Rebuilt Engine is Knocking

[Chilezen]

I am/was in an engine rebuilding class at school. The semester has now finished. The car was towed home this week, and today I made the final touches. I followed the sequence, primed the oil and fuel, turned over and started.

Damn. It can almost hold an idle, but intermittently there is a loud metal knock. This slows the idle but the engine tries to bring it up again.

I don't have an engine hoist at home, which means I can't lift the engine up to take off the oil pan and have a look. But if I could, what should I be looking for? I know I torqued all bolts and the crank turned over by hand easily during the rebuild. What happened? Could it be that I installed the timing belt a tooth off? I know I didn't... Would it be detonating for any reason?

I may be able to get a video tomorrow for the sound, if that's necessary for you to help diagnose.

[jlevie]

The know could be nothing more tha a bad misfire. First figure would why the engine doesn't want to idle. Since it has been rebuilt start by checking cam timing. Then start at the top of what is below and work to the bottom without skipping any checks.

Idle or hard starting problems are most commonly caused by intake leaks and/or
a sticky or defective Idle Control Valve (ICV). The only reliable method of
locating intake leaks is to have a smoke test run on the intake and crank case
and to test the brake booster with a gage and vacuum pump. The complete list
of possible causes of an intake leak is:

Intake boot
Throttle body gasket
ICV hoses & connections
Brake booster, hoses, and connections
Crank case breather hose
Evaporative control hoses, valve, and expansion tank
Fuel pressure regulator & hose
Injector seals
Valve cover gaskets & bungs
Oil filler cap
Dip stick o-rings
Oil return tube o-rings
Pan gasket or oil level sensor gasket

While leaks in some of those can be found by inspection or by spraying carb
cleaner on suspect areas, not finding leaks that way doesn't eliminate the
possibility. Only a smoke test will really work.

Once the possibility of intake leaks is eliminated, the ICV needs to be
removed and cleaned with carb cleaner until the vane inside moves freely. When
the ignition is switched on you should be able to feel vibration from the
ICV. If no vibration the ICV is bad, there's a problem with its wiring or
connector, there's a problem with the TPS, or the DME (or Idle Control Module
(ICM) on an ETA car) is faulty.

For the DME (or ICM) to control idle, the idle switch in the TPS must work
correctly. The switch should close when the throttle stop is 0.030-0.060" off
the idle stop screw. Hearing a click doesn't mean the TPS is working. Check
with a meter or test light.

The fuel system should be tested via the suite of tests in the Bentley manual
as invalid rail pressure can be a contributor to idle and starting problems. A
simple injector check is to pull the injectors, jumper the fuel relay to run
the pump, and see if the injectors are leaking. You can also point the
injectors into a towel, remove the coil wire, and crank the engine to see if
all of the injectors appear to be spraying in a similar fashion. The best
approach to possible injector problems is to have the injectors cleaned and
flow tested. Since raw fuel can or will be released in these tests, have a
fire extinguisher handy.

While a bad check valve in the high pressure pump can result in longer than
normal cranking, if the fuel system is working as it is supposed to the rail
will reach normal pressure in a few turns of the engine. A weak pump, clogged
filter or leaking FPR in conjunction with a failed check valve can result in
longer cranking and/or idle poroblems.

The O2 sensor can be a contributor to idle problems. The O2 sensor is a
scheduled maintenance item with a useful life of no more than 100k. If the
sensor has that mileage or more (or is of unknown age), replace it.

The AFM can be a contributor. If the vane doesn't move freely or the
resistance track is worn the DME may be receiving invalid data from the
AFM. And if someone has fiddled with the bypass air adjustment the DME may be
unable to stabilize idle. The bypass air adjustment should only be adjusted
per the procedure in the Bentley and with an exhaust gas analyzer. And even
then everything else associated with engine management has to first be
operating properly. If the AFM becomes a suspect, replacement with a good used
unit is the best approach.

Improperly adjusted or malfunctioning valves will affect idle and starting. As
can compression issues from ring or cylinder wear. A valve adjustment is
called for every 15k. A useful diagnostic is to run compression (dry and wet)
and leak down tests on the engine. Aged ignition wires, plugs, distributor
cap, or rotor can cause problems. Insulation does break down with time and
heat. And since the youngest E30 is going on 20 years old, if the ignition
system is original or the plugs are old replacement is indicated.

Although not usually a problem, a bad DME temp sensor is a possibility. That
generally won't cause an unstable idle, but can cause hard cold or hard hot
starts and/or a rough idle. As can problems with the timing reference
sensors. Although not commonly encountered, a bad harmonic balancer on an
M20B25 or M30 engine will cause problems.

When all other possibilities have been eliminated and idle or starting
problems persist, replacement of the DME, or if applicable the ICM, is
indicated.

In many cases the cause of problems will be a combination of factors. So it is
important to test and repair all of the possible causes.

[Chilezen]

Video: http://youtu.be/lLHa2snORQw

[gath]

I maybe wrong but that sounds more like the upper part of the motor.. you can try to isolate the location of the noise by listening closely with a metal piece/rod to the motor or with a stethoscope.

[efficient]

Yup does sounds like the head part of the car. You can take thr valve cover off and see whats making the noise. A little messy

[ahlem]

Check the pads on the rockers to be sure they haven't been worn to a concave. This is where they hit the lobes on the cam. If they are concave and you stuck your feeler guage under there real far when you adjusted your valves, you may have 3x the required clearance when you thought you had it right.

[E30Gus]

Did you re-adjust your valves after torquing the head bolts? They will/can change drastically after torquing.

[Chilezen]

Check the pads on the rockers to be sure they haven't been worn to a concave.

Did you re-adjust your valves after torquing the head bolts? They will/can change drastically after torquing.

The rockers are new. I adjusted the valves after the head was torqued.

I removed the oil pan. There is no damage to the block from underneath. That's good.

I am bout to remove the valve cover.

I am postponing looking for vacuum leaks because I want to find mechanical damage before continuing to run the engine in this state.

[whodwho]

That sounds like you didn't get the timing belt aligned up correctly and valves are hitting or maybe you didn't install the rocker shaft locking plate and rockers are off the valve stems.

[Chilezen]

That sounds like you didn't get the timing belt aligned up correctly or maybe you didn't install the rocker shaft locking plate and rockers are off the valve stems.

I double checked, and the marks on the timing gears line up with their respective marks on the head/timing cover.

I did install the rocker shaft locking plate, and all 12 brackets that hold each rocker arm. I took off the valve cover and everything is aligned; there is no visible damage anywhere in the head. I will check clearances tomorrow. I had previously set all to 0.009" at the correct location, between the valve stem and rocker eccentric.

Since I don't see any damage to mechanical parts, maybe it's detonation?...

[ak-]

That's not what detonation sounds like, but holy crap don't turn it on again till you figured out what's wrong lol.

[Chilezen]

I agree with you, but I can't find vacuum leaks without first creating a vacuum in the engine first...

With the valve cover and oil pan and acc. belts off, what else should I check?

Since the timing of the engine can't be adjusted (and the belt is on correctly), would the wires or coil cause this?

Anyone near Torrance, CA that wants to help? lol

[Chilezen]

I FIXED IT

For any of you who have replaced the oil pump, you know that there's a rod/shaft going up from the pump to a gear (and another gear to the T-belt). THAT ROD had fallen during reassembly, thus was knocking/being hit as the engine rotated.

Also yes the valves need to be readjusted, that's the more prominent sound on top.
But the engine runs now, I just broke in the rings and she's cooling down.