Interference engines / timing belt

Going back in time, lets say 2 decades, maybe a little longer all engine valve timing was done with timing chains or gears, and non interference engines. I don’t know if any of the big 3 might still use a timing chain. Even on diesel engine I am not aware of interference engines and a timing belt.

If you broke a chain, the engine shuts down with out destroying the engine. For some reason I don’t understand, auto companies have decided to build ‘interference engines’ with a timing belt that if the belt breaks the engine suffers serious damage or destruction.

What is the advantage of a interference engine and timing belt ?

THANKS
ENOK

 

Higher Compression ratios? Better combustion? Going back several decades, cars had a small timing chain from crank to cam sprocket. No OHCs then. “Big three” used pushrods for a long time in most vehicles.

 

Ok, but I must be missing something. My 1970 Corvette Was a LT-1. The engine was
a 350 cu in/375 hp, 11:1 compression ratio and of course push rods. It was a animal on tires. Why change a proven design concept to a interference engine. Are interference engines cheaper to build ?

 

And that car was lucky to get 15mpg at 3500# and needed rebuilding every 75-100k miles. Emissions too. Mainly emissions.

 

IIRC my daughters Escape had a timing belt bathed in oil

 

They cant sell you a new truck if the old one wont break. Same reason they have 0 wt oil, turbos, and 10k mile oil changes now.

 

The 3.0 V6 had bad timing chain guides. I think they were some kind of plastic. They would wear out prematurely. The engine wasn't bad overall though, just terribly underpowered for a V6. That's the only reason I can think of as to why Toyota started using timing belts on the 3.4 and 4.7's. Planned obsolescence probably.

 

Thanks all for your replies. Mr Bee may be speaking more fact than fiction ????
Enok

 

I doubt it

 

It's all about technology and obtaining more power and usable power from a motor.

Pushrod motors are good. Ford still makes one with teh 7.3l. OHC motors are known for being higher revving. At least early on, before variable valve timing. You can't have separate intake and exhaust variable valve timing on a pushrod motor.

Also, not all timing belt motors are interference. Belts are quieter but result in maintenance. Chains should last much longer but require quite a bit of work should they need replacing.

 

Interesting, thank you. Wonder why Ford still uses push rods on the 7.3L, I would guess
it also has a timing chain, not belt?
Enok

 

Some advantages of pushrod motors? Mainly packaging. Much smaller by displacement than a SOHC or DOHC engine. Also simpler design should equal better reliability, but that's more in the engineering than the design.

Oh, and cost. Let's not forget the most important one.

 

Exactly. If you've seen a Coyote DOHC 5.0 motor next to an LS 5.7, the heads on the Coyote are huge, much more difficult to package with a lot more going on.

 

Too much freedom with ICE. They want to control how much you can charge your car, and shut it down if you dont fall in line.