checking for pushrod length

[Omie01]

I am finally to the point that I can check for pushrod length. I have the comp hi-tech 7.800-8.800 checker, light springs, 1:73 scorpion rockers on 7/16" studs. I tried to do the correct geometry thing, but studs are too short to start off with centerline 90 degrees to valve retainers. My "light" springs still depress the lifter plunger when I spin the motor. How can I still get the right pushrod length? And remember, I still need .030to .040 for pre-load.

 

[Don C]

What you are looking for is for the swipe of the rocker tip to be even on both sides of the valve tip centerline. When the lifter is at the top and bottom of its stroke the tip of the rocker will be on the back side (push rod side) of centerline on the valve stem. When the rocker is at 90* to the stud (or approximately half way through the lifter stroke) the rocker tip will be on the front side (away from the push rod) side of the tip. You adjust the length of the push rod length checker so the swipe is as close to even on both sides of centerline as possible.

The lifter will depress unless it is completely full of oil when you turn the engine over, unless the light spring is light enough for the spring in the lifter to overcome it and not push the oil out of the lifter. The lifter has to be manually filled with oil, by soaking it in oil and depressing the plunger several when the lifter is submerged in oil. It's not possible to keep it full of oil when you turn it by hand, unless you spin the oil pump with a drill at the same time, with normal valve springs and if the light spring is not light enough. It's not necessary to have the lifter pumped up when you check the pre-load, with the lifter at the bottom of its stroke and the valve closed, just takes a more delicate feel and touch.

 

[jbojo]

Here is a video of how to determine the pushrod length. You only need to check 2 cylinders on each side, both intake and exhaust. Use the adjustable pushrod until you get the center wear mark on one cylinder and then check a few others and that length should work for the rest of them with the same wear pattern.

 

[Jeff73Mach1]

go buy a set of ARP rocker arm studs that are longer. Try something like these after measuring your existing ones. With the roller rocker arms, sometimes the stock studs are too short.

 

[barnett468]

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the video above is incorrect . . the primary objective is not to have the roller centered on the valve stem tip . . it is to have it make the narrowest pattern possible or to have it sweep towards the outside of the stem [towards the outside of the engine] reaching its fartnest point at full cam lift . . the roller will then end up wherever it ends up on the tip.

one of these methods will create an increasing ratio and max valve lift . . the other will create a decreasing ratio after 1/2 lift . . either will work.

 

[TommyK]

.

the video above is incorrect . . the primary objective is not to have the roller centered on the valve stem tip . . it is to have it make the narrowest pattern possible or to have it sweep towards the outside of the stem [towards the outside of the engine] reaching its fartnest point at full cam lift . . the roller will then end up wherever it ends up on the tip.

one of these methods will create an increasing ratio and max valve lift . . the other will create a decreasing ratio after 1/2 lift . . either will work.

+1000

The idea is to get the geometry of ALL the components of the valvetrain right, not just the rocker sweep. You can have your roller tip pattern centered and tight and wear your valve guides out in a thousand miles because your pushrod angles are fubar'd.

This is especially important with a canted valve design.

 

[woodsnake]

How much cam did you put in the engine? Do you have a fully adjustable valve train? Do you have a 12 inch digital caliper, to measure your final adjustment? When you get ready to order your push rods, keep in mind that there are three different points that they are typically measured from.

http://www.compcams.com/Products/CC-%27Pushrods%27-0.aspx

I have had a very hard learning curve with spring rates, installed height and push rod length! And paying machine shops for their "knowledge"...I find very often, that they are good at taking money, rather than 'just the facts'...

There is another really good article on sbf tech...

http://sbftech.com/index.php/topic,317.0.html

 

[Omie01]

I think I finally locked down a length, I have an extra set of lifters, so I measured cup depth on both sets and they were identical. So I disassembled one, took the spring out, put a washer in the bottom and put the plunger back in with the retainer to make sure it was sitting right. (no slop). I then started with no. 1 cyl, and checked 90 Degree at 1/2 lift, full lift and the sweep pattern, finally at 8.550 got everything to jive, then checked the length in all 4 corners of the motor and got consistent swipes, about .060 wide, and proper angles so I feel I finally found the right length, called comp cams and ordered a set of their Hi-techs 5/16 by 8.550 chrome moly with .080 walls. Wish me luck!!! Its starting to look like a motor Again!!

 

[c9zx]

.060 is very good indeed. You done good! Chuck