Why interference engines?

No one seems to make non-interference engines for cars anymore. Why?

I don’t understand. What kind of interference?

Shoot me if I’m wrong but I understand that Honda still do.

Actually, I thought most Hondas had interference engines. It also seems to be somewhat corelated with the presence of Variable Valve Timing - Engines with VVT were usually interference.

I was having a conversation with a BMW mechanic just last week with regard to this. He had managed to get the timing belt on one one cog out and smashed all the exhaust valves when he started it.

He also told me about being faced with a Honda Accord with a snapped belt and expected the same problems or worse but the guy in charge told him just to change the belt and set up the timing as there would be no damage. There wasn’t.

For years Honda had only interference engines and DIDN"T have a suggested belt change interval for their rubber timing belts. :rolleyes: Many a Honda owner in the 1980s found out the hard way about the design of their engine.
Higher compression ratios, multiple valve engine, variable valve timing all make interference engines easier to design would be my guess.

A little googling reveals that the Honda F-series V6 used in older Accords was probably non-interference, but it seems to be the exception.

It seems to me that one can make a non-interference engine by having cut-outs on the piston to accommodate the valves - I believe the legendary Toyota 4A-series engines used this arrangement, and those suckers revved to the moon.

On an interference engine, the the valves and the pistons occupy the same space, at different times of course. If the timing belt breaks and everything goes haywire, they can hit each other and damage the valves. On a non interference engine, if the piston is at top dead center AND the valves are pushed all the way down, they still can not touch, so a timing belt mishap doesn’t do as much damage.

I’ve always heard that if you have an interference engine, you should change the timing belt at 100,000 miles. I have no idea if this is true or not though. Rick, what’s the service interval on them now? I have a 2006 Civic, which I may drive into the ground if I can’t get my milage penalty waved at the end of the lease. Does a 06 Civic have an interference engine?

It seems that with a few exceptions, most Honda engines are of the interference type, and unless you enjoy being stranded on the side of the road, it would be advisable to replace the belts (or chains, I believe both the R and K series engines on the newer Honda Civic use chains) before they break, regardless.

If you don’t want to be stuck on the side of the road, changing them before they break would be advisiable for both interference and non interference engines, it’s just that on an interference engine you’ll do alot more damage if it breaks. But ANY car, regardless of engine, if the timing belt breaks, the car ain’t moving anymore.*
*This is one of those blanket statements that Gary or Rick are gonna come up with a counter example to, isn’t it.
C’mon, there’s an engine out there that can run with a broken timing belt, right?

My '72 Chevy LUV could!

(I could crank it while it was in gear - in low gear, it would move pretty good with just the starter.)

Wankel Rotary Engines (hah!) have no valve trains at all, so no timing belts/chains to worry about. Maybe you should have bought a RX-7?

Are there any pushrod engines where the camshaft is directly actuated with gears? Wikipedia says there might be, but I doubt any are used in production cars.

Ah. Thank you. I thought this was going to be about radiated electrical interference.

Older BMW motorcycles, as well as derived russian bikes are examples I have worked on.

Belt change intervals Read the manual. I know of some engines that required changes at as little as 30,000 miles. I know of other that go to 150,000 miles. Lots of engines get belts at between 60,000-100,00 miles. I would be hesitant to make a blanket statement of 100K. If your car calls for it at 75 and you try to stretch it to 100 you are really taking a chance. So read the manual.
Gears / Chains vs belts Yes both gears and chains have been used in addition to rubber belts. Both are more expensive and are louder when the engine is running. (Gear drive cams on American V8 hot rods emit a very loud, very noticeable whine. As in I can hear some of them a block away.). While they can break both chains and gears are considered a life of the engine installation. On some old Toyota engines the chain would stretch so much it would slap against the front cover and needed to be replaced at about 100,000-125,000 miles (20R-22R engines) Failure to do so would cause the chain to stretch to the point it would fall off the crank pulley. Factory gear drive motors include old Volvo inline 4 cylinder engines that used a fiber gear for noise reduction, that would require replacement every so often due to wear. Also air cooled VW engines, and some Chryslers and Fords IIRC. If I’m wrong about the Chryslers I am sure Tuckerfan will be by shortly to correct me.

ETA: Joey P no argument from me. The technical term for a busted t-belt is that the car owner is now in Reebok mode. As in he is walking home.

I’m not sure if you looked at the same article that I did, but it says “The OHC system can be driven using the same methods as an I-Head system, these methods may include using a timing belt, chain, or in less common cases, gears” in the article on overhead camshaft.

My Civic is at 32,000. I’ll check the manual. In fact I’m about to run to the post office (I do have to go, but it’ll get me out of work (yeah, like I’m really working here) for a few minutes). I’ll check the manual when I get back.

When Honda first started recommending belt changes it was at 60K IIRC. I’m fairly sure it has probably gone up since then.
but it never hurts to check.

Some Hybrids will run w/out the timing belt.

When changing the timing belt (I lean for 75,000 miles) I also change the water pump.

Maintenance intervals are different for most cars, so the proper answer is to check the manual and then do it earlier if that makes you sleep at night.

I couldn’t find it in the manual. It did say to inspect the “drive belt” at what I think is 15,000 mile intervals, is a drive belt the same as a timing belt?
I’ll have to ask the service writer next time I have my oil changed.