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charlie74
Jedi Warrior
Offline
Hello all,
I am in the middle of an engine refresh and (hopefully) have just completed my cylinder head. During the machining I asked the shop to mill 0.120” off to increase the compression ratio to better take advantage of the Newman BP270 cam that will replace the original, pitted cam that currently resides in the engine.
Yesterday, I was jubilant in having reassembled my head with it’s freshly reground but original valves. All the studs were installed and I spent quite some time imagining how it will look in the engine bay with new hardware and tarted up manifolds and carbs etc etc…
But then I remembered this. The old inner spring is on the left, er bottom… (no idea why it’s on it’s side but you get the idea):
on my ‘74 head there was a small collar that resided on the outside of the valve guide that the smaller inner valve spring sat on and the larger spring sat directly on the head. I placed these much longer springs on top of the collar and now everything is back on the head. You’re probably seeing where this is going about now…
With the BP270 cam, which according to the specs on their (BPNW’s) website has a maximum lift of 0.410” max lift on the intake valve (exhaust is 0.400”) and also, according to their website the springs will support a cam with 0.420” lift. With the collar installed, do you think that these longer inner springs reach their full compression leading to failure of my rockers? Or, would I be better off removing the longer springs and put the old ones back in as long as their free length is ok? Or removing the collar? Or, of the valve can be fully compressed and as long as the travel is greater than the cam lift, then I should be ok?
Waiting in anticipation of a wisdom plus a hopefully just gentle chastising due to my inexperience in these matters(!),
C74
ps, I did search but couldn’t find anything quite like this…
I am in the middle of an engine refresh and (hopefully) have just completed my cylinder head. During the machining I asked the shop to mill 0.120” off to increase the compression ratio to better take advantage of the Newman BP270 cam that will replace the original, pitted cam that currently resides in the engine.
Yesterday, I was jubilant in having reassembled my head with it’s freshly reground but original valves. All the studs were installed and I spent quite some time imagining how it will look in the engine bay with new hardware and tarted up manifolds and carbs etc etc…
But then I remembered this. The old inner spring is on the left, er bottom… (no idea why it’s on it’s side but you get the idea):
on my ‘74 head there was a small collar that resided on the outside of the valve guide that the smaller inner valve spring sat on and the larger spring sat directly on the head. I placed these much longer springs on top of the collar and now everything is back on the head. You’re probably seeing where this is going about now…
With the BP270 cam, which according to the specs on their (BPNW’s) website has a maximum lift of 0.410” max lift on the intake valve (exhaust is 0.400”) and also, according to their website the springs will support a cam with 0.420” lift. With the collar installed, do you think that these longer inner springs reach their full compression leading to failure of my rockers? Or, would I be better off removing the longer springs and put the old ones back in as long as their free length is ok? Or removing the collar? Or, of the valve can be fully compressed and as long as the travel is greater than the cam lift, then I should be ok?
Waiting in anticipation of a wisdom plus a hopefully just gentle chastising due to my inexperience in these matters(!),
C74
ps, I did search but couldn’t find anything quite like this…