Air cooled Volkswagen Terms

Air cooled Volkswagen Terms

This glossary contains many of the words, acronyms and jargon commonly used when referring to air-cooled VW’s. Hopefully this will help folks new to VWs to better understand what other VW enthusiasts are talking about as well enable folks to be more fluent in the art of speaking “Air-Cooled-eze”.

Since making a list from scratch is more difficult than first imagined, I probably only have a fraction of the terms on here. If you have a good term that you think should be listed here, e-mail it to me so I can add it in.

NOTE: Acronyms and nick-names for terms are in brackets

A – C

Align Bore
This is a machining process in which the bore in which the crankshaft journals are trued. Typically they are bored .020″, .040″, .060″ or .080″ over the standard bore size. Most machine shops will stamp this number at the top of the case under where the oil cooler mounts. Whenever this is done, you will need to use bearings with an over-sized O.D. to ensure a proper fit.

The small sheet metal area between the front and rear fenders located below the trunk & deck lids.

A unique style of automatic transmission VW used for many years. It basically was a 3 speed transmission with no clutch making it fun to drive but with nothing to “learn”. A novel idea that was ahead of it’s time. Note many new car makers offering auto-sticks in performance luxury coupes and sedans and marketing them as something “NEW”.

Barrel Shims (“Cylinder Shims”)
There are thin, round pieces metal that are placed beneath the cylinders when building an engine. These move the cylinders out; increasing the deck height and LOWERING the CR. using these is a popular way to adjust the CR to the desired amount.

This mark on most aftermarket crank pulleys, refers to the compression stroke of the #2 & #4 pistons. Set it to the seam in your case, then pull off the distributor cap and note which plug wire it’s pointing to. That’s the piston ready to fire.

The size of the inside diameter (I.D.) of any machined hole. Typically this refers to the I.D. of the cylinders.

Bore Out
Machining process in which a bore is INCREASED in size. Typically this refers to increasing the I.D. of the cylinders.

Refers to all the parts as an assembly within and including the engine case. Normally folks will not just rebuilt the bottom-end since you must disassemble the top end to get to it.

Bowden Tube
The bent, flexible tube in which the clutch cable passes. Located on the driver’s side of the transmission. This tube should sag between 1″ – 1 3/4″ in order to provide smooth clutch engagement.

Breather Box
A small box found on high performance engines. Helps separate oil from crank case vapors. It also provides a central point in which to route breather lines from the case and heads prior to being routed to the carbs.

A part of the short block, the cam is responsible for timing the opening and closing of the valves as well as determining how far they open up.

Cam Plug
A small plug that fits between the case halves at the end of the cam on the forward end of the engine. It MUST be installed with the flat side forward (out) so that the cam will not ever have the possibility of rubbing on it.

Carburetor (“Carb”, “Carbie”)
A metering device which meters fuel into the in-coming combustion air. Carbs work directly off of vacuum.

Case Saver
A double threaded insert which is used for the head studs to help prevent the threads from getting pulled out over time.

The friction disk that is mounted to the transmission input shaft. This is what rubs between the flywheel and pressure plate and engages the drive wheels via the transmission.

Crankshaft (“Crank”)
This is the heart of the engine. This is what spins and provides the motion for all the other parts in the engine (con-rods, pistons, transmission, etc.). All other parts in the engine work toward getting the crankshaft to turn fast and powerful.

Combustion Chamber
The area in the head where the fuel/air mixture is compressed and ignited by the spark plug. Fly-cutting reduces its size, porting and hemi-cutting increases its size.

Compression Ratio (CR)
This is a numeric amount which represents the amount that the intake fuel/air charge is compressed, during the compression stroke (7.5:1), as compared to the ambient air pressure (7.5:1). As a general rule, the higher the compression; the more horse power and heat is created.

Connecting Rod (“Con-rod”, “Rods”)
These are the parts that “connect” the crankshaft and the piston assemblies. The crankshaft side is large and has an end cap which is held on with 2 nuts. The pistons are held on the small end of the rod with a hollow wrist pin.

