This appears to be a verifiable bug in the software's search logic - perhaps it should be referred to the vendor for investigation?
It's not a bug, but I now think I know what you've been trying to do.
We actually had two types of searches available on the
forum website.
1. The first which allowed searching posts and thread titles using exact text. This is what I think you were using. When you searched for "liner head pistons clearance" the search wouldn't have found anything, as that string in its entirety didn't exist.
2. The other type of search is probably the one you should've used, and searching for that string of text now presents you with a number of hits.
Going forward, I have removed the ability for anyone to do the first type of search, as it clearly creates confusion.
You can enter the search facility by either of the two methods above. Both will give the same results.
Sorry for any confusion about the two types of searches.