# Fuck interference engines **URL:** \ **Category:** The BBQ Pit\ **Created:** [April 29, 2013, 10:07pm UTC](https://boards.straightdope.com/t/fuck-interference-engines/657050 "2013-04-29T22:07:34Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Inigo\_Montoya](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/inigo_montoya/32/124_2.png) [@Inigo\_Montoya](https://boards.straightdope.com/u/Inigo_Montoya)\ **Post date:** [April 29, 2013, 10:07pm UTC](https://boards.straightdope.com/t/fuck-interference-engines/657050/1 "2013-04-29T22:07:34Z")
Hey look, we knew the car was not mint–that’s why we only had to pay 20% of the book value for it. Head gasket was blown, water pump was bad, other predictable and involved maintenance–stuff gets old and fails, I get it. But the service docs said the timing belt only had 75k miles–still safe, but we’ll do it anyway when we address the other stuff next week. Unless… Pop! goes the timing belt. And just like that, I have 4 green monsters violating their little valves, saying, “Piston SMASH!” Really engine designer guys? Your little 4-banger only makes 105 hp when it’s fresh. You couldn’t put some divots in the piston tops, or maybe built just a little more clearance for the valves in the head? You just HAD to design self destruction into the engine, and trust to a little bit of rubber and nylon to prevent it? Who the fuck does that? None of my Toyotas ever did that, the Mitsubishi didn’t do that. My dog is smart enough to know what happens when you put two things into the same space at the same time, did you just miss that part of engineering school? So, $500 and a valve job later (German parts, whatareyagonnado?) I’m strapping the new head down and…ok, and I’ll take the blame for this one: I slipped a tooth when intalling the new timing belt which problem only manifested itself after attempting to start the car. A process which went something like: “chugchugchugchugwhirrrrrrrrrrrrrrrrrrrrrrrrrrrrr.” You know, it’s not the money involved with me getting the valves re-redone–that’s just the price of education & learning better install techniques. It’s the fucking principle of the thing, and the hours spent re-removing and re-reinstalling the head. Just because some sadistic assclown engine designer didn’t take The Real World into account. Sorry folks for limiting the vitrol–there are some things I need to keep in check. But I totally welcome yours. And knowing my luck with pit threads, the whole interference engine thing will somehow be my fault anyway. ---
**Author:** ![phouka](https://avatars.discourse-cdn.com/v4/letter/p/c5a1d2/32.png) [@phouka](https://boards.straightdope.com/u/phouka)\ **Post date:** [April 29, 2013, 10:23pm UTC](https://boards.straightdope.com/t/fuck-interference-engines/657050/2 "2013-04-29T22:23:25Z")
Ow? I know very little about cars (still thrilled that I managed to change my air filter without shedding blood), but that sounds frustrating, aggravating, and frustrating. I sympathize enormously. ---
**Author:** ![knifebreaker](https://avatars.discourse-cdn.com/v4/letter/k/e56c9b/32.png) [@knifebreaker](https://boards.straightdope.com/u/knifebreaker)\ **Post date:** [April 29, 2013, 10:28pm UTC](https://boards.straightdope.com/t/fuck-interference-engines/657050/3 "2013-04-29T22:28:31Z")
I would welcome a detailed answer as to why an engine would be designed in this manner. What would be compromised by adding more clearance to the valves? To my non-engineering mind, this seems like a fatal flaw that should have been phased out 30 years ago. ---
**Author:** ![Leaper](https://avatars.discourse-cdn.com/v4/letter/l/4bbf92/32.png) [@Leaper](https://boards.straightdope.com/u/Leaper)\ **Post date:** [April 29, 2013, 10:41pm UTC](https://boards.straightdope.com/t/fuck-interference-engines/657050/4 "2013-04-29T22:41:27Z")
Some theories [from the first Google result](http://www.dodgeintrepid.net/showthread.php?t=173827) for “why do they make interference engines”. [Yahoo Answers topic](http://answers.yahoo.com/question/index?qid=20070722221612AACSDqN) from the same search. Edited to add one more [from the Car Talk forums.](http://community.cartalk.com/discussion/2147458/interference-engines-why) ---
