Engine Build Pre-Assembly (pushrod length measurement)

 

Next up on the pre-assembly checks to do list is to figure out what size pushrods I will be needing.  To do this I will be bolting the cylinder head on, torquing it to spec, and then setting up the valvetrain for the #1 cylinder.

 

Below is the head gasket installed

 

Torquing the head bolts down in the proper sequence to 75 ft/lbs

 

 

I will be using my solid lifters that I explained in my last blog entry.  Here they are in the #1 intake and exhaust lifter bores.

 

 

 

To determine the pushrod length pushrod checkers are used.  They are basically a pushrod that has a threaded section so the length can be increased or decreased in size.  Because big block chevrolet motors have 2 different size pushrods for the intake and exhaust, I had to get 2 different pushrod checkers.  One that measures 7.5" to 8.7" used to measure the intake side and one that measures 8.5" to 9.8" used to measure the exhaust side. 

 

Before I did this I had gone on to Comp Cams website and was looking at the sizes of pushrods they offer.  I noticed they had a kit for a 454 Engine with their retrofit cam.  I thought I would set my checkers to their sizes and see how they fit. 

Next to do was to set the rocker arm up.  To do these checks I had to swap the normal valve springs for light checking springs.  If the regular springs were used with the pushrod checkers there is enough pressure that they could be bent.

The picture below shows where the rocker arm would sit if the pushrod was too short.  The roller is sitting too far inboard on the valve stem.

 

As the pushrod is lenghthened the roller now sits more in the middle of the valve stem.

 

In order to make sure the pushrods are the right length I needed to see where the roller tip on the rocker is actually riding during opening and closing.  To do this I coloured the top of the valve stem with a sharpie before putting the rocker on.  As I spin the engine over and the rocker, pushrod checker (set to length) and lifter open and close the valves the rocker tip will wear a pattern in the marker.

In the picture below is example of where the pattern should be.  I lucked out and the Comp Cams pushrod set that they have is a perfect fit and provided good results

Pushrod checker set to length

Setting the pushrod checker to the desired lengths

 

  

Below, I am installing the rocker arm on the valve at "zero lash".  This means that with the lifter on the base of the cam lobe (lowest point) the locking nut on the rocker stud is tightened down just until all slack is taken out of the pushrod, no more.  When I go to install the pushrods and rockers on final assembly I will be taking them to zero lash and then turning the locking nut another half turn, which puts a "preload" on the hydraulic lifter.  I will explain more on this when doing the final assembly.

 

This picture below shows a wear pattern too close to the outboard side of the valve.  In this case the pushrod would need to be shorter.

 

When I was done and I was happy with the wear patterns on both the intake and exhaust valves I ended up ordering the Comp Cams push rod set with 7.725" intake pushrods and 8.684" exhaust pushrods.  Once I get the pushrods I will do this test once more to double check correct length.