Tune It Up
By Sam Smith
It’s been a long, cold winter in New Hampshire, with more snow than anyone has seen in years. The weather is a little milder at our location on the coast so we have not had the depth of snow many of our neighbors have endured. Snow up to the eaves? Hard to imagine and tough shoveling.
Among the winter issues we all face are the rising costs of all types of fuel, gasoline in particular. And most of us use the more expensive 93 octane or better in our British cars. So I’m always interested in trying to tune the car to get the best use out of every drop. Thinking of how I’ll soon be ready for some top-down driving, a few pointers might be helpful.
Rolling resistance comes to mind. The smoother the car rides and rolls, the less fuel it will take to push that ton of mass along. Making sure the wheel bearings being are properly lubricated and adjusted and that the differential and transmission are topped off with the correct type of fluids used is important. While the original owner’s manual may have specified 90 weight gear oil in the transmission, some of the cars will perform just as well with 30 weight motor oil and with slightly less resistance. New cars use engine oil as low as 0W-15 to reduce friction and improve gas mileage, but that’s something I don’t recommend in our classics.
Brakes that release correctly will minimize the drag on the wheels. Old flexible brake hoses can cause the brakes not to release all the way, as the inner lining of the hose collapses and restricts the brake fluid from returning to the master cylinder.
Tires are more and more in the news and I see quite a few advertisements. One with Mario Andretti is my favorite. Although I can’t remember which tire company he’s speaking for, he advises checking tire pressures on a regular basis. That’s something I’m very familiar with on these old British cars. Almost all of the cars coming into our shop have low tire pressures and the correct pressure will help them roll along with less friction. The old timers (I use the term gently as I fast approach that qualification) used to over inflate their tires to gain a few more miles to the gallon.
But keeping the engine in good running order and in tune is the best way to stretch each gallon of gasoline as far as possible. I read lots of manuals and see many procedures to tune an engine, many just different, although not wrong. Here are the areas I like to look at, generally in the order I’ll attend to each one.
Check the charging system. The proper voltage is essential in getting a good, clean spark. I like to see around 12.5 volts at the battery and 14.5 volts when the engine is running and charging the battery.
I start tuning the engine by removing the spark plugs. I inspect, clean and regap them or replacing them if they’re worn, with the electrodes rounded off, not sharp-edged. If they have the little screw-on adapter to snap into the plug wires, check to make sure it’s on tight.
I’ve grown to like the NGK brand, having changed from using Champions in years past. The NGK’s have always given me good service. That’s my preference, not a requirement. There are many high-quality spark plugs on the market.
The next step to do is to adjust the valves. With the spark plugs still out, follow the instructions in the shop manual. I look for loose valve clearances, and more importantly, tight valve clearances that might indicate the valves are receding into the head. I will go through the steps several times trying to get the valve adjustment the same and as even as possible on each valve. This can be trying on a worn engine as the wear between the valve stem and the rocker arm can result in what I call spooning, nestling into each other and prevent the feeler gauge from getting an accurate reading. A noisy valve will result.
Another thing to watch is to see if all of the valves are traveling about the same distance. Any differences can be a wake-up call about wear on the cam shaft lobes.
I will then perform a compression test. Everyone likes to see high readings but I’m generally happy if each cylinder is within 10 to 15 percent of each other. I drove a great running car the other day that had only 85 psi or less in all cylinders. But in general, low compression is an indication of a worn engine that won’t make best use of the fuel it gets.
After all that fun stuff with the internals of the engine, put those spark plugs back in place. Check the rest of the ignition components for condition, wear and defects, replacing items as required. Clean and gap the ignition points to the correct specification. While you have the distributor cap off it’s a good time to ensure the distributor plate will rotate freely. A drop of oil in the top of the shaft under the rotor will assist that.
Examine the condition of the rotor and terminals inside the distributor cap and the plug wires for cracks and age. Crusty terminals can reduce the voltage getting to the plugs, as can old or fluid-soaked wires that leak voltage. That means a weaker spark and unburned fuel.
Having checked and put these parts back to their proper places, connect a timing light, start the car, warm it up and check the timing. Loosen the distributor clamp bolt and adjust to spec. Some times I’ve found advancing the timing on a worn engine can let the engine run better, but trial and error prevails here.
The final step is to check over the carbs. Look to make sure the linkage adjustments work together, the throttle shafts are tight and everything visually appears in good order, including the air filter. You should only make adjustments while the car is warmed up. Most of the time a properly tuned carb set will stay correctly adjusted for a long time. I like to see the idle at around 800 to 1000 rpms, with equal air flow at each carb in multi-carb setups. Then set the idle mixture, usually for smoothest idle. As there are many different carburetors fitted to these cars, you will need to consult the manual for the exact tuning specs.
If you want to dive in a little deeper you can check for the correct needles and make sure they are installed at the right height. Racers will play with different needles searching for just the right mixture. Tens, if not hundreds, of needle combinations are possible. Once all these tasks have been completed, drive the car a little. Sometimes a little fine tuning, of the timing or carb is necessary to help the engine run as strong as it can.
The days are getting longer and we’re seeing temperatures above the melting point most days now. But while I wait for the frozen snow piled up in front of my LBC, my next enjoyable job is to go over the toolbox. In order to accomplish all of the above services I know I’ll need a voltmeter, test light, feeler gauge, compression gauge and many various small hand tools. Many hours can be spent searching online, in tool catalogs or at the local tool outlets for the right tool at the right price. Did I also mention I probably should be in a support group? Wait a minute, I am a member of several clubs, and doesn’t that qualify?