**Author:** ![Library\_Boy](https://avatars.discourse-cdn.com/v4/letter/l/cab0a1/32.png) [@Library\_Boy](https://boards.straightdope.com/u/Library_Boy)\ **Post date:** [April 29, 2013, 10:41pm UTC](https://boards.straightdope.com/t/fuck-interference-engines/657050/5 "2013-04-29T22:41:35Z")
> [@knifebreaker](#): > > I would welcome a detailed answer as to why an engine would be designed in this manner. What would be compromised by adding more clearance to the valves? To my non-engineering mind, this seems like a fatal flaw that should have been phased out 30 years ago. Interference engines allow for the highest compression ratio, which allows the best performance and mpg from a given engine. Honda still uses them in some of their cars. ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [April 29, 2013, 10:57pm UTC](https://boards.straightdope.com/t/fuck-interference-engines/657050/6 "2013-04-29T22:57:29Z")
Volvo 240. 2.4L 112HP non interference engine Volvo S60/V70 2.4L 168HP interference engine. Or if you add a turbo 240 2.1L 161HP still non interference S60/V70 2.3L 300HP interference engine. Answer your question? To the OP you did a head gasket and water pump and DIDN’T replace or inspect the belt? Wow. Oh and for future reference anybody that puts a t belt on and doesn’t turn the engine by hand through 2 complete revolutions is just begging to get but fucked by Mr. Murphy. Plus while I won’t say they don’t exist I have never personally seen an engine that would bend valves at one tooth off. On the Volvos above it takes 4 or 5 teeth before there is an issue. YMMV but you might want to spend some extra time lining things up next time. ---
**Author:** ![Inigo\_Montoya](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/inigo_montoya/32/124_2.png) [@Inigo\_Montoya](https://boards.straightdope.com/u/Inigo_Montoya)\ **Post date:** [April 29, 2013, 11:16pm UTC](https://boards.straightdope.com/t/fuck-interference-engines/657050/7 "2013-04-29T23:16:04Z")
> [@Rick](#): > > To the OP you did a head gasket and water pump and DIDN’T replace or inspect the belt? Dear gawd I hoped you’d have thought more of me than that! No, the belt broke about a week before I was going to replace it just because I was going to be doing some deep work anyway. In talking things over with my shop guy what most likely happened was I had #1 at TDC, ready for the head, and the valves for #1 were probably open as I was tightening it down–so I was fucked before I even put the key in the ignition. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [April 29, 2013, 11:21pm UTC](https://boards.straightdope.com/t/fuck-interference-engines/657050/8 "2013-04-29T23:21:16Z")
> [@knifebreaker](#): > > I would welcome a detailed answer as to why an engine would be designed in this manner. if you need a certain amount of flow capability, you need valves of a certain size. you also need a higher static compression ratio to wring efficiency out of the engine, so you’re pretty much screwed. there comes a point where you simply can’t put reliefs deep enough into the piston to mitigate this. > [@](#): > > What would be compromised by adding more clearance to the valves? compression ratio, inlet air swirl, cam profiles, valve springs, etc. you don’t just “add clearance” to valves. You re-design the entire top end of the engine. > [@](#): > > To my non-engineering mind, this seems like a fatal flaw that should have been phased out 30 years ago. as far as I know, every single diesel engine out there has this “fatal flaw.” unfortunately the physics of the situation demands it. of course, I’ve seen plenty of “non-engineering minds” ask questions like “why don’t they just move the gas tank?” Yeah, sure, give me four years to re-design the entire fucking car and I’ll get right on that. the only thing I can get behind is that interference engines should never have a timing belt. chain or gears only. ---
