I have a B&S 28N707 1135-E1 15HP vertical. Motor lost compression, I pulled valve cover and saw valve was no longer attached to valve spring collar. I found what looked like a valve stem cap, fits on top of valve, but found no typical valve keepers, looked at top of valve and all seems normal/as it should. Removed spring collar from spring and it does not appear to be a typical cap that uses two separate keepers. I know this engine has never been apart. Did B&S use any different set up for spring collar/keepers? Part # calls for typical set-up....which this does not look like. If they did use something different, could you give me the part number? Thank You