Mercruiser 3L push rod bent, rocker arm off center, clanking noise from engine

[Maxum1800MX]

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.

[mmwjr]

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.

[Gugi47]

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....

[donald]

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.
Don

[Maxum1800MX]

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

[jrsick]

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.

[Maxum1800MX]

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.

[mmwjr]

Originally Posted by Maxum1800MX

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.

[mmwjr]

Originally Posted by jrsick

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.

[jrsick]

Originally Posted by mmwjr

This would not explain both push rods bending.

Mike, if the exhaust rod bent first then the cylinder pressure can't escape and could bend the intake valve.
1800MX, the picture looked to me like the stud had risen, sorry for the confusion.
I agree that water in cylinder is most likely cause. Gugi has good advice, and I would also recommend a borescope. You can find some inexpensive ones online. Borescope would help you locate water, see if there is cylinder head damage, and check for foreign material in cylinder.
I doubt the nick in the stud is causing the rocker to shift. Try cleaning the stud base and rocker nut, then stripe them with a marker. Start the engine and see if either shifts during operation. Rocker nuts will lose their crimp with repeated adjustments and need to be replaced.
Take this step by step and you will find the fix.

[mmwjr]

Originally Posted by Maxum1800MX

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.

[Gugi47]

The stud is bend?
Find somebody who is good in TIG welding.
Make 2 hols in a 1/4x1 flat for holding the stud when welding.
But Mike is right. Take the plug out and check for water.
After yo remove the plug take a napkin role it and introduce true the plug hole 1" and hold it there. Somebody have to turn the engine 2 sec.
If the napkin get wet you have water, if not, you OK.
Good luck

[Maxum1800MX]

Gugi47 and Mike, Great tips about the water in cylinder, I'll try that

[jrsick]

Mike,
intake valve opens just prior to TDC, when cylinder is on up-stroke. Exhaust valve has been open and escaping exhaust gases help draw in intake gases during valve overlap. If exhaust valve does not open then intake valve is trying to open against max compression.
I've seen the two bent pushrod scenario 3 times in my corvette club. In these three cases replacing the rods and setting lash fixed the problems. Causes remained mystery even though there were expert mechanics that disassembled the engines. Of course these were LS engines vice boat engines.

[mmwjr]

Originally Posted by jrsick

Mike,
intake valve opens just prior to TDC, when cylinder is on up-stroke. Exhaust valve has been open and escaping exhaust gases help draw in intake gases during valve overlap. If exhaust valve does not open then intake valve is trying to open against max compression.
I've seen the two bent pushrod scenario 3 times in my corvette club. In these three cases replacing the rods and setting lash fixed the problems. Causes remained mystery even though there were expert mechanics that disassembled the engines. Of course these were LS engines vice boat engines.

I accept this as plausible but would still be concerned of bent valve stems. Also the force to bend the push rod is enough to pull the rocker studs out some.

[Maxum1800MX]

Originally Posted by jrsick

Mike,
intake valve opens just prior to TDC, when cylinder is on up-stroke. Exhaust valve has been open and escaping exhaust gases help draw in intake gases during valve overlap. If exhaust valve does not open then intake valve is trying to open against max compression.
I've seen the two bent pushrod scenario 3 times in my corvette club. In these three cases replacing the rods and setting lash fixed the problems. Causes remained mystery even though there were expert mechanics that disassembled the engines. Of course these were LS engines vice boat engines.

Hi jrsick,
According to mechanics manual incorrect valve adjustment can cause those push rods to bent. The other odd thing I've found is that there were 2 different push rods on cylinder #3 than on all the other cylinders. Those 2 are long and have straight ends but the other 6 were new style with a little balls on each side. The 2 new ones I've got have also little balls.

Given all those worn out parts, it looks like my next option is to remove the head and replace the worn out valve (or both). Then replace both rocker arms, push rods and the sliced stud.

jrsick, looking at the pictures do you think it's necessary to replace the exhaust valve?

[mmwjr]

Originally Posted by Maxum1800MX

Hi jrsick,
According to mechanics manual incorrect valve adjustment can cause those push rods to bent. The other odd thing I've found is that there were 2 different push rods on cylinder #3 than on all the other cylinders. Those 2 are long and have straight ends but the other 6 were new style with a little balls on each side. The 2 new ones I've got have also little balls.

Given all those worn out parts, it looks like my next option is to remove the head and replace the worn out valve (or both). Then replace both rocker arms, push rods and the sliced stud.

jrsick, looking at the pictures do you think it's necessary to replace the exhaust valve?

You valve must be removed to tell if it’s bent.

[jrsick]

So the faulty pushrods are different than the others? That may explain the problem. Pushrods that are the wrong length will affect rocker geometry.
Do your bad pushrods have oil holes in them and good pushrods do not, or vice versa?
When you tested the engine after installing the new pushrods it ran smooth. Why do you think a valve stem is bent?
I'm undecided on the nicked stud and why the rocker wanders to it. I'm thinking the nick occurred when the rod bent and the rocker came off of the valve. The nick seems to low to affect rocker operation. Do you see metal shavings at base of the nicked stud? How about corresponding damage to the rocker?
I'll repeat my borescope suggestion. If piston head looks good then it may not have contacted the valve.
I only have my own experience here, and that is that a pushrod can be damaged without damage to any other component.

[mmwjr]

Jrsick I suggested the valve stem may be bent as you have stated is may only be a bent pushrod. The only way to know is to remove the valve and inspect it. I only suggest this because if it’s damaged it could break and drop the valve and I have seen the results of this and they aren’t pretty.

Just looking out for the OP best interest.

[mmwjr]

Since you have the engine running perform a compression test on that cylinder, if the valve is bent it would not seat properly and the compression would be low. Then you would just need to decide what to do about the stud.