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Old 05-20-2018, 06:32 AM   #1
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Post Mercruiser 3L push rod bent, rocker arm off center, clanking noise from engine

2007 Maxum 1800 MX, Mercruiser Alpha 1 Gen 2 engine. Smooth sailing until I've heard a very loud clanking noise. Towed the boat back, took the rocker cover off and found out that cylinder #3 rocker arms were off to the side sitting on cap rotators instead of valves (exhaust more than intake).

Took nuts off both rockers and found out that both push rods were bent. One rocker arm stud had a deep cut (exhaust side) and even the head had a notch grinded by the push rod! (see pictures).

Got the new parts (rods, rocker arms, stud) but I'm not sure about 2 things:
1) what could possibly cause those push rods to be bent?
2) how to replace the rocker arm stud

Could a faulty hydraulic valve lifter cause that? Perhaps the valves weren't adjusted properly? Has this happened to you? Any ideas?
I just bought this boat few months ago. The previous owner had the cracked head replaced a year ago.
Attached Images
File Type: jpg RockerArmsOffCenter2.jpg (242.5 KB, 11 views)
File Type: jpg RockerArmsOffCenter.jpg (260.3 KB, 10 views)
File Type: jpg RockerArmStud.jpg (219.4 KB, 15 views)
File Type: jpg BentPushRods.jpg (78.8 KB, 12 views)
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Old 05-20-2018, 11:42 AM   #2
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Hard to say why they bent but I would pull the head to check the valves as the stems could be bent as well. Maybe they went set right from the last repair, studs could be pulled out some as they are pressed in. Maybe water in that cylinder, since both valves this could be the cause. Pull the spark plug to look for water. I have not seen a collapsed lifter cause this but it may be possible.
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Old 05-20-2018, 02:04 PM   #3
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Hard to say but have to be inside the engine...Broken cam shaft? or damage piston?
If you don't know how engine should be fix, don't try to fix your self. You end up to pay more then you should.
Sorry for your problem considering the summer just start....
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Old 05-20-2018, 03:08 PM   #4
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1+ for what Mike said.
Pull the plugs out and check for water.
If no water pull the head off you will probably find bent valves.
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Old 05-20-2018, 04:57 PM   #5
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Thanks for the tips. I'm trying to avoid taking the head off as this would be a major job. There seems to be no water in the engine, the oil is clean. I've installed new push rods, re-adjusted all rocker arms and started the engine. The engine runs fine, steady and quiet but because of that cut in the stud, one rocker arm slides right into it and shifts to the side almost immediately unless you hold it in the position manually by hand.

I'll take off the push rod cover next and check the hydraulic valve lifters.

No, I'm not a mechanic, I'm a software developer but I've got a good friend who is machinist to help me out plus I've got the service manual and the fellow boat owners to share the knowledge When I called the shop they told me $1000 just to diagnose the issue, so trying to save the dough and learn something in the process
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Old 05-20-2018, 06:27 PM   #6
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I believe the loose stud is the cause of your problem.
Looks like the rocker stud loosened from its mount which created excessive lash. The rocker became a hammer and bent the pushrod.
The only way I know to fix that stud is to tap the stud hole and screw in a new one.
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Old 05-20-2018, 10:40 PM   #7
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Hi jrsick, unfortunately the stud is not loose. I've put 2 nuts on it to try rotating it and nothing. It sits solid in the head.

The original studs have thread on one side only (16-34522). Is there a replacement stud with threads on both sides? Can't find any on their site other than original.
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Old 05-20-2018, 10:58 PM   #8
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Quote:
Originally Posted by jrsick View Post
I believe the loose stud is the cause of your problem.
Looks like the rocker stud loosened from its mount which created excessive lash. The rocker became a hammer and bent the pushrod.
The only way I know to fix that stud is to tap the stud hole and screw in a new one.
This would not explain both push rods bending.
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Old 05-20-2018, 11:00 PM   #9
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Quote:
Originally Posted by Maxum1800MX View Post
Hi jrsick, unfortunately the stud is not loose. I've put 2 nuts on it to try rotating it and nothing. It sits solid in the head.

The original studs have thread on one side only (16-34522). Is there a replacement stud with threads on both sides? Can't find any on their site other than original.
The OEM studs are pressed in and require sealant as they go into the coolant passage. If she is not making any tapping noise the lifters are not the issue.

There are screw in studs but the head should be removed as you will need to cut threads to install it.
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Old 05-20-2018, 11:01 PM   #10
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Quote:
Originally Posted by Maxum1800MX View Post
Thanks for the tips. I'm trying to avoid taking the head off as this would be a major job. There seems to be no water in the engine, the oil is clean. I've installed new push rods, re-adjusted all rocker arms and started the engine. The engine runs fine, steady and quiet but because of that cut in the stud, one rocker arm slides right into it and shifts to the side almost immediately unless you hold it in the position manually by hand.

I'll take off the push rod cover next and check the hydraulic valve lifters.

No, I'm not a mechanic, I'm a software developer but I've got a good friend who is machinist to help me out plus I've got the service manual and the fellow boat owners to share the knowledge When I called the shop they told me $1000 just to diagnose the issue, so trying to save the dough and learn something in the process
No water in the oil doesn’t mean no water in the cylinder.
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