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MG MGB Technical - Rocker Cover bolt

Hi..
The engine is an 1800 twin carb for my MGB GT 1974
A query I have is regarding the rocker cover bolt that is attached to the engine for which the rocker cover bolts to this. As we have two either end of the rocker cover, I have found that the one has sheared of. I have managed to unscrew the half that was attached to the nut that tightened the rocker cover down, but the remaining half I am struggling to remove. My question is can I remove this and replace with a new part? It seems it is either seized or a part of the cylinder head?
Any advice would be much appreciated.
regards

Jim
J Giddins

Hello Jim, the rocker cover is held in place with a long stud that goes into the cylinder head through the rocker shaft pedestal, which in turn is secured by a nut, the rocker cover cap nut just screws onto the protruding stud, so the other nut should not be at all tight unless some ham fisted person has well over tightened this cap nut. It shouldn't be a problem removing the rocker cover.
john wright

Jim

We need to know where it has sheared.
If it has sheared just below the rocker securing nut, you can unscrew the nut on top of the rocker pedestal and then remove the remains of the stud. If that is the case, you can use two nuts locked together on the stud - if there is enough thread remaining - to remove the stud.
If it has sheared below the pedestal nut - i.e. there is another nut on the broken stud on the inside of the rocker cover - there is not going to be enough thread left on the broken stud to use the two-nut method.
You will then need to remove the rocker assembly to provide access to the broken stud, which can then be removed with mole-grips...also known as a Mexican socket set!
Removing the rocker gear necessitates releasing the tension on the cylinder head studs/nuts and, more than likely, replacing the head gasket.
Do you have a workshop manual?
Dave O'Neill 2

Dave, John,

Pic's attached showing the bolt sheared and the opposite bolt in place.
If is a case of a quickly removing and replacing, any idea where I can pick up the correct part. Just spent £600 + on welding, water pump and brakes plus a new battery..really need to get it back on the road.
Also I am converting the from 2 x 6 volt to 12 volt batteries, I have read you need to loop the spare leads, if you have a clear 'How to guide' as still a little unclear on earthing the car..just don't want to fry the electrics after spending the pennies.
Big thanks

Jim

J Giddins

Hello Jim, all you have to do is remove the rocker shaft, leave the head nuts alone, use visegrips to remove the broken stud.
john wright

Why remove the rocker shaft? Just remove the nut and then use the Mexican spanner.
Art Pearse

Hello Jim, you should be able to get the studs from either MG owner club, Moss or Octarine service, they shouldn't cost much, if all else fails try the scrapers, any "B" series engine should be OK.
john wright

If you remove the rocker shaft you will be able to use the two nut method which is best. If you use mole grips and it won't budge, you may not get nuts on after.
c cummins

Use a hammer to lightly rivet over the broken stump and then undo the nut - it should carry the stud with it.

The stud is part number 51K893 - Stud - Long - Rocker shaft - £1.45 inc VAT from the club.

Use 2 nuts locked together to screw the new one in place, remove nuts and fit washers and one nut to finish off.

DO NOT remove the rocker assy - you can only do so by undoing the head stud nuts and the head nuts need to be all loosened in the correct sequence and retightened - the head gasket may be disturbed in the process.
Chris at Octarine Services

Thanks Guys..I will look to have a look at the local scrap dealers first then go through Mg club for correct Stud.
I will let you know how I get on..

thanks again

Jim
J Giddins

Ok..I have managed to undo the nut and removed this from the sheared threaded shaft..but now the sheared shaft is really tight to move..what is the best option to remove this?

thanks

Jim
J Giddins

As Chris said, put the nut back on without the washers, peen the top of the broken stud over - the hammering might even help to loosen it - and then try undoing the nut.

If that doesn't work, another option is to weld a nut to the broken stud and then undo it.
Dave O'Neill 2

Dave

He's going down a sticky path if he peens the top of the broken stud over, or even welds a nut on the top. If the stud then doesn't move, he's *****d! How is he going to get the rocker shaft, and/or the cylinder head, off if he needs to get a pair of stilsons lower down the remaining stud to get any leverage on it, without sawing/grinding the nut off and risking covering the cylinder head and engine bay in metal filings?

In my opinion, if he has tried to remove the stud by the usual methods mentioned above, then he has to bite the bullet and remove the cylinder head. It will cost a new head gasket and a long stud (51K893 - Stud - Long - Rocker shaft as Chris said) but at least he should be able to get penetrating oil to the base of the stud and apply some 'welly' to the stud and, if necessary, get a stud extractor to it.

This assumes, of course, that the stud is only corroded in the thread in the block, and not through the cylinder head itself! Any suggestions for that scenario?

Robert

Robert Lynex

Robert,

If the secured nut doesn't shift the stud then it will probably twist off. But my view is that it will shift it - the lower thread on the stud is a coarse one and is unlikely to be corroded.

The stud in question only goes 1/2 inch into the head - it doesn't go into the block at all, so your last comments are irrelevant.
Chris at Octarine Services

Thanks guys for the advice..51K893 ordered, have booked in with my local garage, who can extract the offending stud, as I don't want to mess with the cylinder head. Will let you know how this works out..

thanks again

Jim
J Giddins

Chris

My apologies, you are quite correct in saying that the stud didn't go down into the block. It was probably a little too early in the morning for me!

You would still need to remove the rocker shaft before welding/peening or problems would/could arise.

I still believe that a pair of stilsons would shift it, once the rocker shaft had been removed.

Robert
Robert Lynex

I have no doubt that a pair of stilsons / moles / stud extractor would shift it once the rocker gear was off, but why disturb the head as you will do by removing the rocker gear when there is a good chance of getting it out without doing so.

The OP seems to have little mechanical knowledge so try the simple stuff first!
Chris at Octarine Services

Chris, thanks for the suggestions..as you suggest my knowledge is limited on the mechanical side..which is why any help is much appreciated. I would attemp to fix myself, but I don't want to create more problems and expense!!...just want to get the old greaser rumbling again..
Thanks

Jim
J Giddins

And don't make the mistake of torqueing the new stud into the head, it should be oiled and lightly screwed in till it bottoms, that is all. Makes you wonder how the stud was sheared off in the first place, unless it was cross-threaded, the special rocker cover nut is only suppsoed to be nipped up to lightly compress the cork gasket and rubber compression washers under the cupped washer under the nut.

With converting from twin 6v to single 12v you simply remove the interconnecting cable and move the earth cable from the left-hand cradle to the right-hand, which is where the new battery should go.
PaulH Solihull

Hi..just an update..removed bolt without snapping, new bolt in position, just waiting for new rubber rocker seals and gasket..

thansk

Jim
J Giddins

Well done, these "Bs" are fairly simple engineering.
PS don't over tighten the rocker cover capnuts.
john wright

Just a quick update..Rocker cover installed with new gasket, rubber seals, with new bolt..!, hopefully start battery conversion tomorrow..
Thanks to all

Jim
J Giddins

This thread was discussed between 14/08/2010 and 18/08/2010

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