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 Gauge

Compression Gauge

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.

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.

VW Beetle Compression Ratios

1954 to 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

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

Written by David Slone, Copyright 2008 all rights reserved.

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10 Comments

  1. Mark says:

    what is acceptable compression in a 1978 2.0 litre engine

  2. victor pacheco says:

    HI, I JUST GOT A 92 VAN V.W. AS YOU KNOW THIS ONE HAS A COOLING WATER SYST. SO TELL ME THE DIFERENCE(BETWEN AIR COOLING) IN TAMING, TUNNING AND THE REST OF THE MAINTANENCE STEPS TO KEEP THIS VAN IN A GOOS RUNING CONDITIONS..THANKS

  3. victor pacheco says:

    HI.. PLEASE SOME BODY.. HOW DO I REPAIR MY GAS UNIT (THE ONE IS INSIDE THE TANK) I HAVE A VW KOMBI 72, AS FAR I KNOW I NEED TO REPLACE A RESISTENCE, BUT WHAT KIND OR WIRE SHOULD I USE , LOT OF THANKS.. SOME BODY!

  4. Josh says:

    “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” The tune up page says that a tune up must be done in a particular order and this is number 1. If we’re supposed to adjust the valves first, I think those should be #1 on the list instead of #2. Also, how does the compression ratio relate to the pressure readout? Should a ratio of 7.5:1 show 14.7*7.5 psi?

  5. Jake says:

    Hey I am in Brasil and I have a Brasilian 1600 Kombi which was produced in 1984.

    Whats the difference do you know?

  6. nevada says:

    My 1973 bug will start after sitting a few hours. It will run for like 30 seconds then all rpms just drop and it dies. I have changed spark plugs and cables they were fouled pretty good. Poured carb cleaner in the gas and replaced fuel filter. After doing all that it idled better than it ever has. I pulled it around in the yard but went to take off got to second gear and it died. Now it will start every few hours run and die. I am getting frustrated anybody have an answer. Thank you

  7. Anonymous says:

    Ok so, you take the compression test. Each cylinder has it’s respected rate, ie 120 120 118 120. So, you gave the compression ratio, but what would a new engine read in lbs?. 160 160 160 160 or ? thanks mw

  8. johan says:

    ehm…. compression pressure has very little to do with compression RATIO!!!!

    obviously this guide is wrong……

    you should always check valve clearance before checking compression PRESSURE else you might get a low reading

    make sure the pressure reading is close between the cylinders if one cylinder has lower pressure than the other its leaking through either valves or piston or the cylinder head

    dunno about the beetle but it should be in the higher end, a regular car has about 10-20 kg/cm in pressure that would be about 140-280psi

    good luck

  9. johan says:

    after checking, the compression reading on a beetle should be about 130psi (not lower) on stock camshaft

    good luck

  10. Ryan says:

    I have a 73 bus with a 1800 dual carbs. The weekend we took it for a trip over the Skyway bridge in St Pete,Fl. Made it over but on the way to the park ,I had the peddle to the floor nothing she died on my.Let her sit for an hour then headed back on the road again. Same thing again in twenty mins. What is wrong!Plugs look good. Thanks Ry

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