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SeVVenth Samba Member
Joined: August 18, 2005 Posts: 678 Location: Winterset, Iowa
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Posted: Sun Apr 16, 2006 10:10 pm Post subject: Rocker Geometry |
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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? |
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vwcalbug Samba Member
Joined: December 30, 2004 Posts: 25
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Posted: Sun Apr 16, 2006 10:48 pm Post subject: |
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build the engine up, and use the adjustable pushrod to get them at half lift...let the valve train do the work....
-JustinD |
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nsracing Samba Member
Joined: November 16, 2003 Posts: 9471 Location: NOVA
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Posted: Mon Apr 17, 2006 3:09 am Post subject: |
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vwcalbug wrote: |
build the engine up, and use the adjustable pushrod to get them at half lift...let the valve train do the work....
-JustinD |
Oh yea sure. The adjustable will probably bend like a copper wire.
You were supposed to mock up the motor only with light springs to set the rocker geometry. What happens now if you find out that you do not have correct piston to valve clearance after you find the right geometry???
If this is a stroker motor with high compression...deep flycuts..and high lift cam, you can bet you will need some piston valve reliefs to clear the valves.
It is very hard to get the rocker geometry work up after you have already final assembled the motor. Now you have to find some very stiff push rods to do this mock up in close enough length so you can figure out the final lenght.
YOu can remove the springs and install light ones. There is this tool that was factory to change weak springs while the heads are installed.
I just use the Type IV rocker springs..yea the skinny ones. I install them in the mock-up stage and check full rocker geometry movement and at the same time see piston to valve interference. See how long the push rod has to be for the correct attitude, and move the intake valve to full lift with the piston at TDC. Install a dial indicator and push on the intake valve by hand. Watch the depth of the dial indicator...this will be your clearance. Add the reliefs accordingly.
Good luck man. |
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mharney Samba Member
Joined: June 01, 2002 Posts: 8353
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Posted: Mon Apr 17, 2006 5:45 am Post subject: |
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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. |
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Dusty1 Samba Member
Joined: April 16, 2004 Posts: 1429
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Posted: Mon Apr 17, 2006 6:23 am Post subject: |
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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. |
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steel buggin Samba Member
Joined: March 24, 2003 Posts: 415 Location: Arcadia,Ca
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Posted: Mon Apr 17, 2006 8:13 am Post subject: |
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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 |
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turboblue Samba Member
Joined: October 09, 2003 Posts: 4216 Location: Central Indiana
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Posted: Mon Apr 17, 2006 8:29 am Post subject: |
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steel buggin wrote: |
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 |
Same here.
Threw away the aluminum version and made one out of CM.
No fuss no muss and no screwing with valve spring removal.
CB sells CM pushrods individually. _________________ Gary
Turbo VW Sand Drag Buggy
"If you don't run into the Devil every once in awhile, you must be going in the same direction!" |
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mharney Samba Member
Joined: June 01, 2002 Posts: 8353
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Posted: Mon Apr 17, 2006 8:46 am Post subject: |
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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. |
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Mad Manx Samba Member
Joined: September 30, 2004 Posts: 304 Location: Redondo Beach California
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Posted: Mon Apr 17, 2006 8:58 am Post subject: |
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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. |
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SeVVenth Samba Member
Joined: August 18, 2005 Posts: 678 Location: Winterset, Iowa
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Posted: Mon Apr 17, 2006 9:57 am Post subject: |
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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. |
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mharney Samba Member
Joined: June 01, 2002 Posts: 8353
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Posted: Mon Apr 17, 2006 10:08 am Post subject: |
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SeVVenth wrote: |
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. |
Yeah, you are *just* getting into the area where you should run dual springs with that setup. Kinda makes it a pain in the ass, huh? Single springs might have a little trouble controlling those valves at 6000 with the 1.25 rockers. IIRC, that cam is similar to a 110 grind. With 1.1's you wouldn't really need the dual springs, but you're smart to go ahead and run them with your combo.
Good luck! |
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SeVVenth Samba Member
Joined: August 18, 2005 Posts: 678 Location: Winterset, Iowa
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Posted: Mon Apr 17, 2006 8:53 pm Post subject: |
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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. |
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mharney Samba Member
Joined: June 01, 2002 Posts: 8353
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Posted: Mon Apr 17, 2006 9:09 pm Post subject: |
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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. |
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SeVVenth Samba Member
Joined: August 18, 2005 Posts: 678 Location: Winterset, Iowa
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Posted: Mon Apr 17, 2006 9:17 pm Post subject: |
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Compress the spring until all the coils touch? |
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mharney Samba Member
Joined: June 01, 2002 Posts: 8353
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Posted: Mon Apr 17, 2006 9:27 pm Post subject: |
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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. |
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SeVVenth Samba Member
Joined: August 18, 2005 Posts: 678 Location: Winterset, Iowa
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Posted: Mon Apr 17, 2006 9:58 pm Post subject: |
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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 . |
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Max Welton Samba Member
Joined: May 19, 2003 Posts: 10697 Location: Black Forest, CO
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Posted: Mon Apr 17, 2006 10:15 pm Post subject: |
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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.
Max _________________ 1967 Type-3 Fastback
Under the Knife https://shoptalkforums.com/viewtopic.php?f=24&t=151582
Home Stretch https://www.thesamba.com/vw/forum/viewtopic.php?t=767836
Last edited by Max Welton on Sat Jun 13, 2009 8:49 am; edited 1 time in total |
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SeVVenth Samba Member
Joined: August 18, 2005 Posts: 678 Location: Winterset, Iowa
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Posted: Mon Apr 17, 2006 11:04 pm Post subject: |
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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... |
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mharney Samba Member
Joined: June 01, 2002 Posts: 8353
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Posted: Tue Apr 18, 2006 4:21 am Post subject: |
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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. |
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nsracing Samba Member
Joined: November 16, 2003 Posts: 9471 Location: NOVA
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Posted: Tue Apr 18, 2006 6:27 am Post subject: |
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SeVVenth wrote: |
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... |
I think you are getting it Sev. Good for you! Fully compressed means = as far as the valve can go... all work done by the cam and rocker. You choose which. Just MAKE SURE the retainer does not bottom out to the guide. I do not think you have to worry about coil bind.
YEs..the "lash" clearance will decrease what your NET LIFT measurement will be by that much (lash). But it is small..0.006" I would not worry about it too much. You are talking smiggins.
You have to get passed this Full Lift and Half lift business because you have bigger fish to fry doing the ROCKER GEOMETRY! YOur goal here is to find the correct length push rod and set the rocker tip movement correctly... as it moves across the valve tip.
The C35 is 286degrees Duration, 0.410" lift @ 0.050" checking clearance.
Somebody correct me on the specs.
By calc... 0.410 x 1.25 (ratio) = 0.512" Net lift (valve side)
... 0.5125 devided by 2 = 0.256" Half NET lift
So about 1/4 inch @ half lift! This is very important measurement because this will tell you if the rocker tip is in the correct position or not..with relation to the valve stem axis line. More of this later. I am sure a few here will walk you through it.
Just get done with this Half lift thing. |
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