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L28E TDC Verification


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Rebuilt L28E, unsure if head was shaved, bored out, new pistons, etc.

 

Here is where it sits now, explain to me what the engine assembler was thinking and how it can all be adjusted back to OEM specs.

 

 

So I set the crank pulley by hand to 0° verifying the piston is TDC, however between 10° and 0° per the crank gauge the piston doesn't move up or down.

 

IMAG0195_zps77f45b3b.jpg

 

 

Here is where the cam gear notch sits:

 

IMAG0196_zps857aed8d.jpg

 

Cam pulley orientation, stamp 3 to the right and stamp 1 lower left corner of pic, obviously 2 is out of the shot:

 

IMAG0201_zps86210b05.jpg

 

 

Cam lobes pointed up like bunny ears:

 

IMAG0197_zpsd273b856.jpg

 

 

Distributor points here and was pointing at plug #1 on the cap.  Engine did run, just not smooth:

 

IMAG0198_zps4a1d895a.jpg

 

Farther out:

 

IMAG0200_zps33777e4a.jpg

 

 

 

So I call the expert builders to chime in and get me to set this all back in order.  Thanks for your time and advice, it is much appreciated.

Edited by AdreView
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Before you go further, make sure the tight side of the chain (driver's side) is actually tight.  If you're moving the crankshaft back and forth, you could have the tight side loose.  Set the pulley mark at zero and use a wrench on the sprocket bolt to tighten it up, without moving the crankshaft.

 

If it is tight, then it looks likes someone was anticipating a lot of chain wear.  You're in the after-after adjustment zone.  Pretty sure I've seen where guys have advanced the sprocket and cam to the 2 hole to move the power curve to the low end.  Gives the feel of more power, but the top end is gone.  If so, move it to hole 1 and see where things end up.  Don't forget to wedge the chain.

 

Nice pictures.

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Before you go further, make sure the tight side of the chain (driver's side) is actually tight.  If you're moving the crankshaft back and forth, you could have the tight side loose.  Set the pulley mark at zero and use a wrench on the sprocket bolt to tighten it up, without moving the crankshaft.

 

If it is tight, then it looks likes someone was anticipating a lot of chain wear.  You're in the after-after adjustment zone.  Pretty sure I've seen where guys have advanced the sprocket and cam to the 2 hole to move the power curve to the low end.  Gives the feel of more power, but the top end is gone.  If so, move it to hole 1 and see where things end up.  Don't forget to wedge the chain.

 

Nice pictures.

 

NZ,

 

Chain and sprocket are tight per spec with crank pulley set at zero.  I was only moving the crank clockwise to align.

 

Can you enumerate a bit more on the after-after adjustment zone.  Are you referring to the cam and the sprocket or just the sprocket?

 

From current settings I have posted, can we take a guess where the actual mechanical timing is set at?

Also, is the distributor in the correct position?

The distributor set screw is at the most counter clockwise position, what does this indicate with the rest of the motor settings?

Edited by AdreView
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Not sure what you are asking exactly.

 

If you are 0 on the crank then your mechanical timing is at 0.

 

Cam looks to be in the right position via bunny ears.

 

Usually the distributor is checked with the rotor off and a screw driver is used to align it, but if it is pointing at spark 1 then it should be correct.

 

Do you mean the mechanical timing of the crank vs the cam shaft?

 

The cam sprocket can be moved depending on how old the chain is there is a stud so it can only be moved to one of 3 positions. each one advances or retards by 4* if memory serves. It is used to account for chain stretch, some people do move this to move the power curve around a bit. Looks like the cam drive train was advanced by a few degrees, so it will open the valve a little earlier. If everything is new and the fact that the cam sprocket is not lined up bothers you, use a timing chain tensioner tool and hold the cam via the flat spot with a wrench, making sure the wrench isn't biting into the soft aluminum. Loosen the bolt, and with a rubber mallet knock the sprocket off. Remove the bolt and move the sprocket to the other positions until the timing mark lines up. Reassemble and torque everything to spec.

