Servicing your B
ENGINE OIL
This can be a touchy subject with classic and vintage car owners but there's plenty of good reliable information out there if you look for it. Oil technology has come a long way since the B series engine was designed and developed but the basics are still true today, even if the formular has changed. The factory recommended 20W50 for engine and gearbox for a reason and modern oils do work better but they also aren't designed for our engines. Thinner oils are now the standard because thinner oils cause less drag and give better fuel economy figures. Modern engineering also works on much tighter and more accurate tolerances so oils can be fine-tuned for these new engines. What you want in your MGB engine is a decent quality 20W50 that contains some ZDDP (Zinc Dialkyl DithioPhosphate) in quantities of up to 1200PPM. This additive was removed from oil because it harmed catalytic converters and newer engines don't use flat tappets directly on the camshaft like our engines do. This rubbing of cam on tappet wears the surfaces and can cause damage quickly without an additive to protect the 2 surfaces. Modern oils can have other additives that can replace the zinc levels that work just as well depending on the detergent packages, but if you can get a good quality 20W50 with zinc mentioned on the label, or one that is recommended for classic or vintage engines, that will work well. There are lots of choices again now for good oils in the 20W50 range with zinc contents so choose one that suits your budget and change it when you should. I personally use Penrite HPR30 which is a mineral oil with zinc, and I have found it to be very good for pressure and longevity. Penrite also make a PMO20 that will work well. I like Penrite oils, but the brand is up to you. Just do some research.
The engine oil change is simple and is a job you should get used to pretty quickly. Take the car for a decent run and get the oil temperature up to as hot as you can. As I've mentioned elsewhere this can be over 20 minutes of driving, not just idling in the driveway or going around the block. Once you've got it hot jack the car up at the front of the car and put it on stands or drive the front of the car up on ramps. Open the bonnet. Put your cardboard/carpet/mat under the car and remove the drain plug from the back of the sump. Drain the hot oil into a suitable container being careful not to burn your arm or any other part of your valuable body. Go to the driver's side front guard of the car and remove the oil filter. This task can be anything from simple to frustrating depending on what type of filter you have and how tight the last person to put it on did it up. Go and have a cup of tea while it drains. When it's stopped dripping refit the drain plug. Fit your new oil filter making sure to wipe a little bit of old oil or grease around the rubber seal before fitting and tightening it as recommended by the manufacturer but basically hand tight and then twist it a little bit more if it will go. Remove the filler cap from the rocker cover and pour in roughly 4.5 litres (less if you don't have an oil cooler) of your fresh new engine oil. Let it settle and check the dipstick. Add more if needed to get to the top level.
Now, remove the high-tension wire (or similar) from your coil and turn the engine over without starting it. You should see oil pressure within 10 seconds of cranking. This is filling up your filter and oil galleries that emptied when you drained the engine. Once you have some pressure hook up the coil wire and you're good to go once you've put the car back on the ground.
GEARBOX OIL
Early MGB gearboxes had a dip stick in the top of the box accessible through the cockpit just in front of the speaker brace on the transmission tunnel. This was a fiddley and thankless job so lots of people just never checked and/or serviced their gearboxes. Later boxes have the more usual drain style plug halfway up the box on the driver's side that you take out and fill the box until it starts to leak out of this hole. Both versions are tricky to navigate but essential to become proficient in.
My car originally had the dipstick version, but when I fitted my new engine I swapped to a later gearbox and it has the side fill plug so I'm familiar with both versions. After draining I use a big syringe with a hose to squeeze oil into the box while lying under the car. It's not too bad really. The factory recommended 20W50 oil (same as the engine). I use a Valvoline 20W50 without friction modifiers or additives for my gearbox as the Laycock de Normanville overdrive used in MGs uses the same oil in the clutch systems and you don't want friction modifiers or detergents in there. You can certainly use heavy gear oil or synthetic detergent oils in non OD MG gearboxes if you want and some people use it in their OD gearboxes and seem to have no issues but while 20W50 mineral oil without additives is commonly available and is what was recommended originally I will keep using that.
As I said the job can be a little challenging but it's not particularly hard or time consuming. Jack the car up at the front and put the car on stands or drive the front of the car up on ramps. Make sure you can get the filler plug out and then drain the oil from the drain plug into a suitable container. Go and have a cup of tea while it drains. Once it's stopped dripping replace the drain plug and using a syringe or oil pump refill the oil through the filler hole until oil starts to leak out the hole. Replace the filler plug and give the are a quick clean.
DIFF OIL
This is another subject that can get off track a little, but you basically want a good quality heavy GL4 gear oil. I use the Nulon 75W-85 GL4 gear oil in the squeeze pack as it's easier to refill the diff with this package. You need to look for GL4, not the more common GL5 as it has a higher sulphur content that doesn't play well with brass and copper, which the MGB diff has. The task at hand is pretty straightforward. You'll need to jack the car up and put it on stands or drive the back of the car up on ramps. make sure the filler plug can be removed and then remove the drain plug and let the diff drain fully while you have a cup of tea. Refit the drain plug and use the squeeze bag container to refill the diff housing until oil starts to come out of the filler plug hole. Refit the plug and give it all a quick wipe and clean.
SETTING ROCKER CLEARANCE
Rocker (or valve lash) clearances are vital to an efficiently running engine however absolutely perfect clearances are not vital to a good running engine. Let me explain. Rocker clearances are set so that thermal expansion does not bend or break moving parts that heat up and cool down over the life of an engine. These thermal changes are very slight and for the most part don't cause issues, especially on fairly "loose" parts like the rockers. The factory recommended 0.015 in. set with the engine cold. The workshop manual recommends 0.015 in. cold or 0.013 in. hot. This difference allows for thermal expansion. If you're starting out and getting your MGB running properly or just want to maintain it this is the setting you should use for all your rockers. Don't obsess about getting the thou absolutely spot on. 0.013 in. could be 12, it could be 14. It's not going to matter. After 60+ years your valve train is worn enough that measuring to thousandths on this is not essential but try and get close. If you want to play around with these settings, then read and understand how the valve train works and then try setting your exhaust gaps at 0.014 in. hot and your inlets at say 0.011 in. or vice versa. This will delay or advance your valve opening and closing times slightly and you will be able to feel what's happening in your engine. Don't go any tighter than 0.010 in. , especially the middle 2 exhausts, and of course the wider open you have the gaps the more noisy they will be but all flat tappet engines are inherently noisy, especially when old and cold.
With the engine hot (unless you've just assembled the engine or it hasn't started for a long time and you're reawakening it) remove your rocker cover and inspect the rockers and assembly for any visual signs of wear or damage. You can set the rocker gaps using the rule on 9 or the quick way. Either will get you where you want to be. You must be able to turn the engine over while doing either procedure so it's usually easier with the spark plugs removed. You can turn the engine over with a big socket on the crankshaft, you can put the car in gear and rock the car, or you can short out the starter solenoid with wire or a simple home made engine starter. The rule of 9 is that you adjust number 1 valve (the closest to the radiator) with number 8 fully open. You then adjust number 2 valve with number 7 fully open, and so on. The numbers always add up to 9. The quick way, which is how I adjust and check mine is to understand that the valve doesn't have to be fully open for the corresponding valve to be fully closed. The valve is closed for most of the rotation of the camshaft which means 2 corresponding valves are nearly fully open. Looking at it this way we have valves 1 and 3 open simultaneously, then valves 2 and 5, then 6 and 8 and then 4 and 7. So with these valves open together we have 2 corresponding valves closed together so you can set 2 valves at a time. So with 1 and 3 open you adjust 8 and 6 together. With 2 and 5 open you adjust 7 and 4 together. With 6 and 8 open you adjust 1 and 3 and with 4 and 7 open you adjust 5 and 2. You can see the relationship here. I usually do 2 full adjustment rotations to recheck the gaps once set and sometimes they do need readjustment. This is all part of that wear I was talking about earlier.
IGNITION SYSTEM
The original ignition system on the MGB is very basic and easy to maintain and diagnose if there are issues. This is an area where a not so well maintained car might need some attention but if the car starts, idles and runs well that's a good sign but it's probably still worth going through it to make sure it is reliable. It's OK, there's no computers, or ECUs or Energy Polarizers in the MGB. It's your basic points based distributor with a coil and a handful of low and tension wires. I won't go through all the technicalities now but if you're interested (and you should be) there's plenty of info available online or in books. The basics of this system had been around for years and is essentially no different to millions of other cars built before and after the MGB. Starting at the end, check your sparkplugs. They're easy to remove. Clean the business end and check and make sure all the gaps are the same at 0.25 thou but a well maintained and tuned B series engine will happily run at 0.30 (I run mine at 0.32) which gives you a slightly better spark if your ignition system is in good condition. Check your plug leads and replace them if they look damaged or cracked. You can check the resistance with your multimeter if you're curious or having issues. The distributor cap should be removed and cleaned and checked for cracks or any damage. Clean the 4 electrodes especially if they have deposits on them. Check the button in the middle moves up and down easily and is clean. You can measure all of these between electrode/button and brass insert in the cap where the plug leads plug into. The rotor should be a tight fit on the distributor shaft and clean. Remove it and clean the brass tip. Check all the internal wires in the distributor and then remove the points. Clean the points contact pads with a points file (not sandpaper or similar) and refit and set them to the right gap. The workshop manual will tell you the points gap needs to be 0.14-0.16 thou. but you want to set it to at least 0.16. If your ignition system is healthy and working well you can set the gaps slightly wider and the car will run fine at 0.18. I usually do all of the distributor work with the dizzy out of the car as my fat fingers and bad eyes find it much easier on the bench. The distributor is not hard to remove and replace and the time it takes I've found more than cancels out the time leaning over the front guard trying to set the points. Check your leads to the coil and make sure all connections on the coil + and - tabs are clean and tight. You can measure your coil with your multimeter if you think it's suspect. The only other real reliability points of the ignition system are the condenser inside the distributor cap and the white wire that runs from the ignition switch, through the tachometer and to the + terminal on the coil. Now, go for a drive.
SU CARBURETTORS
The SU carburettor is one of the most misunderstood automotive components in history. Designed and developed in 1904 by the Skinner brothers, they went through many developmental design changes in the years between then and when they were fitted to the MGB in 1962. Like many, many British cars but especially Morris developed cars after 1936, the SU proved to be a well designed and very reliable carburettor in any state of tune. An absolutely amazing and ingenious design they tended to be overlooked and even ridiculed by many possibly because they were so common and came on very cheap daily transports, but have proven their worth having been on world speed record cars along with winning every major and minor auto sporting event in the world up to the 70's when fuel injection started to take over from carburettors.
People seem almost scared to take on these funny looking devices after being told they're complex, fussy, temperamental and unreliable. Nothing could be further from the truth. These carbs are simple, robust and eminently reliable with a little TLC. There are some very good books and website around about understanding the basics of the SU so if you're going to maintain yours I suggest you read them. Like everything in this blog, education is key to understanding.
The tuning process is simple but first you must make sure your SUs are in reasonably good condition. Partly because of this lack of understanding about them people tend to panic and get their carbs rebuilt, or buy replacements at great cost without really needing to or knowing why. The SU will run reliably and close enough to right with wear but will be harder to tune correctly. If you're just starting out check the basics. The dashpot (the big shiny bulb on top) has a plastic lid that you unscrew and fill with oil. There's a lot of talk about the type of oil you should use here but if you're just getting going or keeping your MGB on the road, the same oil you used in your engine and/or gearbox is fine.
The whole process of tuning twin SUs is to essentially make sure both carbs are exactly the same (jets, needles, floats etc.) and that both are doing exactly the same thing at exactly the same time. Once you've read those books and sites this will become clearer and you will be able to see what's happening. For now, assuming car is idling OK and running fairly smoothly, check that the throttle linkage, which is the bar that runs between the 2 carbs at the front opens both carbs at the same time. You can do this without pulling anything apart. Carefully watch both carbs and make sure that after the small amount of play in the linkage, both throttle spindles open simultaneously. If the car is running OK, there's nothing else to do at this time. I will explain more in-depth SU details including removal, disassembly, reconditioning and tuning in more depth elsewhere. For now, go for a drive.
COOLANT SYSTEM
The MGB has a very reliable and capable coolant system for the standard car when maintained properly. The radiator up front in the engine bay takes hot water from the engine via a pump on the front of the engine and cools it as it moves through the radiator and back into the engine. The B series had good water jacket placement in both block and head and as long as this system is clean, functional and not leaking you will have no issues with temperatures.
