Ok, this may be a dumb question, but I was talking to a guy today that has grown up around cars and spent a lifetime working on them. He's built numerous racecars, rebuilt engines, etc.

He stated that if the belt breaks, there should be no damage. The belt is driven around the gears at the end of the two camshafts. If the belt breaks, the engine shuts off. Now I know it's been said that "if the valves are in the down position, there's not enough clearance and the piston will hit." Ok, isn't a crankshaft pretty much rotating in a stationary position? Do the pistons move any higher than they normally would if the belt wasn't broken? I don't see where the belt is "holding" anything in place from moving up and smacking a valves. The belt is simply wrapped around the cams to the crank to keep the valves in time. The camshafts do not move up and down either. Is it because the car gets "off time" from the belt breaking and the piston comes up at the same time the valves are down? Even so, when the belt breaks, the car shuts off, so is there that much time for the piston to rotate upward when the valves get off time and are in the down position?

I may sound totally stupid, but when he told me this, it made sense. Could someone clarify this for me?

Oh yeah, when I broke my t-belt on my 88 Civic, guess what--no valve damage then either.

 

Nevermind. I did some additional reading and figured it out. I guess the engine is still turning a small bit before it stops whereas the camshaft stops immediately when the belt breaks, thus making the piston hit any valves that are down.

I guess this guy has worked on mostly Ford and Chevy blocks as a racecar builder so he's probably not as familiar with imports.

I feel dumb now. I thought there was potential to do damage.

 

There is potential for damage-

 

From my experiences a broken timing belt or chain = messed up motor about half the time. The cam(s) will stop pretty quick when breakage occurs, but the pistons and crank have more rotating mass so they want to keep moving. Any valves that are open, or being pushed down into the cylinder by the cam, can get a little to cozy with the piston. Here is something to think about, slow cruise = 2,000 rpm acceloration can see 3,500+ depending on how heavy tour foot is.
2,000rpm = 33.3 complete revolutions a second. I dont know about everyone else but I think that's pretty quick!

 

Its called a Zero Tolerance/Clearance engine
When/If the belt breaks- some valves will be open and the piston will contact for sure
The engine may keep running as the belt shreds before breaking- some drivers may even try to rev the engine to see whats making that bad noise!!!!!....

Seen it happen on other hondas will same engine design- massive destruction is a pretty good description of the results- replace engine is usually the best repair option
Sure there is margin in time-miles change at 105, but if you run it hard or live in hot places- early wont hurt- read the book

 

I wouldn't let that guy work on your car.

TONS of engines are interference engines, where when that belt breaks, usually pistons bottom out.