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superbtl
Samba Member
Joined: March 03, 2005
Posts: 687
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 Posted: Sun Feb 19, 2006 7:19 am Post subject: push rod length ??? |
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| i have a 2275 that i will be installing wedgeports on. my question is i am having the m shaved so i can get 9.5 compression, will i need to cut my push rods or will stock push rod lenght work. i just need guestimates, i havent pulled my old heads and measured deck hight yet to know for sure. i just looking for an educated guess on whether stock length push rods would be ok |
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Glenn 
Mr. 010
Joined: December 25, 2001
Posts: 79369
Location: Sneaking up behind you
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| Posted: Sun Feb 19, 2006 8:19 am Post subject: |
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Stock pushrods with a 2275?
There's no way to know what length to use until you measure them. That's the only way to ensure correct rocker geometry.
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Glenn
74 Beetle Specs | 74 Beetle Restoration | 2180cc Engine
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עַם יִשְׂרָאֵל חַי |
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kakarottt
Samba Member
Joined: December 05, 2003
Posts: 719
Location: Hazard county, Maryland
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| Posted: Sun Feb 19, 2006 9:26 am Post subject: |
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strokers open up a can of worms when it comes to rocker geometry.
Buy yourself an adjustable push rod tool, and hit the search button, there were a whole lot of usefull links posted when I was asking about rocker arm geometry. |
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smkn_vw
Samba Member
Joined: August 22, 2004
Posts: 809
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| Posted: Sun Feb 19, 2006 9:36 am Post subject: |
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| Get the new heads on and measure, measure, measure to get the length, better to do it right the first time especially after spending some dollars for those heads. |
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superbtl
Samba Member
Joined: March 03, 2005
Posts: 687
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| Posted: Sun Feb 19, 2006 3:09 pm Post subject: |
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| i am not using stock push rods i was asking if stock lengthwould be ok. |
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Max Welton
Samba Member
Joined: May 19, 2003
Posts: 11016
Location: Black Forest, CO
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| Posted: Sun Feb 19, 2006 5:17 pm Post subject: |
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| superbtl wrote: |
| i am not using stock push rods i was asking if stock lengthwould be ok. |
Right. What we are telling you is that you will have to mock it all up to tell what the correct pushrod length is for your engine.
BTW, this is true for a stock-stroke engine just as it is for a stroker.
And the next question will be "How do I do that?"
I am rather new to this myself, but I'll take a shot.
First, we must assume that deck height has already been set. So you won't be adding or removing cylinder shims or otherwise changing the relationship of the head to the case.
Second, know that one of the primary goals of properly configured valve train geometry is recognized by the alignment of the adjustor with the valve stem at 1/2 valve lift. That alignment means that the angles formed at zero lift and at full lift will be roughly equal.
Great. So we will need a way to measure valve lift and we will need the above mentioned adjustable pushrod.
To measure valve lift I use a dial gauge with a magnetic base. Like this:
The adjustable pushrod can simply be made from a stock pushrod. I used a 6mm tap and threaded rod. The length can be adjusted by turning one end. The longer the threaded rod is, the more stable the pushrod will be. I made mine with a range of adjustment that was 1/2" centered on the length of a stock pushrod.
Now that you have the tools, do a trial assembly. Place the head on the cylinders and torque it to spec. Do not use pushrods tube during this process.
Rotate the crankshaft until the lifter for this valve is fully "down".
Adjust the pushrod to its shortest length and set it in place. Place the rocker assembly in place and torque it down. Rotate the valve adjustor to a position that will allow full range of movement plus a couple of threads above the rocker arm.
Since the adjustable pushrod is at its shortest position, things should be very loose at this point. Now lengthen it in place until all the lash is taken up.
Using the dial-gauge, rotate the crankshaft until the valve is at 1/2" of its maxminum lift. Observe the adjustor - valve stem angle.
If the 1/2 lift angle leans towards the rocker shaft, you need to add shims under the rocker stand and adjust the rod length.
Here is where I wound up on my 1776:
full lift:
half lift:
zero lift:
The above 1/2 lift angle isn't too bad. I have .165" shim stack and 285mm pushrod.
Oh yeah. Those shims come in three sizes; .015", .030" and .060".
Max
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Last edited by Max Welton on Mon Jun 29, 2009 11:13 am; edited 1 time in total |
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superbtl
Samba Member
Joined: March 03, 2005
Posts: 687
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| Posted: Mon Feb 20, 2006 7:58 am Post subject: |
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| i just ordered my adjustable push rod tool. from 1 to 10 how difficult is it to set the geometry. let me see if i got this right. i should torque down my heads and put in my adj. push rod , adjusted to short as possible. then install my rockers and begin adjusting the lash while periodiclly turning my crank to check geometry. once i get the length of the push rod correct , i can cut my push rods to length. |
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Max Welton
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Joined: May 19, 2003
Posts: 11016
Location: Black Forest, CO
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| Posted: Mon Feb 20, 2006 7:03 pm Post subject: |
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| superbtl wrote: |
| from 1 to 10 how difficult is it to set the geometry |
Short answer: It Depends. (You just knew that was coming, right?  ) What is an example of a "five" for you?
