Can anyone explain valve to valve clearance? I am setting my spring pack for a larger cam. It was brought to my attention that my current heads don't have enough valve to valve clearance to accomodate my new cam. I currently have .010 and need to sink the valves into the head to achieve around .070. Can anyone explain this?
Thanks,
Augie.

 

what cam are you running? it is detrmined by your cams TDC lift,be carefull sinking the valve in the seat, as this will start shrouding the the valve,losing air flow at lower lifts.have someone who knows valve jobs and head porting do this

 

And when sinking the valves, another issue surfaces, and that is stem protrusion, which affects spring pressure.
Scott

 

good point,will also affect valve geomitry if over spec,so like i said,have someone do it that knows heads,and how to set this stuff up.once again,what cams are you running? would have to have ALOT of TDC lift to only have .010 between valves,are you useing the right specs or measuring right?

 

We are going from the woods TW-8-6 to TW-9F-6. It is a reputable shop that is performing the work. They said I had .010 with the valve to valve on my set up with the TW-8-6, but needed more, stepping up to the TW-9F-6. I have been racing alchohol injected big and small block chevy's for 25 years or so, assembling our own motors, transmissions, and rears. I just got into the HD thing a couple of years ago. I am just having some difficullty wrapping my mind around this one!
Thanks,
Augie.

 

valve to valve clearance is not a harley thing
it is an all and every engine thing
why you would need .070 clearance is beyond me though
that is a lot
clearly .010 is not enough
but .060 is generous, .040 is enough and .030 is tight but workable

 

I appreciate the responses, but no one is really telling me what this is . What are we looking at, how do you check this , what is the theory, how does it come into play between different camshafts. Obviously I am not a machinist, but I've checked piston to valve clearance, degeed cams in, set backlashes, among other things, when assembling. I'm trying to understand the mechanics,and understand what we are looking at here.
Thanks,
August.

 

as the exhaust valve closes, the inlet opens
this is known as the overlap
the valve heads obviously pass each other during this action
at some point they will reach their closest proximity
that is the valve to valve clearance
if it is too little, as in a negative value, they will clip(hit) each other
the minimum gap between them at any time needs to be(for a street type engine) around 0.040
with different cams duration and lift is also likely to be different, so there is a need to make sure you have adequate v2v clearance
oversize valves is another common issue
there are tools made especially to check this
they are also commonly used on flow benches to measure cfm at different lifts
you may also be able to see via a port, or plug hole

 

you didnt check TDC on your alky race motors?? hmm. its not a "harley" thing,is a CAM thing.TDC lift is the amount your valves are open @ top dead center on the non-firing stroke of the motor,can be checked very easily by removing springs,marking the TDC lift +.030 on each valve stem from the guide,move both valves down to the marks and measure the clearance between valves (your looking for .060).this is a way to check it at home,trock makes valve tools (what we use)to measure exactly,but this will tell you if your in the ball park.looking at the 6 or 8 woods cam specs,im surprised you only have .010 unless your shop aint doing it right,or you got some big valves in the heads

 

Don't forget to use roller rockers with that 9F. If going to 1.725's, it'll kick the lift to .688".
Scott