Cool Tin
Under cylinder air deflector tin originally used on T-3s. This type of tin forces more of the cooling air completely around the cylinders providing better, more even cooling.

Counterweighted Crank (“CW Crank”)
A crankshaft which has large counterweights placed on opposite sides from the rod journals. By having these counter weights added, the crankshaft distorts less under stress, is able to reach higher RPMs, and has a much smoother operation resulting in longer life for the crank and case. Counterweights can be added by welding to an existing crank or they can be either forged or cast in when the crank is made.

Cross Bar Linkage (“X-Bar”)
A type of linkage for dual carburetors which typically has a hexagonal bar which reaches from air cleaner to air cleaner. There are then adjustable heim joints which connect to the carb butterflies on either end. This type of linkage is usually superior to the center-pull type since carb function is un-effected by engine temperature.

Cylinders (“Jugs”)
These are the large rather round parts with the deep cooling fins on the outside. The I.D. bore is where the piston assemblies ride.

D – F

Deck Height (“DH”, “Deck”)
The distance measured in thousandths of an inch between the top of the piston and the top edge of the cylinder. This measurement is one component in the CR formula.

Deck Lid (“Bonnet”)
You VW’s engine cover.

Dellorto (“Dells”)
A popular brand of Italian performance carburetor. Dellortos are no longer made new and most will agree that they are superior to Webers in both performance and flow. Dellorto made top quality dual 2 barrel carb sets (DRLA) available in 36mm, 40mm, 44mm & 48mm sizes. Also available is a dual 1 barrel set (FRD) in 34mm

Distributor (“Dizzy”)
The part of the engine which solely controls the timing of the ignition spark going to the plugs. On your VW, you will have a plastic cap which has 1 center wire coming in from the coil surrounded by 4 wires going to the spark plugs. Inside, you’ll find the points; the condenser (with the green wire) hangs off the side.

Distributor Drive Gear
The brass gear on the rear of the crankshaft which engages the distributor drive pinion which in turn turns the distributor.

Distributor Drive Pinion
The vertical pinion gear which is driven by the brass drive gear on the crankshaft. This directly drives the distributor. It also has a cam in the middle which is for the stock fuel pump check rod. This also drives the fuel pump. This is a busy little part!

Doghouse Cooler
The type of oil cooler found on ALL ’71 and later T-1s. This cooler is mounted in front of the fan shroud so that it doesn’t pre-heat the cooling air to the #3 & #4 cylinders. The shroud has extra ducting which takes cooling air from the fan and routs it directly onto the cooler. The warm air is then routed out of the engine compartment through exhaust tin. This is the best, most efficient oil cooler system VW ever produced for the T-1.

Doghouse Shroud
The late model fan shroud (’71 and later). Incorporates the ducting and necessary tin required for using the late model oil cooler.

Dowel Pins
Pins which keep bearing from spinning in their bores in the case OR pins which lock the flywheel to the crankshaft with the help of the gland nut.

Dropped Spindles
Front wheel spindles which have the wheel spindle moved typically 2″ higher. These provide a lowered front end without compromising the ride quality or handling.

Dual Carbs (“Twin Carbs”, “Dualies”)
Two separate carburetors on one engine. This can refer to both single barrel carbs like Kadrons AND two barrel carbs like Webers and Dellortos.

Dual Port
Refers to the number of individual intake passages into the head. Dual ports have 2 per head.

Dyno Testing
This is where an engine or whole car is placed on a dynometer and its performance is tested in real-time. This is the only real way to see just how much horse power and torque an engine produces. It’s also the best way to tune an engine for maximum performance since you can see what subtle changes in jetting and timing make, enabling you to squeeze the most out of what you have.

Fan Shroud
Large sheet metal part which directs the flow of air coming directly off the cooling fan. Two styles are used; early – non-doghouse (through ’70) & late – doghouse (’71 and later).

Air deflectors which are part of the thermostat system. These are located at the base of the fan shroud and are actuated by the thermostat bellows /check rod. When the engine is cold, the flaps are closed reducing the amount of cooling air that reaches the cylinders and heads. As the engine warms up, the bellows expand causing the check rod to open the flaps and allowing a full amount of cooling air to blow across the cylinders and heads. These are often removed.

