interference vs non-interference engines
 

How does Toyota offer non-interference engines and seemingly no other manufacturer does? Contemporary Toyota 4-bangers don't even have a timing belt service interval for normal duty. I think it's 90K miles for severe duty, whatever that is for a timing belt. So you putter along, the engine quits, the car is towed to any shop, $300 later you're on your way with a new belt. Same thing you'd pay to have it replaced before it snaps. If the belt snaps on any other car you're out a cylinder head and possibly an engine.

It's only geometry - why hasn't this caught on throughout the industry? Does Toyota have a patent?

Sixto
87 300D

hmmm. I think they want to motor to be trashed so you can buy a new one or buy a replacement engine at mucho markup.

don't know. but i love the A series engine in my Tercel. I've never had the belt break. because i change it like every 3-5 years. but before i got the car my mom had one break on her. we towed it home and my dad changed it. very easy.

takes me about an hour to change the belt if i have to remove the radiator, 30 min if i don't have to remove it. the engine it the tercel is not transversely mounted, so it all depends on what puller i have for the harmonic balancer. my dad made one that i now have that is just the right size to take off the balancer without taking out the radiator.

Volvo's are the same way.

Not *all* of them. Some of the turbo motors aren't.

But my old VW Rabbit was non-interference, and my Miata is non-interference as well. Both of those have been tested. ;)

I had a Dodge Omni some years back. Surprisingly fast and fun to drive. I guess 2.2 liter is halfway big for a car that small.

Anyway, I busted a belt and came out smelling like a rose. Good thing too, cuz that car would have been instant junk with an interference engine.

Lately Toyota has been using chains. Don't know when they went that way but I do know the 07 and newer are all chains.

That confirms the replacement engine theory :)

Sixto
87 300D

Well a chain shouldn't break or ever need replacing. So when the car gets old junk it, its just a cheap Toyota.:D

My is300(toyota altezza) has an interferance engine. Timing belt was fairly easy to replace though, much much much easier than on my audi a4 2.8 thats for damn sure....

pretty sure the rabbits not.

I have a piston with some nice valves marks in it here...

My VW air-cooled motor was even better! The horizontally-opposed configuration used two large gears for the cams and crank...no chain, no belts, no anything!

Just tweak the carb every other week, adjust valves every other month, and finally a weekend overhaul at 80K...including the replacement of that burnt third piston... :(

To answer the OP - my impression is that any manuf. can build a non-interference engine...up until recently.
Obviously, if toyota did it, then its not an engineering impossibility, I figured that its more a design/cost thing than than anything else. The Toyota engineers were told to design an engine that is non-interference. The designers of the Altezza motors were not.

I get the impression that you give up a few things in a non-interference engine. First off would be a 4v/cyl valvetrain - to stuff all those valves in you must put them at an angle, and then open them as far as you can (to optimize breathing) and unless you give up a stack of compression ratio (ie- make the combustion chamber really big or the stroke really small) the valves will hit the piston when fully open at TDC. I'd be curious if any of these non-interference motors are 4v per cylinder.
I mentioned valve lift - no matter how many valves you have, or what your bore x stroke is, the farther you open your valves (to a point) the better the engine breathes, which means more power, better fuel economy, or some combination of both. Engine makers are always looking for these and probably have no problem opening a valve so far that an otherwise non-interference motor becomes an interference motor when you 'tune' it so far.

I say "up until recently" because the bar has been raised so high for engines as of late, that its probably tough to build an engine efficient enough for modern power/emissions standards that is not non-interference. Okay, Toyota can do it for bread-and-butter 4cyls, can they do it for 300hp truck V8's ? (I don't know)
From what I remember - back in 1990, the 2.0l 16v VW 4cyl made 130hp- it got 30mpg if you didnt beat it too hard. My wives 1997 neon had a 2.0l 4cyl, 16v, better emissions (OBDII), made 130hp and got 36mpg with an automatic transmission. This isnt a good apples to apples comparison, but I think we can agree that engines have come a long way in the last 5 or 10 years, and if someone tried to stuff that 16v 2.0l vw motor in a car today, it'd never sell. (not that I don't love old VW 16v's....)

