Cam bearing tower machining marks? Ever seen this?
#1
Cam bearing tower machining marks? Ever seen this?
So I need to replace the valve stem seals on my NB and I have run into these odd machining marks on the rear of all four exhaust cam bearing towers (or whatever they are called). They are raised enough that I can't get the lifters out past them. It's not a huge deal, going to use a dremel and very carefully get the back flush, but any idea where/how this happened?
Engine is original to the car, early NB made in January of '98 (did they make any NBs in late 97?). 183k miles on it.
Engine is original to the car, early NB made in January of '98 (did they make any NBs in late 97?). 183k miles on it.
#4
The process used in the original machining would’ve required the head to be repositioned after the roughing of the bucket bores to another station where the finish tool would then complete the diameter and roundness. Looks like a fixture clamp didn’t lock causing the location of the 2 processes to be different. Maybe machining chips pushed the locator out of position…? The lifters were assembled into the bores by a mechanical press (or pneumatic) so likely the misalignment wasn’t enough to cause a fault in the process for anyone to notice.
A typical process used today would involve a tool change so the head would not be repositioned. Some of the Japanese mfg still used the inline process though up through the past 10yrs. Old habits are tough to break.
A typical process used today would involve a tool change so the head would not be repositioned. Some of the Japanese mfg still used the inline process though up through the past 10yrs. Old habits are tough to break.
#5
The process used in the original machining would’ve required the head to be repositioned after the roughing of the bucket bores to another station where the finish tool would then complete the diameter and roundness. Looks like a fixture clamp didn’t lock causing the location of the 2 processes to be different. Maybe machining chips pushed the locator out of position…? The lifters were assembled into the bores by a mechanical press (or pneumatic) so likely the misalignment wasn’t enough to cause a fault in the process for anyone to notice.
A typical process used today would involve a tool change so the head would not be repositioned. Some of the Japanese mfg still used the inline process though up through the past 10yrs. Old habits are tough to break.
A typical process used today would involve a tool change so the head would not be repositioned. Some of the Japanese mfg still used the inline process though up through the past 10yrs. Old habits are tough to break.
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