Thread: piston to valve clearance, JWT c3 cams

If you over-rev (missed gear, etc.) you can find yourself in a valve-float situation, which means (worst case) your rocker arm stands a VERY good chance of coming off the HVLA (lifter) but still being lodged between cam lobe and valves... basically, your lifter will be stuck vertically between your retainers and your cam, and it can COMPLETELY DESTROY your cam, cam cap bolts, and in extreme cases, the cam journals themselves. I have done this personally - first hand experience.

Without the stoppers, it may come off, but, it will not stay in the way. The valves simply won't open, and, you'll come to a stop. This is actually a "side-of-the-road fixable" situation.

This is not to say it is certain you will throw rocker arms, but, if it happens and you have stoppers installed, it will most certainly cause permanent damage.

Should stiffer valve springs not inhibit valve float, and consequently the rocker arms stoppers are required?>

hmmmm, well this is what I would like to know. IF sr16 pistons are used how can you get higher than 11:1 compression??? He is using a DET head. So that equals 10.2:1. The VE head is what gives the higher compression because the chamber is smaller. Therefore 8.5:1 DET pistons in a VE are approx 9.3:1.

Perhaps I could be wrong, but I have built 4 VE's over the years and I have had to deal with the piston issues.

The sr16 piston will give you higher compression, but I am not sure how much. The valve notches are very deep though. The N1 pistons are domed and coated and will give you much higher compression with a decked head. I don't think you will have to worry about clearance issues even with those.

The stock 20VE pistons are dished slightly and give the VE 10.3:1.

The SR16V has a NET dome of 8.6cc, the N1 piston has a net dome of 6.8cc or so, it works out to 11.8:1 for the 16V pistons with std clearances, but you do need to measure your engine really.
Both are coated, the N1 has a smaller dome.

Mike

Stiffer valvesprings will help, but it may not solve the possibility completely.

If you're looking to bulletproof your head, I'd recommend installing grooved shims on both sides (this requires milling/sanding of the rocker arm, and the shims) and using stiffer valve springs. Making sure you've got the rockers shimmed flat also helps.

Springs, rockers & shims, and functional (i.e. not collapsed) HVLAs, IMHO. After all that, most people see no problems.

Thank you for the quality info.

you don't have to mill or sand the sims.

Sure you do.

This assumes a conversion to two grooved shims, as opposed to one grooved and one flat.

The right side of the rocker arm (as seen from top) has to be sanded to fit inside the grooved shim - this leg of the rocker arm is thicker than the other. I would assume, since the grooved shim piece only comes in one size, you'd have to sand or mill one or both of the grooved shims down to get the rocker arm completely flat, no? From what I understand, having that rocker arm flat is reasonably important to keep the head un-scrambled when revving to the moon.

The flat ones come in sizes, yes. These will need no milling; just swap them out. The grooved ones, however, were what I was referring to.

IIRC, the grooved shims comes in more than one size just like the other one.

Quick Update:

My cams, and bronze valve guides have arrived from Greg at Gspec. As soon as I can afford to have the head off for a few days, I will get all the new goodies stuck in there, and hopefully soon I will be running my N/A monster in.. (: