Weak Timing Chain Doesn’t Make a Squeak

Question: When I took my 1985 Toyota Celica to the dealer to have a cold start problem fixed, the mechanic told me the squeaking noise coming from the engine was a signal that the timing chain was about to break. My car has 84,000 miles on it and I intend to keep it for a while. What are the indications of a bad timing chain? What are the implications if the chain actually breaks?--K.W.

Answer: The engine in your 1985 Toyota was actually a modified truck engine, the last of its type used by Toyota in its passenger cars. It does have a timing chain, as opposed to a rubber timing belt, to operate the camshaft and engine valves.

Timing chains generally have the reputation of being more durable than rubber timing belts, which have to be changed as often as every 60,000 miles, depending on the model.

The chain runs between two sprockets, one on the crankshaft and one on the camshaft. It’s a very short chain, only several inches between sprockets, but it operates at very high speeds and high loads. So, it is important that it have the correct tension and that the sprocket teeth not be worn.

When a timing chain wears out, it doesn’t squeak. It makes a rattling noise, sounding something like a towing chain being dragged across a bumper. But the noise only occurs for a few seconds during start up. If your noise differs, it is probably something else.

The implications of a broken chain, however, are quite serious. Once the belt breaks, the camshaft would stop and the engine valves would also stop. Some valves would be in the closed position and some would be in the open position. For a few seconds the pistons would continue to move up and down inside the cylinders. Inevitably, a piston would hit the open valve, because the whole engine would be out of its proper synchronization.

At the very least, the piston would bend the valve, requiring you to have the engine head pulled off and rebuilt. Worse yet, the piston could be damaged, requiring the entire engine be torn down and rebuilt. That would certainly cost more than the truck is worth.

In later Toyotas with a rubber timing belt, the pistons were designed so that even if a belt breaks, the piston will not hit the engine valve. Toyota is one of the few auto manufacturers to use this design.

So, even though the squeak does not seem like a timing chain problem, you should have it inspected. An inspection should not cost a great deal and it would give you some peace of mind. If the chain is ready to break, a repair will cost several hundred dollars but far less than the cost of a damaged engine.

Q: I have a 1985 Honda Accord with 80,000 miles on it. It’s in great shape, but I confused about oils. My first dealer used a 5W-30 oil, which seemed to work fine. A second dealer then went to a 10W-30, which was also OK. But a BMW mechanic now wants to use 20W-50. What weight of oil would you suggest?--C.H.B

A: In 1988, Honda began recommending 5W-30 across the board in all of its cars. But the car maker originally recommended a 10W-30 in its earlier cars. You can go with either a 5W-30 or a 10W-30 motor oil, but it is not advisable to go up to a 20W-30. The heavier weight oil is simply too heavy for any modern engine and will cause higher wear at start up and may reduce your gasoline economy.