TheSamba.com :: View topic - 1.9

Tue Nov 18, 2008 10:37 am

Quick dumb question....
Is the 1.9 WBX an interference engine?

thx!

Tue Nov 18, 2008 10:50 am

I dont know. I dont think so, but as far as i know it will only interfer if the gears on the cam/crank go. then youve got some serious problems. its not like a modern car that has a belt that could break.

Tue Nov 18, 2008 11:05 am

Maybe not a dumb question, but a pretty academic one. Questions of valve interference are important in the context of engines with belt or chain-driven camshafts, where if the drive fails the valvetrain will stop in a certain position while the crankshaft can still spin. It wouldn't be important to know about interference if those drive types never failed, but in fact they do, frequently enough. Although camshaft gear-drive failures aren't completely unheard-of (there was a guy here just recently whose engine, it seemed, might have sheared the cam-gear bolts), they are so rare in the center-cam boxer world that the question of interference just doesn't come up, at least on stock or near-stock engines. Once you're looking into higher valve lift or longer valve timing, interference does become an issue.

And that's why I don't have an answer for you, because it's never been important for me to know.

You can figure this out yourself by knowing the actual valve-lift of the 1.9 wbx, and measuring the depth of the valve relief pockets in the piston crown. If the height above the cylinder seal surface is greater than the depth of the pocket, then yes, there is the potential for interference should the cam gear-drive ever fail outright.

But in dealing with a stock engine, especially a 1.9, I can't imagine many instances where the info would actually be worth having.

Tue Nov 18, 2008 11:06 am

The only dumb question is that which is not asked.
Interference or non-interference apply to engines that have a belt or (in the past) a chain. This belt or chain is the connection between the bottom half of the motor (crank, pistons, block) and the upper half (camshaft, exhaust valves, intake valves). When it’s timed right everything moves together in synchronicity. But if the belt or chain breaks then the valves stop opening and closing where they are, and the pistons keep pounding (until the car gets to side of road or you get it in neutral).
If you have an interference motor, there is not enough space between top dead center of the piston travel and the extended valves and crash, valves get bent or better. With non-interference engines, when the belt breaks, you can still spin the engine and the topmost piston travel isn’t high enough to connect with a fully extended valve and (then it’s just a pain in the butt to get a new belt and put it back together).
With that explained, your 1.9 has neither a belt nor a chain. The “bottom and top” halves are indeed physically connected and geared together. So if your valves are not opening and closing, but your pistons are still moving? You’ve got some real problems of which I can explain no further.

Hope that clarifies,
Jere

Tue Nov 18, 2008 11:31 am

I think three of us were hammering away at the same thing at the same time. I hate it when I work on an answer and finally post it only to find someone else has just said the same thing, and usually in far fewer words. This time I won second that little race we didn't even know we were in. Yippee.

Quote: The only dumb question is that which is not asked.

I say the only dumb question is the one asked without even trying first to find the answer for onesself. I don't see rhpaw's as that kind, because I doubt he would have found anything on this, but jeez, there are a lot I don't respond to because the asker could have easily found the thing out with a little effort.

I hope those guys are reading this.

Tue Nov 18, 2008 11:47 am

Let me just add one thing that helps one determine whether valve/piston interference is an important thing or not: Is the engine "Overhead Cam" or "Overhead Valve"?

All the old VWs are overhead valve (OHV) engines. That means there is NO timing belt or timing chain to break, so, like 10cent explains, it's not important to know.

For those of us that have converted to a Subaru powerplant, it IS important, as they have "Overhead Cam" and thus a timing belt. My 2.2L is not an interference design, so if the timing belt goes, I'm probably just inconvienienced, as I'll have to get a tow and then do the timing belt maintenance I should have done anyway. On my 2.5L, it IS an interference engine, so a major rebuild or new engine will quite likely be necessary if it breaks. So I should be way more careful to change the timing belt and pulleys per the maintenance schedule on that engine.

Hope that adds to the detailed information the other posters gave.

Tue Nov 18, 2008 11:58 am

Quote: Is the 1.9 WBX an interference engine?

No.

Tue Nov 18, 2008 12:04 pm

That's a pretty useful distinction, Rich, except it doesn't include OHV engines that nonetheless have chain-driven camshafts. Older American V8's were of this type, I believe, but they've mostly gone to OHC as well. Don't quote me though, I don't know anything that ever came out of Detroit, except me (grew up there).

Tue Nov 18, 2008 1:14 pm

tencentlife wrote: That's a pretty useful distinction, Rich, except it doesn't include OHV engines that nonetheless have chain-driven camshafts. Older American V8's were of this type, I believe, but they've mostly gone to OHC as well. Don't quote me though, I don't know anything that ever came out of Detroit, except me (grew up there).

Uh, oh, you are right! I guess there were some those with OHV and timing chain, including a older Ford truck I owned! Duh... I crunched it before I ever did any chain maintenance, so I forgot that distinction.

Tue Nov 18, 2008 3:16 pm

funagon wrote: Quote: Is the 1.9 WBX an interference engine?

No.

Perfect, thank you.

I know if perfect world we wouldn't be worrying about cams and valves kissing pistons, but let's just say-
"I was doing something inappropriate and I may have had some valves fully extended, and some pistons rotating"

hence, I was just wondering..
:)

Tue Nov 18, 2008 3:39 pm

tencentlife wrote:
I say the only dumb question is the one asked without even trying first to find the answer for onesself.

So what is the definition of a question that is asked, and two verbose replies are tendered.. neither of which actually answer the original question?

