2G Weird theoretical question

[waltah]

Will these engines run at all with one of the camshafts 180 degrees out?

I have a parts car which was said to have been driven several hundred miles to where I bought it, then shortly it 'lost power,' then the new owner started working on it but lost interest. Then Craigs List, a deal, and it got trailered here. I've swapped most of the interior, the rear bumper, just finished swapping the A/C evaporator since the avatar car one was leaking but it's really too good a car to simply scrap -- it looks grubby, lots of minor stuff but there's little rust, only minor body damage other than that. So I thought I'd see if the engine runs. Tonight I tried to line up the timing marks and when the exhaust cam sprocket mark points toward the intake camshaft and is level with the deck, the mark on the intake cam sprocket points toward the rear of the car -- not toward the exhaust camshaft.

Tough to wrap my head around this. The exhaust valves would be open during the compression stroke so there wouldn't be much mixture there when the spark hit it. Could it possibly have run that way? Or did the P.O. mess up the timing as an early step in his 'working on it'?

 

[Mech Addict]

I would think with one cam 180 degrees out of phase, the intake and exhaust valves would collide as they both tried to open at the same time, given the hemi-head layout (even if it’s technically called pent-roof).

I’ve never actually had my head removed (that sounded weird), but the illustration says it all.

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[DSMPT]

Maybe I am not understanding very well how the situation is, but if I understood correctly, no it won't run. IF only the intake cam is 180 degree off (at cam), it means when the cylinder is in intake stroke, the intake cam position would be in power stroke, which means the intake valves are fully closed. So the cylinder wouldn't draw fuel and air while in intake stroke. And when the cylinder is in power stroke, the intake valves would open and draw the air, but next stroke would be exhaust, so the air would be purged.

 

[pauleyman]

Personally I wouldn't worry about the how or why. I would remove cams, verify all the valves are closed (not bent) and reinstall cams dowels up and proceed with a timing job.

 

[steve]

Tonight I tried to line up the timing marks and when the exhaust cam sprocket mark points toward the intake camshaft and is level with the deck, the mark on the intake cam sprocket points toward the rear of the car -- not toward the exhaust camshaft.

Where were the camshaft dowels when the mark was like this?
The cam sprockets usually have marks almost 180* apart so that they can be used on both the intake and exhaust cams.

 

[Mech Addict]

I’m picturing that when one cam dowel is pointing down, the other is straight up? Honestly I would not try turning the crank by hand in this scenario, let alone try to start it. Of course if this is simply a scrap engine, you can conduct some primary science. Who knows: maybe it makes twice the power of a “normal” setup.?? Get a video if you try it

 

[waltah]

Well this all helps stretch my mind. Especially 'valves might collide.' I hadn't thought about that possibility.

The observation I started with was all I did at the time -- just at dusk last night. Didn't look any further (dowels, other marks on sprockets, etc.) but will try to do it today.

There is NO chance I try to start the engine like that just to see what happens. I'll do the basic valve timing job starting with dowels and when it's properly timed, check compression. Maybe it is a scrap engine but I'm not going to create that situation if I can help it.

I'll try to get a couple of pics.

 

[steve]

Well this all helps stretch my mind.

It's a good mental exercise to think through what happens to the crank, pistons, two cams, and four valves as the engine goes round and round.

If you do, you'll quickly see why the engine doesn't work with the intake cam 180* out of phase and is likely to have multiple parts trying to occupy the same space at the same time.

Once you have that worked out, add two balance shafts when one runs at an odd multiple of the crank speed.

 

[waltah]

The cam sprockets usually have marks almost 180* apart so that they can be used on both the intake and exhaust cams.

Bingo!

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The yellow mark at the left is the only one I saw on the exhaust sprocket last night but there are two and that's the wrong one. Dowels (also marked yellow) are up and this is with the crank at TDC per the notch on the pulley and marks on the lower timing cover. About 3/4 tooth error.

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With the cam sprocket marks aligned, this is what you get -- crank (vertical line at right) is about 5 degrees past TDC (horizontal line).

The engine was said to have 'lost power' shortly after driving it across a few states. Could this be a one-tooth skip on the exhaust cam sprocket? I suppose that would cause a loss of power and it seems to me that with a fairly slack tensioner you'd get a standing wave on the tensioner side that would cause a skip there first. The tensioner is at least not correctly adjusted. If you put the slack in the belt between the cam sprockets you can deflect the belt by about 1/2" with little pressure.

The belt looks near-new as do the accessory belts.

So at a minimum, remove the lower timing cover and inspect, readjust the tensioner, and advance that exhaust sprocket by one notch?

I do need to provide some profile or project info on this car -- it's a '95 GS-T M/T with 150k on the clock.

 

[DSMPT]

Bingo!

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The yellow mark at the left is the only one I saw on the exhaust sprocket last night but there are two and that's the wrong one. Dowels (also marked yellow) are up and this is with the crank at TDC per the notch on the pulley and marks on the lower timing cover. About 3/4 tooth error.

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With the cam sprocket marks aligned, this is what you get -- crank (vertical line at right) is about 5 degrees past TDC (horizontal line).

The engine was said to have 'lost power' shortly after driving it across a few states. Could this be a one-tooth skip on the exhaust cam sprocket? I suppose that would cause a loss of power and it seems to me that with a fairly slack tensioner you'd get a standing wave on the tensioner side that would cause a skip there first. The tensioner is at least not correctly adjusted. If you put the slack in the belt between the cam sprockets you can deflect the belt by about 1/2" with little pressure.

The belt looks near-new as do the accessory belts.

So at a minimum, remove the lower timing cover and inspect, readjust the tensioner, and advance that exhaust sprocket by one notch?

I do need to provide some profile or project info on this car -- it's a '95 GS-T M/T with 150k on the clock.

Valve timing is complicated but actually people are making it more complicated because they set cam position first and then try to see how much off.
The way to think about valve timing is always one way, the valve position against piston position (No vice versa). So to know how much the timing is off, you have to properly set the crank mark at TDC first, and then see how much the cam gears are off.
We can't make it off by a half tooth, 3/4 tooth etc. If it's off, it would be from minimum 1 tooth. According to the pics, you have 15 teeth on the belt between intake and exhaust gear's 12th tooth (Counting from the horizontal timing mark. 12 o'clock tooth). If only exhaust side is off by 1 tooth retarded, the count should be 16 teeth. So to me, it looks like both intake and exhaust cams are 1 tooth off (retarded).

 

[Mech Addict]

Hope your tensioner is only out of adjusting and not failed. JNZ just announced that 7bolt tensioners are nla.
Skipped tooth seems plausible, and from what I’ve read a milled head or block will be difficult to all line up too, so perhaps it had that done. If I’ve misunderstood this, let’s just say it’s not my first time.
If you want to “stretch your mind” a bit more, consider this question that I’ve not solved yet:
You go to time the motor, line all the marks properly, but with the dowels 180 degrees off. I first started pondering this, of course, when I inadvertently went through the whole tbelt swap and had my dowels 180 off. At the time I couldn’t think of a good reason mechanically to fix it. I did fix it because it wasn’t that hard and I was not curious enough to risk catastrophic destruction (not a parts-motor like yours). Now I can only think that the fuel injection would be all messed up, trying to spray into cylinders that were on exhaust stroke. But mechanically I thought it would all work. Ignition-wise, too, because wasted spark (right?).
Begin stretching—

 

[pauleyman]

Valve timing is complicated but actually people are making it more complicated because they set cam position first and then try to see how much off.
The way to think about valve timing is always one way, the valve position against piston position (No vice versa). So to know how much the timing is off, you have to properly set the crank mark at TDC first, and then see how much the cam gears are off.
We can't make it off by a half tooth, 3/4 tooth etc. If it's off, it would be from minimum 1 tooth. According to the pics, you have 15 teeth on the belt between intake and exhaust gear's 12th tooth (Counting from the horizontal timing mark. 12 o'clock tooth). If only exhaust side is off by 1 tooth retarded, the count should be 16 teeth. So to me, it looks like both intake and exhaust cams are 1 tooth off (retarded).

