Stumped in New Mexico

[djwarner]

Christian,

From what I've learned you should definitely be checking the timing with the vacuum hose disconnected and plugged to get to the 10 BTDC setting you are reading about. I've started another thread in Engine and Drivetrain (S30) discussing timing.

The remaining issue you may have is your 7000 ft altitude. I have Weber carbs and don't have experience with SUs but you elevation may require a jet change.

[robox]

Those are float bowl vents and should be left open to atmospheric air.

Thanks... yeah, that makes sense.

I thought you had already gone back to your previous timing before this.

I did in fact play with all sorts of timing settings, with no results... but that was when I had the Pertronix inductive ignition module installed. It was not until I re-installed the original set of points that the engine decided to work again. All the info stated above regarding engine performance respective to timing is pertinent only to using the points. With the Pertronix module, the engine simply would not work, regardless of timing.

As stated earlier, you need to get this issue resolved(timing). If you are going to own a Z , this is right to passage to work on these engines. There are hundreds of threads on this so get searching

I will start reading. I would like to get a better idea what it really means when a car will only run happily with such ridiculously high advance. I don't yet understand what that means. Maybe a badly stretched cam chain? Just a guess....

Thanks

[robox]

Christian,

From what I've learned you should definitely be checking the timing with the vacuum hose disconnected and plugged to get to the 10 BTDC setting you are reading about. I've started another thread in Engine and Drivetrain (S30) discussing timing.

The remaining issue you may have is your 7000 ft altitude. I have Weber carbs and don't have experience with SUs but you elevation may require a jet change.

Thanks djwarner. To answer an earlier question of yours that I never addresses... no my car is not an automatic.

I will read your thread about timing, and probably several others.

Yes I know that a re-jet for my altitude may be in the offing. Might help with the super-stinky exhaust!

[Stanley]

What rpm is giving you 30 deg advance? Do you have one on those fully degreed race type pulleys (or a dial-back timing light)? My pulley is only marked at 0,5,10,15, 20.

At 7000 ft the air is thinner so you need to lean the mix so the air/fuel is correct. But when it's cold the air is denser so you need a richer mix setting. There's a graph in FSM for baseline settings. But if the needles/nozzles are worn it could be way off.

[Stanley]

Checked the graph in the engine manual, for 7000 ft and 32F baseline is about 2.5 turns down. But at 68F it should be about 1.5 turns down, and at 86F about 1 turn down.

Looked for that graph in the pdf engine manual online at xenon but it wasn't there, Don't know what year that manual is but it's in my 1972 manual.

[robox]

Here is the timing degrees scale on my engine:

It's slightly hard to see, but the scale does go up to 30º.

I am getting the 30º reading, with attendant good engine operation, at an idle rpm of about 800-850 (tachometer broken, so I am guessing). When I rev the engine, the timing light shows the pointer going up to about 45º (off the scale, obviously, so guessing on this one as well.)

Regarding the idea of the distributor being off one tooth...

My thinking was that maybe, just maybe, the drive gear might be 10 teeth. If it was off one tooth, or off by 36º, then maybe when the timing light shows 36º it's actually at 0º. If it showed 40º, that would really be 4º advanced, and so forth. I wasn't advancing this as a theory about why the engine wasn't running previously, but rather as a theory to explain the weirdly advanced timing settings that the engine seems to need to work properly.

Thanks, as always!

[Zed Head]

The timing mark that you see is only relative to piston #1's position when the spark occurs in the wire to cylinder #1. Doesn't really matter how the spark happened, the oil pump could be off 80 degrees. That is assuming that the mark on the damper pulley is in the right place. Have you checked piston and camshaft position when the mark is at zero? The piston should be at the very top of its stroke (top dead center/TDC) and the camshaft should have both valves closed. Dampers do go bad and the mark can move. You might have a bad damper and a misplaced timing mark.

Your pulley is kind of odd looking, with the teeth on the pulley. But I have a 280Z so maybe that's normal for the 240's.

[JRSGTS]

Zed's right.. Check for your static timing. Pull #1 plug, bump the starter till compression blows your finger off the hole. Check your mark. You might need to rotate it a bit to get to zero. The check under your Distributor cap, make sure rotor is pointed to #1. If not, you can either move the dist. or the wires. Just make sure you don't mess up the firing order. Also helps determine if timing jumped or not.

To check for timing chain stretch. With your timing mark in view. Rotate engine by hand one direction ( I know it's a bitch) Note timing mark position. This is the hard part. Now you have to watch the mark as you rotate the engine back the other way. Stop as soon as the rotor starts to move. The more degrees of engine rotation before the rotor moves, the worse it is. On a V8 we generally allow around 10-15 degrees max.

[robox]

MYSTERY SOLVED!

I enlisted the help of a friend to hold a piece of 3/32" welding wire in the #1 spark plug hole while I slowly rotated the crankshaft with a ratchet handle and socket. We worked together to find absolute TDC on #1, and....

The timing pointer points at 30º when cylinder #1 is at TDC !!

So 5º past the end of the scale is actually 5º advanced. When I first timed the car it was somewhere between 35º and 38º, so 5º - 8º advanced. Sounds about right.

Maybe the damper (I guess that's the name for the pulley that carried the timing pointers) was installed incorrectly at some point in the past. Or maybe the little scale with the degree markings was installed incorrectly. If (when) I rebuild the engine, perhaps I will figure out what happened.

I guess the next step for me will be to put the Pertronix ignition module back into the distributor, armed with this new info, and see if it was really defective, or if my lack of knowledge about the quirks of this particular engine invalidated the earlier tests... if you know what I mean

Oh, and also... I did the "rotate the crank one way, then rotate it the other way, while watching the distributor rotor and also the timing marks and degree scale" test to determine the dead space, and it was about 6º-7º. Seems like probably not a source of concern.

C

Edited December 3, 2013 by robox

[madkaw]

Looking at the pic I'd say you have a late model L28 in your 71!

Did I miss something or did you say this was a 71 240z because that is NOT a 71 damper or timing scale

[JRSGTS]

Or your Pulley has slipped... Take a good look at it. If it has slipped it means it is about to fail...Never a good thing. Looking at your pic. it appears the rubber is deteriorating. When that spins apart bad things can happen. I'd order one, if it has moved, it is junk.

JR.

[robox]

OK, thanks guys. I will look carefully at the pulley (and try to find the rubber you are referring to) in order to see if it looks like I've got an imminent failure around the corner.

Regarding the possibility that this is an L28 engine: It wouldn't surprise me. A convincing argument could be made that the purchase of this car (by me) was somewhat impulsive. I bought it without ever having seen it in person... from two guys who in retrospect have been proven to be shysters, liars, swindlers... whatever. The car had WAY more problems than I was led to believe. The selling points for me were that it was a Series 1 car with a basically straight body and an intact interior, and a reasonable price (although I quickly came to feel I'd paid too much). Mechanically the car was on the verge of falling apart from neglect and/or uninformed tinkering. I was told that it was not the original engine, but if it's an L28 that is news to me. It's a project, and obviously a big part of that project is learning about what I've really got.