Fly Cut
A machining process which removes material on the head where the cylinders seal to the head. This can be done to true a sealing surface with grooves or other damage. Fly cutting REDUCES the combustion chamber size and raises your CR. If you have one head fly cut, you MUST have the other fly cut to match so that your CR is even between both sides of the engine.

The large, heavy round plate which is held on the front of the engine with the gland nut. This is part of what couples the transmission to the engine. The clutch pressure plate mounts to the flywheel. The gear teeth on the outer edge are what the starter engages to start the engine. There are actually 3 types of flywheels for the T-1; a 6V for a 180mm clutch, a 6V for a 200mm clutch (rare) and a 12V for a 200mm clutch. ALL VWs prior to ’67 had the 6V/180mm type with VERY few ’66 models which had the 6V/200mm type. ALL ’67 and later U.S. models had the 12V/200mm type. The “6V/12V” refers to the voltage of starter which its used to engage the ring gear. A 6V starter CANNOT be used on a 12V flywheel and vise versa.

Fuel Pump
A mechanical device used for pumping fuel. There are electrically driven pumps and mechanically driven pumps. The stock mechanically driven pump is located on the rear of the engine between the distributor and the generator/alternator stand.

Full Flow (FF)
A modified oil pump system which routes ALL the oil directly from the pump into an aftermarket filter and sometimes a cooler and then routes back into the case via a fitting which is drilled & tapped into the oil galley about 2″ from where the pump is. This is the ONLY way to have truly 100% filtered oil and is probably the best single upgrade to any engine you can make on build-up.

G – J

Generator (“Dynamo”)
Produces the electricity necessary to run the engine and re-charge the battery while the engine is running. The cooling fan mounts to the front if it. It’s mounted to the fan shroud and is driven by the fan belt by the crankshaft pulley.

Gland Nut
A hollow bolt actually, it’s the large 36mm bolt which attaches the flywheel to the front of the crankshaft. This baby is torqued to between 225 and 250 ft/lbs!! It also has a set of needle bearings in it which support the transmission input shaft. Don’t forget to add a little grease to this any time the engine is out.

Brass bushings in which the valve stems ride. These are pounded into place with a special driver and a hammer. Then they are reamed to fit the stem of the valve. If you have a puff of blue smoke out of your car as soon as the engine starts, chances are the guides are worn and allowing oil to pool in the cylinders.

The part of the engine which goes on top of the cylinders. They house the valves, rockers, spark plugs and combustion chambers. Probably no other single part is more capable of making real horse power than the head, that’s why good ones cost so much.

A performance exhaust system in which ALL runners are of equal length before the collector. This helps to maximize power. A header exhaust is normally mandrel bent and has smooth bends for smoother, higher flow.

Head Gasket
A round copper ring that fits between the tops of the cylinders and the heads. Your VW did NOT come with a head gasket (believe it or not!!), but many folks add them to high Performance engines to help ensure a tight seal.

Helical-Cut Gears
Gears which are cut at an angle so that more than one set of teeth are engaged at one time. Helical-cut gears are quiet in operation, but creates an amount of side load (thrust) on the gear. ALL gears within air-cooled VWs are this type with the exception of the starter ring gear and the reverse transmission gear (that’s why it sounds different backing up than going forward).

A machining process which finishes the surface of the cylinders and smoothes/restores a clean gouge-free surface for the rings to ride on. Honing is one of the few machining processes that the home mechanic can do him/her self.

Inside Diameter

This refers to the carburetors being synchronized; pulling the same amount of fuel & air. NOT to be confused with a teeny-bopper singing group who grabs all the Grammys from REAL artists!!

Jack Point
A small square hole in which a factory jack can be inserted to change a tire. On T-1s there are 2; one on each side just in front of the rear wheel under the running board. On T-2s there are 4; two on either side – one in front of the rear wheels and one behind the front wheels.

The polished surface on either the crankshaft or cam in which the bearings rub. The crankshaft has both main journals and rod journals. The cam has only bearing journals.

K – P

These are little tapered half-round parts which lock onto the valve stem by the grooves. The outer diameter of the keeper is tapered. This in turn locks into the retainer which holds the valve spring in place.

Lifter, Solid (“Cam Follower”)
The mushroom-shaped part which rides on the cam lobes and transmit torqueing motion to pushing motion. There are 8 per engine. These move in bores in the case and actuate the push rods which eventually move the valves.

Lifter, Hydraulic (“Cam Follower, Hydraulic”)
Same as the solid lifters only these are designed to be self adjusting (no need to adjust the valves with these). Hydraulic lifters dramatically quiet the operation of the engine since they are made to run at ZERO clearance. These are what most every other modern car on the road has. Running these REQUIRES a FF oil system since the tiny metering orifices inside can be clogged by minute particles in oil.

Lightened Flywheel
A stock flywheel which has had material from the outer edge removed on a lathe. Generally these are available in 12# and 10.5# weights. Having a lightened flywheel allows your engine to spin up in RPMs faster and will read more HP on a dyno as well as give the car a feeling of more HP. However, lightened flywheel make for a jerkier ride and slightly reduced fuel mileage from a severe loss of inertia causing the engine to work harder to keep a constant speed.

Refers to the engine assembly from the crankshaft out to the valve covers and everything in between. Not included are the accessories and engine tin.

Main Bearing
The bearings in which the crankshaft spins in the case.

Merged Header
Generally the same as a standard header but the collector comes together at less of an angle. This helps flow characteristics and actually helps to scavenge exhaust fumes by creating a vacuum on the other cylinders as each cylinder expels it’s exhaust. It’s a more efficient system at the higher RPM ranges.

Outside Diameter.

Original Equipment Manufacturer.

The frame of your VW in which the suspension and drive train are installed.

The part which compresses the combustion fuel/air mixture in the cylinder on the compression stroke. Pistons come in 3 basic flavors; domed top (high CR), flat top (standard CR) and dished top (low CR).

Piston Rings
These provide a good seal between the piston and the cylinders wall. There are 2 top rings, or compression rings. The bottom ring is actually in 3 pieces (2 rings and a spacer). This is your oil control ring. Many racers or folks building high performance engines will substitute the top 1 or 2 rings with Total Seal® Gapless® rings to ensure minimal leak-down and top performance.

Pressure Plate
This bolts onto the front of the flywheel and squeezes the clutch disk tightly against the flywheel’s friction surface. These are available in two basic styles; the spring-type (which is the stock style) and the diaphragm-type (Porsche style). Both are further available in multiple pressure ratings so that they can be used on mild street engines (light-duty) or wild race applications (super-heavy duty).

Push Rod (“PR”, “P-Rods”)
Long hollow round rods that transmit input from the lifters to the rocker arms. These fill with oil and route all the oil to the heads while the engine is running. They come is various lengths to allow for proper set-up of the rocker arm geometry. High performance engines which use dual or triple valve springs use PRs made of chromoly.

Push Rod Tube
A cylindrical tube which has a series of bellows on either end which fit between the case and the heads. These provide a route for the used oil from the head to gravity drain back into the case for re-use. There are 4 basic styles that can be used on a T-1 engine; the standard, the windage style (which has a longer end that sticks out past the bellows on the case end), a spring-loaded adjustable type (normally used for replacing a broken PR tube, and finally a machined adjustable type (normally found on high dollar of-road rigs (these provide a degree of protection against damage to the PRs).

Q – U

A machining process done to crankshafts and cams which restores the wear surfaces to correct specs. When this has been done to a crankshaft, you must ensure you get replacement bearings with the correct I.D. to ensure a proper fit.

A round disk which goes on top of the valve springs and with the help of the keepers, lock the valve to the springs.