This exactly as it should be stated. Everything is relative to the crank, not the other way around. Also do not trust the balancer to give you TDC. Trust the sprocket.

So waltah, was this always both dowels up and we have misread something? I'm a little confused.

 

[DSMPT]

the fuel injection would be all messed up, trying to spray into cylinders that were on exhaust stroke.

Right but it would be spraying on power stroke.

mechanically I thought it would all work.

Unlikely happens and I have never tried that but it should work, if you would switch the fuel timing between cylinder 1 <-> 4 and 2 <-> 3.

 

[Mech Addict]

If the CAS were modified so that it would also fit on the back of the cam “backwards”, and both cams fitted 180 off, should work normal: right? Or why not?

 

[DSMPT]

should work normal: right? Or why not?

Yes it should.

 

[pauleyman]

Right but it would be spraying on power stroke.

Unlikely happens and I have never tried that but it should work, if you would switch the fuel timing between cylinder 1 <-> 4 and 2 <-> 3.

I dont think this is right. TDC is TDC. Power or exhaust stroke is all about cam position. Only way ecu knows anything is CAS (in phase) or for 2g Crank sensor also.
Those sensors are fixed. Cams line up dowels down every other turn of crank. If you accidently set timing dowels down all I think it would do it mess up balance shafts assuming you still had them.

 

[DSMPT]

I dont think this is right. TDC is TDC. Power or exhaust stroke is all about cam position. Only way ecu knows anything is CAS (in phase) or for 2g Crank sensor also.
Those sensors are fixed. Cams line up dowels down every other turn of crank. If you accidently set timing dowels down all I think it would do it mess up balance shafts assuming you still had them.

I think there is a confusion or maybe you got me wrong. Yes TDC is TDC but it's cam position and piston traveling direction. I meant 180 cam degree from intake stroke is in power stroke. Not exhaust stroke. I am just speaking about only pistons/cams position as it's mentioned mechanically.

I always think the way below when I adjust valve clearance for solid lifters. Also useful for leak down test to know which cylinder's valves are fully closed. Hope this would explain better than my english vocabulary.

When you set the valve timing properly following the timing marks, the event sequence would be like below.
Cyl #1 : C, P, E, I, C, P, E, I, C, P, E, I, C, P, E, I
Cyl #2 : P, E, I, C, P, E, I, C, P, E, I, C, P, E, I, C
Cyl #3 : I, C, P, E, I, C, P, E, I, C, P, E, I, C, P, E
Cyl #4 : E, I, C, P, E, I, C, P, E, I, C, P, E, I, C, P

If you accidentally set the IN/EX cams 180 degree off, it would be like below.
Cyl #1 : E, I, C, P, E, I, C, P, E, I, C, P, E, I, C, P
Cyl #2 : I, C, P, E, I, C, P, E, I, C, P, E, I, C, P, E
Cyl #3 : P, E, I, C, P, E, I, C, P, E, I, C, P, E, I, C
Cyl #4 : C, P, E, I, C, P, E, I, C, P, E, I, C, P, E, I

If you accidentally set only intake cam 180 degree off, it would be like below. (This is what I tried to explain in my first comment)
Cyl #1 IN : E, I, C, P, E, I, C, P, E, I, C, P, E, I, C, P
Cyl #1 EX : C, P, E, I, C, P, E, I, C, P, E, I, C, P, E, I
Cyl #2 IN : I, C, P, E, I, C, P, E, I, C, P, E, I, C, P, E
Cyl #2 EX : P, E, I, C, P, E, I, C, P, E, I, C, P, E, I, C
Cyl #3 IN : P, E, I, C, P, E, I, C, P, E, I, C, P, E, I, C
Cyl #3 EX : I, C, P, E, I, C, P, E, I, C, P, E, I, C, P, E
Cyl #4 IN : C, P, E, I, C, P, E, I, C, P, E, I, C, P, E, I
Cyl #4 EX : E, I, C, P, E, I, C, P, E, I, C, P, E, I, C, P

