Motor Vehicle Maintenance & Repair Asked by Birdman on January 26, 2021
Engine-valves usually get tighter as they’re used.
The symptoms of engine-valves that are too tight, are as follows:
The manual for my scooter states that the engine-valves should be checked/adjusted every 4000 kilometers.
I’ve got 1 cylinder with two valves on my GY6 engine.
My question:
Is it really neccesary to slavishly check the clearance on my engine-valves at the stated interval? Can’t I just check/adjust if one or more of the three listed problems happen?
With only two valves I imagine problems will be much more noticeable compared to an engine with more valves.
The answers so far has been focusing on adjusting the valves – I am questioning the checking/verification of the valve-clearance.
I have found a reply on another site that answers my question:
"I disagree with the gist of this thread which is that out-of-spec valves display immediate symptoms. Valves that are anything but radically out of spec will have the same immediate symptoms as not changing your oil - NONE - the bike will run perfectly fine.
As valve clearances shrink (the typical result of valve wear), but not so much minimal clearance goes away, the bike will run better as valve lift is increased. But once all clearance at operating temp is lost, katy-bar-the door as you'll start losing compression and risk overheating a valve, at best leading to hard starting and poor running, but at worst, catastrophic valve failure. There's little problem with tight valves until they get too tight, then all hell breaks loose.
As valve clearances grow (which is not typical but does happen), the bike will gradually lose power (but probably not enough to notice) and the valve gear might be a bit noisier. Valve train wear will increase somewhat as now the valve is being "slapped" open rather than brought off the seat gradually with the opening/closing ramps. But all these things are gradual and won't show up for quite some time.
Bottom line is that there are VERY FEW SYMPTOMS OF IMPROPER CLEARANCE. That's why valve maintenance - like oil changes - is preventive maintenance to reduce the risk of valve failure and to insure normal valve life. It is not something you should do after symptoms appear. And, like oil changes, you check the valves at some mileage compromise between the maintenance expense and the risk. Unless you have better data or some kind of intuition that the mfg doesn't, it is probably best to follow their recommendations, more or less.
It always amaze me that so many owners are perfectly happy ignoring the mfg's valve check intervals because they hear on the internet that "they never need adjusting", but wouldn't think about not changing their oil 2x or 3x more often than the mfg's recommendations. This makes zero sense. - Mark"
The answer can found at http://advrider.com/index.php?threads/symptoms-of-valves-out-of-spec.627694/
Correct answer by Birdman on January 26, 2021
Valves get “too tight” because the seats are eroding causing the valves to (usually) recede into the head. The clearance is a symptom not a causal condition. So adjust the clearance and do a leak-down test to actually learn the condition of the valve/valve seat.
Answered by TomO on January 26, 2021
It is not necessary to adjust the valves if you are satisfied. You will not be damaging the engine permanently.
Answered by Carguy on January 26, 2021
Check the valve clearances as you are supposed to. It will take you 5 minutes the first time and 2 minutes each time after that. It is a very easy job with a feeler gauge and can prevent costly damage to the cylinder head that would occur if the exhaust starts to blow hot gas past the valve when the engine is warm due to tight valve clearance. The tight valve will burn the exhaust valve and valve seat away.
Answered by r.anderson on January 26, 2021
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