MGB & GT Forum

I have been doing engine tech articles in my Vendor Market forum page thread now for 14 years, it covers a lot of engine rebuilding tech and tips, and how to post, most with pictures. I did it there to keep it in one place for future reference. AS we know on the forum pages thing can get buried pretty quickly n ca at time be hard to find with searches. I also when I post these type of threads here I make sure to make the title of the thread what people would use in a search engine app, so they can be found easily, instead of some generic title, like,"look what I did today."

I had to rebuild a MGB rocker assembly for a MGB street performanc engine I am finishing up, and thought it was good time to do one for this job, to help show folks how they can do this themselves, and thought posting it here might be helpful to some.

Almost all MGB rocker assemblies when rebuilt, just need a new shaft; the rocker bushings are bronze and do not wear, the shift on the bottom side is the place that wears. So a new shaft was used, and I replaced all the 5/16"-24 half-height jam nuts with new grade 8 jam nuts. Over time and with a few valve adjustments, these hex nuts will get a corner or two worn off due to wrench slippage when adjusting the valves. This rocker arm assembly was no different, so they were looking a bit worn, and were replaced. Now let's talk about the adjustment bolt. This is one part where you would like to retain your OEM adjustment bolts. Now they do offered new ones, but the new ones leave a lot to be desired. First off the the black oxide plating is very sloppily done, and it is best to wire brush the plating off the threads, and often they are so poorly plated they will try to strip when threading them into the rocker, if it is not wire brushed off. Wait, it gets worse, the new replacement rocker adjuster bolts also have a bad reputation for breaking out of the screwdriver adjustment slot on the top. I have seen this happen 5, or 6 times, all with the replacement part on both street and race MGBs. It is just not a new part I can trust, so I do not use them. The adjustment bolts hardly show any sign of wear, so re-using the ones you already have is what I recommend.

OK, for me the first step is to get all the old varnish off the rocker assembly I do that here with a soak vat. I use a local chemical provider (Socar Chemical) their water based chemical, Grease Lightening, it is the best degreaser i have ever used, and does an amazing job on steel and cast iron. Normally, I just put the entire rocer arms assembly the vat and let the chemical do its thing. I might let it soak for days. Anyway, after that, I disassemble the entire assembly and keep every part arranged in it order (pic #1) then I further clean every part of the assembly on the bench grinder with a wire brush which does an amazing job. I take my new rocker shaft, some will have thread set crews at the two ends, if so, make sure they are tight, some new shafts will have like freeze/core plugs in them. Then I lube up my new shaft, I use the same assembly lube I use in many places in the engine, Staylube CRC moly assembly lube. and then start loading the new shaft up with all cleaned parts in the same exact order as removed (pic #2) also notice in the pic, how much nicer the rocker arms, and pedestals look after wiring brushing, like new. I normally start with installing the rear oil pedestal which lock down to the shaft with a screw (pic #3) and also the end rocker arm, spring washer, end washer and cotter pin. Now go to the other end and load up all the remaining rocker arms, spring spacers, and pedestals exactly as they were before disassembly. That is really all there is to assembly, just make sure to keep everything in order as it was.

Now let's talk about wear on the rocker pad where it contacts the valve tip. They wear divots in them over time, and part of the rebuilding process includes resurfacing the pad to be new again. Now, the divots are normally not that deep, a few thousandths of an inch. Now this is the biggest hurdle for the novice in their home shop to do, and I will save that for another time, as I play with methods where a person in their home garage could refinish the rocker pad with less complicated tool than I use. However, you can see in (pic #4) a comparison of old worn rocker assembly waiting to be rebuilt and the rebuilt on how a worn pad looks vs a refinished pad. I like to polish my refinished pads, this just adds to surface hardness. OK, here a picture of the new grade 8 5/16"-24 jam nuts. I source them from McMaster Carr, I can not say enough good things about this company, they have an incredible inventory of fasteners, in all sort of grades, and specs (pic #5)

OK last picture (pic #6) shows the finished rebuilt MGB rocker arm assembly ready to be installed on the engine. So hopefully, this post helps you to take on rebuilding your own rocker arm assembly. Feel free to ask any questions you may have.
Note, this thread is full of engine rebuilding tech, most anything you can think of is covered, and I have started to expand it more regularly and will continue to do so as projects come up. No obligation to buy anything, it is my gift to the hobby and members here.