I : Intake (Piston goes down)
C : Compression (Piston goes up)
P : Power (Piston goes down)
E : Exhaust (Piston goes up)

Firing order : 1-3-4-2

 

[pauleyman]

I think there is a confusion or maybe you got me wrong. Yes TDC is TDC but it's cam position and piston traveling direction. I meant 180 cam degree from intake stroke is in power stroke. Not exhaust stroke. I am just speaking about only pistons/cams position as it's mentioned mechanically.

I always think the way below when I adjust valve clearance for solid lifters. Also useful for leak down test to know which cylinder's valves are fully closed. Hope this would explain better than my english vocabulary.

When you set the valve timing properly following the timing marks, the event sequence would be like below.
Cyl #1 : C, P, E, I, C, P, E, I, C, P, E, I, C, P, E, I
Cyl #2 : P, E, I, C, P, E, I, C, P, E, I, C, P, E, I, C
Cyl #3 : I, C, P, E, I, C, P, E, I, C, P, E, I, C, P, E
Cyl #4 : E, I, C, P, E, I, C, P, E, I, C, P, E, I, C, P

If you accidentally set the IN/EX cams 180 degree off, it would be like below.
Cyl #1 : E, I, C, P, E, I, C, P, E, I, C, P, E, I, C, P
Cyl #2 : I, C, P, E, I, C, P, E, I, C, P, E, I, C, P, E
Cyl #3 : P, E, I, C, P, E, I, C, P, E, I, C, P, E, I, C
Cyl #4 : C, P, E, I, C, P, E, I, C, P, E, I, C, P, E, I

If you accidentally set only intake cam 180 degree off, it would be like below. (This is what I tried to explain in my first comment)
Cyl #1 IN : E, I, C, P, E, I, C, P, E, I, C, P, E, I, C, P
Cyl #1 EX : C, P, E, I, C, P, E, I, C, P, E, I, C, P, E, I
Cyl #2 IN : I, C, P, E, I, C, P, E, I, C, P, E, I, C, P, E
Cyl #2 EX : P, E, I, C, P, E, I, C, P, E, I, C, P, E, I, C
Cyl #3 IN : P, E, I, C, P, E, I, C, P, E, I, C, P, E, I, C
Cyl #3 EX : I, C, P, E, I, C, P, E, I, C, P, E, I, C, P, E
Cyl #4 IN : C, P, E, I, C, P, E, I, C, P, E, I, C, P, E, I
Cyl #4 EX : E, I, C, P, E, I, C, P, E, I, C, P, E, I, C, P

I : Intake (Piston goes down)
C : Compression (Piston goes up)
P : Power (Piston goes down)
E : Exhaust (Piston goes up)

Firing order : 1-3-4-2

No I don't think that's right because the cam sensor is directly bolted to intake cam. So no matter what you do cpei is always relative to that sensor. This would not be true if we had a distributor but with what we have that doesn't happen. If I'm wrong I'm completely not following.

 

[DSMPT]

No I don't think that's right because the cam sensor is directly bolted to intake cam. So no matter what you do cpei is always relative to that sensor. This would not be true if we had a distributor but with what we have that doesn't happen. If I'm wrong I'm completely not following.

Yes the sensor is attached to intake cam. And now I know what's the confusion, 1g vs 2g. On 1g if CAS would be installed after cams are installed 180 degree off = CAS is 180 degree off. And here I am talking about only the mechanical timing, and it would fire if cylinders have good compression/spark/fuel in the right timing.

 

[waltah]

So waltah, was this always both dowels up and we have misread something? I'm a little confused.

Looking at the valve timing in poor light and without knowing that sprockets could have two marks I got the wrong one on the exhaust side and paying no attention to the dowel positions said "This looks really wrong." Actually it was almost fine -- seems like one skipped tooth on the exhaust sprocket. The error was mine, in taking the data.