944 timing belt loss

[GrtWest@aol.com]

Dear Porschefiles:
My 17 yr old son chewed the teeth off the cam belt (not him , the car). He
said it just went dead. The cam parked itself where it is not in
interference with the pistons. Dare I replace the belts, pull the plugs,
test for compression and fire it up? Assuming the compression test is good?
Or in everyones experience, does a cam belt failure ALWAYS mean bent valves,holed pistons & other unthinkables? Pray for us!

Vince S.
GrtWest@aol.com

[1.2gees]

If the car was running, or starter engaged, yes.

Also:

I've heard of a couple people, who bent their valves, trying to find the correct timing between the crankshaft, and the camshaft. I don't know how true this is, but be carefull...
Ahmet

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It's all the driver...

[KEEFER]

Originally posted by GrtWest@aol.com:
Dear Porschefiles:
My 17 yr old son chewed the teeth off the cam belt (not him , the car). He
said it just went dead. The cam parked itself where it is not in
interference with the pistons. Dare I replace the belts, pull the plugs,
test for compression and fire it up? Assuming the compression test is good?
Or in everyones experience, does a cam belt failure ALWAYS mean bent valves,holed pistons & other unthinkables? Pray for us!

Vince S.
GrtWest@aol.com

IT WON'T COST YOU ANYTHING BUT TIME TO CHECK THE COMPRESSION BUT HAVING BEEN THROUGH THIS RECENTLY I DOUBT IF YOU WILL BE ABLE TO "FIRE IT UP " AS BAD AS IT IS IT IS NOT THE CATASTROPHE SOME FOLKS MAKE IT. THE ACTUAL JOB IS A "NO BRAINER" . A $15 HAYNES MANUAL SPELLS OUT 90% OF IT. THE PARTS , ALL NEW VALVES, GUIDES , BELTS, ROLLERS, STUD AND GASKETS CAN BE HAD FOR ABOUT $400 WITH A LITTLE SHOPPING. I PAID A GOOD LOCAL MACHINE SHOP $120 TO DO THE HEAD WORK. TOOK ME ABOUT 6 HOURS TO DO THE JOB AND I'M OLD. CHECK THE MOTOR MOUNTS WHILE YOU GOT ALL THE MESS OFF THE TOP OF THE ENGINE. MAKES THAT JOB EASIER.
I STILL CAN'T BELIEVE I DROVE MY CAR UNTIL THE BELT BROKE BUT THAT'S ANOTHER STORY. GOOD LUCK.

[lm6y]

At the very least, replace the belts BEFORE you do anything. Like Ahmet said, if you don't get it right and crank it with the starter you can bend things. After you get the belts changed, take the plugs out, and turn it over by hand with a socket and breaker bar. This way you can "feel" if anything binds before it breaks.

[drew1]

Hi Grt West,

Don't Know Keefer, But Ahmet & Imy have always given good advice ever since I've been watching this BBS.

If this was my car, I'd think thwe valves were messed up. I've even seen it on noninterference motor, Ford 4 cyl, with broke timing belt. Dkipping a thooth or two probably causes a valve to hit then clears 6the theeth.

But I would do a compression test anyway.
remember that the crank turns twice for every time the cam turns, estimm
ate the timing, pull plugs & go easy, put a belt on, go to TDC, time them in, turn the crank 2 revs feeling for interference & rhen check compression. If all OK, fite her up.

Good luck,

drew1

[GrtWest@aol.com]

We put new belt on & sure enough no compression in #3 so....My son gets a lesson in removing a cylinder head!
Please keep you advise coming, it is greatly appreciated.
I plan on using the tension devise from krikit it is supposed to cost only $13 dollars. http://hmc-international.com/krikit.htm

[T86951]

I can just tell you my experience. My belt broke idling up to a stop light. I checked and all pistons were where no valve should have been touching a piston. I thought all right! But a test showed I had bent valves on 2 cylinders. My shop said they have never seen a belt broken with no valves bent. They said it was possible but they had never seen it. I spent $1500 but I had it all done at a shop. The shop I use I trust very much for many years. I wish u luck and hope yours are not.

[AMCPorsche924Powerhaus!]

First of all, was there compression in cyl 3 before the belt broke? hehehe it is possible that you just coincidentally had a belt break, and you have been driving the car with a blown head gasket and not knowing it!!
Your gonna have to pull the head anyway since there is not compression in cyl 3, but make sure that compression gauge was hooked up properly, mine busted and didn't read anything (I didn't pull the head because of that, I saw it bust, leaked around connection)

[This message has been edited by AMCPorsche924Powerhaus! (edited 01-12-2001).]

[AMCPorsche924Powerhaus!]

What I meant was, make sure you had compression in the cylinder before you broke the belt!
I accidently pulled off my wire on #2 cyl on my 931, and left it off when I started the car:
-starter her up, started normal, first time, faster than ever.
-backed car out no noticable rough running, idle a little lower 750RPM usually 850
-drove normally, wondered why a little power loss was there, just assumed she hadn't warmed up.
-came home, popped hood to check somthin else for fun, noticed spark wire was missing!!!
-this was good news for me, yes good news. If a car runs on 3 cylinders without you noticing it, you got a really really special little car. And a very happy smile on your face that your car is in good enough shape to be running on 3 cyls not noticing it!

I put spark wire back on and the car idled at 900 sure enough! This was after I put the head back on, a spark plug wire is actually easy to miss when you are looking at everything but the simple things after puttin a cyl head back on
Bottom line, yeah you probably bent valves, or you blew the head gasket, on 928's if you are off one notch you blow the engine (my bud told me)

[AMCPorsche924Powerhaus!]

