Timing marks on pulley are very far from the pointer.

[kjohnson2444]

I went to check the timing on my '70 240z (all stock ignition) because it starts and idles fine, but stumbles under acceleration and completely breaks up over 4500 rpm. The timing notches on the pulley are over an inch below the pointer. I moved the distributor all the way in both directions, but could not get the nearest mark any closer than about an inch from the pointer (but could move it further away). Any thoughts? I've searched the forums, and there is a lot about timing, but I didn't see this particular issue. Any thoughts?

[cozye]

I've heard that the mark can get off, forgot exactly how. Either the pully slips or something like that. Like some cars have the rubber piece between the harmonic balancer and the pully, i can't remember if the z is like that.

In any case, pull #1 plug, use a wooden dowel in the plug hole to get any accurate measurement of TDC, then make a new mark at 0 on your pully. Use some white paint

[Zed Head]

Your distributor shaft might be off a tooth or two. Apparently it's not uncommon. Or your plug wires could be off one spot at the distributor cap.

If you find that the pulley mark is at TDC, you can either moved your plug wires over one spot or see if the distributor shaft can be moved. Two options.

[beermanpete]

+1 for the harmonic damper being out of whack. The crank pulley is two pieces bonded together by a rubber layer. The bond can break, allowing the pulley (and timing mark) to slip. As Cozye said, find true TDC and check the timing marks to see if they are correct.

[johnny haywire]

Sorry to wake up an old thread, but to the original poster - did you ever determine if your pulley had slipped? I just installed a working tach on my '78 280 and was excited to finally check the timing on the car tonight...only to find that with the 'strib all the way advanced, it left me only at the 0 degree mark. I'm suspecting a spun pulley and will check for TDC before doing anything else.

[kjohnson2444]

Johnny, you are not going to like my answer... Not long after this post, I dropped my timing light and it broke. Not wanting to dive into the potential repairs to the crank pulley, harmonic damper, etc., I started adjusting the timing by simply listening to the engine, adjusting the timing and tweaking it until it ran smoothly and responsively throughout the rpm range without any detonation. It's been running nicely ever since and I have no idea what the timing "looks like" on the notches. (A valve adjustment also went a long way towards smoothing out my rough running.)

[240260280z]

The outer part of the pulley slips when the rubber fails:

If this happens and you still want to set the timing, simply put the car at Top Dead Centre and paint a new dot on the edge of the pulley where the timing pointer is.

But you should buy a new pulley ASAP.

Edited June 21, 2012 by Blue

[Jeff G 78]

My 260 damper failed during a race. I was lucky not to break the crankshaft. Once I removed the damper, it spun like a bearing!

Guy (Diseazed) was kind enough to send me a good used damper he had left over from an engine build. Now, I run a radial paint mark across the damper hub and pulley so I can immediately tell if it fails again.

Edited June 21, 2012 by Jeff G 78

[Zedyone_kenobi]

That is a brilliant idea Jeff!

[johnny haywire]

Thanks for all the excellent advice - I love this forum! I'm going to check my BTDC vs. the original mark and remark it just to get the timing correct for now, but a replacement pulley has now moved to the top of the list. Any tried and true methods to test if the replacement pulley has spun at all (before installing it)? Perhaps orientation in relation to the key slot?

[Jeff G 78]

There are several ways to get close to TDC using simple tools. Try this method. Remove the valve cover, distributor cap and #1 spark plug. Turn the engine over until the cam lobes for #1 are both pointing up. Now, check the distributor to be sure it's pointing towards the front and then stick a small wood dowel, drinking straw, or screwdriver into the spark plug hole until it touches the top of the piston. Now rotate the engine back and forth slightly with a 27mm socket and breaker bar and try to get the piston stopped exactly at TDC. It will dwell for a moment right at the top, so you want to find the spot that has a bit of delay each direction before it starts dropping. The dowel/straw, etc. will help you feel the spot. When you get there, mark the crank damper with a white or yellow paint pen right at the "0" mark on the pointer. Like I stated above, also mark the damper such that you can see if it has moved again. I simply extend the "0" mark forward and down. I put a dot on each of the pulley's "V" peaks and draw a line down the front face to the center of the bolt head.

Edited June 21, 2012 by Jeff G 78

[BoldUlysses]

I might need to do this. Having trouble getting mine timed correctly as well.

Jeff, any danger the timing chain will skip a tooth or two if the engine is rotated backward? I've heard horror stories of BMW owners destroying their valves because they turned the crank pulley backward and the timing chain jumped.