OMC Cobra outdrive issues after exhaust shutter fail

[alekseyss]

Good evening, hopefully some of y’all knowledgeable in boats could point me in the right direction. I really don’t know much about boats but I’ll do my best to explain. I have a 1992 Four Winns Horizon 190, OMC 5.0 with Cobra outdrive. Just want to go ahead and throw it out there that my max speed was always about 30 to 35 on this boat (not sure of RPM) but the prop was a 14x21. One day I slowed down fast to avoid a shallow spot and water came through the Y pipe and hydrolocked the engine. I was able to unseize the engine, in the course of spinning it through 8-10 sec at a time to spray out the moisture from plug holes, I melted the impeller housing and didn’t realize it until I took it out on the water and it started overheating on me. It would start to accelerate and then it would feel like it was straining very very hard and then it would just lock up. I replaced the impeller and the housing and verified water going through the thermostat. I let it idle for about 40 minutes in my driveway with no problem in the engine temperature never went over 160. My problem now is, even though the boat will idle forever with no issues, if I slightly rev it on neutral it will lock up in about 2 to 3 seconds and make a shudder which seems to be more noticeable on the outdrive but I’m not sure. My personal thought is that the old exhaust shutters weather melted or deteriorated are clogging something in the engine is back pressuring when I put accelerate. Because it does the exact same thing whether in neutral or reverse or forward. I took off my lower unit today but I did not see anything stuck and also the white pipe seems to be clear of any debris. If anyone has any advice or suggestions I would greatly appreciate it.
PS: The water spout inside the lower unit seems to have melted plastic around it I do not know if this is something that needs to be replaced or not.

 

[Scott Danforth]

If you think its the shutters, pull the exhaust elbows and look. If you ran without cooling water long enough to melt bits in the drive, you long ago burned up all the rubber bits in the exhaust

You do need to replace all burned and melted bits

You should also replace the exhaust hoses because they are probably burnt on the inside. Rubber melts at 250F, and exhaust without water is 900F to 1200F

 

[alekseyss]

Thanks for the reply. I will check out the exhaust hoses. As far as the shutters I already replace them but I have no idea what happened to the old ones. I’m thinking of pulling the exhaust manifolds and risers and checking if any of them got stuck inside of there

 

[alekseyss]

Update: I ran the engine today without the outdrive and it runs like a champ. I reved it forward and reverse on neutral with no issues whatsoever. So what could possibly be causing this that’s located in the outdrive?

 

[Bondo]

So what could possibly be causing this that’s located in the outdrive?

Ayuh,..... Bad bearings, bad gears,..?? drain the oil, 'n look for metal,.....

 

[PITBoat]

Yeah I don't know what happened to mine either; it seems like I pulled a piece of one out of the top of the drive last year. I don't know how bad of an exhaust restriction it's possible for that stuff to create in the drive passages; I was more worried about interference with the shift rod. I used an inspection camera to look around in it.

I went to a single home-made flapper at the transom opening(?), with nothing in the U-pipes (and no exhaust bellows of course). I can't recommend it, I can just say it has worked so far. And my brother chopped the throttle good one time, with no bad results.

But if you're drive is messed up such that it won't even let the engine spin freely in N, this doesn't help you. Just throwing it out in case it's possible your restriction idea is right.