The timing belt tensioner bearing failed after a dust storm while on
the free way. The belt burned up and the cam shaft valving didn't
work.

I got all kinds of contradictory answers on the kinematics of the
engine, not only from mechanics and parts stores, but in the
literature.

Is there any reliable guide to engines where the pistons occupy the
same space as the valves [at different times]?

I seem to have zero compression after installing the new belt and
tensioner.

Even igniting starting fluid is impossible.


Bret Cahill

On 2 May 2007 18:27:35 -0700, Bret Cahill <BretCahill (AT) aol (DOT) com> wrote:

Try:
http://www.gates.com/chooseCountry/index.cfm?CFID=7524569&CFTOKEN=81457788

Pick your country and scroll down to : Auto Aftermarket - Timing belts

Scroll down some more and find interference engines - fill in the
blanks. and get all the Gates data for your application (belts, hoses,
caps, )

Pete

Do bent valve stems mess up the holes in an aluminum head? Does this
require a lot of machine shop work or can I just replace with new
valves?


Bret Cahill

On 3 May 2007 10:20:03 -0700, Bret Cahill <BretCahill (AT) aol (DOT) com> wrote:

need some machining or replacement heads or you get lucky and no
damage. It all depends on where the valves were at the time of
breakage. Ive had it both ways and wound up replacing a head from a
broken valve that pierced a water jacket. I've had bent valves that
just required replacement and lapping in - no machining. Who can say
what actually happened to yours without doing some testing or
teardown.

If your sure you got the engine timed in correctly, pull the spark
plugs out, squirt about an ounce of oil (5/6 squirts) in each hole and
do a compression check. When you spin a engine over trying to start,
the fuel still goes into engine and gives you gasoline wash and lose
of compression and high wear from dry rings and pistons. Do this
first before taking the engine apart.

Then do a pressure test - air pressure in each hole (needs a threaded
hose in the park plug hole and a compressor) and listen for leaks in
the intake and exhaust. You have to roll the engine over to a
compression stroke while doing this for each hole.

This might be hindsight to tell you that timing belt change schedules
are cheaper that engine work. And when buying a used car, check and
replace the timing belt immediately, if there is no tag saying when
it was replaced.

Pete

"Bret Cahill" <BretCahill (AT) aol (DOT) com> wrote

You might be able to just replace the valves.

But, the pistion hits the valves. This can destroy a piston. I have seen a
piston with a valve stuck in it (with the stem in the top of the piston).
And the cylinder head itself can be destroyed.

You need to get the engine apart to see how much damage there is.

Better yet, change the belt when you're supposed to.

Jeff

That just made things more confusing.

I'm not a forensic scientist but I couldn't see any damage. I
couldn't even see where the valves knocked any crud off the pistons or
vice versa. Turning the cam shaft, all the valves _looked_ like they
were seating properly.

The pistons have indentations machined into their tops to accomodate
the valves when they are open. Open at the right time or any time, I
do not know. But the depth of these wells plus the head gasket
thickness is just about the same distance as the maximum extension --
at least _after_ the timing failure -- of the open valves past the
head seating surface.

So maybe it is a non interference engine. Or maybe it was a non
interference engine before 1/16" of crud formed on the pistons.

I measured the clearances as closely as I could, to ~ 1/32", and
figured it wouldn't make much sense to design an interference engine
with a pressure ratio of 8:1 when you could have a non interference
engine with a pressure ratio of 7.95:1

Finally I checked the valve "lash", the distance between the valve
stem and the rocker arm when the valve is closed, and all measured
0.027".

All this indicates a non interference engine.

Yet I suddenly have zero compression.

Before I removed the timing belt I checked the timing marks on both
the crank shaft and the cam shaft and they were both on top dead
center at the same time.

Actually it was the tensioner pully bearing that probably failed
first. Had the belt failed first the tensioner would still be
rolling.

Nevertheless I either knew or, as the lawyers say, "should have known"
that all the dust storms we've been having out here in the SW desert
destroy machinery. I'm almost afraid to look at my air filter.

Yesterday a local Auto Zone store had an ad on the door:

"Replace your tensioner and extend your timing belt life."

I thought, "yea, NOW they tell me. I bet they don't run these ads in
the Pacific Northwest."


Bret Cahill

Bret, it really sounds like your valve timing is 180deg off. You say
the timing marks are both at TDC, did you check a manual to see if you
had them lined up right? If both marks were at the top of their
pulley's and the marks are supposed to be next to each other that would
do it.

Jeff DeWitt


Bret Cahill wrote:

Maybe it's off 120 degrees.

The cam sproket was designed for several different engines and has
three different marks 120 degrees apart and can fit on the shaft 3
different ways.

On several previous t-belt or seal or head gasket replacement jobs I
never thought about the sproket being on the cam shaft properly but
just used the kinematics to determine timing.

The sproket was probably on wrong and since I never took it off this
time around, I assumed it was on correct and didn't bother checking
the position of the valves as before.


Bret Cahill