As to the maintenance requirements - I don't think that manufacturers care as long as the engine will make it to 100k (the req'd US emissions warranty) with no trouble. After 100k, the manufacturer gains nothing from having a long lasting-chain vs. a belt that needs replacing.


-John

I've heard that Toyota's 16-valve fours ARE interference engies. In any case, Toyota (like most other Aisian makes) have used 4 valves-per-cylinder on their fours since the late '80s. However, the Corolla (and Chevy Prisim) switched to timing-chains for '98, and the 4-cylinder Camry (as well as the 4-cylinder Honda Accord) switched for '02.

Happy Motoring, Mark

Even though its been quite awhile I'm pretty sure my old 93 Camry was an interference engine. I think when I changed the T belt I spun the cam around to see.:D

I thought I read once about a rotary valve setup, sorta like a ball valve -- I can see there'd be problems there but sure seems like you could have a bigger opening w/o interference and virtually no loss of compression from a big cavity.

http://upload.wikimedia.org/wikipedi..._desmo_8x6.jpg

Mercedes used those for a bit in the 1930's as well.

If you want to build a 10k+ rpm valve train, get rid of the spring. Don't let it jump time though...

I think the more preformance you force out of an engine, the closer the valves are to the pistons.

You forgot about piston design. most have a cutout for valve clearance

My 2000 Toyota Tundra (4.7L V8) was a VVT-i engine and was an interference engine. On the other hand, the same year the 3.4L V6 they put in the Tundras as the base engine was not.

In comparison, my 1991 Lexus LS400 (4.0L V8) has a non-interference engine. Strange that Toyotas FIRST V8 engine was a non-interference one, but that changed in 1998, when the Lexus switched to a VVT-i engine and it became an interference one. Still mixed thoughts on to whether the 95-97 LS400 is interference or not.

The Ducati setup look to be what's refered to as a babbit ear setup. As mentioned Mercedes used it in the 30's, I think. Also OSCA, formed by the Maserati brothers, used it in the late 50's early 60's. I think the other poster is refering to a new setup, thats still being patend.
There are also cam less engines. Ford research these in the 60's. Renault used a camless engine in F1, during the late 80's early 90's. It was pneumatic powered. They were 2000 RPM above Honda and Ferrari's redline at the time. CAT and Cummins and some developement engines that were camless and I think BMW too. I am thinking with the cost of Piezo electronics, this might be a possiblity. Also, any friction or drag in an engine is becoming a concern. It effects MPG.
Briggs & Stratton had some rotary valve engines on there were some for model airplane engines, HP and Austrian company I think.
I've had two cars break their timing belts. One was a 78 Honda Civic. Non-interference. I just put on a new belt, that was fairly easy. The other was a '96 Ford Contour. The first belt went for 126K, when it was changed. The belt that broke went about 45K. The 2.0L Zetec is listed as an interference motor. I was doing about 20 to 30 mph and slowing down to turn, when it broke. I replaced the belt and the motor had a slight tick. I did check the valves by turn the motor over to see if any stuck. They seemed OK. The motor is running OK at a bit over 200K.
Tom

Several years ago, I got to change the timing-belts, including the balance-shaft belt, on a friend's '90 Accord. The ordeal wasn't helped by having to rig a special fixture to hold the crank-pulley, as the Honda pulley bolt is installed with about 250 foot-pounds!

Having owned a few timing-belt vehicles myself, a timing-chain helped move a '98 Nissan Altima to the top of my shoppng list a few years ago, when it replaced my rusty, tired '84 Honda Accord. Plus the fact that used '90s Nissans are reliable, but tend to sell for much less than comparable Toyotas and Hondas. While my Altima isn't as refined, I was willing to trade some refinement for not having to perform an immediate timing-belt job on a used Camry or Accord.

Happy Motoring, Mark