Rocker shaft broke, possible negligence, where to find parts?

[sailingunity]

Originally Posted by Carl-T705

I never heard of backing off on head bolts and retorquing them. There absolutely no reason to retorgue head bolts, What you may do is check the torque on the head bolts. I would never back off head bolts after the engine assembled and the gasket had been compressed, you would be asking for problems. Unless you are running a copper head gasket I wouldn't waste the time unless you question your workmanship.

All I did was recheck the head bolt torque with the engine warm (1080 inch pounds is the spec). I didn't back them off.

I also changed the oil before I restarted the engine - assuming the oil is where the fuel went, but I didn't see any diesel in it.

[Dieseldude]

Originally Posted by goboatingnow

To be honest in a most engine you can easily Re torque with any accuracy anyway especially using click torque wrenches

If you do Re-torque it’s better to slightly slacken and redo. This helps to overcome the stiction issues that can lead to low clamp load

Every time that the torque is checked, a slightly higher torque is applied. But for head bolts, it is probably not significant. Consistency of torque values is more important than precise value (within reason). Example, if 100 pound foot is specified for a larger bolt, 102 pounds is not likely to damage the head or gasket. But for small fasteners, two pounds could be significant. There are dry torque and wet (lubricated thread) torque spec's. Wet torques are by formula based on what the dry torque would be and lubricity of the lubricant. Bolts could be backed off very slightly first, but I consider that the risk of decompressing the gasket is greater than a very slight over torque. You are not likely to need to touch them until next overhaul, so there will be no big accumulation of over torque. But fasteners that are repeatedly checked for torque should be backed off slightly. This was found to be a problem for the small 1/4 titanium bolts on ROV manipulator arms that I'd maintained. The manufacturer gave instructions to back off slightly first. These were checked periodically, so slight over torque would accumulate.

[Bill Seal]

Due to differential expansion, iron heads should re-torqued hot, but aluminum heads after cooling off.
At least that's what I've been told.

[Dieseldude]

Originally Posted by sailingunity

All I did was recheck the head bolt torque with the engine warm (1080 inch pounds is the spec). I didn't back them off.

I also changed the oil before I restarted the engine - assuming the oil is where the fuel went, but I didn't see any diesel in it.

Suppose that you did not save a sample of the old oil. But you could do your own viscosity test with a simple device called a viscostick, visflow or viscosity stick.

https://marinetestingsolutions.com/products/viscostick/

[Shaneesprit]

Originally Posted by Celestialsailor

Although I would not back off head bolts, I most certainly would retorque back to specs. I learned this from the motorcycle industry. I always found after 10 hours of use on a head job, the head showed that it needed to be retorqued.

Follow the engine manual, although I can’t think of one that suggests backing off to re torque. Generally if re torque is suggested by the manufacturer then it’s due to needing to be tightened. Not loosening, generally I would think this applies on older engines.
Tightened plenty of heads without the use of torque wrench but you have to know the torque required especially if it’s a low starting torque, followed by angle torques.

[Dieseldude]

Originally Posted by Shaneesprit

Follow the engine manual, although I can’t think of one that suggests backing off to re torque. Generally if re torque is suggested by the manufacturer then it’s due to needing to be tightened. Not loosening, generally I would think this applies on older engines.
Tightened plenty of heads without the use of torque wrench but you have to know the torque required especially if it’s a low starting torque, followed by angle torques.

Good observations. It is likely that head bolts will go a bit slack over time. But there is no guarantee that torque values have actually decreased by the time re-torquing is done. If re-torqued several times, fasteners will likely accumulate extra torque. The inertia of just starting the bolt to turn causes this. For large fasteners, this may not be significant though. To prevent over torque, the torque can be set just slightly lower than spec. Then you should end up with an actual torque close to spec. Even if slightly less, it should not matter in most situations. When thermal expansion happens, clamping pressure generally increases. Repeatability is more important than absolute values, within reason of course. As stated earlier, I learned this from maintaining ROV manipulator (robotic) arms that had plenty of small fasteners of about 1/4 inch diameter. It was found that bolts were failing, and over torquing during periodic maintenance checks was the cause.



I've heard of guys making the claim that they have "torqued" fasteners without a torque wrench. It is fantastic to have such a skill, and I would envy it. But I personally was not born with a calibrated arm, nor do I know how to train an arm to precise calibration. Even if I torqued many fasteners daily and developed a feel for to it, I would likely lose my judgement if I stopped a few weeks or months. So I'll chose to use a torque wrench on critical threaded fasteners. Even a cheap torque wrench which has never seen a calibration shop since leaving the factory will be much more precise than my judgement. I have compared old torque wrenches to new ones, and observed little difference in values. I would not risk a major engine or machinery failure for want of a $50 to $300 instrument. Most fasteners on a small vessel or vehicle can be torqued with a low cost 3/8 and 1/2 inch drive torque wrenches. Fasteners aboard a boat do not need the same TLC as aboard an aircraft.

[Jim Cate]

This means rotating engine with head off, so cam shaft timing marks need to be paid attention to.

I'm confused here! Why would simply turning the engine over with the head off make any change in the cam timing? You have not disconnected the cam from the crank (via chain or gear train) so the timing will remain as before... won't it?

Unless,of course, you have an overhead cam diesel... rare beasts, those!

Jim

[Dieseldude]

Originally Posted by Jim Cate

I'm confused here! Why would simply turning the engine over with the head off make any change in the cam timing? You have not disconnected the cam from the crank (via chain or gear train) so the timing will remain as before... won't it?

Unless,of course, you have an overhead cam diesel... rare beasts, those!

Jim

The cam shaft is mounted on the head. When the head is removed, the timing gears are parted or timing chain is uncoupled. Turn the engine, and the timing relationship is lost. Put the head back on, and you will not have proper cam timing unless you line up the timing marks first.

[Uncle Bob]

Originally Posted by Dieseldude

The cam shaft is mounted on the head. When the head is removed, the timing gears are parted or timing chain is uncoupled. Turn the engine, and the timing relationship is lost. Put the head back on, and you will not have proper cam timing unless you line up the timing marks first.

I am with Jim here, the only marine diesel engines that I have had anything to do with have overhead valves driven by pushrods from the cam mounted in the block. I am curious now, can you identify those that are built with overhead cams.

[Bill Seal]

Look at post #1, there's a picture of his broken rocker shaft with pushrods.

[Jim Cate]

Originally Posted by Uncle Bob

I am with Jim here, the only marine diesel engines that I have had anything to do with have overhead valves driven by pushrods from the cam mounted in the block. I am curious now, can you identify those that are built with overhead cams.

Exactly! The title of the thread involves a broken rocker arm shaft, and that really rules out an overhead cam IMO... and t hat is why I was wondering about the cam timing issue.

JIm