|The MGA With An Attitude
ENGINE OVERHAUL - BE-201B -- Pg 2 of 5
Cylinder Head and Valves
Section A.7, Removing and Replacing the Rocker Assembly
With throttle cable of correct length you should not need to disconnect the throttle cable to remove the rocker cover. You should be able to lift the rocker cover slightly and tilt it away from the carburetors to remove it while lifting the throttle cable slightly. See additional notes on Shims for rocker pedestals, Valve adjustment, Valve cover gasket, and Re-bushing rocker arms.
One common characteristic here is that the steel rocker shaft will wear on the bottom side faster than the bronze bushings. It is common to replace the rocker bushings only every second time the rocker shaft needs replacing. To check for wear on the shaft push the rocker arm aside and run a finger along the bottom side of the shaft. If you feel a significant step in the bottom of the shaft, it is worn and should be replaced. You could use a micrometer to measure the wear on the shaft, but if it has a noticeable step it's shot anyway.
To check for wear in the bushings twist the rocker arm back and forth sideways (not rotation on the shaft) to see how much it wiggles. Then push the rocker arm down the shaft a bit to an unworn position on the shaft and try it again. If the wiggle goes away the bushing is good to go, and you only need to replace the shaft. If you need to replace the bushings, refer to Re-bushing rocker arms.
When reinstalling the rocker assembly, follow book instructions carefully. Use heavy steel flat washers (not thin and flexible hardened steel washers) to prevent damage to aluminum pedestals. You could replace the aluminum pedestals with cast iron pedestals from an MGB engine (watch alignment of the oil feed hole in the rear pedestal). You can if you wish also install the .010" thick shims (MGB parts) under the #2 and #3 pedestals to preload the rocker shaft to prevent motion and wear on the shaft in the pedestal journals. When the factory did this they recommended adding the two shims to earlier engines whenever they might be disassembled for servicing. This recommendation can also apply to the MGA engines for the same reasons.
Double check the length of the longer rocker bracket mounting studs. Broken studs and pedestals may result if these studs are too long and the cap nuts bottom out on the end of the studs. Breakage may also occur if the nuts have been overtightened and the valve cover has been crushed down to the point where the cap nuts may bottom out on the pedestals. See Broken rocker pedestals. For reassembly be sure all of the original valve cover attachment hardware parts are present, including the thick spacer under the hex head.
Section A.8, Removing and Replacing the Cylinder Head Assembly
Start with Why doesn't my temperature gauge work?, and seriously try to avoid that problem. Use only a proper Flare nut wrench. The temperature sensor "conductor" is actually a small pipe wrapped with steel wire for protection. DO NOT CUT THIS PIPE. The pipe was originally routed along the side of the cylinder head with a "P" clip on the lower stud of the heater valve mount, and a flexible stress relief coil at the back of the head before attachment to the heater shelf with another "P" clip, and running through the bulkhead. Quite often this small pipe has been re-routed to run from the head to the inner fender with a stress relief loop, anchored to the inner fender with a "P" clip, and run along the inner fender to the heater shelf and through the bulkhead. The fender routing is more convenient for servicing the cylinder head, but not original.
See also Removing a stuck thermostat cover. Before replacing the thermostat housing, check on the condition of the mounting studs. Use lots of penetrating oil and patience to remove the studs from the head (hopefully without breaking the studs). During reassembly use thread sealant on the base threads of the studs, as two of these studs go through into the water jacket.
The vacuum pipe running from bottom of rear carburetor to the distributor vacuum unit should be attached to the rear head stud with a P-clip for mechanical mount and strain relief. Very early in production the plain pipe was changed to include a fuel separator bulb. This has a bracket for mounting on the second stud from rear of manifold. The fuel separator should stand vertical with the carburetor end down and the distributor end up to allow any fuel accumulated in the separator to return to the carburetor connection. Lots of people find it more convenient to mount this bracket on the rear manifold stud, but not original.
Before replacing a head gasket be sure to clean away all residue from the prior installation. If this is giving you a problem you may want to remove all of the head studs for cleaning of the top of the block. See (off site) details of a nifty Stud remover socket. Otherwise just double nut the studs and unscrew them with wrenches. If the studs have raised a small burr around the top thread in the block, you can remove this burr with a light touch of a countersink tool in a power drill.
