Interference Engines ?

Bob wrote in news:i7jb1k$i2l$ snipped-for-privacy@news.eternal-september.org:

A quick Google reveals...

In a nutshell, pistons and valves like to dance by themselves. If one steps on the other's toes, expensive chaos ensues.

Some manufacturers design the valves and pistons to have their own private dance floor. Honda makes those parts /share/ the dance floor (or at least parts of it), meaning that something has to tell the first dancer when to leave so the second may perform without interfering with the first. That's the job of the timing chain or belt.

Why does Honda do this? Apparently the engine works better when the valves and pistons share a dance floor.

Check this as well.

Erik wrote in news: snipped-for-privacy@news.dslextreme.com:

or simply put,if the timing belt breaks,the valve train stops turning,and valves may be left in a position where a piston can strike a valve,damaging both the valve and piston.

making a very expensive repair.

Thus spake Tegger :

news:i7jb1k$i2l$ snipped-for-privacy@news.eternal-september.org:

And they do this dance twice per cycle.

If the intake cycle starts to open while the exhaust valve is still open (with electronic port injectors helping out) fresh air improves the exhaust.

Some of the high, high end makes have experimented with electronic or pnuematic "cams" to improve this depending on piston speed. Think F1. Think a team that quit at the end of last year.

If it were an 11 to 1 race car, I could understand this concept, but not a street car.

In fact, many of the high compression pistions I've seen are sculpted. To accomadate the valves, that usually have much higher and longer lift.

Thus spake Jim Yanik :

Yeah, our 84 Escort GT did this with a little over 3000 miles on it. It took almost a year and calls from our lawyer to Ford's general counsle to get paid for the repair, the tow, the legal fees and "general inconvenice". We wanted a recall, they insisted on a TSB. And we got an agreement on no NDA after 6 yeas.

news:i7jb1k$i2l$ snipped-for-privacy@news.eternal-september.org:

that's called "overlapping" valve timing, and it's been used on overhead cam car engines since about 1923. it's got nothing to do with "fresh air" in the exhaust but everything to do with scavenging the contents of the cylinder and improving volumetric efficiency.

not exactly. all variable valve timing systems are mechanical with electronic control. "piston speed" is also grabbing the wrong end of the stick - it's all about the overlap needed to scavenge successfully.

no, think honda v-tec. think toyota, think bmw, think fiat, etc. the pneumatic systems used in f1 are simply reverberation-free valve return springs and have nothing to do with variable valve timing - something f1 typically doesn't bother with since the engine is used in a narrow rev range where variable valve timing is irrelevant.

that's because of the valve's lift and duration. variable valve timing has nothing to do with it.