Useful answer: Setting up the geometry is straightforward if you can visualize how everything moves and how a change in one thing will affect the others. It will be hard if you can't.
Having a dial micrometer and the adjustable pushrod on hand makes it much easier. Having the right tools makes any job easier.
| superbtl wrote: |
| let me see if i got this right. i should torque down my heads and put in my adj. push rod , adjusted to short as possible. then install my rockers and begin adjusting the lash while periodiclly turning my crank to check geometry. once i get the length of the push rod correct , i can cut my push rods to length. |
Close. You will need an assortment of shims so you can try different thicknesses, adjusting the stack and the pushrod length until you get the right 1/2 lift adjustor alignment.
I started with one .060, then two .060s, then three (.180 total). At that point I had overshot and replaced one .060 with a .030 and .015 for a total of .165".
Max
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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 |
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Terry Cloyd
Banned
Joined: March 23, 2004
Posts: 2218
Location: Valley Center "SO CAL"
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| Posted: Mon Feb 20, 2006 7:07 pm Post subject: |
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Max, what a super picture of 1/2 lift do you work for Steven Spielberg  That is 1/2 lift at it's best. You must be a star Terry |
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Max Welton
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Joined: May 19, 2003
Posts: 11016
Location: Black Forest, CO
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nsracing
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Joined: November 16, 2003
Posts: 9737
Location: NOVA
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| Posted: Sat Apr 22, 2006 10:42 am Post subject: |
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I do not use any shims under the rocker posts when I set the geometry.
I just machine the pushrods down some. NO shims to mess with.
There is beauty in simplicity. 
Nice presentation Max. |
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Max Welton
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Joined: May 19, 2003
Posts: 11016
Location: Black Forest, CO
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| Posted: Sat Apr 22, 2006 2:59 pm Post subject: |
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I guess I'm not following that Nick.
If the angle formed by the valve stem and the adjustor at 1/2 lift isn't zero (a straight line) changing the length of the pushrod can't correct it unless it's already close enough to make up by screwing the adjustor in or out.
The two things that will change that angle significantly are the height of the valve stem and the height of the rocker shaft center. Of those, changing the rocker shaft height is the easiest.
Max
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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 |
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buggnuttz
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Joined: January 28, 2006
Posts: 404
Location: southern cheeseland
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| Posted: Sat Apr 22, 2006 3:51 pm Post subject: |
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Stock length ? NO. Do a little more research and go the custom length
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nsracing
Samba Member
Joined: November 16, 2003
Posts: 9737
Location: NOVA
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| Posted: Sun Apr 23, 2006 5:37 am Post subject: |
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| Max Welton wrote: |
I guess I'm not following that Nick.
If the angle formed by the valve stem and the adjustor at 1/2 lift isn't zero (a straight line) changing the length of the pushrod can't correct it unless it's already close enough to make up by screwing the adjustor in or out.
The two things that will change that angle significantly are the height of the valve stem and the height of the rocker shaft center. Of those, changing the rocker shaft height is the easiest.
Max |
Actually Max.. deep flycuts will be the biggest source of rocker geometry corrections. If the heads were stock and the case was stock too, going to 1776cc should not do anthing different..given using stock rods. If you machined the decks of the case and flycut the heads the motor just got shorter. In essence, the push rods got too long and the only way to put the rockers back to baseline is gain some altitude with the rocker posts.
Remember that the rocker posts do not get machined. Just the inside of the heads and spigots on the case.
YOu would have to grind the hell out of the seats and valves to get that much change... 0.050" plus...to effect that kind change in valve stem heights. I would love to see someone grind a seat 0.050" depth.... There would not be much seat left. Don't think so.
So...if the heads got flycut and case machined, by shortening the push rods you do not have to use rocker post shims.
The shims are necessary if using swivel feets since they are really freaking long adjusters. I give you that. But with stock adjusters? Don't think so. Deep flycuts and stock adjusters, you just machine the pushrods down some to put the rocker geometry back to stock.
Clear as mud?  |
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Max Welton
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Joined: May 19, 2003
Posts: 11016
Location: Black Forest, CO
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| Posted: Sun Apr 23, 2006 7:28 am Post subject: |
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| nsracing wrote: |
Actually Max.. deep flycuts will be the biggest source of rocker geometry corrections. If the heads were stock and the case was stock too, going to 1776cc should not do anthing different..given using stock rods. If you machined the decks of the case and flycut the heads the motor just got shorter.
In essence, the push rods got too long and the only way to put the rockers back to baseline is gain some altitude with the rocker posts. |
The way to correct pushrods that are to long is to shorten the pushrods.
