Rocker Geometry

SeVVenth · Posted: Sun Apr 16, 2006 10:10 pm Post subject: Rocker Geometry

Yes, I know there have been a million posts about rocker geometry, and believe me... I've read them all.
My question is, how exactly do I get my valves to half lift with Dual springs? I have to use channel locks to even budge them. I know I could put some light springs in there, but I'd have to find someand then get them put in somewhere else (I don't have resources to take these out, they are just too damn stiff). I've seen some pics of people with their (what look like HD springs) at half lift. Are they just that strong? Is there any way around this?

vwcalbug · Samba Member Joined: December 30, 2004 Posts: 25

build the engine up, and use the adjustable pushrod to get them at half lift...let the valve train do the work....

-JustinD

nsracing · Posted: Mon Apr 17, 2006 3:09 am Post subject:

mharney · Samba Member Joined: June 01, 2002 Posts: 8353

Buy a spring removal tool. There is a bench mount model that is made specifically for T1 heads, that will not cost much. Then you can switch to some weak springs. Look at Aircooled.net for the tool and the springs.

Dusty1 · Samba Member Joined: April 16, 2004 Posts: 1431

There's the ol' tractor mechanic's method of removing valve keepers to get the springs off with the engine assembled.

It's easy enough to get the keepers off with the good ol' benchtop prybar setup for VW heads, you can use the "C" clamp style valve spring compressor if the head are off but how do you hold the valve in place with the engine assembled?

Simple. Buy yourself a length of clothes line. Pop the spark plug out on the cylinder you're workin' on, then feed a wad of clothes line into the spark plug hole. DON'T FORGET to leave the end stickin' out so you can get it out! THEN carefully crank the engine by hand, the clothes line will wedge between the piston crown and the valve head.

I improvised a pry bar fulcrum that bolts to the head studs to get the keepers off... if the valves are held in place!

The ability to make and use tools is what seperates us from the animals.

steel buggin · Posted: Mon Apr 17, 2006 8:13 am Post subject:

Make a adjustable push rod very easy take a chromoly push rod cut about 1'' off and tap with a 8mm then us a 8mm stud thread it in and take the end to a bench grinder or belt sander and make the end of the stud round this has worked for me for year's I've set up geometry with engine that have dual Chevy K-motion 800 springs and never bent my tool easy and cheap. Good luck

turboblue · Posted: Mon Apr 17, 2006 8:29 am Post subject:

mharney · Samba Member Joined: June 01, 2002 Posts: 8353

Yeah, that's a good way. I just fear lobe and lifter damage because it takes me a lot of messing about to feel like I have it right. I don't like any more strain on the lobes and lifters than I have to have before I start it up.

Mad Manx · Posted: Mon Apr 17, 2006 8:58 am Post subject:

I am right there with turboblue, I built one of these C/M adjustable push
rods back in the late 70's and have been using it ever since and it as
never bent like a piece of copper wire. Back then the steel push rods
where about .05/.06 thick - heavy but strong. But I have only run the
VW dual springs, nothing as stiff as the Chevy springs. Wink

SeVVenth · Posted: Mon Apr 17, 2006 9:57 am Post subject:

Thanks for the replies, I know I dont have clearance issues - C35, 8.5:1 CR, and only 1.25 rockers. I think I'll just buy or make a HD adjustable pushrod.

mharney · Samba Member Joined: June 01, 2002 Posts: 8353

SeVVenth · Posted: Mon Apr 17, 2006 8:53 pm Post subject:

Alright, I've got my method. I have a stock pushrod that I'll use (with something between the rocker and the pushrod if the longer length is needed) to move the rocker to half lift. Then when I've found the shimmage I need, I'll make my stock pushrod into an adjustable - All bases covered.

But I have a new question... How do I calculate my "half lift"? I know you can do it with a dial indicator, which I'm borrowing soon, but how do I know what half lift is? I can't seem to find the answer that I'm looking for.

mharney · Samba Member Joined: June 01, 2002 Posts: 8353

Half lift will be what you measure half lift to be. You can set the dial indicator on the spring retainer, set your lash to basically zero on that rocker, and record what the dial indicator reads when the spring is out. Then rotate until the spring is fully compressed (the dial indicator's reading will reach a minimum, and start back out). Do the math on the difference and shoot for the midpoint when you rotate it. That's half lift. If you have a degree pulley, you can just record the degrees it reads and use that so you can pull your dial indicator off.. That will keep you close and honest. It's also a good idea to take the time to make sure the pulley really is showing TDC when the piston apexes. With that in mind, and your dial indicator in place, you can check to make sure your cam is degreed perfectly too, using your cam card. Doing all this at once is handy during mockup.

SeVVenth · Posted: Mon Apr 17, 2006 9:17 pm Post subject:

Compress the spring until all the coils touch?

mharney · Samba Member Joined: June 01, 2002 Posts: 8353

No.. I'm talking about doing the geometry with the longblock together. That's when you do it. When you rotate the engine, well, that will actuate the rocker and push on the spring. Until you have the deck set, and the heads down, and the rockers on, you cannot effectively set the geometry.

SeVVenth · Posted: Mon Apr 17, 2006 9:58 pm Post subject:

I've got everything set and the rockers are sitting on the studs. I'm just confused on what fully compressed is. Is it just the amount that the valvetrain will push the spring to? I hate rocker geometry, too bad the local shop went under Sad

.

Max Welton · Posted: Mon Apr 17, 2006 10:15 pm Post subject:

How to measure lift:

Take a measurement with the valve completely up (open).

Now rotate the crank until the valve is as far depressed as cam will move it and read the gauge again.

The difference between these two measurements is total lift. Half of that is half lift.

Image may have been reduced in size. Click image to view fullscreen.

Max
_________________
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SeVVenth · Posted: Mon Apr 17, 2006 11:04 pm Post subject:

So I need to make everything tight? Have the pushrod tight against the rocker and then rotate it, because as I see it, if it isnt as tight as it can be, then the total lift done by cam won't be the actual amount. If that makes sense...

mharney · Samba Member Joined: June 01, 2002 Posts: 8353

As I said:

Half lift will be what you measure half lift to be. You can set the dial indicator on the spring retainer, set your lash to basically zero on that rocker, and record what the dial indicator reads when the spring is out. Then rotate until the spring is fully compressed (the dial indicator's reading will reach a minimum, and start back out). Do the math on the difference and shoot for the midpoint when you rotate it. That's half lift. If you have a degree pulley, you can just record the degrees it reads and use that so you can pull your dial indicator off.. That will keep you close and honest. It's also a good idea to take the time to make sure the pulley really is showing TDC when the piston apexes. With that in mind, and your dial indicator in place, you can check to make sure your cam is degreed perfectly too, using your cam card. Doing all this at once is handy during mockup.

nsracing · Posted: Tue Apr 18, 2006 6:27 am Post subject:


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