Rocker Arm (“Rocker”, “Tappet”)
The part you see under the valve cover. This part transmits the pushing force from the PRs to the valve stems by pivoting on a center shaft. Stock rocker arms have an output to input ratio of 1.1:1 but they can commonly be bought in the ratios 1.25:1, 1.4:1 for more valve lift without having to change the cam. Before using the high ratio rockers, check with your cams manufacturer to see if those rockers will work well with the cam.

Rod Bearing
A thin metal wear surface that is placed between the crankshaft and the large end of the connecting rods. These are made of softer metals than the crank or rods and will endure most of the wear and abuse from normal use. A “sacrificial layer” so to speak.

This refers to the engine assembly that is contained INSIDE & INCLUDING the engine case. This assembly contains all the parts for the bottom-end of the motor (ie: case, crankshaft, rods, cam, lifters, distributor drive pinion, etc.)

Single Port
The early style of head which has only ONE EXTERNAL intake hole (or port) which splits off into two separate ports internally to each intake valve.

This is the large, concave washer that is fitted onto the rear of the crankshaft. It’s installed with the center angled forward. The slinger helps keep the oil from spitting out from around the crank pulley since it’s un-sealed. If you have a problem with oil spewing out from around the crank pulley, you may have a slinger installed backwards.

Super-Differential (“Super-Diff”)
This is a heavy duty version of the part that the ring gear mounts to in the transmission. The main difference between a “super-diff” and a stock differential is the addition of 2 extra spider gears (for a total of 4). This provides a much stronger differential and less chance of breaking when the clutch gets dumped at high RPMs.

The German OEM manufacturer for ALL air-cooled VW carburetors.

Spark Plug
The part that threads into the top of the head and arch’s a spark when energized by the ignition system. This spark causes the fuel/air mixture to explode and push the piston down.

Spark Plug Wires
Special high-tension wires that deliver the pulse of high energy from the ignition system to the spark plugs.

Spot Face
A machining process which ensures that the surfaces of a series of like bores are all equal in depth. This is often done to the case cylinder bores to ensure they are all the same level in relation to the center line of the crank. This will help ensure you have the same DH on all cylinders. This can also be done to any surface on which a nut and washer is places. This will ensure the surface is flat and smooth for consistent torquing.

Straight Cut Gears
Gears that have the teeth straight across the surface. This type of gear only engages a couple teeth at a time and is much louder than a helical gear. There is no side load placed on a straight-cut gear. This is a common replacement for the cam gears since it eliminates the side-load (thrust) placed on the cam and gives a more precise cam timing. Straight cut cam gears are loud but sound kind of “mean” on the right car but will probably be too loud for a daily driver.

The stock excuse for an oil filter. Goes between the sump plate and the pick-up tube and helps reduce the large chunks from getting sucked up into the oil pump. If you run a true FF oil filtering system, you can toss this thing out.

Stud Set
Refers to the long studs which thread into the case/case-savers on which your cylinders and heads are mounted and torqued. There is 2 basic types; a SP set and a DP set. These available in the early 10mm variety and the later 8mm variety. The 8mm is actually better since they are able to expand at the same rate as the engine parts resulting in consistent head torques. The 10mm type are more prone to pulling the threads out of the case since they do not expand as well and torque increased as the engine warms.

The amount that the crankshaft moves the pistons within their bores from the bottom to the top. 69mm is stock for all 1500/1600 bases engines.

Refers to a crankshaft which gives the pistons a longer stroke within the bores. A longer stroke gives the piston more leverage in which to turn the crank resulting in more power. A longer stroke also increases the engine’s displacement. A stock crankshaft can have the stroke increased by welding beads on the outer ends of the rod journals and then regrinding the journals further out from the crankshaft centerline (hence the name “welded stroker”). A crankshaft can also be forged or cast and then ground as a new stroker crank.

The bottom of the engine case where the oil pools and gets sucked up into the oil pump. Some will add “deep sumps” to the bottom of the engine to increase oil capacity for hard driving that way the oil won’t slosh away from the pick-up tube and there is always sufficient oil ready.

Swivel Ball Adjusters
These are an aftermarket style of valve adjuster that have a ball bearing with a machined flat spot on it which give a more consistent valve gap and will not mushroom the valve stems over time. These are often times in-correctly referred to as “swivel feet” adjusters.

