what that means, right?

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You do understand that it's a dry sump system, and what that means, right?

I think so. I have been around them on race cars ans the basic principle looks the same but with the 450 it looks like the "tank" is incorporated into the motor. What I'm used to calling the scavage pump seems top be called the "rotor"

I don't see the oil diagram in my manual so I will try to look at the link you posted instead

THANKS

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Page 2-19 for the diagrams.

"Rotor" is a component of either pump (there are two, of course). The manual does refer to the return, or scavenging pump in that way, yes. But if you opened up the feed pump, you'd find another set of trochoid rotors there as well. And, yes, in the '06+, the "tank" is integral with the crankcases, but still a separate volume.

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The diagrams helped me a bunch. I have one more passageway to test that goes to the transmission to make sure oil is not escaping too easily there. I see that it branches off of the feed to the top end so that could be the culprit if the top end was not set mistakenly in some way. I'm thinking that although that is not common it may have happened in this instance because the intake cam is still perfect and it would seem that if we ran the top end without sufficient oil there should be at least some intake cam journal damage too.

Page 2-19 for the diagrams.

"Rotor" is a component of either pump (there are two, of course). The manual does refer to the return, or scavenging pump in that way, yes. But if you opened up the feed pump, you'd find another set of trochoid rotors there as well. And, yes, in the '06+, the "tank" is integral with the crankcases, but still a separate volume.

I did open up the feed pump too but everything seemed fine. Just normal wear but not worn out.

Edited by davecampbell

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It is typical of branched oiling circuits that each branch will have an orifice somewhere in the line that limits the flow to that branch in the event of a major leak, like a plug blowing out, or a bearing failure. This allows the pump to maintain a normal head of pressure against the rest of the system. That way, a bad bearing in the trans won't cause the cams to starve.

Cam seizures and the associated damage are not uncommon, but they are rarely caused by oil system faults. Normally. it's incorrect torquing procedures at tha caps that are to blame.

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Cam seizures and the associated damage are not uncommon, but they are rarely caused by oil system faults. Normally. it's incorrect torquing procedures at tha caps that are to blame.

We thought we were careful with the torque on the cam bolts but on re-assembly we will be extremely careful. A this point we have split the cases to double-check everything and should start the re-assembly Thursday night.

Thanks for all the help

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