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Old 10-11-2015, 04:31   #16
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Re: broken rocker arm shaft mounts

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Originally Posted by jonahmcg View Post
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.
jonah, I think there were a few here that were just having an off day... Sorry for the under the weather attitudes...

Anyway... Obviously decking diesel heads is tricky business... The bit about checking clearances and shim/head gasket thickness is fairly standard...

Sounds like to us, you simply don't have enough room for the valve travel, and you've got piston contact with them...

Yes, cranking more than a few times without firing can definitely lead to water flooding the cylinders... Maybe this happened instead of too little clearance... You'll know when you pull the head...

Take lots of pictures and well get this sorted out I promise !
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Old 10-11-2015, 05:32   #17
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Re: broken rocker arm shaft mounts

In any event I'd pull the head, just because I strongly suspect bent valves and I would have to rule that out.
Of course an easy way to check for a bent valve is once the head is off, lay it on it's side and fill the intake or exhaust ports with alcohol, a bent valve will leak badly.
Look for shiny spots on the pistons, usually looks like little crescent moons.

I've seen a few hydro locked motors, but never seen the valve train damaged by a hydro lock, not bent pushrods etc.
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Old 10-11-2015, 05:51   #18
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Re: broken rocker arm shaft mounts

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Originally Posted by a64pilot View Post

I've seen a few hydro locked motors, but never seen the valve train damaged by a hydro lock, not bent pushrods etc.
Good point Mr. P, me neither... Maybe his piston to valve clearance was < water film thickness... ???
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Old 10-11-2015, 08:50   #19
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Re: broken rocker arm shaft mounts

I once borrowed a used Rambler station wagon for a move on a really hot weekend (118 degrees F). It overheated and blew the head gasket. Shop rebuilt the engine, decking the head. When started it immediately did what the OP described.

Turns out the engine had been previously rebuilt including decking the head with the net result being piston to valve contact on all cylinders.

Probably not the same cause here since it ran initially, but worth considering?

JK
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Old 10-11-2015, 09:01   #20
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Re: broken rocker arm shaft mounts

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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?
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Doesn't take long does it for the critics to play their hand
How is your criticism helpful to this post.
If you can't offer any help with this situation maybe keep your thoughts and conclusions to yourself.
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Old 10-11-2015, 10:50   #21
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Re: broken rocker arm shaft mounts

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Originally Posted by jonahmcg View Post
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.
If you "got the head skimmed" and you didn't adjust the valve clearance on reassembly that could happen very easily. Your valve clearance might be + 8 thousandths of an inch ( 8 thou ) and your head may have been skimmed -8 thou removing that clearance which always should be adjusted on reassembly or every few years.
When your engine warms up after "15 minutes" everything expands and without clearance the valve gear can jam.
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Old 10-11-2015, 10:54   #22
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Re: broken rocker arm shaft mounts

You may not be in as much trouble as you think; I have seen similar damage on other makes of engines. What usually happened, was that a valve (or more) did not return to its seat causing the push rod to drop out of its' socket, the rocker to ride on the edge of it, resulting in the old "kiss of death" as valve meets piston. Not always a fatal condition, sometimes a new push-rod was all that was needed.
If it ran ok for 15 mins, then it probably was assembled correctly.
Check for sticking valves (could be gummed up from poor oils, excessive low temp operation etc.) Also check that rocker arm bushings were not binding. Check the valve springs for correct compression strength (most auto garages have this kind of test tool). Weak springs will not allow valve train parts to maintain contact with the cam.
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Old 10-11-2015, 11:03   #23
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Re: broken rocker arm shaft mounts

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Originally Posted by GrahamHO View Post
I
When your engine warms up after "15 minutes" everything expands and without clearance the valve gear can jam.
It must have been a close call. The new gasket, the re-surface job and then not re-adjusting the valves, temp makes a difference but probably only a few thou.
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Old 10-11-2015, 17:52   #24
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Re: broken rocker arm shaft mounts

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Originally Posted by HappyMdRSailor View Post
jonah, I think there were a few here that were just having an off day..

Sounds like to us, you simply don't have enough room for the valve travel, and you've got piston contact with them...

Yes, cranking more than a few times without firing can definitely lead to water flooding the cylinders... Maybe this happened instead of too little clearance... You'll know when you pull the head...

Take lots of pictures and well get this sorted out I promise !
There should be maximum allowable amount to skim the head specified by the manufacturer, that would safely prevent valve piston contact. If the valves were going to hit the pistons due to too much head skimming, I would think they would do that on start up. He ran 15 mins OK.

Hydraulic-ing from water entering the cylinders through an exhaust valve due to overcranking would likewise happen on start up and most likely bend a conrod. That can be checked with a straightedge across the top of the cylinders with the head removed. A feeler gauge between the straightedge (on edge) and each piston might show a difference. There should be a specified amount, or flush.

However if the head were not torqued down correctly the head gasket may leak and cause a hydraulic-ing after running a while. But again I don't think that would bend pushrods etc. I think again, and know, it can bend a conrod.
I'm old fashioned and coat the head gasket both sides with waterproof grease on assembly.

It could also be a case of too much head skimming COMBINED with too little valve clearance. Then the valves might hit the pistons after warm up.
There will be damage visible on the piston heads if that happened.
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Old 10-11-2015, 20:24   #25
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Re: Broken Rocker Arm Shaft Mounts

Well, I hope he comes back with some pictures, because I'm curious to see the split rocker shaft pedestals...


