PackardV8 wrote: ↑Sun Dec 03, 2017 2:13 pm
Thanks, Mike, et al. I knew we couldn't claim exact, but 1/10th of a degree is close enough for the obsolete guys I go with.
The problem I've found with regrinding is you are making a master off of a lobe. Then you use that master to make a lobe. It's never exactly the same as the original. The only way I will regrinding a cam is if the guy who is doing it has a properly made master, not a copy of a lobe. . . . What about making a master from an existing lobe? Is it possible to even copy a lobe like that and make it exactly the same?
For true; one would never use a copy master if a custom master were a possibility. But for many projects, the perfect is the enemy of the good enough. In the real world of obsolete engineering, usually the only way you're going to get a 50-100-year-old one-off cam reground is to make a master from the best used lobe available. Agree, the result is not what a current max-effort-no-budget-EMC-build would accept, but making a master from a lobe always works and is always better than nothing.
Another FWIW; close enough is usually good enough for most restorations. Many times, there is no cam core available and/or no good-enough lobe available to copy. Slightly off topic, but a local shop was doing a $250,000 restoration of a very rare classic. When the owner was told there was no cam master available and the cost of a custom generated master, he said, "Would the judges ever know the difference when I am driving across the lawn at Pebble Beach?" We work with a cam grinder who specializes in obsolete, looked at all the scarce OEM specs available for that engine, lifter diameter, head and valve train design, compression ratio, RPM range and chose what seemed to be the most compatible match master from the hundreds he has on the rack. The engine seems to like that cam better than the original.
What is not understood by most people is that in order to remove just .010" from the reground lobe of the specific original cam core, it takes re-grinding THAT profile.
Another like profile from a differing application which is almost the same may remove more than .010" in a few places yet only remove less than .010" in some others.
Doing that may be better off in the long run if the regrind is a more modern, later designed lobe profile having better valve train dynamics.
Simply because it will be a bit smaller does not present a real problem in 99% of the cases.
PackardV8 wrote: ↑Sun Dec 03, 2017 2:13 pm
Thanks, Mike, et al. I knew we couldn't claim exact, but 1/10th of a degree is close enough for the obsolete guys I go with.
The problem I've found with regrinding is you are making a master off of a lobe. Then you use that master to make a lobe. It's never exactly the same as the original. The only way I will regrinding a cam is if the guy who is doing it has a properly made master, not a copy of a lobe. . . . What about making a master from an existing lobe? Is it possible to even copy a lobe like that and make it exactly the same?
For true; one would never use a copy master if a custom master were a possibility. But for many projects, the perfect is the enemy of the good enough. In the real world of obsolete engineering, usually the only way you're going to get a 50-100-year-old one-off cam reground is to make a master from the best used lobe available. Agree, the result is not what a current max-effort-no-budget-EMC-build would accept, but making a master from a lobe always works and is always better than nothing.
Another FWIW; close enough is usually good enough for most restorations. Many times, there is no cam core available and/or no good-enough lobe available to copy. Slightly off topic, but a local shop was doing a $250,000 restoration of a very rare classic. When the owner was told there was no cam master available and the cost of a custom generated master, he said, "Would the judges ever know the difference when I am driving across the lawn at Pebble Beach?" We work with a cam grinder who specializes in obsolete, looked at all the scarce OEM specs available for that engine, lifter diameter, head and valve train design, compression ratio, RPM range and chose what seemed to be the most compatible match master from the hundreds he has on the rack. The engine seems to like that cam better than the original.
What is not understood by most people is that in order to remove just .010" from the reground lobe of the specific original cam core, it takes re-grinding THAT profile.
Another like profile from a differing application which is almost the same may remove more than .010" in a few places yet only remove less than .010" in some others.
Doing that may be better off in the long run if the regrind is a more modern, later designed lobe profile having better valve train dynamics.
Simply because it will be a bit smaller does not present a real problem in 99% of the cases.
What's interesting too about "stock" cams is how different they can be from the original OEM camshaft. A year or two ago I rebuilt a Slant 6 for a customer with a late '60's Dodge pickup. His original cam had the fuel pump lobe worn out so I ordered a new stock cam in an engine kit. For fun I plotted both of them and then new cam had more lift, more duration and a different set of centerlines than the original cam by quite a bit. I think it was an improvement and the customer is pleased with how the truck runs.