**Author:** ![leftfield6](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leftfield6/32/18780_2.png) [@leftfield6](https://boards.straightdope.com/u/leftfield6)\ **Post date:** [April 30, 2013, 12:04am UTC](https://boards.straightdope.com/t/fuck-interference-engines/657050/9 "2013-04-30T00:04:25Z")
I have three vehicles (two cars, one motorcycle) with timing belt driven valve trains. All 3 are interference engines. My motorcycle has belt changes scheduled every _ **12,000 freaking miles.** _ Not a misprint, every 12K miles. PITA. It is a damn fun bike though. ---
**Author:** ![Inigo\_Montoya](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/inigo_montoya/32/124_2.png) [@Inigo\_Montoya](https://boards.straightdope.com/u/Inigo_Montoya)\ **Post date:** [April 30, 2013, 12:08am UTC](https://boards.straightdope.com/t/fuck-interference-engines/657050/10 "2013-04-30T00:08:27Z")
> [@jz78817](#): > > the only thing I can get behind is that interference engines should never have a timing belt. chain or gears only. This is probably what’s got me the pissedest. But still, this is a 1.8L 4-cylinder. All Volkswagen needed from it was 105 hp and some fuel economy and still they gave zwei daumen auf to 8 big old valves and interference. At least 8 years earlier Toyota had a 1.8L 4-banger making 115 hp (the 4AGE) that had similar economy and avoided interference. Presumably they just figured, “Hey, let’s go with 16 (and later, 20) smaller valves, or maybe a linger stroke I dunno, so we can keep them out of the way of the pistons when something goes wrong.” No fucking excuse. The Germans aren’t/weren’t exactly new to making mechanized stuff in 1992 when they made this car. VW did it on purpose because they’re dickweeds. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [April 30, 2013, 12:21am UTC](https://boards.straightdope.com/t/fuck-interference-engines/657050/11 "2013-04-30T00:21:15Z")
I will never figure out why people think buying VW vehicles is a good idea. > [@](#): > > But still, this is a 1.8L 4-cylinder. All Volkswagen needed from it was 105 hp and some fuel economy and still they gave zwei daumen auf to 8 big old valves and interference. hey, know what the funny thing is? The current Jetta’s base engine is a 2.0 liter 8 valve wheezer with 115 hp. _Progress._ ---
**Author:** ![Inigo\_Montoya](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/inigo_montoya/32/124_2.png) [@Inigo\_Montoya](https://boards.straightdope.com/u/Inigo_Montoya)\ **Post date:** [April 30, 2013, 12:26am UTC](https://boards.straightdope.com/t/fuck-interference-engines/657050/12 "2013-04-30T00:26:30Z")
> [@jz78817](#): > > I will never figure out why people think buying VW vehicles is a good idea. They really are Europe’s Pontiac. Ours was a cheap fix n flip recreational wrench toy. Even after this fiasco we will turn a nice profit on it–or give it to one of the kids as a first-car. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [April 30, 2013, 12:27am UTC](https://boards.straightdope.com/t/fuck-interference-engines/657050/13 "2013-04-30T00:27:58Z")
> [@The Great Sun Jester](#): > > They really are Europe’s Pontiac. Ours was a cheap fix n flip recreational wrench toy. Even after this fiasco we will turn a nice profit on it–or give it to one of the kids as a first-car. do you hate your kids? ---
**Author:** ![Inigo\_Montoya](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/inigo_montoya/32/124_2.png) [@Inigo\_Montoya](https://boards.straightdope.com/u/Inigo_Montoya)\ **Post date:** [April 30, 2013, 1:29am UTC](https://boards.straightdope.com/t/fuck-interference-engines/657050/14 "2013-04-30T01:29:36Z")
VW ownership builds character. Ok, yeah. Sometimes I do hate 'em. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [April 30, 2013, 1:34am UTC](https://boards.straightdope.com/t/fuck-interference-engines/657050/15 "2013-04-30T01:34:32Z")
“German Engineering” = “Why use one moving part when six will do?” ---
