Manifold, Riser Replacement Help

I have an 86 Bayliner Capri 21' OMC 5 Liter engine. Tested the compression today 138 to140 on all cylinders. Also noticed some JP weld on water jacket, I have had boat out and ran it hard without any problems and engine runs at 140 degrees, so I think I am ok with JP weld to the water jacket. When I pulled the plugs all them looked very good except for #4 it appeared to have been exposed to minimal amounts of water, thus my reason for replacing manifolds, boat has never ran hot but manifolds look like they need to be replaced.

I am looking for any guidance in changing out the manifolds and risers? Also, noticed a couple of the bolts on the engine mount are loose will not tighten into stringer, wondering if I can set a bolt into another hole on the steel mount above the stringer, I think they are lag bolts but not sure of the size and length? Any help much appreciated.

Any links or info on manifold replacement would be helpful, what torque to use bolts etc., what gasket sealer etc. Also any links showing how to change out impeller and do drive service. Not finding any information anywhere.

Thanks in advance for any assistance.

Re: Manifold, Riser Replacement Help

You do know that OMC went out of buisness a good 10 or so years ago? I have heard that it is hard to get parts for them sometimes. I do know that there is alot of OMC stuff on ebay, I get alot of things off the bay for my 1989 (also sometimes hard to find parts for) 4.3 Merc. Sounds like you haven't had the boat very long so yeah, I would (and did) get all new manifolds and risers so I know I'm not playing with fire running old suspect manifolds. Since you found evidence of water intrusion, I would say it's time to change 'em. Don't know about the motor mount problem, but there are alot of OMC guys out there, hopefully some of them will chime in for you soon! And if you don't already have one, you should get a manual for your boat/engine/drive, torque values and troubleshooting, etc. are in there.

Re: Manifold, Riser Replacement Help

Doh! Look right above your post, there are a bunch of links to OMC stuff! Just now saw it!

Re: Manifold, Riser Replacement Help

cohibakid said:

I have an 86 Bayliner ......

Also, noticed a couple of the bolts on the engine mount are loose will not tighten into stringer.

Click to expand...

Are you sure that your stringers are not rotted out? that age of a liner, and the problem described sure sounds like it.

Re: Manifold, Riser Replacement Help

Replaced the manifolds easy to find on internet. Wood is solid on other engine mounting bolts so I think the stingers are ok. I am going to try to fill hole with dowel.

Started engine ran at 140 degrees, engine seems to be strong. Just a little concerned with JP weld on water jacket, but seems to be holding just fine.

Also wondering if the timing for this GM 5 litre is thirteen degrees BFTDC. Also wondering if replacement engines are easy to find.

Thank-you for your input!!!