Here it is,
we don't have valve spring problems nearly as much as we have increased resistance from high combustion chamber/head temps causing the tubes the lifter/bucket/spring caps slide in to "stick " and also cause early bucket failure.
The heat causes the head to expand making the hole for the bucket tighter and causes the valve to stick even from slower closing in the cycle which lets it hit the head. I have noticed this twice , once when I improperly bled a coolant system and overheated the head on a dirtbike and popped a valve via head cylinder disaster and once when a friend overheated his quad a spun a flywheel which is another heat related failure in my opinion
I have pulled the buckets out and they have very close tolerances it wouldnt take much to make them get stuck or stick and cause slower closing and harder opening which would translate into deeper impressions on the bucket cap from the shim/retainer cap. Timbo mentioned the buckets sticking on some heads I am just stating my opinion regarding why.
Regarding flywheel when a crank eats a big end bearing or particularly a flywheel side main it can get very hot and transmit through the crankshaft to the flywheel hub which will expand and loosen the grip the center hub has on the outer flywheel casting and after multiple heat cycles and high rpm changes they simply spin, which pinning can probably prevent but not totally repair problem. ( I have all my flywheels pinned , and most of my friends )
Please read and post your comments I am here to learn - not show off everything I know in one post
theory
-
cannondale27
- Posts: 0
- Joined: Wed Mar 10, 2021 10:41 pm
I think sticking buckets is for sure part of the problem but we also have valvesprings that arent in spec even when new.It is weird how many worn cams it will be one lobe on intake and one on exhaust.Sticking buckets might explain that.Guy would have to heat a whole head and buckets to a overheat condition and see how the buckets fit.
I'm wondering what type of engine oil was being used when the bucket problem happens on motors were the buckets are still oringinal.
Or is it just happening after they been worked on ??
I dont know why, maybe I shouldn't say it, but I haven't had a single problem yet. We change our oil often (like every tank full of fuel)
Is it a thermal break down of the oil ?? how old is the oil ??
Once that oil starts turning brown, it's done, time to change it.
Lets hear from other people that changes their oil as often as I. Have you had any problems ??
Or is it just happening after they been worked on ??
I dont know why, maybe I shouldn't say it, but I haven't had a single problem yet. We change our oil often (like every tank full of fuel)
Is it a thermal break down of the oil ?? how old is the oil ??
Once that oil starts turning brown, it's done, time to change it.
Lets hear from other people that changes their oil as often as I. Have you had any problems ??
azcannon,
I think you may be on to something. I am very proficient at mechanics and internal combustion motors, and they are all the same in the end. Some have different fuel delivery, different cam arrangements, etc. Yet the basics are pretty much the same if you understand the different designs.
I have torn down one dale motor that had a worn exhaust cam with one lobe being fine and the other being severely worn. The lobe was essentially round and the bucket extremely worn. Perhaps the most difficult thing was removing the bucket from the head. I had a VERY strong magnet trying to remove the bucket, yet it was difficult to remove. This head still had oil all through it and it was still hard to move at all.
Would a spring cause excessive wear because it was out of spec? Most definitely. But in this one situation I would clearly lean towards the bucket clearance.
All of these new breed 4 strokes are built to having every last pony being wrung out of them. The thing we have to realize is that they must have very tight tolerances to make them as efficient as possible. There is a fine line between max performance and a grenaded motor.
I think you may be on to something. I am very proficient at mechanics and internal combustion motors, and they are all the same in the end. Some have different fuel delivery, different cam arrangements, etc. Yet the basics are pretty much the same if you understand the different designs.
I have torn down one dale motor that had a worn exhaust cam with one lobe being fine and the other being severely worn. The lobe was essentially round and the bucket extremely worn. Perhaps the most difficult thing was removing the bucket from the head. I had a VERY strong magnet trying to remove the bucket, yet it was difficult to remove. This head still had oil all through it and it was still hard to move at all.
Would a spring cause excessive wear because it was out of spec? Most definitely. But in this one situation I would clearly lean towards the bucket clearance.
All of these new breed 4 strokes are built to having every last pony being wrung out of them. The thing we have to realize is that they must have very tight tolerances to make them as efficient as possible. There is a fine line between max performance and a grenaded motor.