I have 081 heads and I'm planning to upgrade to full roller 1.6:1 rocker arms. The higher ratio causes the pushrods to move out from the centerline of the engine slightly. I think they are rubbing slightly on the outward face of the pushrod slot. I'm not willing to elongate the pushrod holes for clearance. I don't feel like ripping the engine apart again.

I'm wondering if I can use slightly longer pushrods. It seems that a slightly longer pushrod would locate itself inward a little. It might give me the clearance I need.

I checked the current contact patch between the roller tip and the end of the valve. As you can see from the witness marks in the photo, the contact point is slightly outside of the center of the valve tip.



I think that a slightly longer pushrod would move the contact point inward a little. Hopefully on center or maybee just slightly inside of center.

My research indicates that the stock pushrod length is 7.195" - 7.200" .
I found a pushrod that measures 7.290"in length.

Does anyone have any experience using longer pushrods to correct valvetrain geometry? Do you think that the extra .095" will be too much or too little of a change to eliminate my clearance problem? How much will an extra .095" move the contact patch inward?

I may just order them and give them a try but as always I wanted to get a few opinions first. Thanks.

 

Only a stock engine should have factory length pushrods. My engine although it's a BBC has much longer pushrods to keep the geometry correct. I also have longer than stock valves to allow longer valve springs.

The only solution is to lose the 5hp you gained from the 1.6 rockers and install 1.5 rockers or pull the heads off and elongate the pushrod holes. Looking at those witness marks, they're about where they should be. The rocker tip should be slightly to the outside when the valve is closed. It should be in the center at 1/2 travel then slightly inside at full lift. Unless you install lightweight check springs, using a pushrod length checker, you can't check full travel or you'll break the test pushrod because of the high spring pressure when the valve is fully open.

 

I've used a pushrod checker at full travel and had no problems whatsoever.
IMO you need to get different length pushrods. Your witness marks should be center not outside.
Can't tell you for sure what length you'd need without a checker.

 

This has me baffled. When you go to 1.6 rocker arms the pushrod should be closer to centerline of the stud. Not out towards to outer part of the pushrod slot. Maybe I miss understood the problem.

 

Are the pushrod slots in line with the rocker stud and valve stem? Maybe they're cut crooked, Are you using guideplates? From the look of the rocker studs I'd have to say no. What about self aligning rockers?

Scroll down to page 264
http://www.compcams.com/technical/Ca...07/248-265.pdf

 

These are center bolt heads and require self aligning rocker arms. The 1.6 ratio moved the pushrods toward the stud and they now rub on the "bottom" of the pushrod slot.