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Marlin Sportster, Cabrio, Berlinetta and Roadster builds Enthused or Confused about your vintage Marlin build? Ask away here or show off your build.

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Old 14th May 2023, 22:19
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Patrick Patrick is offline
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Default BMW M20 Timing / Cam belt change

It’s been too long since changing the cam/timing belt on the M20. It’s nowhere near the mileage limit but it’s far too many years overdue. I ordered a new Contitech CT 520 belt and a new tensioner pulley.
I took a few things off to get proper access to the front of the engine – bonnet, side panels, nose cone and the radiator.

With good access, I removed the distributor cap, upper timing cover, alternator/water pump v belt, water pump pulley, vibration damper/lower pulley, alternator bracket and lower timing belt cover.

I set the engine on its timing marks ensuring both the crankshaft and cam shaft were positioned on the marks before proceeding.

Loosed the timing belt tensioner pushed the spring to full compression and re-tensioned the bolts. With the tension off the belt, it was possible to remove it. It’s a little tricky around the crankshaft as there is not a lot of space.

The old timing belt was in pretty good condition, seen below next to the new belt, but given the M20 is an interference engine I feel a lot better knowing it has a new belt.

The old tensioner bearing had a bit of a gritty feel, not too bad but the new one is very smooth again.

Installed the new pully, seen here with the spring under full compression and bolted down ready to install the new belt.

Here are all the bits taken off the engine, gave them all a good clean. Not too bad just little bit of dirt and greasy in there.

Put the new belt on, loosened the tensioner, and ensured the tensioner was using the spring push against the belt. Re-tightened the bolts so the tensioner could no longer move. Gave the engine two full rotations from the crank to make sure everything is running smoothly.

Reassembled everything else; lower timing belt, water pump pulley, vibration damper/lower pulley, alternator bracket, cover, alternator/water pump v belt, upper timing cover, distributor cap, wiring holders and that plastic cover that keeps dirt out of the timing belt area.

The last steps were to reinstall the radiator, after giving it a good flush, the nose cone, side panels and bonnet. Finally filled up with new coolant and bled the system after bringing it up to temperature.
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