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Good afternoon. I'm brand new to this forum, but not a newbie when it comes to the RC51, having owned mine since 2005. Up until now I've never ever needed this forum because my bike has been so damn reliable. It's a 2001 SP1 with 40000km (24850 miles), which is actually less because it had a smaller front sprocket on it when I got it, which I changed back to stock.

I took it out for my first ride of the year in June, on a warm but not hot day. About 30mins away from home I had to slow down to go through a town, wait at a red light, and then was able to continue on. Of course, the bike got a little warm, showing a high temperature of 93 Celsius (about 200 Fahrenheit), which is normal for my bike having to slow down. When I was able to increase my speed, I did so gradually, and started hearing a loud ticking sound coming from the motor. It didn't last too long because the bike stopped running right after the sound started and, once stopped, wouldn't even crank over. I had it towed home, let it cool down and dropped the oil out of it, but didn't find any metal in it. Once I replaced the oil and filter, I started it to see if the noise was still present, and it was.

It sounded like a very expensive noise, so I parked it until last week when I started taking it apart to check the valve clearances thinking that could be the problem. I started it once again and isolated the noise to the top end of the rear cylinder. When I pulled the valve cover off, I noticed some small metal shavings above where the left (looking from behind) intake valve is. I checked the valve clearances as per my Honda service manual and came up with the following:

Left Intake - .025in (.635mm)
Right Intake - .014in (.356mm)
Left Exhaust - .010in (.254mm)
Right Exhaust - .011in (.279mm)

I was shocked at the amount the intake clearances were off from the factory specs, especially when the exhaust clearances were so tight. Upon further investigation I discovered some metal in the wells next to the valve lifters, and then discovered what appears to be damage to the intake cam journals. I've attached some pics to show what I'm referring to. Sorry for the long post, just wanted to give as much info as possible. Thanks.
 

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I hate to say it, but your top end on that cylinder is probably gone.
And I'd inspect the remaining head for damage as well, to be sure.
You'll need to replace the entire head assembly.
I bet if you pulled the cam, it will probably show the cam and head journals destroyed.

What I also find puzzling from the photos is, that cam lobe and shaft discoloration looks almost like rust (brownish color).
It looks like a case of oil starvation causing failure as the cam lobes and shaft are totally dry (no oil film).

Besides having to replace at least one head assembly, you're going to need to be extra careful that all the oil passageways are clear, from the oil strainer upwards.
Oil starvation is what may have caused the problem, and if not corrected, it will trash another set of heads just as quick.

It may be cheaper and quicker to look for a good used engine assembly, and swap out the engine.
 

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X2 sub, the rust in the top end is kinda weird, kinda hints at maybe it hasn't been oiling good for a while, or either sat for a long period of time without being cranked. This is mine a 18k miles just as a reference

 

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Discussion Starter #4
Thanks for the quick reply SubSailor. Once I discovered the damage to the cam journal and realized that the lower journal is part of the head and there's no insert bearing in there, I figured the head would need to be replaced.

Also, thanks for answering my next 2 questions. It is definitely a lot drier than the exhaust cam so I figured oil starvation was the culprit.

What's the best way to ensure the oil passageways are clear?
 

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Discussion Starter #5
It did sit most of last summer, save for a few km's up and down my road before putting it away. Also, it is stored in a bit of a humid/damp garage, which didn't help I'm sure.
 

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So your exhaust clearances look OK (if that's what you meant by "tight") but your intake is way to big. Not the usual situations so I suspect that your inlet cam lobes have worn through the case hardening giving you excess clearance.
Also the parts look very dry. Did you wash everything down with degreaser first? If not, you've suffered oil starvation so likely the head, and possibly the motor are toast. Sorry to see that.
 

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Thanks for the quick reply SubSailor. Once I discovered the damage to the cam journal and realized that the lower journal is part of the head and there's no insert bearing in there, I figured the head would need to be replaced.

Also, thanks for answering my next 2 questions. It is definitely a lot drier than the exhaust cam so I figured oil starvation was the culprit.

What's the best way to ensure the oil passageways are clear?
No easy and 100% sure way with the engine in one piece.
The best way would be to pull the engine and disassemble it, the inspect every nook and cranny for debris lodged somewhere.

And since that head is for sure gone (and I wouldn't trust the other head either, give the current damage), it may simply be easier to locate a good used engine and swap the damaged one out.

I say this because, we had a member from S. Africa who had his head(s) destroyed by oil starvation, had it repaired by a local shop (which didn't fully ensure the oil passageways were clear), and then had the same problem occur again.
I think on the 3rd pair of heads, he finally got a working engine after making sure all the passageways were clear of debris from the first incident.
 

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You can pull the plugs, remove the cam covers and then turn the motor over on the starter. You should see oil coming out the back of the cams.
 

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It did sit most of last summer, save for a few km's up and down my road before putting it away. Also, it is stored in a bit of a humid/damp garage, which didn't help I'm sure.
I see you live in Canada, and condensation can form on cold metal parts during the winter, especially if not in a heated area.
But even then, the I think the part should still have an oil film, even if sitting for a few months.
 

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And if you do repair that engine use NEW bolts on the cases and cam caps also look at the arrows and keep the caps matched-up;)
 

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IMO, the discoloration came from the heat generated when it ran out of oiling (it looks dry too). It isn't rust from what I can tell by pics and it makes no sense to be.
 

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Discussion Starter #12
How would something like this be repaired by a shop? I'm guessing they would bore out the damaged cam journals and then use an insert bearing to bring it back down to the original size.
 

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I would say most shops wouldn't attempt it, you might be able to find a machine shop that will align bore the cam journals and install roller bearings, but it ain't gonna be cheap, probably be better off starting over with some different heads
 

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Honestly, considering the mileage on that engine, I would search for a nice low mileage complete engine before investing the money in that one. Chances are you can find a good engine, with less than half the mileage, for less than the parts and labor to fix that one. Then you have the question of where else metal has gone. Metal could be spread to other places in the engine and done damage.
 

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Discussion Starter #15
Thanks for the info. I'll definitely scratch the repair idea off my list. I'll probably take it apart some more and try to give it a thorough inspection, and then make a decision from there.
 
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