2002 RC51 valve Clearance Issue - Honda RC51 Forum : RC51 Motorcycle Forums
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post #1 of 26 (permalink) Old 02-17-2016, 11:56 AM Thread Starter
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2002 RC51 valve Clearance Issue

I have done some searching & didn't find anything useful on this specific subject. So, if this is covered in another thread, please just point me in the right direction...

So, the other night, I decided it was time to check my valve clearance. My valves are too tight, all of them!
I have the actual measured numbers written down in my shop manual at home. I will post later when I get home from work because I know someone will ask how far out they are. They are a good bit out, way past the +/- listed in the shop manual.
If anything, I assumed that they would be loose!
My question(s) is: How does this happen? Do you think the Guy that I bought the bike from had the valves shimmed and they installed too large shims?

This is an interference motor, correct?
Also, the valves being too tight could cause my hp to be lower, because the combustion chamber is not properly sealed, correct?

Any help is much appreciated. Let me know if you need more info.
Thanks in advance!

Background Info:I bought (stole, $2,800.00!!) the bike from a Guy 2 years ago. It currently has about 28k miles on it. I have put a few thousand on it since I bought it. I think the bike had 21k miles when I got it.

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post #2 of 26 (permalink) Old 02-17-2016, 02:27 PM
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Tight clearances can result from either burnt valve seats or burnt valves.

It could be that someone's been in before and set them too tight, but the best way to find out is to do a compression test.
It wouldn't be conclusive as a lower compression could be ring/bore wear, but you can identify if that's the case by adding a teaspoon of engine oil down the spark plug hole (it's called a wet" test).
Measure the dry one first, then do a wet test.
If the readings are much the same, then a lower compression reading will be valves.
If the readings differ, it will be worn bores, or possibly both.

But you have to be sure that you have no head gasket leaks- if there's oil foam or milky sludge in the coolant filler neck or expansion bottle, or you lose water or oil- leaks appear on the head area usually- then you need to pull the heads off to replace the gaskets.

So, to be absolutely sure, pull the heads, but a compression tester is a cheap way to check it out without getting into the engine.

It's not falling off, it's an upgrade opportunity
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post #3 of 26 (permalink) Old 02-17-2016, 02:53 PM
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The valves always go tight not loose, just shim them and see how it goes
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post #4 of 26 (permalink) Old 02-17-2016, 03:31 PM
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One of the biggest reasons we see for tight valves is the excess of carbon buildup on the valve or the seat. It's amazing how quick it happens, especially with ethanol fuel. We had a CBR1K motor apart the other day and the build up on the valves was staggering. The valves ended up being like .008 out. We scrubbed the valves and seats and didn't even reshim and then they were back in spec. It's unreal how fuel can do that to a motor.
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post #5 of 26 (permalink) Old 02-17-2016, 03:32 PM Thread Starter
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Originally Posted by Tony.mon View Post
Tight clearances can result from either burnt valve seats or burnt valves.

It could be that someone's been in before and set them too tight, but the best way to find out is to do a compression test.
It wouldn't be conclusive as a lower compression could be ring/bore wear, but you can identify if that's the case by adding a teaspoon of engine oil down the spark plug hole (it's called a wet" test).
Measure the dry one first, then do a wet test.
If the readings are much the same, then a lower compression reading will be valves.
If the readings differ, it will be worn bores, or possibly both.

But you have to be sure that you have no head gasket leaks- if there's oil foam or milky sludge in the coolant filler neck or expansion bottle, or you lose water or oil- leaks appear on the head area usually- then you need to pull the heads off to replace the gaskets.

So, to be absolutely sure, pull the heads, but a compression tester is a cheap way to check it out without getting into the engine.
Tony.mon,
That's great advice. I will perform these tests as recommended. However, I do hope that you are wrong about burnt valves/valve seats & the worn bore!
The bike makes good power, but I do not have another RC to compare it to.
Hopefully it's just shims that are too big.
Again, Thank You for the advice

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post #6 of 26 (permalink) Old 02-17-2016, 03:38 PM Thread Starter
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Originally Posted by Quizzy View Post
One of the biggest reasons we see for tight valves is the excess of carbon buildup on the valve or the seat. It's amazing how quick it happens, especially with ethanol fuel. We had a CBR1K motor apart the other day and the build up on the valves was staggering. The valves ended up being like .008 out. We scrubbed the valves and seats and didn't even reshim and then they were back in spec. It's unreal how fuel can do that to a motor.
Quizzy,
Thanks for the heads up on this. I knew that ethanol gas is horrible on gaskets & plastics & especially carburetors, but I had no idea that it would cause bad buildup on valves. I'll do the testing as stated above and see how that goes and then I pull the heads as needed. Or, maybe I should go ahead and pull the heads... Hmm

Thanks for your help Guys, I would be lost without forums like this one!

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post #7 of 26 (permalink) Old 02-17-2016, 03:39 PM
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Quote:
Originally Posted by Quizzy View Post
One of the biggest reasons we see for tight valves is the excess of carbon buildup on the valve or the seat. It's amazing how quick it happens, especially with ethanol fuel. We had a CBR1K motor apart the other day and the build up on the valves was staggering. The valves ended up being like .008 out. We scrubbed the valves and seats and didn't even reshim and then they were back in spec. It's unreal how fuel can do that to a motor.
wouldn't a build up on valves or seats make the gaps open up?
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post #8 of 26 (permalink) Old 02-17-2016, 03:42 PM Thread Starter
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Originally Posted by Tony.mon View Post
Tight clearances can result from either burnt valve seats or burnt valves.

It could be that someone's been in before and set them too tight, but the best way to find out is to do a compression test.
It wouldn't be conclusive as a lower compression could be ring/bore wear, but you can identify if that's the case by adding a teaspoon of engine oil down the spark plug hole (it's called a wet" test).
Measure the dry one first, then do a wet test.
If the readings are much the same, then a lower compression reading will be valves.
If the readings differ, it will be worn bores, or possibly both.

But you have to be sure that you have no head gasket leaks- if there's oil foam or milky sludge in the coolant filler neck or expansion bottle, or you lose water or oil- leaks appear on the head area usually- then you need to pull the heads off to replace the gaskets.

So, to be absolutely sure, pull the heads, but a compression tester is a cheap way to check it out without getting into the engine.
Quote:
Originally Posted by Quizzy View Post
One of the biggest reasons we see for tight valves is the excess of carbon buildup on the valve or the seat. It's amazing how quick it happens, especially with ethanol fuel. We had a CBR1K motor apart the other day and the build up on the valves was staggering. The valves ended up being like .008 out. We scrubbed the valves and seats and didn't even reshim and then they were back in spec. It's unreal how fuel can do that to a motor.
One more thing that I just thought of: when I was checking the valve clearance & rotating the crank, getting close to TDC, I could hear air leaking into the exhaust. It was very hard to rotate the crank when I got to the combustion stroke, so I figured that I had good compression. But, I didn't expect to hear air escaping into the exhaust while it was on the combustion stroke. Does this mean anything to you Guys??

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post #9 of 26 (permalink) Old 02-17-2016, 03:44 PM
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There is a bit of overlap but I'm not sure how much for the RC without pulling the manual. But again if there is buildup around the seat a valve could not be closing all the way.
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post #10 of 26 (permalink) Old 02-17-2016, 09:39 PM
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Valve overlap on stock engine: 40 deg

As bad as E10 is, your government (not mine, I don't claim the SOBs) want to move to E15.
I'm sure that will work real fine on older cars, truck, and bikes.
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