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How to Tune Up an Air Cooled Volkswagen

Updated on December 7, 2019
kentuckyslone profile image

I have owned several Volkswagen Beetles. My favorite car. I got my first one when I was still a teenager.

Air Cooled Volkswagen Tune Up Tips

A tune up is important for any car, but it is even more so for an air cooled engine. An air cooled engine will vibrate much more than a water cooled one. This vibration will cause engine components to wander from optimal settings a little quicker. Incorrect valve clearances and/or ignition point gaps can be enough to kill your fuel mileage, power, and speed. Eventually it can leave you broke down, unable to even start.

The better tuned your engine is the less it will vibrate. A lot of vibration will quickly lead to loosened screws and nuts here and there. Something else to check often and be aware. Loose screws in the shrouding can lead to overheating.

If your Volkswagen is getting harder to start and you notice less power and gas mileage or missing then a tune up is probably long overdue. This goes especially for your valve clearances.

When you tune up an air cooled Volkswagen engine you should follow the procedures in a particular order. Some systems are dependent upon other systems to operate properly. For example an accurate carburetor idle mixture cannot be achieved unless the compression, ignition system and valve clearances are correct. In addition, compression readings will be adversely affected by improper valve clearances.

Listed and detailed below is a description and tips for you to do the tune up work yourself. Even if you plan on hiring a mechanic to do the work this is a chance to learn about what is involved.

Most people can learn to tune up an air cooled Volkswagen engine with just a bit of practice.

Do the Tune Up Yourself or Hire a Mechanic?

You can take your VW to a mechanic, if you can find one who is familiar with air cooled engines, or you can do the work yourself. Doing your own work and maintenance will save you money, it will also make you closer to the car. When you do your own work you know what you have and you develop a feel for the way the car runs which helps you notice problems much quicker.

The “official” recommendation for tune ups is around every 10,000 to 12,000 miles, but this is only a very general guideline.

The actual need for tune ups is dependent upon driving conditions and how hard your VW is driven.

Remember, if your VW is getting harder to start and you notice less power and gas mileage or missing then a tune up is long overdue.

As time goes by you will “learn” your air cooled VW. You will know exactly when to do a tune up and you will be able to do it quickly. The trick is to make it a labor of love and not a chore, otherwise consider taking it to a mechanic.

OK, so a tune up is important, but it doesn’t end there. Between tune ups you should check things like your ignition points and oil level. There are also plenty of non tune up things to check, such as; brake fluid level, condition of brakes and tires, battery charging system, exhaust, etc.

Peter Aschwanden from "How to keep your Volkswagen alive" by John Muir
Peter Aschwanden from "How to keep your Volkswagen alive" by John Muir

How to Keep Your Volkswagen Alive

How to Keep Your Volkswagen Alive: A Manual of Step-by-Step Procedures for the Compleat Idiot
How to Keep Your Volkswagen Alive: A Manual of Step-by-Step Procedures for the Compleat Idiot

If you want to learn how to maintain and repair (or customize and hot rod) your air cooled Volkswagen then you need a good manual or two.

My own recommendation is that you get a copy of John Muir’s How to Keep Your Volkswagen Alive and a Bentley Manual appropriate for the year car you have as the bare minimum. I like to have as much info at hand as I can so I have these as well as a few more. The Haynes manuals arent my favorites but they do come in handy too.

How to Keep Your Volkswagen Alive: A Manual of Step-by-Step Procedures for the Compleat Idiot was first published in 1969 and it has been reprinted many times.

This manual of automotive covers all air-cooled Volkswagen built through 1978, including Bugs, Karmann Ghias, vans, and campers.

John Muir's writing is easy to understand and fun to read. His writing style is very laid back and relaxed, humorous and most of all straight forward. The illustrations are killer too.

 

Step by Step Tune Up Tips

When you first begin tuning up and maintaining your air cooled Volkswagen check everything often. As time passes you will learn things like how much oil it uses and what sort of gas mileage you are getting. You will notice quickly when conditions or performance deteriorates and you will know what to do to get that VW running smooth again.