BTW someone said they never saw a car without valves bent......I have changed a broken belt on a volvo 240, a honda accord, another volvo 240, and yet another volvo 240, and the valves never bent.
The honda accord was an interferenve style engine. The volvos I am unsure. (these were not cars, so don't say I am known for not keeping up with the belt properly changin!)
:P Must have all been lucky shots for the owners of those cars...or lucky misses I should say

[Tabor]

I too have broken a timing belt on a zero clearance honda engine without any trouble.

Originally posted by AMCPorsche924Powerhaus!:
BTW someone said they never saw a car without valves bent......I have changed a broken belt on a volvo 240, a honda accord, another volvo 240, and yet another volvo 240, and the valves never bent.
The honda accord was an interferenve style engine. The volvos I am unsure. (these were not cars, so don't say I am known for not keeping up with the belt properly changin!)
:P Must have all been lucky shots for the owners of those cars...or lucky misses I should say

[1.2gees]

You will NOT bend valves on a non interferance engine, if the timing belt breaks.

Some starters MIGHT not have enough power to turn the engine, with a valve in the way of a piston, and it won't bend, and some starters (such as those from a 944) do...

It's also possible that the piston hit a valve in a way which didn't bend it, but just made the entire valve train move... Very unlikely though!

I used to play with the timing of my vw scirocco "S" all the time, nothing ever happened! And it won't! Iterferance or not? That IS the question!!!

Sorry about that
Ahmet

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It's all the driver...

[AMCPorsche924Powerhaus!]

Honda Accord: Interference
someone broke belt, no damage done
I changed it.
The thing is, sometimes the pistons get dints in em. nothing to worry about if they are tiny little nicks, you just smooth em out.
sometimes the belt breaks at just the right time on an interference engine that there is no damage.

[1.2gees]

I doubt that very highly, at least in the Porsche's case, forged pistons will not get dents in them, and since the rotational mass of the bottom end of an engine will likely be much higher than that of the valve train, it'll probably do some damage to the valves...

I would also think that a "tiny little nick", would be quite interesting, you mean the piston would touch the valves, if timing is not controlled only by a milimeter or so?

As far as the accord goes, I've seen MANY of them (a friend works for a Honda Dealership, as the service manager) with bent valves. What year Accord was this? Which engine?


Unless you've checked compression, this engine could've simply snapped the belt at idle (or while the car was off), and it only ended up bending one/two valves. Unless you've checked compression, a bent/stretched (and I suppose a little compressed) valve CAN go unnoticed. Did you have the head off the car at any point?
Ahmet

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It's all the driver...

[AMCPorsche924Powerhaus!]

honda accord 1988 2.0 carb
Person driving 60km/h belt broke, car stalled.
Towed home, I fixed, checked compression, everything to spec, not in low range, good as new. Checked valves, everything to spec, just made a couple minor adjustments, they were within the range, and I just made them the best spec (least clearance). Then a couple months later I found out it is an interference engine! I said "cool, lucky!"
Belts have broke on a volvo 240, that I have fixed, compression up to spec after, and I am not sure if they are interference though.
BTW, the 931 pistons are cast I think...the GTR ones are forged....All the pistons I have seen from a 931 have little valve marks on them, and some have little scratches on em from some nut that dropped a stone throug the spark hole!
When I said nicks, I meant, the piston may be ok, but the valve is bent...depends on the degree of the nick. A 2.5mm deep nick is a bent valve, but a 0.5 mm deep one isn't as bad...thats just an estimate from what I have seen with my bare eye.

[1.2gees]

I don't want to say that I'm positive your friend's accord would really bend the valves if the timing belt broke, cause I honestly don't know.

I was referring to the later model, fuel injected accords, which coincidentally also have much higher compression.

If you want I can find out if this is common, or the owner of the accord REALLY got lucky...

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It's all the driver...

[drew1]

AMC & Amhet,

I've seen some bend the valves and some not. 931: My wife was pulling in the drive way and it quit. About a year earlier I had put a cam in , holding the cam and trying to torque the pulley bolt, no Loctite, I didn't do a good job. The bolt worked loose, key sheared, pulley turned. Bent valves, but this is an interference motor. A 2.3 Ford motor is non interference but I saw a mustang that broke a belt while wound up. Maybe the valves floated, bent valves.

On a 944, I,ve been told that the cam duration is short enough that you can check for leaks in all those hoses under the manifold by shooting compressed air through an old fuel filter into the intake boot because you can have all valves closed. One chance in a million somebody will get lucky.

I have never put a big cam or any kind of popup pistons in a 944, but a rule of thumb is 0.100 or 1/8" clearence between pistons & valves with cam timed in.

Ahmet is going to engineering school in a year or two so he can provide us with the figures from rod stretch due to the force of negative axcelleration close to TDC and the valve resisting the force of the springs trying to hold it to the lifters and the cam. Until he does I'll go by 1/8" on a scale.

drew1

[Blackfoot]

the timing belt broke on my old accord lx-i. out of the 360 degrees of rotation, there is about 18 degrees where the pistons will not strike the valves. 95% chance of contact and i got real lucky.

who knows, maybe you will be lucky too. but no way you should start it without a mechanic giving you the okay.

[AMCPorsche924Powerhaus!]

With a 931 it is easy to tell if you have really bent valves, you just look at the tappets, if they are low, the valves are bent. Only problem is if a valve is bent a tiny bit, you won't notice.
I am not familiar with what happens when the timing belt breaks on the 944, but I know on 928's bad things like blown engines can happen.

[This message has been edited by AMCPorsche924Powerhaus! (edited 01-17-2001).]