Engine Vibration / Port side manifold

[lrlima]

1993 4.3 OMC cobra <br /><br />Was trying to troubleshoot a problem and possibly found another...<br /><br />The engine vibrates badly (boat shakes)at idle and under 1500 RPM - both in the water and on the muffs. Idle is approx 600 RPM. Once over 1500, boat runs great and the vibration isnt there, or at least I dont feel it. Just replaced distributor, plugs, wires, fuel filter and still the vibration. <br /><br />I pulled the outdrive to inspect the gimbal and ujoints - both were in good shape and greased. I then pulled the drive and ran the motor to make sure that the drive wasnt the problem (I used an old water house directly into the bell housing). Vibration is still there, so it cant be the drive. Could it be the engine coupler? <br /><br />Another potential problem, as the engine was warming up, I noticed the port side exhaust manifold was very hot to the touch and the other was cool. I immediatley turned off the engine and temp never got above 100.<br />Not sure if this is normal when on muffs, or was the hose in the bell housing causing the problem?(I had good flow from hose) Perhaps my two problems are related?<br /><br />Thanks for any advice...

 

[Gary H NC]

Re: Engine Vibration / Port side manifold

I had the same type of problem on my 4.3<br />With engine at idle pull one spark plug wire at a time.you should hear a big difference in the engine.Do this on each plug,If one or two don't seam to make a differenc it may be a head gasket.Mine would get warm on one manifold and the other was much cooler.the cool side had a bad head gasket.I know a good mechanic in Albemarle that will do a leak down test and determine if it is the head gaskets.He is just north of town..its called J and J marine.

 

[Don S]

Re: Engine Vibration / Port side manifold

Do a compression check, and "Read" the plugs as you remove them.

 

[lrlima]

Re: Engine Vibration / Port side manifold

Thanks Gary and Don - I'll start troublshooting as you've recommended. Is it ok to warm the engine, or do I risk damaging the manifolds...Thanks again.

 

[lrlima]

Re: Engine Vibration / Port side manifold

Don, did a compression check. Bad news for me. #6 compression was at 15. All others were between 150 - 155. Talked to my local mechanic about doing a valve job and the estimate was approx 12 hours plus all of the other costs for gaskets, heads, etc. Then he said you also dont know what you'll find once everything is open (understandably). <br />The saying is true - breaking out another thousand (and then some).<br /><br />Just looking at my options, I found a 4.3 reman engine on ebay last night. The seller is Engines Direct. They had a 4.3 chevy longblock for sale at $829 plus $150 ship. Included "complete installation gasket set and oil pump." <br /> 4.3 link <br /><br /><br />To me, it makes sense to go this route. My buddy has the tools, hoist and experience to help me do a swap. Does this seem too inexpensive? Thoughts on going through my existing engine or buying this rebuilt for about 1k? Thanks for any advice.

 

[bandsaw48]

Re: Engine Vibration / Port side manifold

Irlima,<br /><br />You might want to pull the valve cover and take a peek at the valve springs just for fun.

 

[lrlima]

Re: Engine Vibration / Port side manifold

thanks bandsaw, my buddy at work said the same thing. Bringing the boat home this weekend...Maybe I'll get lucky...

 

[sailsmanship]

Re: Engine Vibration / Port side manifold

Had same thing happen. Pulled valve cover and found a broken rocker arm stud. New stud and a valve job, back in business... No problems..

 

[Gary H NC]

Re: Engine Vibration / Port side manifold

Still sounds like a head gasket because of one manifold running colder.I replaced mine for 6 hours labor and about 80 bucks in gaskets.<br />Was that price from Engines Direct for a marine engine? Sounds like a very cheap price.

 

[lrlima]

Re: Engine Vibration / Port side manifold

Yes, it was on ebay. I thought it was too cheap as well. The acution has ended however. But I called the guy and he had a 4.3 if I needed it. Thanks for the advice. I'm going to troubleshoot more this weekend...

 

[Gary H NC]

Re: Engine Vibration / Port side manifold

Good Luck! I would pull the valve cover first.<br />If no problem there the next step would be head gasket.I got all my gaskets from napa..let me know if you need part numbers