It appears that there are two types RAVE exhaust valves, ones with two grooves across the face, and one without. Just wondering if they are interchangeable for the 787 – their dimensions are identical?
I’m guessing that the engineers found out that when the valve gets slightly gummed, they do not let enough dynamic exhaust pressure go by the valve for quick bellows movement, and therefore, the reason for the groves. Metal base assembles are Identical, with the same bleed hole for bellows pressure. I also noticed that there are two types of bellows caps, every one of the caps on my boat failed, they were the white wimpy types, the caps broke, or the stems pulled out. The other type of bellows cap is black, and it has a cup on the top around the 10 mm fitting. My assumption is that I did not clean the valves, they stuck, and eventually the caps broke loose. Three of my valves had broken corners, and the valve that did not have the grooves, had a broken stem. All the valve housings were in very good shape, the guide holes were not out of round or worn.
I would like to blame all the failures on myself, and that they were caused by not cleaning the valves – that would be the easy button, just clean the valves; however, the right engine was just rebuilt, and only had 4 hours of operation on it, and the valves moved freely. I’m guessing like you said these were early design valves defect issue, I hope the new ones do better. The builder kept one of the original valves, and replace one with an ungrooved valve.
I should have all my parts this week, and get the boat in the water this weekend. I will just have to check and clean the valves at the end of each season, or twice a season. Once all the valves are working correctly, I should get a better top end. I could go 55 mph with the valves broken and not working; probably get up to 60 with them working properly.