Here are the steps for performing a tune up. These steps are arranged in the order they should be performed:

  1. How To Test Engine Compression
  2. How To Adjust Air Cooled VW Valves
  3. How To Change & Adjust Air Cooled VW Points
  4. Air Cooled VW Spark Plug Service
  5. How To Set Ignition Timing On An Air Cooled VW

How To Test Engine Compression

A compression test is a basic part of a routine tune up for an air cooled Volkswagen engine. With these instructions you can check the engine compression yourself.

Compression is a measurement of the pressure that builds up within a cylinder as the piston rises and both valves are closed. For the fuel mixture to burn properly a certain range of pressure is required.

The two main factors that affect compression are the condition of the piston rings and the valves. Obviously, the valves need to be fully closed on the compression stroke to avoid loss of pressure.

Before you check the compression the engine needs to be at normal operating temperatures. Let your Volkswagen idle until the engine is completely warmed up.Turn off the engine and begin removing the spark plug connectors from each spark plug. Unless you are very familiar with the firing order mark each wire with something like masking tape so you can put them back on the correct plugs later.

Remove all the spark plugs and block the carburetor throttle so that it is fully opened.

Thread the compression gauge into each cylinder making sure that the pressure release button has been pushed and the reading is at 0. Crank the engine for about 2 seconds and write down the highest reading from the gauge. Here it is very helpful to have a friend who can sit in the driver’s seat and crank the engine when you yell. You may also use a remote starter to turn the engine.

Compression Gauge
Compression Gauge | Source

Below is a chart that tells you what sort of compression pressures your air cooled VW engine should have. It is desirable to have high compression and relative uniformity among the cylinders. Variations from cylinder to cylinder should be no more than 14 to 20 pounds depending upon your engine’s compression ratio.

In most cases weak and/or uneven compression are caused by worn piston rings or bad valve seating. Of course improper valve adjustment could also be the culprit, but I am assuming the valves have already been checked and adjusted at this point (If not then see How To Adjust Air Cooled VW Valves). In worst cases there could be a damaged piston, cracked cylinder (jug), cracked head, leak between head and cylinder, or a burnt or broken valve.

Proceed to Step 2 of tune up procedure How To Adjust Air Cooled VW Valves

VW Beetle Compression Ratios:

 
 
1954 - 1960
6.0:1
1961 to 1965
7.0:1
1966
7.3:1
1967 to 1970
7.5:1
1971 to 1972
7.5:1 / 7.3:1
1973
7.5:1
1974`
7.3:1
1975 to 1977
7.3:1

How To Adjust Air Cooled VW Valves

Step by step instructions on how to perform valve adjustments in an air cooled VW engine.

Maintaining proper valve adjustment will help your air cooled engine to run smoother and more efficient. Improper valve clearances are one of the primary core causes of mechanical and efficiency problems in air cooled engines. Due to the nature of the air cooled engine frequent valve adjustments will have a major impact on your classic Volkswagen engine’s life and performance.

If the valve clearances are too small the valves will remain open too long which will cause them to over heat. If clearances are too large the opposite will happen, the valves will stay closed too long and will interfere with the intake of fuel and exhaust of burned fuel. Either way, if your valves aren’t adjusted correctly your air cooled Volkswagen will not run smoothly. Read on to learn how to adjust your own valves.

On many later model Volkswagens the cylinder order is printed on the engine cover. Whether or not your VW has the cylinder order printed on the sticker you can easily determine the ordering. Stand, or imagine standing, behind your VW. The cylinders are numbered from front to back on all air cooled VW engines. The cylinder nearest the passenger side back seat is Number 1. Cylinder Number 2 is directly behind it and nearest the passenger side rear. Cylinder 3 is in the front on the left (drivers side) and 4 is behind it.

IMPORTANT:
The engine must be completely cool when checking and adjusting valves.

1. Disconnect the positive battery cable to help avoid accidents; Engage emergency break or chock the wheels if necessary; Put the transaxle in neutral – Be safe!

