Are my pushrod length's ok?
Thread Starter
Drifting
Joined: Oct 2004
Posts: 1,259
Likes: 7
From: Ontario
Are my pushrod length's ok?
I know it is best to find the pushrod length that centers the rocker in the middle of the valve with a nice narrow pattern.
Is it acceptable to be slightly off center? My pushrod's are currently 8.0's. To be perfectly centered I would have to spring for a slightly shorter set...likely 7.9's.
Attached is my current pattern.
Is it acceptable to be slightly off center? My pushrod's are currently 8.0's. To be perfectly centered I would have to spring for a slightly shorter set...likely 7.9's.
Attached is my current pattern.
Last edited by Retro78; Dec 11, 2007 at 10:29 PM.
Intermediate
Joined: Dec 2007
Posts: 28
Likes: 0
That pattern doesn't look too bad but it's not too common to need to run .200" longer pushrods. I would say that if a set of +.100s (7.900") move the pattern closer to the middle of the valve then that's the way you should go.
Burning Brakes
Joined: Jan 2007
Posts: 1,057
Likes: 4
From: Concord Calif
I know it is best to find the pushrod length that centers the rocker in the middle of the valve with a nice narrow pattern.
Is it acceptable to be slightly off center? My pushrod's are currently 8.0's. To be perfectly centered I would have to spring for a slightly shorter set...likely 7.9's.
Attached is my current pattern.
Is it acceptable to be slightly off center? My pushrod's are currently 8.0's. To be perfectly centered I would have to spring for a slightly shorter set...likely 7.9's.
Attached is my current pattern.
How did you get that pattern? It should be in the middle of the valve at 50% valve lift. If that pattern was done with the vakve closed it looks pretty good. The pattern will move towards the center as the valve opens or towards the stud as the valve opens. hope that helps some.
Drifting
Joined: Apr 2006
Posts: 1,911
Likes: 2
From: gold coast queensland
it looks like you are very close but not perfect. i would bite the bullet and spend the money on another set that are shorter or longer ( whatever is needed ) to get it spot on.maybe invest in a pushrod measuring tool. in your pics it looks like you are only 1 size out or at the most 2. i think you will be losing some performance and valve life if you leave it the way it is. they say pushrod geometry is one of the most important things to get right on an engine. did you just install a roller cam?also how does your pushrod fit up that gap in your guide plate. looks like it doesnt line up with the port in your head?
Last edited by gingerbreadman1977; Dec 12, 2007 at 01:25 AM.
Le Mans Master
Joined: Jun 2004
Posts: 6,231
Likes: 65
From: Seattle WA
St. Jude Donor '14
IMHO the positioning on the valve looks good, but you do want to ensure you rotate the engine to get the full travel - that's a more useful indication of pushrod length.
The valve on the left worries me a bit, as the contact is not across the full face of the stem. This illustrates a side load on the valve from either the valve not being perpendicular to the seat or misalignment of the rocker at the pushrod.
The valve on the left worries me a bit, as the contact is not across the full face of the stem. This illustrates a side load on the valve from either the valve not being perpendicular to the seat or misalignment of the rocker at the pushrod.
Le Mans Master
Joined: Jun 2004
Posts: 6,231
Likes: 65
From: Seattle WA
St. Jude Donor '14
Centered, yes - but it's not contacting the full width of the valve stem. Compare the two - the valve on the right has a full-width "stripe", the valve on the left has a "stripe" that is wide on the right side of the stem and tapers to nothing by the left side of the stem. This is definitely going to side-load the valve.
Tech Contributor
Joined: Aug 1999
Posts: 14,356
Likes: 6,328
From: At my Bar drinking and wrenching in Lafayette Colorado
You can't determine rocker/valve relationship (and pushrod length) with a single contact patch like that. You have to run the rocker/valve through a complete lift cycle and observe the relationship from valve close through valve open. In the closed position, the rocker tip should contact the valve stem towards the intake side of the valve stem. As the valve opens, the rocker should move across the valve stem towards the exaust side, crossing the centerline of the stem at about mid-lift. Your single-point contact line appears to be a static line showing contact point with the valve closed. You need to see where the contact is through the lift cycle and with the valve wide open.
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Melting Slicks
Joined: Jun 2002
Posts: 2,842
Likes: 99
From: Orrtanna Pa.
Pattern looks good,but don't forget to check for rocker body to stud contact,and spring coil bind while you're checking.
My aluminum roller rockers were hitting the rocker stud with a good sweep like what you have,so I went even longer with the pushrods. Mine are 8.050" as compared to the stock 7.80's.
My aluminum roller rockers were hitting the rocker stud with a good sweep like what you have,so I went even longer with the pushrods. Mine are 8.050" as compared to the stock 7.80's.
Thread Starter
Drifting
Joined: Oct 2004
Posts: 1,259
Likes: 7
From: Ontario
Thanks for all your posts... lots of good information.
The pattern was from a full cycle... closed to open. Not static.
Tonite I will drop in an adjustable rod and see if I can get it closer on center, while watching where the roller is at 50% closed as per some of your suggestions.
As you can tell the guides also need adjusting, I will fix that also and repost pictures later.
The pattern was from a full cycle... closed to open. Not static.
Tonite I will drop in an adjustable rod and see if I can get it closer on center, while watching where the roller is at 50% closed as per some of your suggestions.
As you can tell the guides also need adjusting, I will fix that also and repost pictures later.
Race Director
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What are you using for a lifter for this test? A hyd one will compress and cause some erratic readings.
JIM
JIM
