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MG MGA - Off the Road, broken stud

I've sheared off the top of the stud that holds down the rear of the valve cover.

What's the process for removing that stud and replacing? Can it be done without disassembling the rocker assembly and taking off the head?
T McCarthy

It depends where it has sheared. If it is sheared above the rocker pedestal then it is a simple matter of using a stylson to grip it and twist it out. It is a long stud and is screwed into the head. A new one would then simply be installed and everything back to new.

If it has sheared inside the rocker pedestal then the rocker shaft will need to be removed and my advice would be to remove the head at the same time.
Bob (robert) yes Y8 is toast again :)

The rocker arm can, I am told, be removed without removing the cylinder head. But, like Bob, I always remove the cylinder head to do this. I have always wondered what the effect of removing four of the nuts holding down the cylinder head would have on it. Others claim there is not a problem. But, it is not something I am willing to try myself.

Depending on where the stud broke, you can remove it using a stud extractor or the wrench that Bob mentions. Vice Grip pliers also work well. You can probably get a new stud at the local NAPA store or any better quality auto parts store.

Les
Les Bengtson

Remove valve cover. Slacken off all rocker adjuster screws. Remove split pin, flat washer, spring washer, and last rocker arm from back end of rocker shaft. Tap rocker shaft forward just far enough to clear rear pedestal. Remove nut and flat washer from one head bolt at rear pedestal. Lift off pedestal, and remove broken 5/16-inch stud. Reassembly is the reverse of disassembly (using a new stud). In the process you have only loosened one head bolt, the head gasket is not disturbed, and all is well with the world.
Barney Gaylord

Thanks guys.

It was sheared off above the rocker arm. A pair of vice grips and I was able to get it out.

How does one tighten the new one in? I didn't see a spot on the end where one could use a 12 point or an allen wrench to tighten it down.

Oh and what does one torque the nut on the stud that tigtens to the rocker pedistle to?
T McCarthy

>How does one tighten the new one in? I didn't see a spot
>on the end where one could use a 12 point or an allen
>wrench to tighten it down.

Put 2 nuts on the end, jam them together (not too tightly), and use the upper to screw the stud in. Then you can unjam the nuts to remove them.

>Oh and what does one torque the nut on the stud that
>tigtens to the rocker pedistle to?

Less than you used when you broke it the first time!

Just kidding, I can't resist a cheap shot. I don't think that the manual specifies a torque for those nuts. I would guess between 15 and 20 ft. lbs. for a 5/16" fastener, but that's just a guess.

Del Rawlins

"Just kidding, I can't resist a cheap shot."

HA, fair enough. Thanks for the info Del.
T McCarthy

Do NOT torque the studs into the casting. The best installation is if you can screw the stud down to the end of the threads with your fingers. Torque beyond that should be almost nil, like you might apply with a screwdriver, never to exceed 5 lb-ft of torque. Applying more torque to the stud only serves to deform the first thread or two in the top of the block and make it difficult to remove later. In some cases excess torque can crack the casting when the unthreaded part of the stud runs into the threaded hole.
Barney Gaylord

Barney, I am pretty sure he was asking what torque to use for tightening the NUTS that go on the studs.
Del Rawlins

I was talking about that nut Del. But I appreciate the feed back on the stud too Barney, you never know if I was going to get overly enthusiastic on that too.
T McCarthy

Hi Les. I have removed several MGA and MGB rocker shaft assemblies without removing the cylinder heads and without replacing the head gaskets. Removing and replacing the rocker shaft assebly while leaving the head and head gasket in place is no problem as long as the engine is previously drained of all coolant, and all the head and rocker nuts are loosened and tightened in the correct sequence. Barney: I like your slick idea for just removing one rocker pedestal instead of the entire rocker shaft! That possibility had never occurred to me, thanks for the tip. Glenn
Glenn

Okay, if not the stud then the nuts. Big head nuts get 50 lb-ft torque for teh stock iron head (maybe only 40 lb-ft for an aluminum head). The smaller rocker pedestal nuts get 25 lb-ft torque, same as most other 5/16-inch studs or bolts unless otherwise specified (but not that much for sheet metal covers).

A special point of order here. Original MGA rocker pedestals are aluminum and are quite soft. Be sure to always use a steel flat washer on every stud to distribute the load and avoid deforming or fracturing the pedestal.

Also remember that the rocker cover attaches using two of the smaller rocker pedestal studs. Just because the hex size on the cap nut securing the rocker cover is 5/8-inch does not mean you should use a big wrench on it with vigor. The rocker cover nuts should be no more tight than you would do with a strong wrist on a nut driver, or a few fingers on a short wrench handle. In fact there are accessory knurled nuts available, about an inch in diameter, that you can tighten with fingers only to secure the rocker cover.

The bottom flange of the cover must be flat to seal with the cork gasket. To make it flat, see here: http://mgaguru.com/mgtech/engine/ch107.htm

The top fasteners consist of a rubber grommet, a cup washer, thick flat spacer, and the cap nut. The cover bottom flange should never touch the head, only the gasket. The cup washer should never touch the cover, only the rubber grommet. When properly installed the cover is snuggled between the two rubber grommets and the cork gasket, and the pressure from the slightly compressed rubber grommets is all that is needed to seal the cork gasket. The cap nut should never bottom out against the hex nut underneath or against the top end of the stud.

The tension you create on the studs while tightening the cover nuts is added to the tension created by tightening the pedestal nuts. If you over tighten a cover nut you can break the stud. If the stud breaks other nasty things can follow, like this: http://mgaguru.com/mgtech/engine/ch104.htm
Barney Gaylord

Barney,

Thanks very much for that description of over tightening the valve cover. That is EXACTLY what happened.

Fortunately I didn't ruin the pedistle.

Thanks as always! Tysen
T McCarthy

This thread was discussed between 29/04/2007 and 01/05/2007

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