Adjust Those Valves

I have been reviewing the impact of losing ZDDP in motor oil and its impact on the valves of our old MG engines. One of the things we need to do, now more than ever, is to keep the valves in perfect adjustment. This is not a hard process, but one that will keep the engine running at its optimal performance and offset any wear.

On all MG engines, the valve adjustment is done right on the top of the engine, under the metal valve cover, which may be under a couple of hoses, or pipes, depending on the arrangement inside the engine compartment. The first step is to remove these hoses, preferably without disconnecting them, especially one from the heater box which contains cooling fluid. Move them to the side, unbolt the two large screws holding down the cover and remove the cover and or at least push it to the side. Directly under the cover are the valve rocker arms where the adjustment is done. From here, the process is to rotate the crankshaft until each valve rocker is at its highest point over the valve stem and check to gap between the two. The valve stem is the side with the large spring beneath the top.

When each rocker is at the highest point of its travel, measure the gap between the rocker and the top of the valve stem underneath it, using a feeler gauge. The gauge for the proper thickness should slide between the two elements with a little friction, but without any sort of vertical movement possible and not so tight that it won’t go into the gap without forcing. This gap is critical for the timing. This gap is adjusted by loosening the locking nut on the screw on the top of the opposite side of the rocker and then rotating the vertical screw slightly using a slotted screwdriver. Clockwise closes the gap, counter-clockwise widens it. When the gap is perfect with the feeler gauge, grab the screwdriver tightly to prevent any further rotation and then retighten the nut below to lock this position of the screw. It takes two hands an a little practice to insure the screw does not change when the nut is tightened, but the gap can be checked over and over until it is perfect. Then it’s on to the next valve, repeating the same steps until all eight valves are checked. Not hard to do, the access is easy, and the results important for the engine.

I won’t say what the proper valve clearance should be as it varies with each MG engine. You need to check with a manual before beginning to insure you have the correct setting. The setting usually is based on a cold engine too, so if you start checking the gap right after running the engine, you need to add .001 inches to the setting in the manual. And also check if you have changed the cam shaft at any time from the MG factory issue, as this usually requires a different adjustment gap, perhaps even a different setting for intake and exhaust valves. Literature with the cam should tell you.

Valve Adjustment Sequence: There are several methods described in various manuals to determine which valve to adjust first, second and so on. Most manuals have a chart designating when one valve is fully depressed, check another certain valve which will be fully open. There is another sequence rule based on the firing order of the cylinders and the intake and exhaust valves. Personally, I can never remember any of these and often get confused as to which valve I have done and which is next. My process is a little more work, but is foolproof.

These sequence methods noted above are generally based on having to rotate the crankshaft a minimum to cover all the valves. My method involves more rotations, but keeps me from skipping valves. I simply start at the front (valve #1), rotate the crankshaft by the use of a ratchet wrench on the big nut on the end of the pulley, while watching this rocker until it is in its fully risen position. Adjust this valve as noted above and move down the line to the next one. Again, with the wrench, simply rotate the crankshaft until the next rocker rises up and repeat the adjustment. I go right down the row of valves from front to back, in order, simply rotating the crankshaft each time. Probably ends up rotating the crankshaft several more times than in an optimal sequence, but insures me I got each and every valve.

On my MGB, the crankshaft nut takes a 1 3/8” size wrench socket. Bend back the locking tab and start cranking. MG engines rotate in a clockwise direction as you stand in front of the car looking at it, and simply rotate it a few clicks watching each rocker. This rotation can also be done using the nut on the generator/alternator pulley, but I don’t recommend this as it puts a strain on this shaft and the fan belt, but works. And if you don’t have a wrench to fit, the rotation can be done by jacking up one rear wheel, put the car in fourth gear, and rotate the wheel in the air in the forward direction. This is a little bit harder to do precisely as it takes two people, one to turn the wheel and one to watch each rocker rise up, but it works just as well to turn the engine to get each valve checked.

Feeler Gauge: You need a good feeler gauge with wide flat leaves of each thickness. A wire type gauge used for checking spark plugs will not do as it is very hard to get the sliding feel with it. And make sure you have one that is properly marked so you are sure you have the right thickness to get the correct gap every time. The gauge should be marked in every .001”.

Valve Cover Gasket: If you haven’t checked the valves in a long time, get a new gasket before starting. This part of the engine gets very hot as the engine runs and the gasket deteriorates. It will often split when removed. Some gasket may stick to the head also which must be scraped off before installing a new one. If you check the valves fairly often, the same gasket can be reused. I put gasket sealer between the valve cover and gasket when replacing it and smear a little oil on the head side where it seats. This makes a good seal, yet allows the gasket to come free easily next time I remove it.

And when you finish and reset the valve cover upon completion check for oil leaks. Note that if the cover leaks along the sides, further tightening of the two top nuts will usually not cure the problem. Instead of making a better seal, this move tends to bow out the sides of the cover making things worse. The solution is to remove the cover and check each side with a straight edge and push them inwards as necessary to remove any bowing. Then when the bolts are tightened, it should provide a good seal. Another check is the rubber grommets at the top where the bolts penetrate through holes in the cover. This rubber is often cooked hard from the heat and cracked. Oil seeps out here and runs down the side of the cover, making it look like it came from the seal at the bottom. These can also be easily replaced when the cover is off.

So as a nice wintertime activity, get out the wrenches and feeler gauge and check those valves. They are right on top of the engine and not too tricky to do. A little patience and you will have them right on and doing the engine a big favor. And with this issue of no more ZDDP in motor oils, it is more important than ever to keep them set exactly as needed. A little care here can help prevent a costly valve job later on and keep your engine running smoothly.