Strange valve clearances problem.

[VFRkieran]

Thought id start a thread rather than asking in the guide as this one is a bit unusual.

I checked the valve clearances on my NC30 about 8000km ago and they had all tightened up waaay too much i think only one shim was just within tolerance and some where as low as 0.06mm which was a bit worrying, but i bought all the new shims i needed to get it back into spec and everything was fine, ran the bike for as i say 8000 odd kilometers without issue.

Now to the problem, as a few people will have seen im rebuilding the bike over winter and i have just dropped the engine out of the frame to give the heads a bit of love. I thought id check the valve clearances to see how much had changed since i last did them, and it turns out its gone quite badly wrong.

Not a single gap is within tolerance the inlet valves are all sub 0.10 with one as low as 0.04. The EX valves are between 0.11 and 0.15, the only explanation i can think thats causing this is the valves not seating correctly, i am sure i checked correctly. The bike has the oil changed every 4000 miles, is allways warmed up correctly and never revved above 5k in neutral, I really do look after this bike which is why i have no explanation for the clearances tightening up by so much!

Any help with this will be apreciated, i will also upload a few photo's of the valve faces as i have now taken the heads off so hopefully there will be a giveaway there.

Kieran.

[speedy231278]

Assuming the valves aren't damaged, how about lapping them in and doing the clearances again?

[VFRkieran]

Sorry forgot to mention thats what i will be doing along with replacing the stem seals and fitting RVF camshafts, i wasnt even going to measure the clearances because of this, but i thought it would be best to check and see how good/bad they where. Photo's just uploading to photobucket now.

[VFRkieran]

Pictures:








Theres a fair bit of carbon buildup around the valve seats so im thinking this could be part of the problem?

[CMSMJ1]

They do look a bit scabby eh? Get them lapped in and it will close the clearances up some more. You might want to get the valves checked for length too.

The usual closing of the gaps is normal - the valves are smacking into the seats pretty bloody hard and it causes them to recess.

When I set my valves I have always done them at the more loose end of the tolerance

e.g - 0.12 to 0.18 on inlets - I am setting to 0.17 or 0.18

You can imagine how much more efficient your bike is going to be if you lap and clean the valves and the heads (and if you are feeling lively, get the casting flash removed)

The bike will love you for it.

[Drunkn Munky]

Just to echo what mark has said i always set them on the loose side too.

[pip]

Just to echo what mark has said i always set them on the loose side too.

I can understand the logic in this, however, surely in normal use when everything is correct valve clearance change would be negligeable - whats the Honda interval 16k & normally they wouldn't/ shouldn'tbe far out after that mileage.

Anyway, just to be contrary, I normally set them somewhere between small (but above minimum spec )& mid clearance - reason being I hate ticky, tappety engines & they always seem to run sweeter with smaller clearances

Havibg said that, there is something not right here - they shouldn't tighten up that much in that mileage.

Pip

[Drunkn Munky]

No they shouldnt, my guess is that you've misjudged it when you first did it.

[CMSMJ1]

You would also expect that the first 16k would result in a little bedding in. The next should be stable and perhaps the valve seats are past their best by the time you come to check again.


I have paranoia about too tight clearances...imagine that poor valve trying to get out the way of that nasty piston rushing up to smack it in the face. just 0.2mm might save it!

[pip]

You would also expect that the first 16k would result in a little bedding in. The next should be stable and perhaps the valve seats are past their best by the time you come to check again.


I have paranoia about too tight clearances...imagine that poor valve trying to get out the way of that nasty piston rushing up to smack it in the face. just 0.2mm might save it!

Hmm, doubt it!
My last '30 had most of the 16 valves tight, some with only minimal clearance. Ran fine up to the redline before & after adjustment - it's a Honda, they are quite good like that

Pip