2. Take off the distributor cap and set it aside so that you can see the rotor button and the distributor rim.

3. The engine needs to be turned so that the appropriate piston is at top dead center (TDC). Using a wrench or socket turn the crankshaft pulley clockwise until the rotor button is pointing at the mark in the distributor rim. Now look down at the timing mark on the pulley, it should be aligned with the seem of the crank case. With your engine in this position the number 1 cylinder is at TDC and both intake and exhaust valves are closed.

4. Remove the cylinder valve cover by inserting a large screwdriver or similar tool into the wire bail and prying upwards. Be careful not to bend the cover or make any dings in the cylinder head rim. Try wiggling the pair of rocker arms toward the front of the engine, on your right as you are facing the cylinder head. The rocker arms should have some clearance. Believe it or not experienced air cooled engine mechanics can tell right here whether or not the valve clearances are correct.

5. Insert the appropriate feeler gauge in between each valve stem and it’s adjusting screw. If the blade slides in and out smoothly or with just a slight tug your valves are adjusted properly. If a valve needs to be adjusted first loosen the locknut then turn the adjusting screw while rechecking the clearance. The trick is to get the locknut tightened back down without altering the valve clearance. Be sure to verify the clearance once a locknut is tightened and readjust if needed.

Now you are ready to go on to cylinder number 2. Rotate the crankshaft so that the rotor button rotates counterclockwise until the button is pointed 90 degrees from the mark in the distributor rim. Cylinder 2 is now at TDC. For cylinders 3 and 4 just repeat the steps, each time rotating the rotor button counterclockwise an additional 90 degrees.

6. Before replacing the valve covers inspect the rocker arms and the oil as well as the rim of the cylinder head. If there are any pieces of gasket material stuck to the head it will need to be cleaned off. Also inspect the inside of your valve covers. Once everything is clean reinstall the valve covers, preferably with new gaskets.

Vintage VW Training Film - Valve Adjustments (Part 1)

Vintage VW Training Film - Valve Adjustments (Part 2)

Proceed to Step 3 of tune up procedure How To Change & Adjust Air Cooled VW Points

How To Change & Adjust Air Cooled VW Points

If you have been following the tune up procedures your distributor cap is already off, if not then unsnap the clips and remove it from the distributor. There is no need at this point to disconnect the spark plug wires.

Pull off the rotor button and look at the tip. Is it burned, pitted or corroded?

Inspect the points. The contacts should be perfectly parallel and their surfaces should be smooth and clean. If the points appear burned the culprit is most likely the condenser.

As part of a routine tune up you will replace the spark plugs, ignition points, rotor button and condenser. You should also inspect the distributor cap and spark plug wires and replace them when necessary.The points are held in place with a small slotted screw and is attached to the condenser with a wire connector. Pull of the connector with your fingers or a needle nose pliers. Remove the screw and lift out the ignition points. Remove the condenser which is held on with a slotted screw.

Attach the new condenser and insert the new points tightening the screw only until it is snug. The easiest way to do this is to hold the points in your left hand then insert the screw into the hole and hold it in place with a screw driver.

When you look at the distributor shaft where it comes into contact with the points you will notice four lobes, or high areas. Turn the engine until the base of the ignition points is resting on the highest point. Here is when your points will be fully open and here is where you need to set the gap.

Loosen the mounting screw just until you are able to move the contact points. Insert a 0.016 in. feeler gauge into the gap and tighten the screw. There is a spot where you can use a slotted screw driver to pry and hold the points in place (See photo).

Be sure to recheck and verify the gap once the screw is tightened as the gap tends to decrease when you turn the screw. This takes practice and you will probably have to redo it several times to get it right. Many experienced air cooled engine mechanics can actually set the point gap by eye balling it!

Now all you need to do is pop on the new rotor button, and if it looks fine, then snap on the distributor cap.

NOTE:

In an emergency you can file the contact points and get your VW back on the road. If you break down and you find that your points are pitted or they have material build up (which causes them to never fully open) you can remove the points and file down the contacts. If you don’t have an ignition point file any small bastard file should work. Keep in mind that it is important that the surfaces be as smooth and even as possible.

