KimvdLinde

When I pulled the head of my 1990 Civic 1.5L engine, I realized why most of the timing belt accidents do not result in bend valves despite being a interference engine. The pistons have cups to accommodate the valves when they interfere:

pimpwagon

That's not why they don't break. The lower the engine speed when the belt fails will likely result in little/no damage. Also valve adjustment plays a role. If your valves are way out of adjustment on the loose side, you not have less lift from your cam resulting in the valves opening less.

KimvdLinde

Sure, that all plays a role as well, but the depressions in the piston do help because the valves have more space when the pistons come up and the valves are in the way.

sstupid

That would mean it was a "clearance-engine." Had anyone bent valves on a D-series due to the belt breaking? I know I haven't, and I've had two break over the past 20 years.

Vcc02

i haven't

pimpwagon

It is an interference engine. If you don't bend valves when the timing belt breaks, you got lucky.

949

usually when the belt breaks the engine and the valves stop relatively right where the belt broke. so it doesnt get a chance to do a large enough rotation to have anything hit. youll notice when you spin the bottom and leave the top, it takes a bit more then a small turn for it to hit the valves.

bbarbulo

most engines have valve reliefs on the pistons. we are lucky for the following reasons: light weight rotating assembly - light crank, light flywheel means engine stops rotating sooner if the belt lets go. ... in addition to what the others said.

i think it's considered interference if it has a theoretical chance to bend valves (ie. at redline and the tightest tolerances on lash, and the cam stops exactly at full lift and the engine makes a full cycle of rotations - i think two crank rotations = one cam rotation? IIRC). it doesn't mean it'll do it every time.

Deetz

I've been wondering if it was an interference engine myself, but question it. A about 15 years ago, when i drove stupid at times, i was blasting down the hiway going pretty much close to being all out at about 110mph, then.....lost all power, yup, my timing belt went at 5500-6000rpm. I got the car back to the dealer, we popped a new belt on, and fixed!!!

pimpwagon

I did a little research and it seems half of the B2's bend valves and half don't. It really is luck. If the head was ever cut, it would be a guaranteed mess. If you had a 1990 volvo 740 like I used to (God I miss that car), It would be impossible to bend valves.