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I was referring to the picture in the book.  As the chain wears the notch (in the sprocket) lags the oblong groove (bolted to the cam tower).  The valves open later.  In the picture, "before adjustment" shows a stretched chain (valves opening late), "after adjustment" shows it repositioned so that the valves open sooner.  Your notch has the valves opening waaayyy sooner.  IF the tight side of the chain is tight.   You can also think of it as the straight side.  It's the side of the chain that gets pulled when the crankshaft is turning.  It needs to be tight to know what is actually happening when the engine is running.

 

The distributor has nothing to do with what you're looking at.  It and the oil pump are in a whole separate world.

post-8864-0-12542700-1396479208_thumb.jpg

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I was referring to the picture in the book.  As the chain wears the notch (in the sprocket) lags the oblong groove (bolted to the cam tower).  The valves open later.  In the picture, "before adjustment" shows a stretched chain (valves opening late), "after adjustment" shows it repositioned so that the valves open sooner.  Your notch has the valves opening waaayyy sooner.  IF the tight side of the chain is tight.   You can also think of it as the straight side.  It's the side of the chain that gets pulled when the crankshaft is turning.  It needs to be tight to know what is actually happening when the engine is running.

 

The distributor has nothing to do with what you're looking at.  It and the oil pump are in a whole separate world.

If you don't know whether/how much your head or block have been shaved, then all bets are off.  The timing mark on the cam sprocket is just to get in the ballpark, and that's when you have an unshaved, unmodified head.  

 

The only way to get what you are asking for is to degree the cam.  Read this thread:

http://forums.hybridz.org/topic/46043-using-a-degree-wheel-to-degree-in-your-l-series-cam%E2%80%A6/?hl=degreeing

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I was looking for that reference guide, thanks. 

 

 

 

Not sure what you are asking exactly.

 

If you are 0 on the crank then your mechanical timing is at 0.

 

Cam looks to be in the right position via bunny ears.

 

Usually the distributor is checked with the rotor off and a screw driver is used to align it, but if it is pointing at spark 1 then it should be correct.

 

Do you mean the mechanical timing of the crank vs the cam shaft?

 

The cam sprocket can be moved depending on how old the chain is there is a stud so it can only be moved to one of 3 positions. each one advances or retards by 4* if memory serves. It is used to account for chain stretch, some people do move this to move the power curve around a bit. Looks like the cam drive train was advanced by a few degrees, so it will open the valve a little earlier. If everything is new and the fact that the cam sprocket is not lined up bothers you, use a timing chain tensioner tool and hold the cam via the flat spot with a wrench, making sure the wrench isn't biting into the soft aluminum. Loosen the bolt, and with a rubber mallet knock the sprocket off. Remove the bolt and move the sprocket to the other positions until the timing mark lines up. Reassemble and torque everything to spec.

 

I'm just trying to validate that everything is near "normal" position, not so far out that valves hit pistons.

You are correct that if 0 on the crank, then "in theory" mechanical timing is at zero if the pulley hasn't slipped due to its bonded design.  

Cam position is correct, yep.

Yes, I meant the mechanical timing of crank vs. cam shaft due to the sprocket being I believe 180 degree out of position.  The sprocket doesn't bother me in this position, I just wanted to verify it's alignment.

 

 

 

I was referring to the picture in the book.  As the chain wears the notch (in the sprocket) lags the oblong groove (bolted to the cam tower).  The valves open later.  In the picture, "before adjustment" shows a stretched chain (valves opening late), "after adjustment" shows it repositioned so that the valves open sooner.  Your notch has the valves opening waaayyy sooner.  IF the tight side of the chain is tight.   You can also think of it as the straight side.  It's the side of the chain that gets pulled when the crankshaft is turning.  It needs to be tight to know what is actually happening when the engine is running.

 

The distributor has nothing to do with what you're looking at.  It and the oil pump are in a whole separate world.

 

That is what I was looking for in the FSM, an explanation to the distance and side these 2 markings can be in relationship to one another.  Thanks, that explains it.  Once I get this back on the road, I'll have to potentially play with the sprocket to hone in on the powerband I desire.

