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MG MGA - Rocker Arms

I'm getting ready to re-bush my rocker arms following Barney's instructions, and have noticed a few of them are fairly worn where they contact the end of the valve stem. Can they be polished smooth in this area, or are they surface hardened only?
Del Rawlins

Hi Del. My understanding is that the entire rocker arm is hardened. The portion that contacts the top of the valve perhaps becomes additionally work hardened. I would not disturb the polished area where the rocker contacts the valve. You could perhaps try lightly grinding the high areas surrounding the valve contact area. The only reason I can think of for doing any metal removal near the contact area would be to allow more accurate valve adjustments. I have seen MG rocker arms that have been ground and polished to lighten them, and make them more resistant to breakage. Given their hardness, I imagine this would be a difficult job, and I suspect the advantages would be minimal with a stock engine. Cheers, Glenn
Glenn

Well, my reason for asking was because of some funny wear in that area; a couple of them actually have a small dent there. I dug the rocker shaft assembly that I took off the spare engine the other night back out of the box, and compared the two sets of rockers. It is clear that somebody (almost certainly my father) has already been at the surface of my original rockers with a grinder, since the rockers from the spare engine show a more normal wear pattern surrounded by a rougher, non worn surface. I had assumed those surfaces were supposed to be completely smooth because that's how the ones I was looking at were, other than the wear spots, damage, and the faint grinder marks that I hadn't noticed before.

So I am probably going to swap the rockers from the spare over to my towers with a new shaft. I may not even need to re-bush them since they seem pretty tight on their existing shaft. Unfortunately the towers from the spare engine are all FUBAR due to improper washers having been used, so if and when I rebuild the spare I'll have to come up with a whole different assembly.

Thanks again for the advice.
Del Rawlins

Hi Del. I assume your rocker towers are the original aluminum ones. You might want to replace the MGA aluminum towers with early MGB towers. They were made of cast iron, and are much stronger, and less prone to breakage. Just be sure to check that the oil supply hole in the MGB tower base is in the same location as the MGA tower. There were at least a couple of different styles of MGB towers, but only the early one is useable on MGA engines. Cheers, Glenn
Glenn

I would suggest seeing a machinist about resurfacing the rocker. I think it's a common practice. It's important to have a smooth surface to ensure accurate valve adjustment. If the top of the valve meets the rocker at the bottom of the pit, your feeler blade bridges the pit, hence a larger gap than you want and one that's not possible to measure. Having them resurfaced was not a big deal, as I recall.
John Vallely
John Vallely

That makes sense. I'll ask about it when I am getting the valve seat inserts installed in the head. As for the rocker towers, the aluminum ones from my original engine appear to still be good, but I'll add them to the list of items to check for cracks with the dye penetrant kit.
Del Rawlins

I don't know if aluminum towers are an issue unless you have uprated valve springs, such as you'd need with a performance cam. Which I can say is a nice thing to have, along with an MGB head.
I'm only going by my own limited experience, but I've only heard of switching to the iron towers in that situation.
John Vallely

Don't use the alloy pedestals as they just help the head gaskets fail earlier as they compress and are harder to torque up. Also the longer studs can stretch more than the shorter ones... not much... granted...

Also if you have several sets of rockers you will notice that they are all slightly different ratios, as the adjusting screw hole is drilled all over the place.

You can measure them individually with a bolt down the adjuster hole, or a dial gauge in the valve cap and rotate the engine....

I pressed in offset bushes in a set of mine once and got 1.5 ratio that way... then went for rollers in the end... 1.6 much better and fuel-efficient.

Cheers
Mark.
Mark Hester

This thread was discussed between 04/10/2006 and 07/10/2006

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