There are 2 critical values in getting your valvetrain geometry correct. Valve install height and spring install height. On some models of cylinder heads, getting these values is easier than it is on a 4g63 cylinder head. On the first Glyptal video, you heard me complain about the complexity of the casting and how hard it was to reach all the nooks and crannies while applying that coating. The casting is very complex on a 4g63 head. There are hydraulic galleries for the lifters elevated above the valvetrain surface which make accessing each valve bore with precision measurement tools very difficult. It's because of this that you need to do some math to get these values correct.
Stuart is going to show you the process for obtaining the stem height and spring height values on a 4g63 head. Using these numbers you can determine other work necessary to correct the spring height value to correct seat pressure, and ensure you have adequate valve travel for your springs to work correctly.
It looks like rocket surgery, but really it's pretty simple. The ultimate goal is to get every valve spring in as close proximity to one another as you can, while doing your best to nail the recommended specifications PROVIDED BY THE CAMSHAFT MANUFACTURER.
Loose valve springs can result in leaky valve seats, valve bounce and deflection that will drastically shorten the life of the valvetrain. If valve bounce is severe, it can cause engine-killing interference with the pistons
Tight valve springs can cause excessive valvetrain vibration generated by the force necessary for the camshafts to push them open. On the narrow side of the spectrum this can increase friction on the cams which can wipe lobes and shorten their lifespan, and on the severe end in not only increases the likelihood of wiping a cam lobe, it can lead to binding valve springs and crashing the valvetrain.
You have to hit the sweet spot.
Valve springs specifications include several variables that help you achieve these goals. The manufacturer rates their springs for their installed pressure and height. They have a compression limit referred to as valve spring bind which tells you how far you can compress them from their installed height before the coils begin to bind and the spring stops compressing.
The valve springs used in this video are rated at 97lbs @ 1.440" installed, and .500" lift. This means they should bind at .940", but my cams will only generate .433" lift, giving me plenty of head room at the top (.067") to prevent binding if they are installed correctly. One thing we found which I wasn't expecting is they're a little on the stiff side of spec. We measured 100lbs at 1.452", so rather than risk setting them up too tight at 1.440", we made 1.452" our tightest clearance's specification for any valve. Our install pressure ended up still higher than spec with a barely-larger-than-spec spring installed height, and it left plenty of room at the valve's fully open position to avoid spring bind.
I don't consider this a defect. It is close enough within the margin of error that it shouldn't cause any problems, and anyone doing this job right will measure and check all of these specifications to ensure these parts are what they say they are. That's what you watched us do. I'm confident that this will work because the 4g63 utilizes a hydraulic self-adjusting valvetrain.
If the stem height is too high, it can be reduced by grinding the ends of the valve stems to shorten them. This will have no affect on spring installed height when the parts are assembled, however; it will change the amount on paper that you'd need to subtract from the stem height in order to accurately calculate spring installed height. If any of the valves have been ground to shorten their stem height, all of the valves should be measured separately with their retainers and keepers assembled, and that new value subtracted from stem height individually to obtain each spring installed height. You can't reduce this value any other way short of replacing the valve seat.
If the valve stem height is too low, you can modify the valve seat or machine the valve spring perches (seat or retainer) to increase the size of the spring installed height. Another method would be to cut the valve seat deeper to recess the valve.
In my video, we show this whole process on a brand new set of Supertech valves. All of them are identical, and all of the retainers are new and identical. Because of this (and yes we checked it), and because no valves required any grinding, we only needed to use one value in our math for all 16 valves.
Hopefully this video clears up the process and covers the options available for making changes if they're necessary. If you land within 3% of spec, you've done your diligence in achieving correct valvetrain geometry.
28 ноя 2013
