Valve timing split.
 

Gentlemen,
I have a 3.2 that has an odd, lumpy sound, at least to my ear. Extensive troubleshooting has found nothing until now- the valve timing check I did, with the engine in the car, produced the following numbers; #1 1.15 mm, #2 1.37mm. Has anyone had any direct personal experience as to the results of such a timing situation? I am debating pulling the engine over the winter to fix this. Before then, I'll check each valve for lift, to see if I have a bad cam lobe anywhere. The sound I am hearing sounds like a cylinder (or cylinders?) not pulling it's weight. It's subtle, but it's there. Any ideas?

In a perfect world, you shouldn't be getting differential timing readings from an adjacent cylinder...

Things to check that could result in differing measurements:

1. Where are you doing the measuring? If your dial indicator is not parallel to the valve when you do the measurement.. If the indicator was at a significant non-parallel angle it would result in a higher lift reading.

2. If your valve adjust is off, low reading

3. A bent valve. Low reading

4. Badly worn cam lobe. Low reading.

Any one of those could result in what you are seeing. I'd check #3 and see which one is off the other two, this is probably your suspect location.

Oh crud. I really shouldn't post while drinking beer. I meant to say that #4 was at 1.37 mm. Oops! So I am really referring to the two cams not being set to the same spec.

They are close enough. I doubt you could tell the difference if you got them the same. When you eventualy rebuild the engine you can set them exactly where you want.

-Andy

Whole different ballgame... Left to right differences could simply be one tensioner with more pressure in it than the other from sitting...

Only way to verify is to manually tension the pulley pivots and check again.

I'm with Andy. The spec is 1.1 to 1.4, so both are within tolerance. I like to get the two a little closer to each other, but I don't think it is anything to lose sleep over, or to go to the trouble of opening up a chain housing and resetting one side. You might reset the valve lash on both #1 and #4 intakes and recheck the valve timing to see what that does to this spread.

For that matter, why not check all your valves' lash? Since you think something is amiss, this is a good place to start. You could even check each valve for maximum lift, which would give you some idea of a cam lobe wearing. Though I think that a visual inspection of each cam lobe (which you could do as part of the lash setting) will tell you, and one doesn't hear much about excessive cam wear absent some disaster, like a blockage in a spray bar. If you have such a thing you will see it at once.

Have you done a leak down? That's a nice, non-invasive diagnostic tool. Checked injector outputs?

Walt Fricke

Walt Fricke

Walt,

I've done a leakdown, compression, injectors removed and cleaned, ignition harness, flywheel sensors, fuel pressure, all DME wiring checked, looked for vacuum leaks, tested the AFM, all the usual stuff. I am now 3/4 of the way through checking the lift on all the valves, nothing unusual so far. If I can find another DME to try, I will. After that, I have no idea. One step at a time!
Thanks for the input.
Rob

These cars don't really have a constant sounding idle if you listen closly you can hear it change a little it won't show up as a rough idle or anything like that. It is really notiable on CIS cars it could just be the duty cycle of the Idle air control valve changing. Just my thoughts

OK

If you are comfortable setting valve timing, you can do it with the engine in the car. Jack the car way up at the rear. Pull the muffler and the rearmost engine tin and the tensioner oiler line. When you take the chain cover off you should get very little oil spilling out (reason to jack up high). Then set the left overlap closer to the right, since both are within spec. I find it hard to imagine this would cause the engine to feel like a cylinder isn't pulling its weight, but since it bugs you - - -. One more thing down.

Do you have an IR heat gun? You can use this on the exhaust manifolds close to the head to see if a cylinder is cooler (or hotter) than the others. Might help if you could put the car on a lift to do this, as all are not equally easy to aim at (nice to have that red dot on the thermometer device).

I suppose you could put it on a chassis dyno, and compare printouts with other 3.2 owners.

Is the lumpy sound only at idle? I understand that the idle air controller can be serviced. The usual complaint is that the idle speed is off, so that's a long shot.

Out of ideas.

Walt

I have listened to this motor. It does not surge at idle, the rpm is fairly steady, but there is a noticable repetetive consistent "beat" in the exhaust note. Very hard to describe.

I have the IR pyrometer with laser pointer if you want to borrow that Rob.

Cheers

Hmm

An acoustic phenomenon? I wonder if pulling spark plug wires one at a time would isolate this, or if the irregularity introduced by running on only five would mask it no matter which one was pulled.

If this is literally a beat frequency, you'd suppose it would be common on all stock 3.2s. Is the exhaust all stock?

Can the frequency be counted/timed? Now I am beginning to see why Rob sees some significance in the very small timing difference. However, isn't the frequency at an idle of 850 rpm roughly 4 Hz? Isn't that sub-audible? A beat frequency would be lower?

A small exhaust leak at a head gasket? When an air injector plug fell out of one of my motors with 2.7 heads I noticed it pretty much right away when idling in the grid. No such plugs in a 3.2, but - - -

Walt

Bad injector (stuck partially open) ???

I believe the injectors have all been cleaned, flow tested and balanced.

Cheers

If you could find someone that has the equipment to do a power balance test . it might lead to which cly. is not hitting correctly....

The thing is that it is very subtle, hard to describe in words. Walt, come on up and give it a listen! :) I was out of ideas when Rob talked to me, hence I suggested checking cam timing and valve lift. He has been very thourogh in checking every other system.

Cheers

Does reading the plugs give you any clues? If one cylinder is not pulling its weight there should be some telltale signs of over-rich or lean condition on the plug tip.
Did Walt's suggestion of inspecting the air injector ports result in anything?

there are no air injection ports on the 3.2.

Checking the plugs again would be prudent though.

Cheers