Valve adjustment - more lessons learned
- Thread starter MGB
- Start date
WJBertrand
Ventura Highway
Astonished to hear the timing chain was shot at such low mileage.
Sent from my iPhone using Tapatalk Pro
Sent from my iPhone using Tapatalk Pro
That intake valve appears to be chipped or something...
Sent from my SM-N950U using Tapatalk
With that many miles, what has been your history on checks and adjustments? Other than that one valve it looks pretty clean given the miles.
Sent from my SM-N950U using Tapatalk
sandro1973
Active Member
I guess if you do lots of long distance riding, it'll last longer, much less stop and go, more linear riding.
Usually in my country, which is much smaller than yours ( less than 350 miles, from north to south, and 135 miles on the widest part....),, the miles on my bike are considered high....most portuguese guys wouldn't buy it on that alone....
SkunkWorks
Well-Known Member
To me, this looks like a classic example of a "Burnt" exhaust valve.
Usually this is caused by the valve adjustment becoming too tight as the valve/seat wear. This in turn causes the valve to overheat due to not spending enough time on the seat to cool down.
Check your valves at the recommended intervals.
Adjust them if they are too tight.
escapefjrtist
Searching for Dry Roads
Large valves are intakes. Classic example of a burnt valve.
~G
~G
Learned my lesson for the day...
"In general, engines exhibit better performance when intake valve size is optimized. Exhaust valve size is not as critical. It's not unusual for the intake valve to be much larger than the exhaust valve. And the result is better volumetric efficiency. The reason the exhaust valves are smaller is because the smaller pressure difference over the intake valves. It's the pressure difference over the valves that drives the flow, and the pressure difference is greater on the exhaust side. "
We already know that there is a high percentage of probability that the valve failure has been due to a tight fit ... but the poor closing of the valve may also be due to an excess combustion temperature, which causes the valve to expand. Outside its parameters, it tends to deform and does not make a perfect seal and the heating process due to lack of heat dissipation increases. That is why I was asking for an “excess combustion temperature”… ..perhaps “a reflash”…. ”Fuel with minerals that stick to the valve and generate hot spots”…. ”Ignition corrections by reflash”… .etc … .If we rule this out first… ..we would increase the percentage that the cause of the failure was due to an over-tight fit
Yes, I know ... I'm too complicated ... my wife always tells me that I always see more problems than there really are. but hey, I'm like that .... I usually leave the most obvious for last ...
Last edited:
WJBertrand
Ventura Highway
I'm not sure I understand the physics why different riding styles would affect timing chain life. It experiences the same loading regardless of throttle application, unlike say a final drive chain. In fact the largest variable the chain would see is RPM, which to my thinking would be worse for long distance, higher speed riding.I guess if you do lots of long distance riding, it'll last longer, much less stop and go, more linear riding.
Usually in my country, which is much smaller than yours ( less than 350 miles, from north to south, and 135 miles on the widest part....),, the miles on my bike are considered high....most portuguese guys wouldn't buy it on that alone....
Berg_Donk
Active Member
Abrupt/snappier throttle on and off puts shock loads on the chain and likely is the biggest wear contributor.
WJBertrand
Ventura Highway
I dunno. I think a lot of perfectly good timing chains are getting changed unnecessarily.
Sent from my iPhone using Tapatalk Pro
Sent from my iPhone using Tapatalk Pro
I don't recall, and too lazy to look it up. Is there a prescribed length limit or check in the manual?
Sent from my SM-N950U using Tapatalk
WJBertrand
Ventura Highway
No, nothing listed on the maintenance schedule about the timing chain.
Sent from my iPhone using Tapatalk Pro
Man, that's as clear as mud. (Especially as hard as it is to see anything in those tight spaces.) For those who elect to replace the chain, I hope you are replacing the sprocket/crankshafts also as a set. Otherwise you may be wasting time and money. Sounds pricey to do it all correctly.
jbrown
Active Member
If someone had decided to replace the chain, I think they'd be likely to just replace the $25 chain first, and leave the $1000 crank and sprockets alone. At least I would. Of course I'd be doing the work myself, so I'm not considering the labor cost.
WJBertrand
Ventura Highway
Of course there are inspection specifications but there is still no recommended replacement interval/mileage in the maintenance schedule. That second illustration seems to be intended for establishing correct timing. Note that it refers to the number of links instead of a measurement. Most timing chains are intended to last the life of the engine.
Sent from my iPhone using Tapatalk Pro
Sent from my iPhone using Tapatalk Pro
Last edited: