How to set Morris Minor A-series engine valve clearances

This guide refers to Morris Minors with a-series engines. Care should be taken when undertaking this job as incorrectly set valve clearances at best will make your car sound “tappetty” and at worst seriously effect performance and lead to valve damage such as warping due to overheating.

The good news is it’s relatively straightforward but if you’re unsure, get a competent mechanic to do it.

I use a Draper imperial feeler gauge. Costs less than a fiver.

This job should be done every 3,000 miles. It’s a good idea to have a spare rocker cover gasket to hand. The cork ones have a tendency to dry out and may need replaced. The rubber type can also become brittle. You’ll also need an imperial feeler gauge, some imperial spanners, a flat headed screwdriver and your starting handle (for turning over, cranking, the engine).

The rocker cover is held in place by two bolts (5/8 AF)

Ensure the engine is cold. Remove the two bolts (5/8 AF) that secure the rocker cover in place. It might be help to remove the air filter hose too. You will then see what appears in the image below, the rocker assembly.

I have numbered the valves 1-8 from front to back to make things easy. We will use the Rule of 9 method when setting the valve clearances. Again, to keep things easy!

Rule of 9 Method

The rule of 9 works like this. When you adjust valve 1 for it to be ready for adjustment you need to ensure valve 8 will be on the opposite peak. This means valve 1 will be perfectly level and ready. Since 1+8 = 9, it’s the rule of 9.

For valve 2 you must ensure valve 7 is on the opposite peak, for valve 3 it’s valve 6 on opposite and so on. Then numbers always add to 9.

From the radiator: 1, 4, 5 & 8 are exhaust valves. 2, 3, 6 & 7 are inlet valves. 

Valve 4 ready for adjustment.

In the image again. We can see valve 5, circled in red, is at the opposite peak (look at the right hand side of it, it’s fully raised) of valve 4. This means valve number 4 is now ready for adjustment ( since 5+4 = 9).

I find it’s easiest just to work from setting valve 1 through to 8 in order to make sure you don’t miss any. It can be done faster by changing the order up, but I’ll keep things simple. Go with 1-8 in order just now and once you’ve done it a couple of times you can change the order up to make it a quicker process if you wish.


Let’s get started

To commence work on valve 1 we will probably need turn the engine over, unless you’re fortunate enough that valve 8 has stopped on the opposite peak.

To do this ensure the car is out of gear and ignition is switched off. You don’t want the engine firing up. Insert the starting handle through the hole in the bumper into the slot (dog) in the engine and turn it clockwise to turn it over. You’ll see the valves move as you do this. Watch as the valves rise and fall until you see valve 8 on the opposite peak.

Tip: You can make turning the engine over a little easier by first removing the spark plugs. This gets rid of the compression.

Once you have valve 8 on the opposite peak you are ready to adjust valve 1. Using a 7/16” AF ring spanner crack the lock nut (on right hand side) of valve 1 anti-clockwise. Then insert a screwdriver, leaving the spanner in place, which is turned clockwise to narrow the gap and anti-clockwise to open it.

Blue arrow points to lock nut on valve 3. Red points to where screwdriver goes. It’s the same for each valve.

Insert your 0.012” feeler gauge into valve 1 (see photo below). The workshop manual specifies 0.012” clearance, so I use that gauge. (Many owners set their exhaust valves to 0.015” as unleaded fuel burns hotter than the leaded these engines were originally designed for. I’ve stuck with 0.012” all round, but it’s your choice. 0.015” will make the engine slightly noisier but some argue it’s better for the engine.)

0.012” feeler gauge on valve 1. Note valve 8 at the back on its opposite peak.

Turn the screwdriver as necessary until your feeler gauge can slide in and out of the gap with just a little resistance on it. You should feel some resistance but it shouldn’t be a fight to get in and out of there. Once the gap is correct hold the screwdriver in position and tighten the lock nut with the ring spanner. Re-check with your feeler gauge, adjusting again if necessary.

Turn the engine over with the starting handle to get valve 2 ready for adjustment by getting valve 7 on the opposite peak. And repeat the process.

Work your way through all the valves one at a time until they’re all done.

Replace the rocker cover and gasket, securing with the two bolts you removed at the start. Don’t over tighten. Reconnect any hoses you removed, and replace the spark plugs if you removed them.

You’re now ready to fire up your engine, which should sound and run healthy.

Good luck.