BerwynCamaro

iTrader: (4)

I have searched a bit and not found the answer I am looking for, so here it goes. . .

I have an lq4 and I am planning on putting milled L92 heads on it. Now, as I understand it, valve drop is the measurement of the valve movement as it is opened until it makes contact with the piston at TDC. I am doing some preliminary calculations and trying to ensure I am headed in the right direction. How is valve drop affected if the heads are milled, say .025"?

KCS

iTrader: (20)

Valve drop is reduced by the same amount the heads are milled.

BerwynCamaro

iTrader: (4)

I thought that valve drop was a linear measurement at an angle to the head surface. This would mean that as the heads are milled there is proportional change in valve drop, but not exactly the same, no? Would you be able to educate me on these relationships a little bit? Where is the error in my thinking? I was hoping you or someone else sharing your level of knowledge would reply- always find your posts useful. Thanks.

KCS

iTrader: (20)

It's parallel to the cylinder, not the valve angle. For example, the way I measure is with a deck bridge and dial indicator. I zero out the indicator on the deck surface of the cylinder head, then drop the indicator down to the valve, run it along the margin of the valve closest to the deck, and record the lowest measurement as the valve drop.

BerwynCamaro

iTrader: (4)

Ok, so you need to measure along line 1 and not line 2 in the image below? I have read multiple posts and articles saying that valve drop is measured by placing the head on a flat surface and determining the difference between a closed valve and on that contacts the flat surface. That would be a measurement along line 2, not perpendicular to the deck, right?

00pooterSS

iTrader: (40)

The flat surface is the piston in this case. So the edge of the valve contacting the piston.. If you have x distance now, and mill 0.030 then you'll lose 0.030. The head surface is milled at the same angle it currently is, the valve angle remains the same, the head is now 0.030 shorter so the valve is that exact amount closer.

dreadpirateroberts

iTrader: (1)

You mean sticking the head on a square surface and using a dial indicator on the valve to measure the amount of "drop"?

that ends up being an approximate measurement, because of the valve angle. It's close, but slightly longer than the actual distance. KCS i think has the correct way of measuring it. The way you stated isn't bad if the heads are on the car and you know the piston is at TDC, you could always just use a little trig. it's also a quick and dirty way if you are dealing with someone who is a n00b and want them to give you a quick measurement.