**Author:** ![pabstist](https://avatars.discourse-cdn.com/v4/letter/p/e99b99/32.png) [@pabstist](https://boards.straightdope.com/u/pabstist)\ **Post date:** [April 30, 2013, 2:22am UTC](https://boards.straightdope.com/t/fuck-interference-engines/657050/16 "2013-04-30T02:22:24Z")
Ya know what’s fucked up? I have a '99 Subaru, last year the timing belt had about 30k miles on it. One of the pulleys for some reason shattered into pieces! The belt was perfectly fine. Of course, bent the valves. I was officially the first person ever to buy a new pulley from Subaru, “They never break!”. It took the mechanic 3 weeks to fix it, and cost about $2,000\*. Apparently, the valves have shims and you have to buy a bunch and through trial and error find the right combo. Trial and error involves removing and replacing the cylinder heads many times, at least for my mechanic… \*A lot to repair an old Subaru, but in Vermont they are hard to find in good shape and cost way more than that used, so worth the price if the rest of the car is mint. ---
**Author:** ![FoieGrasIsEvil](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/foiegrasisevil/32/16638_2.png) [@FoieGrasIsEvil](https://boards.straightdope.com/u/FoieGrasIsEvil)\ **Post date:** [April 30, 2013, 2:27am UTC](https://boards.straightdope.com/t/fuck-interference-engines/657050/17 "2013-04-30T02:27:44Z")
VW’s are the most overpriced, overrated pieces of crap vehicles ever. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [April 30, 2013, 3:07am UTC](https://boards.straightdope.com/t/fuck-interference-engines/657050/18 "2013-04-30T03:07:29Z")
> [@FoieGrasIsEvil](#): > > VW’s are the most overpriced, overrated pieces of crap vehicles ever. followed closely by Subarus. ---
**Author:** ![deltasigma](https://avatars.discourse-cdn.com/v4/letter/d/e5b9ba/32.png) [@deltasigma](https://boards.straightdope.com/u/deltasigma)\ **Post date:** [April 30, 2013, 3:52am UTC](https://boards.straightdope.com/t/fuck-interference-engines/657050/19 "2013-04-30T03:52:49Z")
The engineer was a follower of fellow German Ernst Mach and therefore [did not believe that time is absolute.](http://en.wikipedia.org/wiki/Ernst_Mach#Philosophy_of_science) > [@](#): > > Mach is attributed with a number of principles that distill his ideal of physical theorisation — what is now called “Machian physics”: > > [ol] > [li]It should be based entirely on directly observable phenomena (in line with his positivistic leanings)[[9]](http://en.wikipedia.org/wiki/Ernst_Mach#cite_note-9)[/li][li]It should completely eschew [absolute space and time](http://en.wikipedia.org/wiki/Absolute_space_and_time) in favor of [relative motion](http://en.wikipedia.org/wiki/Relative_motion)[[10]](http://en.wikipedia.org/wiki/Ernst_Mach#cite_note-10)[/li][li]Any phenomena that would seem attributable to absolute space and time (e.g. [inertia](http://en.wikipedia.org/wiki/Inertia), and [centrifugal force](http://en.wikipedia.org/wiki/Centrifugal_force)) should instead be seen as emerging from the large scale distribution of matter in the universe.[[11]](http://en.wikipedia.org/wiki/Ernst_Mach#cite_note-11)[/li][/ol] Therefore, he regarded the timing belt as a superfluous design element and treated it accordingly. 😃 😉 ---
**Author:** ![MikeG](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mikeg/32/4329_2.png) [@MikeG](https://boards.straightdope.com/u/MikeG)\ **Post date:** [April 30, 2013, 5:10am UTC](https://boards.straightdope.com/t/fuck-interference-engines/657050/20 "2013-04-30T05:10:00Z")
Hey leftfield, you got a GL? I can swap the belts on a GL1200 in under two hours 🙂 dont even need to pull the radiator! My new bike is an 85 K100 with timing chains and the entire head is open to the left side of the bike. Quite a shock in terms of ease of access coming from Hondas and Suzukis. But back to the OP, one tooth off should not cause the destruction you suffered. Ive done the belts on Accords three times now and time #2 im pretty sure I was off by a tooth, maybe two due to my wrench slipping and being fed up after trying to get that damn bolt off. [Next page](https://boards.straightdope.com/t/fuck-interference-engines/657050.md?page=2)