Note how the flat tip of the screwdriver is used against the metal tab to adjust the gap while the feeler gauge in inserted between the contact points
Note how the flat tip of the screwdriver is used against the metal tab to adjust the gap while the feeler gauge in inserted between the contact points

Firing Order & Distributor Rim Mark

"Looking down at the distributor, right on the rim you will find a very small notch in the rim where the top of the distributor cap sits down upon. That little notch is where you put # 1. Mark on the bottom of the distributor case with a piece of chalk under where the rim notch is. Then put the distributor cap on and seat it on the base with no wires connected. Take #1 and you will find on on the top that lines up with the mark you made on the bottom of distributor that also lines up with the small notch on the rim. So now you have # 1, then just work clockwise 1,4,3,2." Mike

forums.pelicanparts.com
forums.pelicanparts.com


Proceed to Step 4 of tune up procedure Air Cooled VW Spark Plug Service

"I once owned a bug which the previous owner had nearly stripped the threads in one of the spark plug holes. If I accelerated too quickly it would actually blow that spark plug right out of the hole!"

— David S.

Air Cooled VW Spark Plug Service

Spark Plugs Replace or Clean and Re-gap?

Your spark plugs will not need to be changed at every tune up, however they should be inspected and replaced if necessary. Most of the time you can clean up your spark plugs, check the gaps and reset if needed and get more mileage from your plugs. Some mechanics will replace the spark plugs at each tune up, but that is really a waste of both money and resources. “Experts” recommend that you replace your spark plugs every 12,000 miles.

When you take out your spark plugs be sure to arrange them in a way so that you know exactly which cylinder they came from. The condition of each spark plug when it is first removed from the cylinder head will give you insight into the internal conditions of your engine. For example, if all your plugs are relatively clean except for one that is burned or covered with oil or build up you know you have a problem in that particular cylinder.

Your spark plugs should be dry and have little or no deposits or build up. If the center electrode has become worn and rounded around the edges you will not be able to get a sufficient spark for good performance – replace the plug, and of course, don’t just replace one, get a complete new set.

If your spark plugs are dirty you can clean them, but the engine conditions that caused them to get that way will still be there.

Normally the deposits on your spark plugs will be carbon.

If you see a light colored deposit on the plugs it isn’t anything to worry about as it is normal and usually cleans very easily.

If the carbon deposits are black, but can still easily be removed your air/fuel mixture is too rich and so a carburetor adjustment will be necessary.

If the deposits are black and hardened, burned, or sticky looking you have oil entering the fuel chamber most likely caused by worn rings. If your spark plugs looked like this what was the compression reading?

Setting The Gap On Your Spark Plugs

First look at the electrode end at eye level. The side electrode must be directly above the center electrode. If you don’t have a spark plug tool use small needle nose pliers to adjust the side electrode. Once the electrodes are lined up adjust the gap, then recheck the alignment until both are correct.

The metal gaskets on the spark plugs are important, don’t let them get lost.

The gap setting for nearly all air cooled Volkswagen engines is 0.028 inches.

Before inserting the spark plugs back into the cylinder head wipe a very light coating of oil on the threads. Remember, light, you don’t need oil running down into your cylinders. Thread the spark plugs in as far as you can by hand. A good way to do this is to place a spark plug socket with an extension over the plug and turn it by hand. Once you get the plug hand tightened as far as you can turn it about half a turn further with a ratchet, be careful not to over tighten as that will alter the electrode gap and cause serious damage to the head.

Spark Plug Chart

Use this picture chart to help to determine the condition of your spark plugs and engine operating conditions.
Use this picture chart to help to determine the condition of your spark plugs and engine operating conditions. | Source

Proceed to Step 5 of tune up procedure How To Set Ignition Timing On An Air Cooled VW

How To Set Ignition Timing On An Air Cooled VW

Setting the timing is step 5 in the tune up procedure.

Ignition timing is dependent upon the rest of the ignition system being set up properly. Accurate timing cannot be achieved unless you have sufficient compression, correct valve clearance, correct ignition point gap, correct spark plug gaps and the engine is at normal operating temperature.