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If you don't know whether/how much your head or block have been shaved, then all bets are off.  The timing mark on the cam sprocket is just to get in the ballpark, and that's when you have an unshaved, unmodified head.  

 

The only way to get what you are asking for is to degree the cam.  Read this thread:

http://forums.hybridz.org/topic/46043-using-a-degree-wheel-to-degree-in-your-l-series-cam%E2%80%A6/?hl=degreeing

 

Without pulling the head are there any indicators to determine if either one was shaved?

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TimZ makes a good point about modified parts.  I almost posted something about whether or not that cam is factory or a regrind, if it's a regrind the mark may be irrelevant.  But if it's a stock cam the marks should still be aligned, even if they're not optimum.  The mark tells you what position the valves are in (since they're at the ends of the lobes), in relation to the pistons.  The before and after picture in the FSM is 4 degrees.  You're cam is about 8 - 10 degrees advanced.

 

Looking back to your Tuning with Vacuum Gauge post I wonder if you don't have some bent valves.   It's like a super bad permanent miss.   Or that's just how an engine runs when the cam is way off-time.  Could also explain your high pressure numbers, although those measurements are gauge dependent (I get 185 with my gauge on a stock 78 engine) .  I think Tony D was on the trail with his comment about adjusting the valves, and starting with a basic full tune-up.  Pistons and valves opening and closing at the correct times and to the proper distances is the heart of the combustion cycle. 

 

You need to find square one and try to get there if you can.  Checking the cam timing is a great starting point, but now you have to fix it.

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"So I set the crank pulley by hand to 0° verifying the piston is TDC, however between 10° and 0° per the crank gauge the piston doesn't move up or down."

 

Welcome to the discovery of "dwell", the time the crankshaft is swinging from going down, to going up (and vice-versa)... at BDC this is extra time the cam can be open and velocity filling the cylinder with fuel air mix. That intake valve won't close until that swing is complete, and then the piston may even be moving up in the cylinder slightly... Same at the top where you are exhausting pressure from the cylinder after power stroke. It's not a direct transition from up-down. It's up-swing-down-swing....There are zones in the crankshaft rotary motion that have no linear motion from the piston. That's why multiple cylinder engines seem 'smoother' in power delivery: there's another cylinder still making power when the other is swinging through that dead zone.

 

That's why it doesn't move up or down. Once it stops moving up, that's TDC. and once it stopped moving down that's BDC. 

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TimZ makes a good point about modified parts.  I almost posted something about whether or not that cam is factory or a regrind, if it's a regrind the mark may be irrelevant.  But if it's a stock cam the marks should still be aligned, even if they're not optimum.  The mark tells you what position the valves are in (since they're at the ends of the lobes), in relation to the pistons.  The before and after picture in the FSM is 4 degrees.  You're cam is about 8 - 10 degrees advanced.

 

Looking back to your Tuning with Vacuum Gauge post I wonder if you don't have some bent valves.   It's like a super bad permanent miss.   Or that's just how an engine runs when the cam is way off-time.  Could also explain your high pressure numbers, although those measurements are gauge dependent (I get 185 with my gauge on a stock 78 engine) .  I think Tony D was on the trail with his comment about adjusting the valves, and starting with a basic full tune-up.  Pistons and valves opening and closing at the correct times and to the proper distances is the heart of the combustion cycle. 

 

You need to find square one and try to get there if you can.  Checking the cam timing is a great starting point, but now you have to fix it.

 

The cam has an "A" at the end, which I believe points to oem.

I sure hope there's no bent valves in there, from my previous post on the vacuum gauge, the motor ran smooth up to 3,500rpm's.  It's been parked in the garage for the last 9 months and all I have been doing is verifying operation of all it's FI, emissions, vacuum, electrical bugs, etc....basically giving her a once over.

 

 

I was going to get to the valve adjustment tonight, first wanted to check the TDC reference marks.

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I've seen people slip a link on the chain during head swaps. Makes the engine run gangbusters a lower RPM's but absolutely DIE OFF in power above 4,500 or so... BUT...