The component of the geometry in question is the relationship between the rocker shaft and the valve stem tops. Flycutting, decking, cylinder shims, cylinder head gaskets and cylinder shortening all move the head wrt the case centerline. The relationship between the rocker shaft and the valve stem tops does not change as they both determined by dimensions completely within the head.
| nsracing wrote: |
| YOu would have to grind the hell out of the seats and valves to get that much change... 0.050" plus...to effect that kind change in valve stem heights. I would love to see someone grind a seat 0.050" depth.... There would not be much seat left. Don't think so. |
I'll concede that changing the seat depth is not the way to go. Merely pointing out that it is one of the things that effects that 1/2 lift stem-to-adjustor angle.
| nsracing wrote: |
So...if the heads got flycut and case machined, by shortening the push rods you do not have to use rocker post shims.
The shims are necessary if using swivel feets since they are really freaking long adjusters. I give you that. But with stock adjusters? Don't think so. Deep flycuts and stock adjusters, you just machine the pushrods down some to put the rocker geometry back to stock.
Clear as mud? |
True, swivel feet can make it neccessary to raise the rocker shaft or to take "some" material off the rocker where the adjustor threads in. But as I explained above, flycuts and other things that do not alter the relationship between the rockers and the valve stems only change the required pushrod length. Of course an aftermarket head can easily change things.
And of course the 1/2 lift point moves when use of an aftermarket CAM changes total lift, requiring an adjustment to the geometry to restore the adjustor-to-valve stem allignment.
I say your no-shims method works only in a stock head and rocker assembly situation and is not that useful in general. It certainly is not useful to the original poster in this thread.
Howzat?
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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 |
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nsracing
Samba Member
Joined: November 16, 2003
Posts: 9737
Location: NOVA
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| Posted: Sun Apr 23, 2006 11:20 am Post subject: |
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I think that the original post will benefit from the additional info.
It makes clearer what is actually needed to make the modification or restoring the proper geometry in ANY case. CAm profile changes or swivel feets or otherwise.
Roller rockers are a whole diffent animal.
NASCAR has introduced a better way to do rocker geometries. It does not even follow the things (above discussions) that have been preached over the years. They even show HP gains by just moving the pivot points on the rockers... A lot of good info. It is a machinist's wet dream. |
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myrddin
Samba Member
Joined: November 16, 2004
Posts: 213
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| Posted: Tue Mar 06, 2012 7:17 pm Post subject: |
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thanks for this... I will need to figure this out once i get my heads back from the shop...
2175
78mm crank
w110 cam |
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mark tucker
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Joined: April 08, 2009
Posts: 23950
Location: SHALIMAR ,FLORIDA
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| Posted: Tue Mar 06, 2012 8:40 pm Post subject: |
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HEY!!! look at all the little worms wiggiling around !!!
I dont eff with the 1/2 lift crap. but you might need to depending on what parts you are using.
if you have the elephant feet swivel adjusters, you need to check to see how much angle they can handle, so you dont exceed that.swivel balls rairly have that problem.
I also like to have the adjuster as close to inline at full lift as possiable .thats where the max pressuer is.I dont kare what angle it is at with out any pressure.with that said the 1.1 rockers with a lash cap&swivel foot & no shims will in most cases bind the oe pushrod and need clearancing for that.also the 1.1 in the set up tends to push to the top of the valve the first few thou of lift, probably not enough to hurt any thing with the low spring pressure.but about .045 under those rockers should eleminate that.(I dont remember the coralation between the pushrod&shim thickness on 1.1 rockers but I think it about 2x longer on the pushrod as the shim thickness or close to it) ( I realy should right all that shit down insteade of trying to remember & I have built 1 motor with 1.1 rockers,although I do use them to break in cams often)
the only way to see hat your going to need is to set it upand find out.
also oe aluminum pushrods loose about 2.5-3 degrees each end of duration when checking agnist the same length chromoly pushrod, and lift also, exzact how much probably depends on a lot of things,pushrods,cam,rockers,weather dinner is ready or burnt.
on raito rockers I do try to get the pushrod seat as low as possiable to gain a faster opening lift due to ratio change.but ultimatly the entire system has to be right not just 1 part of it.
yes there is a spelling test in there. what hat was that cat weraing to dinner? |
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Cptn. Calzone
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Joined: June 27, 2007
Posts: 1872
Location: S>E>Alabama
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| Posted: Tue Mar 06, 2012 8:49 pm Post subject: hat |
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The cat wore a red and white striped hat sat on a mat and ate till he was fat. Now will my geometry (rockers) be correct Professor ?
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67 912 Porsche Quintilla
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mark tucker
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Joined: April 08, 2009
Posts: 23950
Location: SHALIMAR ,FLORIDA
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| Posted: Tue Mar 06, 2012 8:56 pm Post subject: |
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| probably not.well not unless oh never mind.nothing is ever right. it may be close, but still a few thou one way or the other. thus the reason for the killer kick ass sound system.so you can look like a kool kat in your hat. |
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