I am asking for any thoughts or suggestions on this vibration.<br /><br />First of all the engine is a 2001 Merc. 7.4 MPI BIII eng. sn OL644969. in a 2001 Bayliner 2655.<br /><br />This vibration started approximatly at 40 hr's. I first noticed it while cruising at about 3200 rpm's, this is a rhythmic/cycling type of vibration that is only noticed between 3100 to 3600 rpm's, engine idles smooth.<br />The shop has determend that it is an engine vibration by running it with the out drive off the boat.<br /><br />First thing done was a cylinder drop test which showed that when #5 cylinder was cut out (dropped)rpm's incresed 5 to 10 rpm's and not decrease as normal. All electrical connections to the injector and spark plug where checked, all of that checked out good. All spark plugs where pulled and they all look normal and all the same condition. Compression has been checked and it was normal.<br />Conclusion was that # 5 injector was bad so they replaced it but the vibration still remains.<br /><br />On Monday they plan to do a leak down test to check further for compression problems.<br /><br />This vibration has been going on for about 80 hr's and I have noticed oil starting to leak from the rear main oil seal.<br /><br />Shop has been very good to work with. They have been in contact with Merc trying to figure this out. They and I are running out of idea's on what could be causing this.<br /><br />I have babied this boat from day one, never have I hit anything with the prop or miss treated it in anyway.<br /><br />Your thoughts would be greatly appreciated.<br /><br />Thanks