piston to valve clearance

[surfsup]

Earlier I posted gt 40 heads on a 86 block, well I did the clay thing and it’s doesn’t seem to be the most reliable way of checking, I don’t have a vale spring tool or light duty springs, or access to one to replace the springs with lighter ones,, so this is my question, I installed the right side head with the used gasket and the number one rods and rockers, I spun the motor over several times by hand with no signs of interference, is it save to assume I wont have problems? I don’t have a piston notched tool, what I do have is a 4 inch grinder a dermal and die grinder that I could use to notch the pistons a little, but would rather not
Stats: 86 bottom end flat top pistons, E cam, GT 40 heads 1.94 intake 1.64 exhaust, 1.6 roller rockers, rpm manifold.

[Jeff Chambers]

Won't be accurate unless you put solid lifters in it. Take an pair of lifters and flip the valve upside down to make it solid. Then do your PV check.

[Gearhead999]

Get some kids clay, playdough, etc. I hope when you say you "spun the engine over" that you did it with a wrench on the crank.

Go to hardware, Homedepot, Lowes, etc. and buy two cheap springs from anything. They should have something in those drawers with all the clips and all in them. You need to make sure this is right, or you'll be real sorry if not.

You need about .100 clearance.

[82 GT]

Originally Posted by Gearhead999

Get some kids clay, playdough, etc. I hope when you say you "spun the engine over" that you did it with a wrench on the crank.

Is there another way to turn a half assembled engine over?

[surfsup]

Well I notched my pistons, not as hard as I thought it would be, I have the pistons from my 85 block that’s out having work done, so what I did was make a card board template of the piston, I then put the template on top of the piston and rubbed the top to get the impression of the valve relief’s, I then cut those markings out, I took the template laid that on each piston and with a sharpie I filled in the valve relief’s cut outs, I then took some playdoh to make an impression of the valve relief’s of the 85 pistons, I then took extreme care with my 4 inch grinder and cut the out line of my markings and checking with the playdoh impressions so not to cut too deep, once I did the rough cutting with the grinder I finished the relief’s with my dermal , and I must say I think it looks real good. I took some pick’s but I can’t get them to load in the post, once I figure out what I’m doing wrong I’ll post the picks.

[Gearhead999]

If the engine was in the car. It may still have the starter hooked up, and somepeople, inexperienced might "spin it over" with the starter.

[Rev]

The best and most accurate way to get piston/valve clearance is to install very light springs on the #1 cylinder valves. Mount the head using the old compressed gasket torqued to 25 lb/ft or so. Put the #1 piston at TDC at the end of the exhaust stroke/ beginning of the intake stroke. Put a dial indicater on top of the spring retainer and push the valve down with your finger until it hits the piston. Do this a few degrees before and after top dead center. As mentioned earlier, use a solid lifter for this measurment set with 0 lash. Record how much further you can depress the valve after it's opened by the cam. That's the piston valve clearance. Do the same thing for the exhaust valve.

I had the machine shop install the weak testing springs which I borrowed from them. I went home and did the test and then came back to them for reinstallation of the real springs. As Gearhead said, you will want .100" clearance. My machine shop guru insisted that I do it that way instead of the modeling clay technique. He said "yeah, it's great if you have a whole lot of extra clearance, but what if it's close? How accurately can you mic that piece of modeling clay?"

Rev

[~The Jester~]

Originally Posted by Rev

The best and most accurate way to get piston/valve clearance is to install very light springs on the #1 cylinder valves. Mount the head using the old compressed gasket torqued to 25 lb/ft or so. Put the #1 piston at TDC at the end of the exhaust stroke/ beginning of the intake stroke. Put a dial indicater on top of the spring retainer and push the valve down with your finger until it hits the piston. Do this a few degrees before and after top dead center. As mentioned earlier, use a solid lifter for this measurment set with 0 lash. Record how much further you can depress the valve after it's opened by the cam. That's the piston valve clearance. Do the same thing for the exhaust valve.

I had the machine shop install the weak testing springs which I borrowed from them. I went home and did the test and then came back to them for reinstallation of the real springs. As Gearhead said, you will want .100" clearance. My machine shop guru insisted that I do it that way instead of the modeling clay technique. He said "yeah, it's great if you have a whole lot of extra clearance, but what if it's close? How accurately can you mic that piece of modeling clay?"

Rev

Yep, what he said!!! I run it the same way, cept I check it with the dial indicator for one FULL revolution. I'm anal about that kinda shyt. Problem with "clay" is how much does it distort when you peel it off of the piston? How much does it distort when you clamp it in your calipers?

We're literally playing a game of .001" and "playdough" is just not accurate enough in my book. Heck, anything that has "play" in it's name has no business near my engines.

I keep a set of used head gaskets on hand for this exact reason!!! Just remember, you play like you practice, so make sure you're using -1 gaskets to check clearance on an engine that's actually going to use -1 gaskets. Checking with -1's and running -2's ain't gonna be accurate!

[zak7711]

Summit Racing sells CCA-4758-2 Competition Cams Low Tension Valvetrain Checking Springs for $3.69 and with some good hardening modeling clay that will consolidate in a few minutes so you wont have much error when you peel it off or separate it from the piston top. With a playdough, the situation is tricky so you're not pretty sure. To me, I dont think a .001" will make any difference when the recommended is .080" and .100" on the exhaust/intake valves. You're looking at a marginal sufficient clearance here.

Note that when you grind or flycut the piston top with an Isky piston notching tool, you will alter the piston weight so the best thing is to use a digital precision scale to keep all the pistons of the same weight or you will have a balancing problem.

For better instructions, read this article http://www.fordmuscle.com/fundamentals/pistontovalve/

[Rev]

Actually, I did it both ways since I was already fooling around with it. In my case, it didn't really matter much, since I had about .150" inch clearance. I think I actually may have hit coil bind (even with those weak checking springs) before I was able to touch the piston with the valve. The modeling clay looked like about .150" more or less as measured with calipers after 2 full crank revolutions. Still, I was happy that I had done everything possible to know for sure that I wasn't going to smack my valves againt the piston the first time I really put the engine to a 6000 rpm 1/4 mile test.

Rev