Cylinder deactivation attempt

[Christ]

Ok, well, not exactly.

I bought this '91 Geo Storm with a bad rod knock (assuming it's a rod) that you can hear while cranking the engine, it's so bad.

I've got a few options that I'm considering playing with, since the car is just a toy to me, really. I had thought originally that I was going to put a 3.0 V6 turbo into it, and make it a "fun" car, but I decided otherwise, for now at least.

So the current thought is that in a couple weeks, when I have time to actually go play with it, I'm going to go pull the head off and pull the pan off, and see how bad the damage is.

I don't want to rebuild the engine, and I'm not going to replace it with another stock engine, either, but I was thinking:

Maybe I remove two cylinders, and run it like a parallel twin? Every 360*, I get a power stroke, while the pistons shake the hell out of the car because they're always either up or down, and the counterweights on the missing pistons add to that shaking, because they're in the same locations as the remaining pistons at TDC and BDC... this poses a concern for the engine literally shaking itself apart.

I have two options, though. I can remove #1 and #4, and leave #2 and #3, giving me a power stroke every 360*, but leaving the pistons in sync with each other at all times through the rotation of the crank.

I could also remove #1 and #2, leaving #3 and #4, which are 180* out of phase with each other, canceling out the huge power pulses and associated vibration, but creating it's own funky vibration by having offset power strokes, where the second power stroke occurs at 180* from the first, leaving a full 640* of slack rotation between them, where no power is produced.

There is a less likely option to run #2, #3, and #4 in their original firing order (3,4,2), which provides a power stroke at 180*, 360*, and 640*, but then leaves the remaining 360* of rotation as a slack.

EDIT - This is not really an option, because of the strange balance that would come of it. Maybe if I get bored one day, I'll try it, but I find it highly unlikely that I'll ever bother.

Whatever I do, whichever piston(s) I remove, I will also remove the valves and associated hardware, and leave the cylinder an open bore with no plug.

EDIT - Removing the valves will leave the intake/exhaust open to oil spray, so the valves should/will be left in, and the rockers removed to prevent them from being in contact with the cam. (Thank you, Frank.)


Anyone have any questions, comments, etc?

Looking for some feedback on this, guys.

[Frank Lee]

That is EXACTLY what I was considering to do to a Tempo!

I think it would work. Disable 1 & 4, or 2 & 3. Did you know pistons in parallel twins go up and down in unison? Yeah, so when you block off the crank journals on the dead cylinders, do it so that your block-off is heavy enough to offset some of the counterweight. I was considering cutting the rods off at the big ends but hadn't come to a solid conclusion about if they should be free to rotate or if they should be affixed to the crank somehow. I think clearances to the block would answer that question.

Ignition: I figured on disabling two plugs by hammering the ground onto the center and welding it. Or making a place to ground the two wires externally.

Lifters: There needs to be something in the lifter bores for the oil gallery to function on my OHV. I thought I'd just pull the pushrods and let the lifters float. If that proved to be unacceptable for some unforseen reason I'd affix them in a neutral (no cam contact) position.

EFI: I figured on just pulling the wires off the injectors for the two dead cyls.

Exhaust/O2: Do nothing. Should be fine.

[Christ]

Here's something that will help some of you understand what it is I'm asking, exactly.



This is how a traditional Otto-cycle 4 cylinder works, the firing order of this engine would be 1,3,4,2.

If you want to properly envision what would be going on with each scenario I posted, just stick your finger over the missing piston from my description and watch the rest of the engine. Notice where the #1 and #4 crank weights are in relation to the #2 and #3 cylinders.

I do think I might be able to alleviate some of the problem with the crank weights by either weighting the journals with something similar to the weight of the piston/rod assembly, or by removing weight from the counter weights on those throws.

[Christ]

Originally Posted by Frank Lee

That is EXACTLY what I was considering to do to a Tempo!

I think it would work. Disable 1 & 4, or 2 & 3. Did you know pistons in parallel twins go up and down in unison? Yeah, so when you block off the crank journals on the dead cylinders, do it so that your block-off is heavy enough to offset some of the counterweight. I was considering cutting the rods off at the big ends but hadn't come to a solid conclusion about if they should be free to rotate or if they should be affixed to the crank somehow. I think clearances to the block would answer that question.

Ignition: I figured on disabling two plugs by hammering the ground onto the center and welding it. Or making a place to ground the two wires externally.

Lifters: There needs to be something in the lifter bores for the oil gallery to function on my OHV. I thought I'd just pull the pushrods and let the lifters float. If that proved to be unacceptable for some unforseen reason I'd affix them in a neutral (no cam contact) position.

EFI: I figured on just pulling the wires off the injectors for the two dead cyls.

Exhaust/O2: Do nothing. Should be fine.

Frank -

Ignition - remove two unused wires (what about ignition advance, though? It won't be optimal with only two cylinders operating.)

EFI - I want to find a way to "spoof" the injector return signal so that the ECM thinks that they're still there and functioning, so that the CEL doesn't turn on.

This engine is SOHC, so I planned on just removing the valves/rockers from the engine for those cylinders, leaving the cam spin freely (which could also create some unbalance).

You've actually made me think when talking about oiling, I will probably just weight the crank, because there needs to be something preventing oil from just flowing out of the rod journals! Maybe I cut the rods off and just add some weight to them?

[Frank Lee]

I think you will want to leave the valves in; you don't want any flow through there.

Re: Ign: Dunno about your engine but I don't think mine would notice two are offline. If there is an ignition indexed in some way to #1, then I'd have to disable 2 and 3, for the easy way out.

Re: Injectors: Perhaps short them out, or measure an injector and stick the appropriate resistor across there.

[Christ]

Ah, yes, I hadn't thought about that... removing the valves also leaves intake/exhaust open to oil spray! Good catch, Frank.

I will remove the rockers for the dead cylinders, though, so the cam doesn't move the valves at all.

[Frank Lee]

That, and the exhaust and intake charges are free to migrate across log and even tube manifolds.

I'd go for shorting out the two unused high tension ign wires because coils don't like conflicting signals. If you don't short out the high tension side, then remove the triggers for the induction side.

On mine I was planning to make it 100% reversible, as I would be starting with a good engine and on the chance this is a failure, would want to restore 4 cyl operation. You don't have that problem though.

[Christ]

Originally Posted by Frank Lee

That, and the exhaust and intake charges are free to migrate across log and even tube manifolds.

Ah, yes, charging the block with exhaust gasses might create some odd noises, eh?

[Frank Lee]

Might play games with the PCV too.

[Christ]

Originally Posted by Frank Lee

Might play games with the PCV too.

Meh. :P

What do you think about the 180* Parallel twin?

Supposedly, compared to the 360* PT of the same specs, the 180 has a flatter torque curve, which might be something to think about for a 2,000lb car that will now have less than 50HP. (The OE config only has ~90, and it's got 100,000+ miles, so probably closer to 70HP... divided by 2 and then some.)

Thoughts?