When to replace manifolds and risers on a OMC?

[Boat Racer]

It is a 1983 OMC Chevy 5.7. I am rebuilding the engine due to a rear main bearing locked up. Grinding the crankshaft to .001 . So it wasn't too bad yet. Do I need to replace them. The manifolds and risers will cost more than the overhaul will. They are stamped 10-82. Maybe I am just being too cheap on this one.

 

[Boatist]

Re: When to replace manifolds and risers on a OMC?

Boat Racer<br />I not sure anyone can give you a time. In salt water I would say 4 to 6 years if you flush motor with fresh water every time you take it out. In fresh water they last much longer. One thing I would say is Manifolds I have seen fail all had lots of rust and scale caught in holes between manifold and riser before the end. Most had enough blockage to cause overheating.

 

[Boat Racer]

Re: When to replace manifolds and risers on a OMC?

They were fresh water use only. Sorry I forgot that.

 

[jasonnb]

Re: When to replace manifolds and risers on a OMC?

Been in your shoes. Back in July I rebuilt the 302 in my boat. The engine had water in it, but I'm not sure the manifolds themselves failed. They looked to be original from 1976. They appeared to be in decent shape, but I decided it wasn't worth it. I didn't want to do all that work and expense of the rebuild, only to have a manifold faila nd ruin the engine. At least now I can be reasonably sure. You have the motor out and it's easier to do now. I would be leery of 20 year old risers.

 

[charleswmoore]

Re: When to replace manifolds and risers on a OMC?

BoatRacer,<br /> look at OSCO's as a competative replacement they aren't that expensive. I'm not super fond of some of the finish work in the casting but they seem to take care of the machined surfaces okay. see previous postings regarding sandblasting of maniflods.<br />A bad one will cost you the engine rebuild price all over again! It just isn't worth it! <br />Charlie