You can also "stone off" the top of the block (and the head) using a coarse grit whetstone (knife sharpening stone) and some oil. A raised burr around the stud hole in the block will show up as a bright polished ring from working the whetstone. Keep rubbing in long elliptical motions with the whetstone until you get a uniform buff finish showing on the entire surface of the block (and head).
Section A.9, Removing and Replacing Valves
See articles on Bad valves, Sticky valves, Stellite exhaust valves, and Oversized valve guides.
One important note about original valve seals is that they do not seal the joint between valve stem and valve guide. The little O-ring seals should be installed in the bottom of the keeper groove on the valve stem to seal the joint between the stem and the spring cap (at the bottom of the cotters). This is to prevent oil from running down the valve stem to the guide. These o-ring seals were originally used in conjunction with an "oil deflector" which fit inside of the springs surrounding the top of the guide.
Very early in MGB production (end of 1962 calendar year) the oil deflector was discontinued, and the design of the spring cap was changed to center and guide the inner spring. See Oil deflector does not fit. The deflector will not fit with the later spring cap, and the later spring cap supersedes the earlier one. This means the earlier spring cap became unavailable. If you needed new spring caps for the early MGB you were expected to replace the original one with the later style part, and toss out the deflector. Presumably this would also apply retroactively to the MGA. Indeed in modern times the early style spring cap may still be unavailable (except as used parts).
The absence of the oil deflector likely makes little difference in oil consumption by way of seepage down the valve guide, except for an excessively worn engine. For other ways to handle the valve seal issue see Alternate valve seals. The easy and commonly recommended solution is to fit "umbrella seals" (Victor 8B45404 or Felpro SS 70373 for a set of 8) on the intake valves only (after the deflectors have been removed).
Section A.10, Decarburizing
This is a process of R&R of the cylinder head to scrape carbon deposits out of the combustion chamber. This used to be quite common with older engines with worn valve guides. These days if the guides are worn, and you have to R&R the head for valve work, it is recommended that you replace the guides.
Section A.11, Grinding and Testing Valves and Seatings
The shop manual is rather brief on this issue, assuming that the mechanic knows how to grind valves and seats. Today this is nearly a lost art for the do it yourself mechanic, but you can learn to do it in short order if you have a mind to. Refer to the shop manual for replacing valve guides, and for special piloted seat cutter tools. Also see Valve seat refacer tools, Bad valve blues, and the off site page Cylinder head replacement. If the valve seats are excessively worn and need replacing, you would likely let a professional machine shop do the machining work to install hardened steel valve seats.
Section A.12, Removing and Replacing Valve Guides
As noted in the shop manual, you can replace valve guides using a piloted punch and a hammer. Just go easy with the hammering as the stock guides are cast iron and may be damaged if you strike them too hard. An arbor press or a hydraulic stand press is a better tool if you have one handy.
If you install bronze guides be aware that the bronze guides need a bit more running clearance to accommodate thermal expansion. You could remove a small burr from the bore with a power drill. If the guide fits too tight on the stem you can hone it out using an old valve stem in a power drill with valve lapping compound. The bronze guides are self lubricating when run against a polished steel valve stem, so you can feel free to install umbrella seals on all of the valves, not just the intakes. The bronze guides may never wear out again in your lifetime.
Section A.13, Removing and Replacing Tappets
This is very straightforward as noted in the shop manual. Just be sure not to mix them up if they are to be re-used on the old camshaft. The challenge is being able to tell if the old cam or tappets are still servicable. I have some additional notes in the Power and Performance section about upgrade cams, the use of short tappets and long pushrods, and adding eyebrows in the block to accommodate increased valve lift.
Section A.14, Adjusting Valve Rocker Clearances
The shop manual is quite clear on this item using a feeler gauge. Some people who like gadgets might use the ClickAdjust tool. I prefer the Quarter turn method and often do not even bother with a feeler gauge (unless I might be in a very particular mood). Success with consistency here depends on the rocker shaft and rocker bushings being in good condition.
Section A.15, Checking Valve Timing
The noted technique with the 0.060 inch valve lash is only used to verify assembly of the timing chain and sprockets for correct valve timing, and it only works with a stock camshaft. If the timing chain is installed one tooth off, the timing mark on the crankshaft pulley will be 18 degrees out of position. If the cam lobe is badly worn this technique might result in odd positioning of the timing mark. If the engine has a non-stock camshaft the valve timing may be different.