You may recall that I broke my buddy's car. Subsequently, my brother and I retimed the motor using the 45 BTDC position on the crank, with the cam sprockets off by a couple teeth (as instructed by several of you, thank you), and got everything back together. The motor turns over just fine, but we could never get it to fire; not even a chug. This seemed odd, considering that even with valve damage some of the cylinders should have fired.

I was literally going to sleep a couple nights ago when it popped into my head that maybe we were 180 out on the timing between the crank and the cams. And maybe I'm smoking crack, but since the crank turns twice for every rotation of the cams, if the cams - which fire the spark - are on the exhaust stroke and the crank - which I believe fires the injectors - is on the compression stroke, we're not going to get anything from the motor. Not even a chug.

So, am I dumb for thinking that we might be 180 out? Or am I ignorant in not understanding how the injectors are fired?

 

Assuming your model year has a distributor then that must be indexed correctly. Whether they can be hooked up 360 crank degrees out I will leave that to those more knowledgeable about the specifics of the 928 distributor as used on the early models. Last car I had with a distributor could certainly be installed incorrectly in the manner you envisage but that was such a long time ago now!!!

 

A previous owner had pulled the dist. on my '81 and advanced(?) it a gear or 2. The adjustment was fully advanced also (turns out the retard vac had fallen off inside dist). The car ran like a raped ape stupid quick for an '81 (u.s. auto) but could only get about 8 mpg no matter what. Anyway I believe (could be terribly wrong) that you can get it out 180

 

If the Harmonic Balancer is installed backwards, the car will not run either.

 

The crank and pistons don’t ’know’ if they are on the power stroke or the compression stroke. It’s all the same to a piston going up or down.

With batch fire port injection (i.e. LH 2.2 and 2.3) it doesn’t matter when you fire the injectors. Since you are firing four injectors at a time, some of the fuel is going to land on a closed intake port and sit there waiting for the next intake stroke to suck in and atomize the fuel.

So, no, rotating the cams 180° doesn’t change anything.

Pedantically, If *all* you do is install the balancer backward the 928 will run just fine. You have to install the balancer and then - with your own hands - do something to screw up the cam timing by changing the timing with the now-screwed timing marks.

 

For single-distributor US cars, you can indeed get the cams 180º away from the distributor timing. Rotate the engine so the cams and crank show TDC on #1 cylinder. Lift the distributor cap and see if the rotor is pointing to #1 plug wire and the index mark on the distributor body. You'll see instantly if it's 180º out.



I don't have a distributor car handy, so use my Generic instruction until someone else offers better 928-specific guidance:

If it is 180º, make an index mark on the bottom of the distributor housing at the clamp on the block, so you can put the housing back exactly where you see it now. Then unbolt the clamp, and lift the distributor straight out some. The gear on the drive is helical, so the rotor will turn some as you lift the housing from the block. Lift the housing until the rotor stops turning, and note the position relative to the housing. Then rotate the rotor in the housing exactly 180º. Carefully drop the housing back into the block, and the rotor will turn on the helical gear to point at the index mark on the body. Tighten the clamp bolt after you've verified that the mark you made still lines up. You should be at the same ignition timing, but it's always a Good Idea to verify with a timing light.


Waste no time contemplating 'just' moving the plug wires 180º on the distributor cap. The wires will be crossed, and the next person that works on the car will end up fixing it anyway. Very likely that will be you anyway, so just fix it now and sleep better.

 

Car is question is an '85S. I assumed it was non-Euro and therefore 32v. If it is 16v, then yes it is possible to get the spark and cam timing out of phase(*) I suppose...

But, in either case, the crank and pistons still don't care which stroke they are on and it doesn't matter when the injectors fire relative to intake port opening.

(*) It is possible to get the spark timing screwed up relative to the cams on the 32v cars. But, you have to really, really try hard and have a talent for !@#$ing $h1+ up.

 

Let's not dismiss anything at this point.

But, no, I don't think the spark timing is messed up. The distributor caps lined up nicely inside the hashmarks on the cam sprockets during assembly. It was the injector pulse I was concerned about, and I don't really understand why more than one injector would fire at once.

 

Since nothing should be dismissed at this point, do you know if the injectors are firing at all? Due you have fuel pressure? Are the spark plugs firing? As the old saying goes, when you hear hooves, think of horses, not zebras.

 

Before you put the distributor caps on, did the rotors point to the cam gear marks too?

What BB wrote is operative: do you have spark? Are the TDC marks on the gears lined up with 0° on the balancer? Is the balancer on the right way? Do you have *any* reason to suspect that the rubber - that has the timing marks - on the balancer is ‘spinning’ on the balancer’s keyed-to-the-crank metal face?

 

You are correct of course.

 

Go back to basics:
1. Compression > 120PSI all jugs (some jugs after valve crash)
2. Stoichiometric fuel air mix of ~ 12:1 air to fuel (no fuel pump relay, use carb cleaner spritz into intake)
3. Properly timed spark for Otto cycle engine ( approx 2-6 degree BTDC)

You need 1) compression gauge, can borrow free from Auto Zone/O'reillys. 2) Can of carb cleaner or two, same source or WalMart. 3) Inductive timing light attached to #1 plug lead - from Amazon, or a buddy, or Harbor Freight, and visible marks on balancer. Stop guessing and do your diligence, then get back to us. Inductive timing light will also verify sufficient voltage to traverse the plug gap.

 

At TDC timing marks should look like this. I put a black pen mark on the front of the cam gears that lines up with the engraved index mark so it's easier to see from the front of the engine.

This motor is an 83 4.7L



.



Distributor may have been off by 1 tooth in the photo below, but there's a mark on the edge of the distributor in that vicinity of where the rotor is pointing that should be aligned. The flash washed out the mark in this photo

 

Yes.

I'm sure the balancer is correct.

Thanks, Doc. This idea occurred to me the other night. I'm out of town, so I'm not in a position to check any of this, I was just asking if this was even a possibility before I go tearing into the car again. And especially since a running motor has already been purchased for this car, and this one will be swapped out and eventually rebuilt. I have to refresh the suspensions on my Boxsters this weekend, but I'll try to at least get a timing light on it.

Just to reiterate: This was a running 32v motor that suffered a timing belt loss (due to my mistake). Subsequent to that, the only thing that was done was to pull the belts, retime the motor, and try to fire it. The motor gave a single 'chug' on the first turn of the key, but now it just spins. That bugs me, since I would have expected something, even with bent valves on a cylinder or two.

 

Follow doc's suggestion to verify compression and report back. As others have said, you can't end up 180° off (cam timing) without making a concerted effort to do so.