mk1-forum.net

Why do A+ cylinder heads have a different valve spring fitted height than Pre A+ heads?
Springs are the same part Number,eg C-AEA526.The fitting instructions for these springs state"The standard heights for pre-A+ heads are approximately 1.32” to 1.37” for small-bore types, 1.40” to 1.42” for large-bore types, and A+ heads 1.35” to 1.38” for small-bore types and 1.35”-1.37” for large-bore types."

its because a plus std springs are longer than pre a plus ones due to the top caps sitting slightly higher when assembled on the valve.

if you measure a triple collect valve and its cap in a bare head you will see the slight difference.