Hey team,
Here's my dialema. I have an H89 head for my new motor, which has had 42mm L series inlet valves fitted to it. It bought it (well) used. And have had my engine machinist replace a cracked seat, and give it a general tidy up. But after a got it back, and studied the hell out of it. (whilest touching myself) I have noticed that one of the valves has been cut down wrong. It has very little material above the new valve keeper groove. (like 1-1.5mm) Now if that peice of valve stem breaks off, (remember this head has done god only knows how much work) the valve will drop into the cylinder, and rape the piston/chamber. (And destroy my new engine)
So I put out my feelers at www.nzdatsun.com to try find new some new valves to use. And in under an hour I had a mate dropping a set in my letterbox.
So, I'm going to get a gifted fitter/turner (who works for free!) to shorten them up for me. But I've read on here (Going back to when I 1st joined this site) that shortened L series valves will need lash caps to prevent the tips burring/mushrooming over. I spoke to a user on here who does head work, that said cut them leaving the same amount above the keeper groove as the Standard A series valves have. (providing that the valves were cut down properly) But given that the L series used Lash caps from the factory anyway, I'd prefer to run lash caps to alleviate any risk of the tips getting burred. Plus if I run a lash cap, that extra tollerance will compomise "ideal" rocker geometry. I've been thinking that I'll measure the thickness of the lash cap, (I'm buying some after work tommorrow) and subtract from the of thickness half of the valve lift beyond the standard lift. Then subtract whatever is left from the material that a standard A series has above the keeper groove. (this would be done to maintain the "ideal" rocker to tip geometry, compensating for the extra lift of a big angry cam.
My idea here is that I'll still have enough material above the keeper groove to ensure reliablity, but without comprimising me rocker geometry. (If you think about how much farther a big lift cam opens the valve, I'm balancing out the extra travel to either side of the rocker travel.

But them today, I was talking to a bloke who I sold my old A14 block to. (this one) http://datsun1200.com/uploads/photos/18987.jpg And he mentioned about how some L series motors use shims under the camshaft journals. (he owns a 240Z) Now, I've always assumed these were to correct the cam timing where the head has been shaved on an L series motor?

But it got me thinking,
if i shimmed up up my rocker posts on my A15, that might enable me to leave a more material above the keeper groove on my shortened L sereis valves, without having to rejig my rocker to valve geometry.

sounds feasible, but longer pushrods would be needed?
some bikes run lash caps, (Ducati) I was looking into running ducati valves in mine as we make them from blanks, and running lash caps,

I run lash caps on mine
With L series valves cut down
However I run rollers and custom pushrods ordered to length
And my mechanic has shimmed the rocker posts to suit as required

So.... all of the above :)

and I'm guessing some decent threads in the head to hold it all together, i.e. Timeserts or something..

Why not just get the valve stem tips heat treated, like A-series, so that a lash cap is not needed?

lash caps are less work. I got a set of 8 manley ones today. $50. (even though I only need 4)

I wouldn't need longer pushrods if I use longer tappet adjuster screws.