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pushrod measurement
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bill jones
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Joined: 21 Dec 2003
Posts: 171
Location: Salt Lake City Utah
4414.80 points



PostPosted: Fri May 23, 2008 10:29 pm    Post subject: Reply with quote

-I think stock pushrods are supposed to be 7.794" long for whatever that is worth.
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-from what I see---if the roller wheel is fairly well centered thruout it's path across the valve tip----then I would try something longer than 7.600".

-you have to juggle the roll out and roll back in against the roller wheel track across the top of the valve tip.

-the imprint of the roller track doesn't have to be dead nuts in the center of the valve tip----but should be close to center----it can be biased outwards or inwards say .040" or so from the tip centerline and nothing bad will happen.
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-when you go to a longer length pushrod say 7.800" which is close to stock----the total roll should be about .040" less which woudl be something closer to .080" total roll out----and then it will probably roll back in .010" or so.
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-as you get closer to achieving the proper roll numbers you'll find that the valve lift will come back to where you'll be real close to the .467".

-just try changing the pushrod length in .050"increments and make up a series of rollout results to look at----AND----pay attention to the roller track position in relation to the centerline of the valve tip with each set of results.

-in a couple of days it'll come to you.
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-but whatever you do----the closer you are to a real life engine the better off your numbers will be for choosing the right pushrods.

-meaning using the correct length lifter which includes your preload----using a headgasket under the head and using the real valve springs.
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-you are on the path now.
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SNJ
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Joined: 14 Jan 2008
Posts: 57

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PostPosted: Sat May 24, 2008 6:53 am    Post subject: Reply with quote

ok bill, thanks, that helps

When I started this, the first thing I did was buy one stock length pushrod (yes, 7.794). The pattern on the valve tip was towards the exhaust and from what I read, that meant it was too long. So, I then bought the adjustable pushrod and started going shorter until I got the pattern "dead nuts" centered.

Thanks for your advice and your patience.
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bill jones
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Joined: 21 Dec 2003
Posts: 171
Location: Salt Lake City Utah
4414.80 points



PostPosted: Sat May 24, 2008 10:52 am    Post subject: Reply with quote

-the distance across tip of the valve is .343"-----and the roller wheel needs to have about .100" for it's track on top of the valve.

-if you had that track dead nuts in the center you have .243" divided by two on each side of that track which is .1215" of free metal left to play with on either side of what most people say is perfect.

-if the entire track width was moved outwards towards the exhaust side say .050"--you'd still be plenty safe and still have about .070" of free metal there before you got to the valve tip edge.

-same deal if the track had to be moved inward towards the intake manifold.

-as far as I'm concerned you can deviate this .050" with no wear issues----if that is what it takes to get the roll out and roll back in looking decent.

-If you look at the total roll out in the first .200" lift it usually always is significantly more than you'll see in the rest of the total valve lift.

-this means that you are looking for the roll to become pretty insignificant as the lift starts to getting up where the valve spring pressure is high--because spring pressure and roll really don't like each other and create valve stem side forces to the valve guide walls.

-if the roller wheel is pushing virtually straight down during the higher valve lifts then there isn't much side force at all to create valve guide wear problems.
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-if running the roller wheel outwards towards the exhaust side say .050" past the valve tip centerline happens to make everything look OK as far as roll out and roll back in---that will also get you the most lift out your combination--because it makes the longest pivot length from stud & trunnion centerline to the roller track centerline.
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SNJ
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Posts: 57

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PostPosted: Sat May 24, 2008 12:46 pm    Post subject: Reply with quote

Boy, you just answered a couple other questions I had in the back of my mind. I'm going out now to get back at it - feeling much better about it too. Fun stuff.

Pardon me for saying bill, but it's very generous of you to share all this information. I imagine there's a lot of other guys learning a lot from this thread also.
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bill jones
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Joined: 21 Dec 2003
Posts: 171
Location: Salt Lake City Utah
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PostPosted: Sat May 24, 2008 2:05 pm    Post subject: Reply with quote

-40 years ago when I was first getting into the SBC's-----it was virtually impossible to find the people who knew this stuff and would actually tell me about what I wanted to know---or even pass along decent hints as to what to look for.

-but I asked enough people and eventually found a few guys who got me onto a path---maybe not the right path but I learned from them how to look at things closer--like with big eyeballs.

-I don't mind helping some people---because I can sort of see the reflection of myself in their questions.
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-I seriously doubt that more than a very small percentage of people have ever really hands on studied this topic.

-BUT---once you get the pushrod length figured out and decide to degree the cam in----that can be another experience.
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MufflerBearings69
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1968 Ford Galaxy

PostPosted: Sat May 24, 2008 11:49 pm    Post subject: Reply with quote

Lots of good info- I am about a week away from my first experience with sorting out pushrod length...

I am going to order a pair of the pushrods that are "recommended" for the setup and a pair of adjustables so i have them

and then Ill be back in this thread....


Agreed- very generous to share this info!
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