pushrod geometry - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


Lounge For casual talk about things unrelated to General Motors. In other words, off-topic stuff. And anything else that does not fit Section Description.

Reply
 
 
 
Thread Tools Search this Thread
Old 05-02-2007, 12:36 PM   #1
Senior Member
True Car Nut
Thread Starter
 
Join Date: Jan 2005
Posts: 3,295
Thanks: 0
Thanked 0 Times in 0 Posts
MyLittleBlackBird is on a distinguished road
Default pushrod geometry

Given a standard hydraulic roller lifter, how critical is it for the pushrod to be perfectly parallel to the lifter? Same question with the exception of the lifter being solid instead. I think it will be fine. Just getting opinions.

Disclaimer: If you feel like saying it will not work, you are obligated to tell me exactly WHY it will not work, what will most likely fail, why it will fail, etc. Solutions are hard to find without the full equation to look at.

So we are clear, we are speaking specifically of the lifter and pushrod. All other things(rocker arm basically) would be in whatever position needed to allow everything to line up and function. It'* more about durability and general points of (potential) failure.
MyLittleBlackBird is offline   Reply With Quote
Old 05-02-2007, 01:09 PM   #2
Senior Member
Posts like a Turbo
 
Join Date: Dec 2006
Location: NHRA Division 3
Posts: 258
Thanks: 0
Thanked 0 Times in 0 Posts
Speedster400 is on a distinguished road
Default

it can be a little off. within 0-4 degrees off from parrallel is workable.

speedtalk.com

Do a search here
Speedster400 is offline   Reply With Quote
Old 05-02-2007, 01:27 PM   #3
Senior Member
True Car Nut
Thread Starter
 
Join Date: Jan 2005
Posts: 3,295
Thanks: 0
Thanked 0 Times in 0 Posts
MyLittleBlackBird is on a distinguished road
Default

Good... good. That gives about + or - .4" at the tip. Further research must be done. Any more comments on this?
MyLittleBlackBird is offline   Reply With Quote
Old 05-02-2007, 01:35 PM   #4
Senior Member
True Car Nut
 
95naSTA's Avatar
 
Join Date: Feb 2003
Location: Philly
Posts: 4,508
Thanks: 0
Thanked 0 Times in 0 Posts
95naSTA is on a distinguished road
Default

I know the GM 60 degree v6'* come with pushrods at an angle. I can try and find pics if you want.
Not sure about solid lifters though.
95naSTA is offline   Reply With Quote
Old 05-02-2007, 02:04 PM   #5
DINOSAURUS BOOSTUS

Expert Gearhead
 
BillBoost37's Avatar
 
Join Date: Mar 2005
Location: Enfield, CT
Posts: 41,391
Thanks: 0
Thanked 0 Times in 0 Posts
BillBoost37 is a glorious beacon of lightBillBoost37 is a glorious beacon of lightBillBoost37 is a glorious beacon of lightBillBoost37 is a glorious beacon of lightBillBoost37 is a glorious beacon of lightBillBoost37 is a glorious beacon of light
Default

As the rocker moves..I would assume the rod does as well. Just make sure that you won't exceed the travel limits of the head where the rod goes through it.
BillBoost37 is offline   Reply With Quote
Old 05-02-2007, 02:08 PM   #6
Junior Member
Posts like a Ricer Type-R
 
Join Date: Aug 2002
Posts: 10
Thanks: 0
Thanked 0 Times in 0 Posts
willwren is on a distinguished road
Default

From a geometry standpoint, there will be less of an ability to take the load the higher the angle is.

If you're going to go at an angle, go with insurance. Get one-piece chromoly pushrods.
willwren is offline   Reply With Quote
Old 05-02-2007, 08:02 PM   #7
Senior Member
True Car Nut
Thread Starter
 
Join Date: Jan 2005
Posts: 3,295
Thanks: 0
Thanked 0 Times in 0 Posts
MyLittleBlackBird is on a distinguished road
Default

More on this was found here.