Hope this helps.

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Hap Waldrop
Acme Speed Shop
864-370-3000
Website: www.acmespeedshop.com
hapwaldrop@acmespeedshop.com



Edited 2 time(s). Last edit at 2025-06-07 03:04 AM by Speedracer.

Very good article Hap. Was always curious about pad resurfacing how far can go on them. I hit them with crocus cloth to finish. My father always resurfaced
Chevy hydraulic lifters like this. Thanks! Good stuff.

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"Only those who have patience to do simple things perfectly ever acquire the skill to do difficult things easily"
James J. Corbett

My understanding is that the heat treating on the rocker pads is deep enough that the few thou of resurfacing that is typically needed is safe. I use a die grinder with a 1/2" X 1" emory drum for this, being careful to keep the surface parallel with the wear pattern showing, not the unworn portion.

All excellent points, Hap, but you didn't mention using only hardened rocker shafts. I find these sometimes need to be polished to remove the residue from the hardening process for proper clearance.

Silas

Yeah, it only takes a few thousandths to clean them up, most hardening treatments go about .030" deep. Then the polishing adds to the surface treatment.

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Hap Waldrop
Acme Speed Shop
864-370-3000
Website: www.acmespeedshop.com
hapwaldrop@acmespeedshop.com

Our valve grinder had a jig to resurface rocker arms so I used it when the shaft assemblies were taken apart on a full engine rebuild. Sometimes the wear was very little on the faces and the customer didn't have the budget to rebuild the rocker shaft assembly, for example when just doing a head gasket or valve job. On those I did something like Silas describes, to remove the ridge and leave the wear area untouched in order to get a more accurate valve adjustment.

I replaced the bushings once back in the late 70s before I figured out just the shaft was all that was needed. Live and learn...

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"If I knew where the good songs came from, I'd go there more often."

Leonard Cohen

Someone should have a rocker tested for hardness.

I suspect they are just forged steel.

Your suspicions are unfounded.

Silas

I don't know if B rockers are hardened or not but I've re-bushed and re-faced a lot of them. They did not grind with any difficulty nor show the sparks that a surface hardened part would. Given that they seem to wear easily, my suspicion is they are simply forged. One word of caution is to always re-bush rockers with the new shaft in hand, as they are inconsistent in diameter from different sources.

I will second Hap's observations on the adjuster bolts. I had a pushrod cup fail (break) due to that coating, it was thick enough to not let the ball seat in the bottom of the cup, the ball was riding on the top lip of the cup. After that I use lapping compound to ensure the ball fully seats in the pushrod cup.

The commonly sourced replacement jamb nuts do seem to be softer and more easily damaged than the originals, the grade-8 is a great suggestion.

I've found a very fine single cut file seems to do a reasonable job on the rocker pads. That's if the tool is in good condition and operator knows how to use it, it takes some practice.

Thanks Hap!

Excellent post Hap. Thank you!

I would only add a couple of points:

1. Note the pads are not perfectly square with the rocker. It’s only very slightly not square because this facilitates turning the valve a tiny bit every time the rocker lifts it. One could do an extreme engineering analysis to find out exactly how much but I doubt this is necessary. As a mechanical engineer I think the most important thing is that it be just off square by a few thousandth or just enough to facilitate the turning process. One could probably simply reference the old unworn portion of the pad.

2. A note about bolt grades. Be careful to not fall into the trap of just getting grade 8 for everything there are very good reasons for not doing so. Bolts are generally graded between 2 and 8. Grade 2 are the least strong and, most importantly, the softest and most malleable. Grade 8 is the strongest but strengthening steel comes at a cost of malleability. The higher you go up the grade chart the more brittle they become. I suspect this is why the slots break on the new ones-they are too hard. Choosing the correct is a thoughtful process that requires balance between strength and malleability requirements.

Any references on a good source for a quality rocker shaft?
Thank you.

Tuftrided (case hardened) are available from Moss.