So, I'm in the garage dicking around. deciding which unfinished part of the project to work on

My #1 piston is at TDC. Dialed in with a dial indicator when the head was off.
I screw in the ARP studs, and bolt down the AFR225, to 30 ft pounds. The cometic is not yet installed (straight head to block)

I decide to pull off #1 valve springs (both ex & int). I put a dial indicator on the top of the valve stem and measure how much play I have until it hits the top of the piston.

The intake is .275" and the exhaust is .300" (actually .276 and 301), so add to that the cometic .040" and I have .315" and .340" of valve travel.

That wont be enough for my cams .595" lift, right? If I remember right, my lifter moved .350" when I was degreeing the cam (with heads off) in July. .350x1.7 = .595"

Am I thinking too much into this, as I am tired, or is what I am doing completely wrong? I was going to clay but thought about doing this first.

IIRC, the Lunati pistons come out of the bore .015", but they have valve reliefs cut into them. and looking thought the exhaust port, I can see that the exhaust valve fits inside the relief perfectly

I'm tired...I've been up too late all week.

 

dude, you lift isn't at maximum when the piston is at TDC. I'd clay it.

Usually you'll have contact, if at all, when the piston is coming up to tdc chasing down the exhaust valve. Or the intake valve opens before the piston moves out of the way on the intake stroke.

 

Your measuring actual valve lift, but what your not considering is the valve timing. The real way to measure clearence is to see were the valves are going to be in conjunction with the stroke of the piston. You can have more lift than clearence at TDC as long as either valve isn't 100% open at TDC. That's why you want to clay it. This gives you the most accurate correlation between the valve location and piston location. FWIW, as long as the heads aren't tremendously milled, a .595" camshaft should clear a stock assembally, much less one with valve reliefs.

 

doh, that's right. What the hell was I thinking. Thats it, I'm off to bed. I'll clay it tomorrow night, so I can be rest assured and close this bad boy up. I've been lagging too long.

Thanks guys.

D

 

What are you measuring is free drop, with a lot of calculations you can get a idea of the P to V with that but it's not exact.

Bret

 

did you degree in the cam? if so you will want to bolt the wheel back on and turn the motor 10* before tdc and 10*btdc and check the drop of the valve in 1 degree increments. That should cover the critical pv clearance points, and give you a close estimate.

 

ROCNDAV, your on the right track but not quite there. I used a method very similar to what you describe with a couple differences (ArKay99 was who wrote the basic procedure, I just modified it very slightly). My procedure:

-Find TDC on compression stroke using dial indicator, make a mark on the crank pulley

-install 2 weak testing springs on cylinder 1 intake and exhaust valves (the springs should be stiff enough to hold valves up with light pressure on them, but easy enough to move the valves by hand)

-put heads on engine, no gaskets, snug a couple head bolts/studs. No need to crank on them hard. Put pushrods and rocker arms on cylinder 1 valves.

-position a dial indicator on top of rocker arm in the flat spot, line the indicator shaft up as close to parallel as you can with the stem. I had a small steel plate that I secured to the engine block as a base for dial indicator. Worked good.

-Turn the motor over until the intake valve starts to open. This will be around 3/4" of a turn more. When the mark on the pulley is within an inch or so from the gauge mark start pushing the valve down with your finger until it contacts the piston. Continue turning the motor over in 1 degree increments and while pushing the valve down with your finger you will find a spot where the valve is closest to the piston. Let your finger off the valve, and push down on the pushrod so it seats compresses the lifter plunger. Set your dial indicator to 0 and press the valve with your finger again until it contacts the piston. Note the measurement on the indicator and that will be your p/v for the intake valve. Turn the motor over to TDC on the compression stroke and repeat the procedure for the exhaust valve. it will be closest as it is closeing, so you'll see it opening, then start to close, that is when you should start to measure it. The exhaust valve is closest when the piston is chasing the valve up, and the intake is closest when the valve is chasing the piston down.

 

Commonly known as the "Valve drop" method. We use it on all of our setups because we know what we are dealing with. If a customer 1500 miles away calls and wants to know if X cam or Y cam will fit with his heads milled and bigger valves, this is the measurement we need to know to determine how big we can go.

Much easier, cheaper and faster than claying if the thing is already together.

 

Thanks Louis, I had good success with this method, and I think if done with some attention to detail can be more accurate than clay.

 

A minor caveat for Bowtieman: If you have pistons heights above the deck, you're going to need the gaskets in there...

 

I have found the best way is to put it all together and check it as mentioned

So a better question is what do you guys accept as minimum? I have seen some nasty numbers out of some of the products floating around here

 

My 495 aluminum BBC has 0.035" with Carillo rods and about 0.007" piston clearances. No contact to date at up to 7,200 RPM. I've heard of as little as 0.025" on a steel rod, 7,500 RPM SBC with close skirt clearances.

 

Any chance you would share that formula?