It mentions going to 20* out of whack.... Hmm.... Thoughts? Comments?
MyLittleBlackBird is offline   Reply With Quote
Old 05-02-2007, 08:30 PM   #8
Junior Member
Posts like a Ricer Type-R
 
Join Date: Aug 2002
Posts: 10
Thanks: 0
Thanked 0 Times in 0 Posts
willwren is on a distinguished road
Default

That sounds about twice the level I'd call extreme. The pushrods are strong against linear compression. On-axis if you will. They are not load bearing. The farther you get off-axis, the weaker the pushrod gets. And when you factor in stronger valvesprings, the potential for problems is magnified.
willwren is offline   Reply With Quote
Old 05-02-2007, 09:11 PM   #9
Senior Member
Posts like a Corvette
 
Join Date: Jan 2007
Location: San Diego, CA
Posts: 1,451
Thanks: 0
Thanked 0 Times in 0 Posts
agrazela is on a distinguished road
Default

Is this perhaps a question about how high a ratio rockers one could run?

I haven't a clue what (if any) angle is already built into the lifter-to-pushrod "line."

I can say this: I just measured my 1.80 and 1.85 modded stock rockers with digital caliper, from oil-hole in pushrod seat to back edge of rocker:

1.85'*: 0.350 +/- 0.004 inch (1% RSD)
1.80'*: 0.28 +/- 0.01 inch (4% RSD)

I don't know where the original seat was, but even if we moved it back ALL THE WAY, i.e., 0.350 inches (obviously not possible, but bear with me), we have created a triangle with an opposite side of 0.35 inches and an adjacent of about 7 inches (stock pushrod length).

A bit of quick trig:
http://www.easycalculation.com/area/triangle-angles.php

gives us a change in angle of only 2.86 degrees at the lifter.

(It'* likely that the seat couldn't have been moved more than 0.20" from it'* original position on the 1.85 modded rocker, and this yields an angle of only 1.64 degrees)

As the rocker travels through it'* motion, you'd have to measure a change in this opposite side of something like 0.5 inches to get to a 4-degree angle at the lifter; however, the valve-tip contact patch on the end of the rocker measures less than a quarter-inch, so that defines the limit of our range of motion.

In short, even with 1.85 (or even 1.9) rockers, the rocker end of the pushrod will never go more than 0.45 to 0.5 inches out of line with its original line. That equates to 4 begrees or less of change from the original angle (though, as I say, I do not know what that original angle is). Furthermore, the change from stock rockers to as high as 1.9'* introduces less than 2 degrees change from whatever the original angle was.

I don't know if this helped you, but it helped ease my mind about high ratio rockers!

(I guess the same analysis would hold for cams up to say .520 total lift)

EDIT: I assume you are talking about a 3800 engine
agrazela is offline   Reply With Quote
Old 05-02-2007, 11:09 PM   #10
Senior Member
True Car Nut
Thread Starter
 
Join Date: Jan 2005
Posts: 3,295
Thanks: 0
Thanked 0 Times in 0 Posts
MyLittleBlackBird is on a distinguished road
Default

Wren, took me a bit to really get it, but I do understand what you're talking about exactly. I would be combating pushrod deflection(I think that'* the term)


Agrazela, that is deffinately worth a read once I'm back to a sober state of mind. It would appear to apply to the application I will be presenting, however, more thought, measurements, and the sort must be done to cover all of the factors.

It does involve the 3800... among two other engines that I had in mind.... Lets hope I can afford to put something together soon to get some results By calculations, the pushrod would only be off about 2* at the tip, valve closed, from it'* initial.... line... if you will.
MyLittleBlackBird is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
Rocker, spring, and pushrod replacment Danthurs 1992-1999 2 12-27-2007 02:18 AM
Matt's L67 Calais ***Bent pushrod, broken valve spring*** avex Your Ride: GM Pictures & Videos 41 11-03-2007 06:33 AM
Lifter or Pushrod issue IBlowstuffup 2000-2005 19 01-14-2007 05:49 PM
Variable valve lift for a pushrod engine? 95naSTA Performance, Brainstorming & Tuning 6 02-28-2005 04:57 PM
Urgent alignment/ELC/geometry help needed willwren 1992-1999 12 10-21-2004 12:49 PM


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -4. The time now is 02:02 AM.


We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.