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Old 09-11-2015, 08:46   #1
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Broken Rocker Arm Shaft Mounts

So here's the story, Bought a sailboat this summer, guy delivering it didn't check the cooling water, blew a head gasket on the way up. Got the head skimmer, put a new gasket in, reconnecting everything. Ran it for fifteen minutes, changed the oil. Seemed to run fine, Tried to start it again, a loud banging was happened every two or three seconds. Took the rocker cover off and found 2 bend pushrods and two of the mounts for the rocker arm shaft have split in two.

any ideas on why/how this would happened.
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Old 09-11-2015, 09:02   #2
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Re: broken rocker arm shaft mounts

Did you check clearances first?

Where the rockers seized or the shafts worn? If you machined the head then the rockers will work on a different segment of the shaft.

Did you tension the head with the rockers and pushrods installed?

Some pics would help...

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Old 09-11-2015, 09:08   #3
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Re: broken rocker arm shaft mounts

Sounds like the pistons hit the valves, could be valve timing, or possibly the head was shaved too much.
Make sure the cam timing is spot on, and then use plastigauge to determine that you have good clearance between the valves and the head, this requires dis-assembly of course.
When you pull the head if there was valve to piston contact, it's very likely there will be marks, and you may have bent valves.

Another possibility is a valve got stuck in it's guide, suspect that if there are no marks on a piston and there is clearance and timing was correct.

I've never seen a head that you could torque without removing the upper valve train
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Old 09-11-2015, 09:22   #4
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Re: broken rocker arm shaft mounts

What kind of engine? A Perkins has rocker shaft mounts that could break apart. If it's a Perkins you should not have "skimmed" the head. There is no allowance for it in the service manual and the valve to piston clearance is very small.
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Old 09-11-2015, 11:11   #5
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Re: broken rocker arm shaft mounts

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Originally Posted by jonahmcg View Post
...any ideas on why/how this would happened.
Assembler didn't have the manual and didn't know what he was doing?
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Old 09-11-2015, 11:39   #6
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Re: broken rocker arm shaft mounts

It's a 40 Hp vetus (mitsubishi base).

I put the whole rocker assembly on after torquing the head down. Checked with the guy who did the head and he said there wasn't much skimmed off the head.
I'll get pictures together tomorrow and post em. The strange thing is that the engine turned over by hand a bunch of times when we were checking the timing and seemed to be all set fine, so not sure what happened. perhaps the photos will help.
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Old 09-11-2015, 12:49   #7
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Re: broken rocker arm shaft mounts

You did re-adjust the valves after you put it together?

By chance are these lifters hydraulic?
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Old 09-11-2015, 13:11   #8
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Re: broken rocker arm shaft mounts

Ran fine for 15 minutes. Possible it got water in that cylinder after you shut it down...?
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Old 09-11-2015, 13:43   #9
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Re: broken rocker arm shaft mounts

i didn't do any valve adjustment.

Im at the point in the process now where i've ordered new parts and am going to take the head back off, check the piston clearances, and put it back together. still havent diagnosed why it happened though so a little worried i might just happen all over again.
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Old 09-11-2015, 13:45   #10
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Re: broken rocker arm shaft mounts

Look in that cylinder for evidence of water. I doubt it was adjustment if it ran 15 mins previously....... unless they were totally not in the ball park..
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Old 09-11-2015, 13:48   #11
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Re: broken rocker arm shaft mounts

is this something that could have happened if someone tried to start the motor too long with the seacock open, and the water from the exhaust backed into the engine?
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Old 09-11-2015, 14:09   #12
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Re: broken rocker arm shaft mounts

Quote:
Originally Posted by jonahmcg View Post
i didn't do any valve adjustment.

Im at the point in the process now where i've ordered new parts and am going to take the head back off, check the piston clearances, and put it back together. still havent diagnosed why it happened though so a little worried i might just happen all over again.

Think you might have answered your own question.
if you put the engine back together after having the head planed but didnt bother to reset the tappets, what does that say for your mechanical competence? It would have been a rhetorical question but for the fact that by omitting the most basic of procedures you've probably trashed your pistons, valves and rockers. Should you be doing your own engine work?
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Old 09-11-2015, 14:33   #13
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Re: broken rocker arm shaft mounts

Quote:
Originally Posted by jonahmcg View Post
i didn't do any valve adjustment.

Im at the point in the process now where i've ordered new parts and am going to take the head back off, check the piston clearances, and put it back together. still havent diagnosed why it happened though so a little worried i might just happen all over again.
Quote:
Originally Posted by charliehows View Post
Think you might have answered your own question.
if you put the engine back together after having the head planed but didnt bother to reset the tappets, what does that say for your mechanical competence? It would have been a rhetorical question but for the fact that by omitting the most basic of procedures you've probably trashed your pistons, valves and rockers. Should you be doing your own engine work?
That's exactly what happened. You didn't adjust to make up the difference the head lost. BTW nice job blaming the chap that didn't check the cooling system...you didn't? Why not?
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Old 09-11-2015, 21:23   #14
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Re: broken rocker arm shaft mounts

From my kubota shop manual , it talked about a shim between the head and the head gasket to obtain proper clearances. Also talked about a "wick" You could remove injector ,feed in "wick" to measure clearance . I'm guessing"the wick". Is made of something soft that gets squeezed when rotating engine over tdc


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Old 10-11-2015, 03:50   #15
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Re: broken rocker arm shaft mounts

hey guys, i did adjust the tappets of course. but thanks for the insults. i didn't check the cooling because i wasn't on the boat. he was delivering it. so sort of hard to get into the engine and check things out. ya know.
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