So, I started the assembly of my 996 heads this weekend and came across a possible problem with the FBF 1mm oversized valves that I've purchased. When installing the inlet valves I noticed that the closing rocker shim did not seat as far down as it did on the exhaust side. At first I didn't take much notice of it until it came time to install the cam and it wouldn't turn due to clearance issues caused by the height even with the smallest shim available installed. Long story short, I've measured the groove on the valve stem that the collets sit on and the intakes are 0.05mm wider than the exhausts. Is anyone able to measure a set of stock valves for me pretty please and let me know the results? I'm assuming that this isn't meant to be and exhaust and intake grooves should be the same. Thanks!
That doesn't look like a valid method of measurement to me. If that collet groove has a round form, the proper way to measure its depth would be to use a pair of round, parallel rods or wires of a slightly smaller diameter. These would be placed in the groove and a measurement taken across them, after which twice their diameter would be subtracted. This is to ensure that the measurement is taken from the very lowest point of the groove. Your method is dependant on the anvils of your caliper being absolute knife edges and also that they sit truly in the bottom of the groove, without their tapered sides fouling anywhere. Having said that, you might expect your method to give the same result on each valve, but I think that the difference you find is more likely to be a function of the inaccurate measurement. ps. Background info .. I speak as an engineer and therefore have some familiarity with such things.
I'm using mbp collets. The difference in size of the collet groove is the only thing I can put my finger on. I've measured all valves and I'm comfortable in saying that there is a thickness (albeit very small) difference between the intakes and exhaust. I've got all exhaust valve closing shims seated properly but none of the intakes will sit properly like the exhausts.
Seem to recall the need for enlarging the inside of the opener shim mentioned on their website last time I looked several years ago.
I've got a set of mbp shims modified to suit the collets. I'm quite confident now that it is a valve issue. After putting the collets on the valve outside of the head, it's clear that the collets on the exhaust side fit snug while the inlets protrude out. I'll try get a photo after work.
Also, installing the intake collets required a squeeze with pliers to get them to sit whilst the exhausts just pushed on by hand Aghhhh why is nothing ever easy!!
After contacting FBF, turns out that the intake valves that they sent me were to suit a 1.5mm collet and not a standard 1.7mm.
