Checking Tappet Pre-load
If you are rebuilding any V8 engine It is becoming more and more essential to check tappet re-load as there have been so many variants of the Rover engine components, and the engine itself now spans over 30 years, so you can't normally "assume" anything, So if you want to be sure of how your engine will end up. don't forget this important issue. Tappet pre-load is the distance between the pushrod seat in the lifter and the circlip, when the lifter is on the heel of the cam and the valve is closed. Not setting the lifter pre-load, will cause premature wear, noisy valve gear, and possible engine failure.!!. Or if your lucky "initial complete loss of compression as the valve will not be able to close fully,
The following information assumes that the following components are in good condition - rockers, pushrods, valve guides and valve stems. a clearance of .020" to a maximum of 0.60" must exist between the spring loaded pushrod seat in the top of the lifter, and the underside of the retaining circlip. This check should be made with the valve gear fully assembled, and the lifter empty of oil, positioned on the lowest point, on the back of the camshaft. The simplest way to measure the gap is by using round wire. Use a piece .020" for the low clearance check, and a piece of .060" for the high clearance check. Check all 16 lifters individually.
There are various ways to adjust the pre-load on the Rover V8. normally a decrease off pre load is required and this is achieved by using the "rocker pedestal shim kit" if the opposite applies the it would be achieved by machining the rocker pedestals however in race and higher end applications adjustable pushrods would be used.
Shim Kits, are inexpensive and include all the sizes you are likely to nee. Adjustable pushrods, are 3/8" and will require the guide holes to be elongated or opened out. Adjustable rockers can be used and are available in a pack. It would be wise to check your valve tip heights are all reasonably the same by putting a straight edge across them. Also, we have seen cases where the rocker pedestal mounting points cast into the head, are not parallel to the cylinder head face. This can make it a long tedious operation. Remember to take into account the rocker arm ratio of approximately 1.6. Make sure the shims are properly aligned under the pedestal so as not to block off the oil supply. Do not use shims of different thickness on the same shaft assembly, as breakage may occur.