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Ford 9N, 2N & 8N Discussion Forum
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OT: Help with 4 CYL Mercruiser Boat Engine

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Hec In Omaha

08-10-2005 04:53:25




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Howdy all,

I thought I would tap into the vast mechanical knowledge on this forum. I have been helping a coworker with his boat. He brought the boat to me and it was only running on two of four cylinders. I verified this by diconnecting one spark plug at a time. Cylinders 2 & 3 were not doing anything. So after replacing cap, rotor, plug wires, and points I still had nothing from cylinder 2 & 3. I figured that there must be something wrong in the valve train. I found the valve clearances way off on Cylinders 2 & 3. After readjusting the valves I fired it up and she ran great (For about 5 mins). The engine started running real rough again. I determined that cylinder 3 was not firing again but the rest were. Took the valve cover off and found Cylinder 3 exhuast push rod completely off. In fact the valve lash adjusting nut had completely backed off. Why would it do this? Colapsed lifter? I reset all the valves and it ran fine again for 5 Mins. I haven't opened it again but I know that Cylinder 3 isn't firing again. The motor is a 1986 Chevy 4 Cyl. 180 Cu. In. I am contemplating replacing all the valve adjustment nuts. Anything else to check.


Hec

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stimw

08-10-2005 05:30:42




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 Re: OT: Help with 4 CYL Mercruiser Boat Engine in reply to Hec In Omaha, 08-10-2005 04:53:25  
The ajusting nut is a lock nut. It might need replacing. You might have the stud backing out. They are just pressed in. When that happens you will have to tap the hole and put a threaded one in. They are the same as most Chevy Engines, that engine is basicly one half of a 350 Chevy. Try to stay away from the dealer, they should have a pistol on you for the prices they charge.
Check the spark plugs for brown color (rust) too. These engines have a water cooled exhaust manifold and when they fail water will get into the engine and cause major damage. At low RPM the engine will suck the water into the combustion chamber. I saw one that sat for a week and locked up, piston rusted to cylinder. It was run in saltwater. tim

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Hec In Omaha

08-10-2005 11:52:37




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 Re: OT: Help with 4 CYL Mercruiser Boat Engine in reply to stimw, 08-10-2005 05:30:42  

Well after a few more tests we have Low compression on #2 & 3 cylinders. The engine was supposedly rebuilt and only has 20 hrs on it. The valve adjustment for these two cyls were either to loose or to tight. I readjusted the valves and checked rocker arm movement to rule out a flat cam lobe and the rockers move equaly on all cyl. Still low compression. I think he has broken valves or pistons and or rings. What do you think?


Oh yeah thanks for everyones input and suggestions.


Hec

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Bob

08-10-2005 12:26:13




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 Re: OT: Help with 4 CYL Mercruiser Boat Engine in reply to Hec In Omaha, 08-10-2005 11:52:37  
Having trouble like thak with 2 adjacent cylinders, have you checked for a blown head gasket?



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Hec In Omaha

08-10-2005 14:14:36




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 Re: OT: Help with 4 CYL Mercruiser Boat Engine in reply to Bob, 08-10-2005 12:26:13  
Bob,

You Win You Win! Just pulled the head off and low and behold it was blown between #2 & #3 cylinders. No its time to see if the head is warped. I hope not. Thanks for the great call.


Hec



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Bob

08-10-2005 21:35:56




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 Re: OT: Help with 4 CYL Mercruiser Boat Engine in reply to Hec In Omaha, 08-10-2005 14:14:36  
DANG!!!

Let's not tell Dell about my mind reading (no make that remote diagnosis) abilities!

I hope a new gasket fixes it for you!



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stimw

08-10-2005 09:52:07




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 Re: OT: Help with 4 CYL Mercruiser Boat Engine in reply to stimw, 08-10-2005 05:30:42  
Bob is right, I had to get the book out and look because I haven't worked on a 181 cu in in years. They use a standard Chevy rocker arm with ball pivot but they use a bolt with a jam nut holding it in the head. They show using a lifter colapsing tool (?) and a feeler gage to ajust. If I look at ajustment specs it says 3/4 to 1 turn. That is with lifter pumped up. Basicly you ajust lifter/valve stem clearance to zero (lifter must be pumped up) and then tighten 3/4 to 1 turn. Which puts lifter in center of it's hydralic travel. Then tighten jam nut to head.

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Bob

08-10-2005 06:34:08




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 Re: OT: Help with 4 CYL Mercruiser Boat Engine in reply to stimw, 08-10-2005 05:30:42  
Some of the Chevy 4-cylinder engines of that ara use rocker arm studs where the nut tightens against a shoulder on the stud, and is not self-locking like other 4-cylinder, 6-cylinder, and 8-cylinder Chevy engines were in the past.

There is enough travel designed into the lifter to accomodate valve train wear, and the nut is simply torqued against the shoulder on the stud. Trying to set valve lash with the nut, rather than tightening it will cause it to work loose in short order.

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Bob - MI

08-10-2005 05:23:54




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 Re: OT: Help with 4 CYL Mercruiser Boat Engine in reply to Hec In Omaha, 08-10-2005 04:53:25  
Hec,

I"m afraid that I can"t really contribute much here but I have the EXACT power plant in my 1986 Starcraft Islander and I"m really interested in what you find.

I have had some success shopping around the "net with other Mercruiser mechanical issues. There are some marine based help boards such as we have here and my guess is that someone else has had this problem too. My boat has pretty low hours and spends more time sitting in the barn than out on the water.

I will knock on wood here but I have always used the suggested oil weight shown in the owner"s manual for that motor which is straight 40W. Fill cap says 10W-30 however.

I wish you the best of luck with this one.

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