 

Degreeing the cam is again, down the road from the basic fact that the valves must be adjusted FIRST in order to get proper readings!

 

Quit dicking around and adjust the valves FIRST, and THEN stroke on about checking everything else!

 

When in doubt: follow the instructions.

 

If there's a big 18" high pile of grassy-twig filled crap in the center of floor, chances are it's the elephant in the room that laid it there, and not the mouse in the corner.

Quit looking for mice. Feed your elephant peanuts so he's bound up and this big wad of crap ceases to be a problem.

 

THEN chase the mice!

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And I second the point on 'it may be just the gauge'... cam timing can cause high cranking compression. But a gauge being uncalibrated and unknown really isn't a great indicator of actual pressures being seen.

 

I, too, have a 225,000+ mile "185psi compression" motor in my 76... It's not the number, it's the relative number over time that you are looking for...

 

I learned that long ago when a certain shop in town kept sending the machine shop overhauls. Guy was using a gauge that probably read 75# low... chronic "needs overhaul" diagnosis... One cheapskate Scot decided to get another opinion and took the car to our shop for a test...our cranking test showed 145psi, where his showed 75-90!!!

 

Gave the guy our gauge to take over to Herb's shop, and had Herb replicate the test... "Hummm, maybe this 'ole gauge has seen better days..." Went out and bought a new one and suddenly the three overhauls a month out of Herb's Shop stopped coming our way. Bummer. I got laid off.

 

Trust your instruments, to a point. VERIFY your instruments regularly to a known good source!

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I've seen people slip a link on the chain during head swaps. Makes the engine run gangbusters a lower RPM's but absolutely DIE OFF in power above 4,500 or so... BUT...

 

Degreeing the cam is again, down the road from the basic fact that the valves must be adjusted FIRST in order to get proper readings!

 

Quit dicking around and adjust the valves FIRST, and THEN stroke on about checking everything else!

 

When in doubt: follow the instructions.

 

If there's a big 18" high pile of grassy-twig filled crap in the center of floor, chances are it's the elephant in the room that laid it there, and not the mouse in the corner.

Quit looking for mice. Feed your elephant peanuts so he's bound up and this big wad of crap ceases to be a problem.

 

THEN chase the mice!

 

Considering I pulled the rocker cover this afternoon for the first time, inspected the head, rotated the crank to ensure it had a timing mark, documented all the pics in the first post, all while doing a coolant flush and refill on a '89 Altima at the end of a long driveway (walking back and forth 4 car lengths) I made some good progress. 

AND I was almost there, seriously, even pulled out the feeler gauge and checked the #1 cam lobe along with 3, 7, 11...and then got pulled aside to clean out the trunk of another car, then dinner, then posting here, looked at time and had to clean up and hit the road....blah blah blah

Problem is I plan to spend some quality time with the Z (it's over an hour away from me) and always get side tracked.

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Cold and Hot valve adjustment completed, across the board cold was out -0.001 on a couple of them.

 

After cold adjustment I took these vids, idle seems smoother for the moment, but fuel is still off.

 

 

Cold start:

 

http://youtu.be/dLG_rGepSF0

 

 

After cold valve adjustment to warm up for hot adjustment:

 

http://youtu.be/3KN7kZ57VJE

Edited by AdreView
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I can't see the photos. But like I said "if they slipped a link" that would do about that...

 

It's the micro approach. Looking at everything and discounting those macro things that the basics tell you to test first. 

 

Low Vacuum when not engine wear related, or leaks, usually is in the valve timing. And the first step to determine this is adjust the valves and do the basic tune up. This takes 45 minutes. With the valves adjusted and the timing and carb/fueling adjusted for best idle....you know your baseline.

 

Now, had that 45 minutes been spent off the bat, and those photos (you can see, I can't...) would SCREAM that the link is slipped---someone did a misinstallation of the cam./head. 

 

Actually, during a valve adjustment, I usually look for that dash alignment on the cam. If it's not right...then you correct it as part of the valve adjustment if there isn't an outward reason for doing it...

 

Like I said, it looks like we eventually backed into it.

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