As an alternate theory, when he put the rocker assembly back on, it was with the shaft inverted, so the oiling was at the top of the rocker arms. From lack of lubrication, the rockers galled, stuck on the shaft, bent the pushrods and split the already over-heat stressed pedestals...


Not knowing the actual model of the engine makes it hard to figure anything out, the inverted rocker shaft may not even be possible.
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Old 10-11-2015, 20:54   #26
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Re: Broken Rocker Arm Shaft Mounts

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Originally Posted by jimbunyard View Post
Well, I hope he comes back with some pictures, because I'm curious to see the split rocker shaft pedestals...
Picture 2 pieces 3/16" of stamped metal spot welded together. They could split apart. Once you see one you will understand.
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Old 10-11-2015, 21:21   #27
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Re: Broken Rocker Arm Shaft Mounts

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Originally Posted by jimbunyard View Post
Well, I hope he comes back with some pictures, because I'm curious to see the split rocker shaft pedestals...


As an alternate theory, when he put the rocker assembly back on, it was with the shaft inverted, so the oiling was at the top of the rocker arms. From lack of lubrication, the rockers galled, stuck on the shaft, bent the pushrods and split the already over-heat stressed pedestals...


Not knowing the actual model of the engine makes it hard to figure anything out, the inverted rocker shaft may not even be possible.
It would be handy to know the engine model. It's always possible the shaft was the wrong way. I recently did that same job on my Yanmar and I don't remember there being any wrong way.

I do remember a DC6 ( 1963?) which was flying into Changi Airport Singapore, and one of its 4 radial piston engines over speeded windmilling on approach and the prop couldn't be feathered.
It went so fast the whole reduction gear with propellor fell away and damaged or knocked off a wing flap. They landed OK with bits missing.

The cause was a gasket under the constant speed unit ( CSU) being put on the wrong way around and blocking an oil hole. Pratt Whitney modified the gaskets after that with an extra hole.

It was one of the planes I used to work on before it was sold to the NZ Airforce.
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Old 10-11-2015, 22:31   #28
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Re: Broken Rocker Arm Shaft Mounts

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Originally Posted by GrahamHO View Post
It would be handy to know the engine model. It's always possible the shaft was the wrong way. I recently did that same job on my Yanmar and I don't remember there being any wrong way.

I do remember a DC6 ( 1963?) which was flying into Changi Airport Singapore, and one of its 4 radial piston engines over speeded windmilling on approach and the prop couldn't be feathered.
It went so fast the whole reduction gear with propellor fell away and damaged or knocked off a wing flap. They landed OK with bits missing.

The cause was a gasket under the constant speed unit ( CSU) being put on the wrong way around and blocking an oil hole. Pratt Whitney modified the gaskets after that with an extra hole.

It was one of the planes I used to work on before it was sold to the NZ Airforce.
Yeah, missing the little details can have big consequences...

Looked around a little bit, my best model guess is a Vetus M4-17, which (from Vetus's own manual, no less) is a Mitsubishi S4L2-61DM, also used in mini excavators.

If that is the correct guess, this is the valve train. It appears (although parts diagrams are notoriously inaccurate) that the rocker shaft is indexed
to be installed in what I would consider an upside down position. Go figure.




At any rate, I'd still like to see the rocker pedestals, which appear to be cast or forged aluminum in the picture on page 35 of this manual,

http://www.vetus.com/media/magentomi...06224939_0.pdf

just out of curiosity and for future reference.

And, since we're all just guessing anyway, I hereby modify my hypothesis to say that the rocker arms galled on the shaft because the oil was thinned when the engine overheated...
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Old 10-11-2015, 22:46   #29
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Re: Broken Rocker Arm Shaft Mounts

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Originally Posted by jimbunyard View Post
Yeah, missing the little details can have big consequences...

Looked around a little bit, my best model guess is a Vetus M4-17, which (from Vetus's own manual, no less) is a Mitsubishi S4L2-61DM, also used in mini excavators.

If that is the correct guess, this is the valve train. It appears (although parts diagrams are notoriously inaccurate) that the rocker shaft is indexed
to be installed in what I would consider an upside down position. Go figure.




At any rate, I'd still like to see the rocker pedestals, which appear to be cast or forged aluminum in the picture on page 35 of this manual,

http://www.vetus.com/media/magentomi...06224939_0.pdf

just out of curiosity and for future reference.

And, since we're all just guessing anyway, I hereby modify my hypothesis to say that the rocker arms galled on the shaft because the oil was thinned when the engine overheated...
Yes we are all guessing. It's a bit like reading an Agatha Christie murder mystery and trying to guess who done it before you finish the book; and receive all the information.
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Old 10-11-2015, 23:23   #30
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Re: broken rocker arm shaft mounts

Quote:
Originally Posted by jonahmcg View Post
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.
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 jonahmcg View Post
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.
A little contradiction there.
Ya... he was delivering but did you check the water and thermostat after the engine work was done. From what i read, you were the last guy to touch it.

Quote:
Originally Posted by GrahamHO View Post
If you "got the head skimmed" and you didn't adjust the valve clearance on reassembly that could happen very easily. Your valve clearance might be + 8 thousandths of an inch ( 8 thou ) and your head may have been skimmed -8 thou removing that clearance which always should be adjusted on reassembly or every few years.
When your engine warms up after "15 minutes" everything expands and without clearance the valve gear can jam.
Good point and also piston clearance. On my Westerbeke W46 there was .010" (Ten thousands of an inch) from the top of the piston to the bottom of the head. Any resurfacing of the head is going to change the dynamics of the function of the engine. This is why it pays to read the specs from the engine manual as to what can be machined safely.
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