i'm in the process of re-building an 18RG, and my old man is doing some head work, he gave me a call the other day to say that i will probably need to get the cam journals line bored because one or 2 of them have some reasonably deep marks...
i've just been thinking, what if i get them bored to the same diameter, but drop the centerline height say.... 10 thou, cam cap mating face (bit where the cam caps sit) machined 10thou also... my thinking is that this would effectively give me (about) 10thou more lift as the cams would be sitting closer to the block, however would mean that when the valves are suppose to be closed the cams are likely to be holding the valve open a touch, which could be solved by re-grinding the cam so as to decrease the base circle. another down side would be that it would upset the cam timing, but could be solved with adjustable cam gears (probably going to be getting them anyway 'cause i plan on decking the block a bit too). another advantage to having the cam journals bored would be an increase in valve spring tension because of the increased lift, though would be minmal gain.
is there any reason my thinking won't work? what other things should i be considering?
wont be any more lift with cams untouched as you have to set clearances anyway.
base grind of cam will give more lift/duration.
no change in spring tension unless you shorten the valves/collet hight, or fit hd springs.
when you take 10thou off the caps you have to line bore so you would only move into the head by 5thou tops (especially seeing you need the marks in the caps removed)
you may have to clearance the head from the lobes (not sure without looking) but that would only be marginal.
yeah, was doing more thinking, and it seems it would be fairly pointless considering you'll need to re-grind the cams anyways setting the shim clearances will take up all the movement...
Maching Cam Journals
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