L26 blowing back through the carburator

[Zed Head]

Here are some answers from his other thread on Hybridz.  - 

 

"I'll definitely be adjusting the valves. The mechanical timing seems OK from what I can tell so far. I guess I need check the crank sprocket to be 100% sure since I have no idea whether the pulley is the original one or not. The ignition timing would be really hard to do given that the car won't idle. That's pretty much my goal at this point - to get the car to idle enough to check things out with a timing light. 

The distributor is from a 280ZX. I guess I forgot to mention that. I'm going to check the compression as soon as I get a chance. That should at least allow me to rule out a valve if the compression is OK. As for the lobes, I don't see anything that jumps out at me as far as wear goes, but I'm not ruling out anything at this point. "

[rossiz]

no numbered position is "preferable" - it's really about setting the timing marks correctly. if the v groove is to the left of the mark, the cam is retarded, if it's to the right of the mark, the cam is advanced. your cam chain shouldn't be loose - there's very little play in it and the tensioner keeps it pretty tight. if it is loose, it could be stretched or the tensioner may not be set correctly.

[siteunseen]

If you turned the crank counterclockwise to get tdc it will cause the chain to be loose. Turn them to the right to stay tight.

[amplogic]

Update :

Just checked the compression and it looked pretty good, so I'm inclined to think that the valves are OK. I guess the next step is to get the cam sprocket lined up where it's supposed to be. Guess I need to make one of those chain tensioner wedges that I've seen mentioned.

These are all dry numbers

#1 170

#2 170

#3 170

#4 172

#5 172

#6 175

[gundee]

Update :

Just checked the compression and it looked pretty good, so I'm inclined to think that the valves are OK. I guess the next step is to get the cam sprocket lined up where it's supposed to be. Guess I need to make one of those chain tensioner wedges that I've seen mentioned.

These are all dry numbers

#1 170

#2 170

#3 170

#4 172

#5 172

#6 175

Those are good numbers. Especially if a cold test.

[Zed Head]

Update :

Just checked the compression and it looked pretty good, so I'm inclined to think that the valves are OK. I guess the next step is to get the cam sprocket lined up where it's supposed to be. Guess I need to make one of those chain tensioner wedges that I've seen mentioned.

These are all dry numbers

#1 170

#2 170

#3 170

#4 172

#5 172

#6 175

The numbers do look good.

 

Check your sprocket to make sure it has the notch.  It looks aftermarket, the factory sprockets have four holes, yours has three.  Some of the aftermarket sprockets don't have the notch.  If it doesn't have the notch, what will you use to reposition the sprocket?  Oddly, S-482 comes up as a Toyota sprocket on the Google.

 

And it's much easier to check ignition timing than to remove the cam sprocket.  You might be getting ahead of yourself.  Do the easy stuff first.

 

Eventually, if you want to be sure on cam timing, just buy a new sprocket, with notch.

[Zed Head]

Maybe that "8" is a "6".  Sure looks like an 8.

 

Here is the Cloyes Datsun part.  Looks like yours.  Pretty sure that I've read that the Cloyes sprockets don't have the notch.

 

 

[Zed Head]

Another thought on cam timing - since your sprocket has been replaced that means someone has been wrenching there.  It's been known to happen that the cam shaft dowels have sheared, so even though in theory the worst the timing could be is at spec., or 8 degrees advanced, it's possible that things are totally screwed up.

 

Still, simple stuff first, especially since it runs and the pressure numbers look good.  Although, removing the sprocket nut is easy and will tell you if the sprocket is loose on the dowel, without actually having to remove it.  You might do that first.  No need to lock the chain, just make sure the sprocket doesn't fall off.  Actually, lock the chain anyway, just for insurance.  You really don't want to tear off the front cover if you don't have to, unless you're looking for a bigger project.

[madkaw]

So have you verified that at TDC #1- compression stroke- that the dizzy shaft is at the proper 11:25 position and that the rotor is lined up with 1 plug?

Please understand with any posts regarding shiny links is irrelevant UNLESS you have the timing cover off to see the crank sprocket.

What ignition issues were you having prior to this?

[SteveJ]

Another Atlanta 260Z? Send me a PM to let me know where you are in the area. We have a pretty good early Z community around here.

[amplogic]

Ok. I just double checked everything. Again.

The sprocket is an S-462. And as far as I can tell, there isn't a timing notch cut into it anywhere. The bright link on the chain is line up with the #2 mark on the sprocket. The chain is stamped "Made in the USA", so it's not the original either.

Also, the chain tension is fine. I must have made my final bump in the wrong direction the other day when I was looking for TDC. Everything still lines up exactly the same now as it did before, even with the chain tight.

[Zed Head]

As madkaw said, forget about the bright links.  If you can't see the corresponding link on the crankshaft gear, it's meaningless.  If you turn the engine one revolution the link will be somewhere else.

 

So you have a sprocket that was designed to be set up one time, with a new chain and never adjusted.  Because there's no easy way to tell if chain/sprocket wear has occurred.  I've also read on the old interweb that Cloyes started adding notches to the later sprockets, and only the old ones are notchless.  Regardless, you have no way to confirm proper valve events unless you add a degree wheel to the damper and measure valve lift.  Kind of a dilemma.

 

Might be easiest to assume the PO knew what he was doing and work on everything else until cam timing is the last possibility.  Or replace that sprocket with one that has the notch.