Jim Grant's Tech Tips
'88 Ford F250, Clanking Sound
Q: I have a question on my 88 Ford F250 which has a 4.9 EFI six cylinder engine. It and makes a clanking noise near the front of the engine. At first the noise was there on cold start up and lasted about 30 seconds, but over the past few years it now makes the noise every time the compressor cycles, or a load is put on the engine. I've been told by one repair tech that it was piston slap and another that it was timing gears. When I removed the belt for testing, the noise was very faint but still there, my question is how or what is the best method to check these two things out. It's not a noise that has the same pattern all the time and it's a clack or clanking noise.
- Randy W.
A: If the information youre providing is accurate, I would rule out piston slap or loose timing gears. Why is that? Neither component cares or knows about the accessories driven by the fan belt. Because removing the fan belt made a change, I would suggest looking closely at the harmonic balancer/crankshaft pulley. A harmonic balancer is a 2-piece component, separated but bonded together with a rubber spacer. The harmonic part of the balancer deadens vibrations from the crankshaft. The balancer part is weighted to balance out the uneven weight of the crankshaft as it spins. You can look at it as weights that are used when balancing tires; it is necessary for any object that spins. When you inspect the harmonic balancer, be sure the rubber spacer is not failing. If the rubber spacer is failing, replacement is needed. Check for metal filings or signs of movement from the bolt that holds the harmonic balancer to the engine. If the bolt is loose or signs of movement can be seen, the harmonic balancer must be removed for inspection. Here is where it gets scary! If the harmonic balancer has been loose for too long it is possible that the crankshaft has been damaged. In addition, there is a key-way on the crankshaft that references the harmonic balancer to the crankshaft. This key-way can break, allowing the balance to move. A harmonic balancer that is loose or failing in some way is very sensitive to load from the fan belt. Things like A/C, alternator or power steering can really make the harmonic balancer speak up. Have the harmonic balancer inspected as soon as you can.