Can't get timing to less than 25 degrees?

[882993md]

Hi everyone, 

My car is using a 280zx distributor, I checked my timing last week in anticipation of fine tuning my carbs. It was set at 15 degrees and I wanted to check on this forum to see what was best for my set up. The consensus  after searching was 10 degrees. 

So I go to use my timing light and holy *** my timing is way off at 25 degrees. When I turn the distributor it will come down to 20 degrees before stopping it's range of movement. 

I thought maybe my harmonic balance slipped and messed up my TDC mark. So I put the engine to TDC with the pulley detent at the zero mark, #1 piston on compression stroke, intake and exhaust valves lobes pointed up and away, notch in cam sprocket aligns with groove. So harmonic balancer is ok.

However I noticed that my distributor rotor is at the 8 o'clock position and not 9 o'clock to line up with the #1 spark plug contact. 

Should I put it back at TDC and pull the distributor to see if the oil pump is clocked at 11:25? 

It totally puzzles me how it can go from normal range to such a high timing?

Howard 

1974 260z 

Edited October 31, 2017 by 882993md

[Zed Head]

Did you mess with the vacuum advance hose?  Maybe it's attached to the wrong port, getting full time vacuum.  Try disconnecting it and see what happens.

[882993md]

When setting the timing I unplugged the hose from the vacuum advance and plugged it. I also capped the the port on the carb that the hose attached to. 

Should I not plug the vacuum advance hose, or does it not matter?

Howard

Edited October 31, 2017 by 882993md

[siteunseen]

When you put the Zx distributor on you may have that plate upside down?  I always plug the hose that connects to the distributor with a golf tee, leaving it hooked up at the front carb.  I have mine at 17 degrees at idle and 34 at 3,000 rpms.  It takes a special timing light though, I guess it's called full advance mode but you run it up to 3 grand and the notch will hit on zero.

This may be of some help?

http://atlanticz.ca/zclub/techtips/distributor/index.html

[SteveJ]

Did you use a ZX distributor mount?

[Zed Head]

5 hours ago, 882993md said:

My car is using a 280zx distributor, I checked my timing last week in anticipation of fine tuning my carbs. It was set at 15 degrees and I wanted to check on this forum to see what was best for my set up. The consensus  after searching was 10 degrees. 

So I go to use my timing light and holy *** my timing is way off at 25 degrees. When I turn the distributor it will come down to 20 degrees before stopping it's range of movement. 

I highlighted what I think is a critical statement.  It was at 15 but something changed.  I went with the easy one of a misplaced hose.

Another thing that can change, on its own, is for the breaker plate to get stuck in the advanced position.  Broken Z and ZX breaker plate bearing assemblies are very common.  One way to check is to reconnect everything then watch what timing does when you apply vacuum to the vacuum advance canister.  If it doesn't move it's probably already advanced and stuck there.  Or you can take the distributor out and examine it, and move it by hand.

[cbuczesk]

I agree with Zed Head. That's the first thing I'd check. You can rev the engine and see what your max timing is.

Did you also happen to put on a Melling high volume, high pressure oil pump? I did that on my race car this summer and it very quickly wore out the crank gear and distributor/oil pump shaft gear causing it to skip some teeth. Happened twice before I found the cause.

Chuck

 

[siteunseen]

2 hours ago, cbuczesk said:

I agree with Zed Head. That's the first thing I'd check. You can rev the engine and see what your max timing is.

Did you also happen to put on a Melling high volume, high pressure oil pump? I did that on my race car this summer and it very quickly wore out the crank gear and distributor/oil pump shaft gear causing it to skip some teeth. Happened twice before I found the cause.

Chuck

 

Oh no. 

I've got them on both my Zs. 

[cbuczesk]

Here are a couple pics of a worn gear compared to a good used gear. The wear took less than two hours to happen on the track. I was doing about 100mph and the car suddenly shut off. It had jumped at least a couple teeth.

Chuck



Sent from my Moto G Play using Classic Zcar Club mobile

[882993md]

Thanks everyone I have my to do:

1. Reconnect everything and apply vacuum and see if timing advances or is stuck. 

2. If stuck check breaker plate.

3. Check for ZX distributor mount.

As far as I know it’s its just a standard oil pump.

Howard

13 hours ago, Zed Head said:

I highlighted what I think is a critical statement.  It was at 15 but something changed.  I went with the easy one of a misplaced hose.

Another thing that can change, on its own, is for the breaker plate to get stuck in the advanced position.  Broken Z and ZX breaker plate bearing assemblies are very common.  One way to check is to reconnect everything then watch what timing does when you apply vacuum to the vacuum advance canister.  If it doesn't move it's probably already advanced and stuck there.  Or you can take the distributor out and examine it, and move it by hand.

 

[siteunseen]

Take the cap off and look for ball bearings, usually stuck to this...

The back side of the stator is made from a brittle magnetic substance that can break easily. Just snug the screws.

[882993md]

Hi everyone here is an update:

I put the vacuum tube back on the revved the throttle and the timing did advance.   I used the advance knob on my timing light to zero the timing and it showed 29 on the knob when revving.

So I pulled the dizzy and verified the oil pump is at 11:25 at TDC.

I did find this piece of metal (looks like a staple) on the stator. I don't know if may have caused a jamb in the breaker plate? Stator appears in good condition.

I totally forgot to verify the zx mount so I have to check when I get home from work today.

I don't have a vacuum pump and I tried to suck on the tube on the diaphragm and the breaker plate moved a little, but I need to properly check it with pump. It seems the unit is in overall good condition except for the plastic collar at the bottom. Anyone know if this is sold separately, or if there is a generic replacement? Or do I have to replace the whole distributor?

Should I continue with disassembly or reinstall and see if that loose metal was the culprit interfering with the timing?

Howard

 

Edited November 2, 2017 by 882993md
Correct spelling