I'm just sayin.... :)

Tue Nov 18, 2008 4:10 pm

The other guys' answers were better than mine, and more accurate too. But I just had to be a wiseguy and give you a one word answer.

My "No" answer is correct if you meant to ask "does the 1.9 WBX have a timing belt that needs to be changed?" But you wrote:

Quote: "I was doing something inappropriate and I may have had some valves fully extended, and some pistons rotating"

So is there some special event that prompts your question?

Tue Nov 18, 2008 4:31 pm

funagon wrote: So is there some special event that prompts your question?
I'll find out tonight when I work on it some more..

I've just always known the term "interference engine" to be relative to whether pistons and valves share space in a combustion chamber like this reference- Nothing related to timing belts or chains..
Depending on the design of the engine, the piston and valve paths may "interfere" with one another and incorrect timing in their movements may result in the piston and valves colliding. (Such designs are also called "interference head" or "interference engines", and include virtually all diesel engines. Conversely, non-interfering engines, such as the Mazda B engine, are called "free-wheeling" or "non-interference" engines.)

Anyway, beyond definitions.. I was doing something and not completely thinking. Just wondering if I COULD have kissed pistons.
As I haven't heard any great horror stories with accompanying pictures, I will assume not.

LIKE THIS!

Tue Nov 18, 2008 4:53 pm

rhpaw wrote: funagon wrote: So is there some special event that prompts your question?
I'll find out tonight when I work on it some more..

I've just always known the term "interference engine" to be relative to whether pistons and valves share space in a combustion chamber like this reference- Nothing related to timing belts or chains..
Depending on the design of the engine, the piston and valve paths may "interfere" with one another and incorrect timing in their movements may result in the piston and valves colliding. (Such designs are also called "interference head" or "interference engines", and include virtually all diesel engines. Conversely, non-interfering engines, such as the Mazda B engine, are called "free-wheeling" or "non-interference" engines.)

Anyway, beyond definitions.. I was doing something and not completely thinking. Just wondering if I COULD have kissed pistons.
As I haven't heard any great horror stories with accompanying pictures, I will assume not.

LIKE THIS!
If the vanagon WAS an interference engine, the only way I can think of (off the top of my head) that you could cause the pistons and valves to hit is to assemble the engine so the cam timing was way off. Well, if the cam destructed due to another assembly error that would cause it, but there'd be damage anyway...

Tue Nov 18, 2008 5:58 pm

wasserbox wrote: tencentlife wrote:
I say the only dumb question is the one asked without even trying first to find the answer for onesself.

So what is the definition of a question that is asked, and two verbose replies are tendered.. neither of which actually answer the original question?

I'm just sayin.... :)

At least the replies actually had something to do with the question! Give us a break here, we're tryin'. But to answer you literally, the replies say nothing about the question, so it's as dumb or not-dumb as it was in the first place.

Whew!

Tue Nov 18, 2008 11:04 pm

wow..
This place is starting to sound like a conversation with my wife...

Anyway.. the rusty is up and running now. no real harm done.

Wed Nov 19, 2008 5:12 am

after 100 posts the relationship becomes common law.

Wed Nov 19, 2008 7:34 am

RichBenn wrote: On my 2.5L, it IS an interference engine, so a major rebuild or new engine will quite likely be necessary if it breaks.

I would call the Subi 2.5L (1999-2007) non Turbo a semi interference engine. The head are design in such ways that if you have a t-belt failure the valve will bent slightly but never to a point that it can destroy the head or piston (i will post pictures later). I have bought many used "Broken" engine (car crash) with bent valves and it's always the same scenario. This was confirm by Subaru Canada. It's still a a pain in the butt for any customers as the heads need to be remove and valves replaces. Most modern engine have belt, some have chain. I think the ZTEC as a chain.

As an example, most Honda engine are full interference, believe me! I use to be a part time mechanic for Honda racing and i was not changing brake :-)

Don't think i vouch that much Subaru engine, for me, my first choice of engine for a conversion would probably be a Honda or Toyota but sadly, they don't turn in the right direction. That said, i have to say that Subaru engine are extremely solid / tough engine crash wise (the t-belt section is the first thing that take a pounding in a front collision). I have seen destroy cars and engine, i mean no more t-belt cover, broken cam gear, broken oil pump, broken water pump, broken valve cover.... i mean scary stuff.... I could not believe i could save those engine (we use them for our own vans / friend / lower price conversion locally) and all those are running better than new. The cam shaft is a monster on 2.5L, i can't believe the beating that thing can take.

I will show you some scary pictures later of broken engine that came back to life easy. I will also show you some bent valves.

By the way, the 1.9L wasser boxer is an interference engine :-)
I had to fix one 2 years ago, the rocker had seize hard on the open position (EX valve), i thin i have picture somewhere. But the mark on the piston was almost non existent and same for the valve. I just know that a valve can touch the piston.

Ben

Wed Nov 19, 2008 8:21 am

Ben, glad to see you love Honda, now the V6 turns the right way........waiting for you to do a conversion!!!!

Wed Nov 19, 2008 8:24 am

wgargan wrote: after 100 posts the relationship becomes common law.

Common-Law isn't recognized in California. Emissions/smog related is my guess.

For what it's worth, my twin overhead cam 16-valve 1987 Toyota 1.6 liter 4AGE motor is a non-interference design. Thank god because I think the timing belt is way past it's life-expectancy (I just bought it). I hate to admit it but this motor is superior to the Subaru Boxer engines, which are far superior to the VW wbx motors. A new love affair begins . . .

Anime version

- Chester

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