Adjusting a camshaft timing belt

The tension of the toothed belt that drives an overhead camshaft must be checked at the intervals set by the servicing routine laid down in the car handbook. Check it also whenever you remove and refit the belt or the cylinder head.

Ford overhead-camshaft engine Alternator Belt tensioner Distributor pulley Crankshaft pulley Fan belt Fan Camshaft pulley Camshaftdrive belt

Ford overhead-camshaft engine

On a Ford overhead camshaft engine, the tension is set automatically when two bolts are slackened on the tensioner.

The belt tensioner is an adjustable plate carrying a jockey wheel or roller. If it is wrongly adjusted - whether too loose or too tight - it can cause noise and rapid wear.

Removing the drive-belt cover

Unscrew the belt-cover bolts.

On most engines, some parts have to be removed before you can take the cover off the toothed belt.

Slacken the alternator adjuster bolts and push the alternator towards the engine to loosen the fan belt or alternator drive belt; ease the belt off. When refitting, tension it correctly as detailed in Checking, adjusting and refitting drive belts.

On some cars, the crankshaft pulley has to be removed. Unscrew the retaining bolt.

Usually, the cover can be removed without taking off the crankshaft pulley. Sometimes, however, it has to be removed; to . release it, unscrew the pulley retaining bolt and prise the pulley off with a screwdriver.

Unscrew the belt-cover bolts and carefully ease the cover off. The tensioner wheel is below the camshaft pulley.

Adjusting the tension on a Ford belt

Pivot spring bolt Locking bolt

Slacken the pivot-spring bolt with a special splined tool fitted to a socket wrench.

The tension is set automatically by a spring when two bolts are slackened — a locking bolt and a pivot-spring bolt.

Slacken the locking bolt, on the left, first. To slacken the pivot-spring bolt you need a specially splined tool that fits into a socket-wrench handle; it can be bought at a Ford dealer's spares department or at most car accessory shops.

Give the crankshaft pulley two full clockwise turns to even out the tension in the belt. Make sure the ignition is switched off or the battery disconnected.

To even out the tension in the belt, use a spanner or socket wrench on the crankshaft-pulley bolt and turn the crankshaft two full turns clockwise.

Tighten the locking bolt first to hold the tensioner in its new position. Tighten the pivot-spring bolt, which has a precise torque setting.

Tighten the locking bolt, then use the splined tool in a torque wrench to tighten the pivot-spring bolt. It has to be tightened to a precise torque setting; check the figure with a dealer or the car service manual.

Refit the drive-belt cover and fan belt.

Adjusting the tension on a Leyland '0' series belt

Camshaftsprocket Camshaft timingbelt Belt tensioner Alternator Camshaftsprocket Water pumpintake hose

On Leyland 'O' series engines, the belt tension is measured with a spring balance and adjusted manually.

The belt tensioner has no automatic spring. To measure the tension, use a spring balance with its hook bent to an L shape to fit flat against the belt. (If necessary, use a separate L hook.) The spring balance must be capable of measuring at least 13 lb (6 kg).

Fit the hook to the belt midway between the camshaft and crankshaft sprockets, at the level of the water-pump intake-hose stub. Pull the spring balance until the edge of the belt is in line with a raised mark on the water-pump intake-hose stub.

The balance should read 11 lb (5 kg) for a used belt, 13 lb (6 kg) for new belt. If it does not, adjust the tension.

The tensioner is a roller which bears on the outside face of the belt. It has two adjustment bolts, one of them fitted over a slot. Slacken both bolts just enough to let you slide the tensioner.

Move the tensioner as necessary to tighten or loosen the belt. Lock it by tightening the bolt over the slot.

Re-check the tension and readjust if necessary. When it is correct, tighten both bolts and refit the timing-belt cover and fan belt.

Adjusting the tension on some VW, Vauxhall and similar belts

Fan Belt-tensioningassembly Crankshaft pulley Alternatorpulley Alternatordrive belt Camshaftsprocket

On some VW, vauxhall and similar engines, the belt tension is checked by twisting and the tensioner is adjusted manually.

The belt tensioner has no automatic spring. Check the tension by twisting the belt with your thumb and forefinger, midway along the longest straight run between the two main sprockets.

If the belt tension is correct, you should just be able to twist it through 90 degrees. If you can twist it more or less than this, the tension needs to be adjusted.

The belt tension is correct if you can just twist it through 90 degrees with thumb and forefinger.

Slacken the single nut in the slot of the tensioning assembly. Slide the tensioner clockwise to increase the tension, the other way to reduce it.

Tighten the tensioner nut and check the tension again. Readjust if necessary.

Slacken the nut and slide the tensioner assembly clockwise to increase tension.

On some VW cars, the belt tension is adjusted by slackening the water-pump securing bolts and levering the pump away from the cylinder block.

When the belt tension is correct, refit the timing-belt cover and alternator drive belt.

Tensioner on a water pump

On some old VW cars, the belt is tensioned round a sprocket on the water pump.

To adjust the tension, slacken the water-pump securing bolts and lever the water pump away from the cylinder block.

We also have this article in

The ultimate video course

We take this car to pieces and then build it again, explaining how every single part works.

By the time you finish watching this, you'll understand everything inside a car.

Watch us take a Mazda MX5 Miata to pieces, and then build it back together again into a modern working car.

  • Every part explained in detail.
  • We've created the most detailed 3D model ever produced so we can show you everything working.
  • Over 20 hours of footage — see the contents.
  • Preorder and download the How a Car Works PDF for free.
  • Support the video by preordering and we'll put your name in the credits.

This will be the most in-depth course on car mechanics ever produced. Pre-order your copy now and save 75%.

Preorder for $20
Normal price $80. Pre-release in July 2017.

Read more essential guides

Cylinder compression test

A good way to check engine wear is to test the compression of each cylinder using a compression ...

Stroboscopic timing

A static timing check with the engine stationary is never fully accurate. It does not allow for ...

Checking for oil leaks

If an engine needs topping up with fresh oil more than usual, or if you see a pool of oil...

How engine timing works

For an engine to work at its best, the fuel/air mixture in each cylinder must fire just as the...

How to remove an overhead camshaft

On some overhead camshaft (OHC) engines. the camshaft must be removed to take off the cylinder h...