of the shim when you are searching for an assortment. When installing valve spring shims you must 1 figure out the size you need (thickness) and also take into account the I.D. Although these problems are pretty rare in occurrence it is vital to check beforehand. When shimming valve springs you are trying to keep the characteristics the same but also retain the seat pressure that you lost from cutting the seat or wear from use.Ī loss of seat pressure could cause valve float, premature wear and loss of compression. N ot shimming valve springs could put your valve train and how it will perform at risk. If for some reason the springs are 1 9/16" I must shim the bottom spring to close the "gap".ģ - what happens if don't shim my valve springs? When I measure valve springs in the head and the valve is closed, my springs should be 1 5/16".
Most modern workshop manuals will give you a figure referring to "valve spring installed height" and you must make sure your valve springs (at the given height) is the same to or as close to the book.įor example, a BSA C15 book with the sports head calls for an installed valve spring height 1 5/16". To accommodate the change you must use valve spring shims under the bottom valve spring collar to make up for what you have lost at the valve seat-Ģ - how do I figure out which shims my head requires?įiguring out which valve spring shims you desire is solely based off of your application.
O nce your valve starts to "sink" into the head your valve spring installed height begins to change.
O ver time as your valve seat starts to wear (and from cutting seats) you're valve will begin to "sink" into the head. Let's answer a few questions that often come up regarding valve spring shims.ġ - why do I have to shim my valve springs? I have done some heads in my time but installing and figuring which valve spring shim you desire is a rather simple process which can make a big impact. I am not an "expert" when it comes down to valve train. Today's Tech Tip post I wanted to briefly touch base with you on is called valve spring shims or valve spring "boosters" and why you should use shims on your next top end rebuild rather that just installing or replacing your springs. The method of shimming valve springs dates all the way back to the turn of century when mechanics and tuners alike would try to retain the stock valve characteristics as much as possible.
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