Timing chain fundamentals

[allegoric1]

I understand when certain timing chains break its not a big deal on some cars and on others it becomes a major repair because it damages other parts of the engine, what is the Camry design and what is the fundamental engine design/layout that makes this difference, probably many people are curious about this too.

[Jimnist]

First of all, the Camry's don't run a timing chain, it's a timing belt

Secondly, i'm pretty sure we have a non-interference engine. So if in the event the timing belt breaks, the piston won't smash up against a valve if it was left open. But, you will loose all power from the engine as well as power assist steering if you have power steering. Luckily, there is a vacuum reservoir so you will still have vacuum assist braking, but it will be limited.

[djb2]

Usually the issue is around timing belts. Timing chains can break, but usually they stretch with wear. A worn-out chain makes enough noise and guide wear from slapping that it's replaced before it breaks.

The Camry has a non-interference engine -- the valves won't crash into the still-moving pistons when the belt breaks. Other engines have the valves and piston "interfere", moving in the same space. They count on the timing belt to make certain that the valves are closed, or at least not fully open, when the piston is at the top of its travel. A broken belt will destroy any open valves, perhaps crack the head and valve train, and sometimes even puncture the pistons.

Why design an interference engine? Because it allows higher performance through higher compression and greater valve lift. The valves can also be angled for better flow, or to fit three or four valves per cylinder.

[toyomoho]

Things changed with the 02 4-cyl and 07ish V6 to a timing chain and VVti. There engines are interferance.

[Jimnist]

Originally Posted by toyomoho

Things changed with the 02 4-cyl and 07ish V6 to a timing chain and VVti. There engines are interferance.

Yes, the 1mz-fe in the 98-04 avalons are interference. So are the 99-03 Camry Solara with the 1mz again and the 04 Camry solara 3mz-fe. These are all the v6's though. AFAIK, none of the i4 Camrys were interference up to 04. I don't know beyond those years XD

[allegoric1]

Great answers, thank you, but what is the basic design difference so if someone asks you about a particular make you can figure in your head if it is a interference design or not?

[Mike Gerber]

You can use the following website to determine what the recommended change interval is for just about any car's timing belt and also if the engine in that car is an interference fit engine:

http://www.gates.com/downloads/downl...older=brochure

Mike

[djb2]

There isn't any rule of thumb, except that higher performance engines usually are interference engines. Engines with more than two valves per cylinder have the valves enter at an off-axis angle and thus are much more likely to interfere.

Pistons with recesses can avoid slight interference, at the cost of being heavier, harder to make and having a less efficient combustion chamber. Often the recesses are shallower than needed to avoid interference, and are intended to allow higher valve lift and thus better breathing.