First post here. Recently got a 1975 Spectra 18' with an Olds 455 with a Jacuzzi WJ pump. Boat has around 300 hours on it. Unsure of the history of the boat. As far as I know, neither the engine or pump have been rebuilt, but both seem to be in good shape. Has GM style Mallory HEI distributor, Edelbrock carb and manifold, but other than that, it seems stock.
Quick background: Took boat out for the first time two weeks ago. Ran and drove great. Stopped at dock for lunch, key chain broke and ignition key fell in lake. Had to hotwire to get going. Kept jumper wire between batt and ign terminal on ignition switch on loose in case I had to shut the motor down quick. Was cruising along at about 40mph and jumper wire came loose and engine shut down like like I had turned the key off, which I functionally did. Boat quickly coasted to a stop. Reconnected jumper, cranked, but engine wouldn't start. Fiddled around for an hour on the water trying to figure out the problem. Couldn't figure it out and got a tow home.
Once home I troubleshooted more thinking something was wrong with ignition system. Ended up discovering distributor rotor wasn't rotating when I cranked engine. Removed distributor, noticed cam wasn't spinning with crank. Took timing cover plate (not sure of correct term) off and peeked in at timing chain. Timing chain broken. Haven't taken off harmonic balancer so can't get a great look inside yet from timing cover plate. But, I think damage is limited to broken chain.
My question is, what about the weird timing coincidence? I am doubtful it is a coincidence. Jumper wire came off and engine shut down and timing chain broke at the same time. Did something cause the timing chain to break after the engine shut down from ~4000rpm and boat coasted to stop? I never heard or felt any strange sounds as I was cranking the engine immediately after the shutdown so I don't think anything else is damaged. And I believe the 455 (stock, anyways) is a non-interference engine. I don't think water came in through exhaust logs and hydro-locked the engine. Exhaust flappers in good shape.
Any thoughts are appreciated.