Front head damage - Honda RC51 Forum : RC51 Motorcycle Forums
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post #1 of 34 (permalink) Old 09-22-2012, 04:39 AM Thread Starter
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Front head damage

38K kilometres on the clock I hear a tapping sound from the front head. Pulled off the front cam cover and found the camshaft journal bolts on the intake loose. That caused damage to the head and journal. Looks like a head replacement coming up. A mate suggested to line bore the head. My question is it possible to line bore the head or is this not advisable.
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post #2 of 34 (permalink) Old 09-22-2012, 11:20 AM
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38K kilometres on the clock I hear a tapping sound from the front head. Pulled off the front cam cover and found the camshaft journal bolts on the intake loose. That caused damage to the head and journal. Looks like a head replacement coming up. A mate suggested to line bore the head. My question is it possible to line bore the head or is this not advisable.
The heads are line bored from the factory. That's matching the journals to the cams.

You could re-line bore if someone made over size cams but no one does or from recollection no one ever did for any bike.

Nope the fix is a head replacement, make sure you get the cam caps if it's used, (pretty sure they come with a new head if that is your route) as they are matched and line bored to each other.



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post #3 of 34 (permalink) Old 09-22-2012, 11:21 AM
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Ya journals looked pooched to me...good luck



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post #4 of 34 (permalink) Old 09-22-2012, 12:03 PM
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I would get a used head from Ben in excellent condition, as he is used to provide, a new head gasket and 4 valve oil seals and bolt it on.
It is the least cost to suffer and the quickest yet durable way to go and be sure that your labor will last.

This looks like human error so I would check the rear head too. Perhaps the error was repeated there too, during it's last valve shim's adjustments....


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post #5 of 34 (permalink) Old 09-22-2012, 12:58 PM
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Makis, would you recommend the cams that are matched to the used head if available? Seems to me that the cam journals on the OP's cams would be pooched also. Nice to have perfect matches.



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post #6 of 34 (permalink) Old 09-22-2012, 01:30 PM
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Makis, would you recommend the cams that are matched to the used head if available? Seems to me that the cam journals on the OP's cams would be pooched also. Nice to have perfect matches.
But of course......sorry if I didn't make that clear. You are very much correct on that.
Buying a replacement head would be optimal if it is the full pack from the gasket up (not the valve cover though).
But even in this case, having a full head replacement, I would consider it a must-to-do to check the oil clearances with some plastic gauge compound. Just to make sure.
The rear cams oil clearance should be checked, as well, even if removing their journals are not any apparent marks or nasty scuffs like was on the front.
Don't forget that a camshaft is made of steel and the journals out of aluminum so it is a natural phenomenon that the journals and head's oil clearance becomes larger by the use of the engine.
Especially during the first 5-7 seconds of those Canadian cold starts


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post #7 of 34 (permalink) Old 09-22-2012, 01:36 PM
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The Canadian cold start would be an issue...but I've been on a MC since I was 8 so that is 39 years.

Not being so green I have realised that riding on those cold, wet miserable days is not my idea of fun and would rather take the car. ; )



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post #8 of 34 (permalink) Old 09-22-2012, 01:45 PM
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That's why I always recommend to cold residence bike owners to use a full synthetic 10W-40 oil (factory recommended API) and their cold start would be to keep the idling up to 2000-2200rpm after hitting the start button so that, the time that the cams and piston pins operate, would be minimized to zero if possible until oil starts to flow through their oil channels.
It's all about keeping the oil pump, pumping as fast as you can, but not exceeding 2500rpm on a cold engine cause then you will have significant piston-to-walls and cam's lobe's wear.....

In warmer zones like were I live, a semi synthetic 15W-50 oil SAE is ok for it's price. But from what I've observed, pulling the choke all the way, the engine idles at 2100rpm so no extra effort on my side.


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post #9 of 34 (permalink) Old 09-22-2012, 04:22 PM Thread Starter
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Thanks guys for your advice. My first thought was human error as well. I should have checked them valves myself when I bought the bike but I did not know any better. I will be checking the rear head next week.

It’s been a steep learning curve the last few months but the satisfaction of getting to know the inner workings of this bike has been worth it.

So if I can get a second hand head I must make sure it comes complete with valves, cams and journals but I can still use the old valve cover.

Since I have an extended warranty cover the other option is to replace the head with a new one. I’m guessing that I will have to replace the valves, cams and journals with new ones too?

Also, I have been using Motul 5100 semi synthetic 20W-50 with OEM oil filters. Is it possible that I have been using the wrong oil here?
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post #10 of 34 (permalink) Old 09-22-2012, 04:40 PM
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What is your average ambient working temperature?

I assume not higher than 32C during summer and not lower than 4C in winter.....


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