If however your MGB hasn't been well cared for and you have leaks, bulging hoses or clogged up radiator, you may have issues but the good news is, it's fairly easy and cheap to fix. If you are having trouble and didn't clean and refill the coolant when you first got the car like I told you to (tsk tsk) then now is the time. Check the hoses for any signs of wear or degradation. If there are any buy new ones. These are available in kits online so you can replace all of them as they are probably all about to fail if one is. If some look newer you can replace them all and have decent spares just in case. Check for leaks around the engine itself. These most commonly appear down the side of the head to black joint on the distributor side or from a welch plug in the block. Check that your fan belt is in good condition and buy another one if suspect. I always have a spare new belt anyway so just buy one. If it looks like your B hasn't been looked at for ages buy a new thermostat as well. They're cheap. Where you live will dictate what temp you get but in Brisbane I use an 82 degree in my stage 2 engine all year round.
When your parts arrive put the car somewhere where it won't matter if water spills everywhere under it but you can work on it. You may wish to drive the car up on ramps but it's not necessary. Remove your radiator cap. Lie under the front of the car and remove clamps on the lower radiator hose or radiator drain plug (whichever is easier) and let the water run out everywhere (I warned you). Go and get a cup of tea. With the water all gone remove the top and bottom radiator hoses and remove the 3 nuts on the thermostat housing on the front of the cylinder head. These can be difficult. They should be studs in the head but sometimes people replace them with bolts which isn't a great idea as 2 of them go into the water ways and corrode badly. I will write a piece on getting these off/out if you have trouble. With the thermostat out clean the old crusty gasket off both surfaces and then go and boil the kettle again. No, you're not making another cup of tea. Pour the boiling wanted into a cup/container and drop your brand-new thermostat into it. You should see it pop open. If it doesn't take it back and get another. I personally haven't had a new one not work but you do hear of stories of some not working. With the gasket areas clean and hopefully no broken or stripped studs/bolts/nuts put your new thermostat in and bolt it all down with a new gasket.
Now attach your old bottom radiator hose back onto the radiator and wrap your garden hose with some rags. Jam the hose and rags into the other end of the bottom radiator hose and turn the tap on full. Water will pour out of the top of the radiator at both cap and top hose outlets. Let the water pour out for a minute or so or until it looks clean. Take your old bottom radiator hose back off and fit your new hoses. The bottom radiator hose goes to the water pump and probably has a heater hose coming off it at 90 degrees about halfway along. The top radiator hose goes to the thermostat housing on the cylinder head. Tighten up all your clamps and refill the radiator with demineralized water and rust inhibitor in the right amounts. Go for a drive. When you get back check for leaks and once it cools check the level and top up if necessary.
THE BRAKES
Luckily for us the brakes on the MGB were always superb and easily capable of stopping the standard, and somewhat worked car. Your standard brakes in good condition is all you need for an MGB in almost any state of tune as long as you keep them well serviced and working properly. The MGB came with Lockheed brakes with 10.75" front discs with 2 piston calipers and 10" rear drums. This was fairly advanced for the time as not many cheap production cars had front disc brakes in 1962. If your brake pedal is reasonably firm and the car stops well in a straight line with some pressure your brakes are probably fine. Check your master cylinder (above the brake pedal in the engine bay) and top it up if necessary. When you have the front wheels off for something else, or you feel like doing it now jack the car up, put it on stands and take the wheel off. Check your discs for wear and grooves and check your pads for the same. If either are worn, even if your pedal feels OK and you stop OK, it's time to think about servicing your brakes. It's not particularly difficulty and they are important.
The rear drums are very reliable and work well when in good condition and adjusted properly. Again, if you have the wheel off check around the drum for any leaking and then take the handbrake off (make sure the car is chocked well) and remove the drum. Be careful, it can be messy in there. If there's no signs of anything "wet" and the shoes look like there's meat on them and are wearing evenly, put it all back together. I'll run you through a brake service and rotor/pad/caliper/shoe/cylinder replacements later but if everything looks OK, go for a drive. Remember, the best upgrade you can do to your MGB brakes if they're working OK is to get better tyres.