Cylinder Head Nuts Won't Tighten

[geoffschultz]

I guess that I broke the cardinal rule of "If it ain't broke, don't fix it."

In doing some PM on my generator, I decided to torque the cylinder head nuts. I broke them free and then used my torque wrench to tighten them. 3 of the 5 nuts wouldn't tighten. The other 2 torqued as expected. The studs on the other 3 aren't spinning, so I can only imagine that the studs are stretching. What are your guesses and solutions?

Note that this is a single cylinder Kubota EA300. It started OK, but I haven't stress tested it yet as I'm in the process of repainting it and want to get that done today.

-- Geoff

 

[Bill Roosa]

Back off the studs and check them

Back off the nut till it is just loose and put another nut on the stud act as a lock nut to try and back it out for inspection. You did not say how old the unit is but if they are rusted they will stretch quite a bit before breaking. Course after you have done this a few times you can tell by the "feel" of the wrench what is going on but you can't teach that.
Here is my stab at it (hope springs eternal)
Does it feel like the stud is yielding? Compare the feel of the studs that tightened to the ones that don't. Do they get to a point and then it feels like you can't get any more toque out of them. That is bad; don't go further till you check the condition of the studs in question.

 

[Rich Stidger]

When I rebuilt an Olds 350 diesel, I learned that head bolts (and possibly studs) are only good for one use. At least on that engine, your marine engine may be the same or different..

On the Olds diesel, the head bolts are torqued to yield. They are never re-torqued after that and if the head must be removed, the head bolts are replaced.

I would check with the manufacturer to see what the correct procedure is for your engine.

 

[Paul Cossman]

When I rebuilt an Olds 350 diesel, I learned that head bolts (and possibly studs) are only good for one use. At least on that engine, your marine engine may be the same or different..

On the Olds diesel, the head bolts are torqued to yield. They are never re-torqued after that and if the head must be removed, the head bolts are replaced.

I would check with the manufacturer to see what the correct procedure is for your engine.

Rich makes a good point. I do know what the manufacturer says on your model Kubota, since I had to remove the head on mine a few months ago (after I stupidly tried to start the engine before remembering to remove the paper towel I had stuffed into the intake manifold--to protect myself from dropping fasteners into it). The manual said nothing about replacing the nuts or studs; only that a new head gasket must be used. On that Kubota you do need to make sure that whoever sells you the head gasket also provides you with a new O-ring. The shop manual notes the requirement, but the part number doesn't include the O-ring. Your parts supplier should be able to include it.

Good luck.

 

[geoffschultz]

Thanks for the feedback. The nuts in question simply don't get tight. I've only turned it about 1 turn, but I don't feel the tension increasing. I've placed a line on the stud and I can see that it isn't turning.

It appears that I should order a new set of studs, nuts, gaskets, etc.

One question I do have is can I back the studs out by using a locking nut and replace the studs without pulling the head off (and not replacing the gasket)?

-- Geoff