3 Methods to set Ignition Timing:

These steps apply to all methods:

Turn the engine using the crankshaft pulley nut until the rotor button (remove distributor cap so you can see the rotor button) is aligned with the groove in the distributor rim and the timing mark on the crankshaft pulley is aligned with the crankcase seem.

NOTE:

If your pulley has two timing marks the one on the right is 10 degrees BTC (before top dead center) and the one on the left is for 7.5 degrees BTC.

If your pulley has three notches they will be, from left to right, 5 deg. ATC, 7.5 deg BTC and 10 deg. BTC (See photo).

Bosch 009 Distributor with Centrifugal Advance

I have a dual port webber with flash arrestors. We just found it in the barn after 22yrs of not running. I think it is a 1970 -- 71 -- 72 ..maybe. The problem is that this distrib does not have a vacuum advance ! So how does it take care of advancing the timing and other chores? got any ideas on how to time this beast? ~ Mikey

Mike, the distributor you have is a bosch 009 with centrifugal advance. You set the timing at 3000-3500 rpm to 28-32 degrees btdc and I believe the idle should sit somewhere around 5-7 atdc. ~ Nate

Method 1 Using A Test Light

You do not need an expensive timing light to adjust your ignition timing. For air cooled Volkswagen engines a simple test light consisting of a 12 volt lamp and two leads with alligator clamps is not only sufficient but recommended. You can easily make one yourself or you can buy one at an auto parts store.

Remove the vacuum hose from the distributor advance unit.
Loosen the clamp at the base of the distributor until you can turn the distributor with your hand.

Connect one lead of your test light to terminal 1 on the distributor and the other to a solid ground.

Turn the distributor body clockwise until the contacts of the ignition points are closed. Turn on the ignition switch but do not start the engine. Turn the distributor counterclockwise until the test light comes on (just as the contact points are opening) and tighten down the clamp.

Method 2 Using A Volt Meter

The steps for using a volt meter to set your ignition timing are the same as those for using a test lamp. Instead of watching for the test light to come on you will be watching for a voltage reading on the meter. When the contact points are closed the meter should show 0. When the points begin to open voltage will be indicated on the meter.

Method 3 Using A Timing Light

If you have a timing light you can use it to set your timing.

Use chalk or something similar to the timing mark on the crankshaft pulley to make it easier to see with the timing light.

Remove the vacuum hose from the distributor advance unit.

Loosen the clamp at the base of the distributor until you can turn the distributor with your hand.

Connect one lead of your test light to the number 1 spark plug wire on the distributor and the other to a solid ground.

Start the engine and aim the timing light at the top of the crankshaft pulley. Rotate the distributor body until the appropriate mark on the crankshaft pulley is aligned with the crankcase seam. Tighten down the distributor clamp.

NOTE: Be very careful of the belt and other moving parts when performing this procedure.

Question About Using Test Lamp or Meter

Question: I’m a bit confused, being an engineer I guess I’m more anal in instructions, using a volt meter or light.

Connect one lead of your test light to terminal 1 on the distributor (is this going to the #1 plug, and if so do I pull the cable out? if I don’t my VW will start right up) and the other to a solid ground.

Turn the distributor body clockwise until the contacts of the ignition points are closed. (how can I tell if I don’t remove the distributor cap?) Turn on the ignition switch but do not start the engine (my engine starts right up, should I pull the coil cable?). Turn the distributor counterclockwise until the test light comes on (just as the contact points are opening) and tighten down the clamp. Brett

Answer: Hi Brett -- Your VW will start up when you turn the key to the on position? Normally you have to turn it a bit farther to engage the starter motor and then let it ease back to the on position once it starts. Your engine should not start when you click the key over to on (in a VW or any other car). It doesn’t matter if the spark plug cable is attached or not but the distributor cap needs to be off so you can see the points and access the clamp.

Have You Ever Owned an Air Cooled Volkswagen?

Have You Ever Owned an Air Cooled Volkswagen?

See results

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2019 kentuckyslone

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