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  #16 (permalink)  
Old 12-03-2012, 10:32 AM
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Originally Posted by 1971BB427 View Post
No. You install rockers on one cylinder with the adjustable pushrod. Then you use machinist dye or a colored marker to the end of the valve stems. You crank or roll the engine over with the valve adjusted and adjust the pushrod until the pattern shows contact on the center of the valve stem. Then remove the rocker and check the length against the stock pushrod to see how much difference is needed. Lots of various lengths available in pushrods to get close to what your measurement shows.
One needs to add that you need to watch the push rod for clearace where it passes through the holes in the head which in older heads will also be the push rod guide, there is a tool sold specifially to open these holes when 1.6 rockers are used or high lift cam is used to provide clearance such that the push rod does not bind where it passes through the head from the valley to the rocker box. If you're using seperate guides that fasten under screw in rocker studs, these also need to be checked for push rod binding and relieved as necessary. Another couple possible contact ponts are the push rod against that side of the rocker and the slot if this is a ball and socket style rocker needs to be checked to insure the slot is long enough not to bind on the stud.

You also need to check for valve spring coil bind, needed .050 inch minimum between each coil. Clearance between the spring retainer and valve guide including the guide oil seal needs to be checked this also should not be less than .050, preferably more.

When you start getting toward .5 inch lift at the valve it's also time to check the clearance between the open valve and piston. Here .080 inch on the intake and .100 inch on the exhaust is considered safe.

If you need them lash caps that fit on the end of the valve stem are available to increase stem length if this becomes necessary to put the contact pattern in the correct place. It's not a bad idea to keep a set around when checking to see if more stem length provides better angles and patterns.

Bogie

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  #17 (permalink)  
Old 12-03-2012, 10:44 AM
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Be sure to check the clearance at the push rod guide hole in the cylinder head. 1.6 rockers will put the p-rod very close to- if not touching it.

You can easily make an adjustable push rod length checker from an old push rod.

Some info:

Valve Train:
Rocker arms has info on ratios and using a Lewis tool to open the push rod guide holes in the head.
Valve spring installed height
Points to check
Geometry
Adjust lifters
Cam break in
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Old 12-03-2012, 11:48 AM
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Yes, clearances can be an issue, especially if you have guide plates, and if you don't have guide plates and screw in studs, then you should upgrade to them! Also be sure to order hardened pushrods when you get new ones, as standard pushrods can wear on guideplates and break.
Buying 1.6 rockers sounds like cheap HP upgrade, but it causes a trickle effect, and can lead to some work, and a fair amount of money to make them work. Be sure you've got valve to piston clearance for the higher lift too, as Bogie mentioned.
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Old 12-03-2012, 11:54 AM
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Generally speaking, it's better to spec the cam for 1.5 rockers from the get-go. There are reasons one might need to use 1.6 rockers, like in the case of the SBC roller engine that doesn't play well w/cam lobe lifts higher than 0.354". Higher ratio rockers is one way around that to get more lift w/o causing the dog bone to lose contact w/the roller lifter. Maybe not the best way, but it is an option that costs less than the better aftermarket roller lifters.

The valve train has a few places that you can get into trouble when adding lift, like spring coil bind, retainer to seal or guide boss interference, etc. Most things like this are covered in the Points to check link above.
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