Swivel Feet Adjusters (“Elephant Feet Adjusters”)
These are the Porsche 911 style of valve adjusters which have a large foot on the bottom which swivels. These work similar to the swivel ball adjusters but have an even wider contact area for the valve stem and are the best you can buy as far as valve adjusters are concerned.

Tachometer (“Tach”)
An electronic gauge which measures engine speed in revolutions per minute (RPM). It gets it’s signal from the engine off of the NEGATIVE (“1” or “-“) side of the coil.

This mark on ALL crank pulleys refers to the compression stroke of the #1 & #3 pistons. Set it to the seam in your case, then pull off the distributor cap and note which plug wire it’s pointing to. That’s the piston ready to fire.

Teflon Buttons
Round little parts made from Teflon which are used to replace the wrist pin clips. These are cheap insurance against a wristpin clip coming unseated and ruining your cylinders.

Refers to the parts of the engine from the pistons and cylinders out to the valve covers and everything in between.

Top-End Rebuild
Refers to replacing or freshening-up of the piston/cylinders/rings and the heads. It’s an easy way to bring a tired, smoking motor back to life again. However, if your engine has low oil pressure, it will do NOTHING to correct that. ONLY a total rebuild will correct a low oil pressure problem. I personally do not recommend doing these. since the bottom-end is usually just as tired as the top.

Throw Out Bearing
The bearing assembly which engages the pressure plate when you put your foot on the clutch pedal. When worn out, they will begin to “growl” or “whine” when the clutch pedal is pressed. These should be changed whenever the clutch and pressure plate are replaced

Refers to the side load placed on bearing surfaces or gear assemblies while the engine/transmission is running.

Thrust Bearing
Special bearings which have wear surfaces on the sides of them which wrap around a bearing saddle. The front main bearing and 1/2 if the rear cam bearing are this type.

Thrust Cut
A machining process which trues the thrust bearing surface for the forward main bearing in the case. Over time as the clutch pedal is pressed the case gets a groove pounded in causing the thrust bearing to move slightly in and out reducing oil pressure. Whenever this process is done on a case, over-size thrust bearings are required so a tight fit is restored.

Trunk (“Boot”)
The front storage area in any REAL car.

A vacuum operated tool which gives a visual indication of the amount of air being sucked unto a carburetor. This type of tool is required to proper synchronize dual carbs. This ONLY measures the amount of air being ingested; NOT FUEL.

V – Z

Valve, Exhaust
The part of the engine which opens in the head and allows the exhaust gasses to escape into the exhaust system. These are the smaller of the two valves in a combustion chamber.

Valve, Intake
The part of the engine which opens in the head and allows the intake fuel/air mixture to enter the combustion chamber. These are the larger of the two valves in a combustion chamber.

Valve Seat
These are steel rings which are pressed into the heads. This is the sealing surface on which the valve rests when it is in the closed position

Valve Spring
A steel coil which provides the tension required to seal the valve against the seat. It also ensures that the valve stays closed until the cam moves the lifter, PR and rocker causing it to compress.

A popular brand of Italian performance carburetor. Weber makes good quality dual 2 barrel carb sets (IDF) available in 36mm, 40mm, 44mm & 48mm sizes. Weber also made the infamous racing carb 48mm IDA. Additionally, Weber makes a dual 1 barrel carb set (ICT) in 34mm.

Windage Tray
This is a specially made sheet metal piece which is placed into the sump area of an engine upon assembly. It allows oil to drain down, but controls the sloshing during hard cornering and fast acceleration/deceleration so that the oil pick-up tube doesn’t suck air momentarily.

Wrist Pin
A cylindrical, thick metal tube which connects the small end of the connecting rod to the piston assembly.

Original location:
This page originally came from and was called How to speak “Air-Cooled-eze”; Nate’s Glossary Of Air-Cooled VW Terms

This web page was posted at the link above but the website is no longer online and I was unable to track the owner down. I felt this web page was too good to disappear.

Learn more about my Revival project, any questions let me know.