Distributor drive gear

[ensys]

If the distributor drive gear has moved (spun) on the spindle shaft, isn't it likely to do it again?

If the gear has moved, doesn't this make tang alignment by gear tooth a crapshoot, timing-wise?

Speaking of which, can anyone say how many degrees of rotation in one tooth?

Wouldn't remedial adjustment screw up the alignment required between the gear punch mark and oil hole? Does this matter?

Is the only reliable remedy (short of the install of a locating pin, if one could determine the gear's original orientation on the shaft) to replace the spindle shaft/drive gear?

Are new spindle shafts available?

 

[Patcon]

I was think a roll pin located that gear. Do you have some pictures?

[BoldUlysses]

^Yeah, thought the shaft and gear were all of a piece or otherwise locked together. 

Having recently dropped the oil pump, there's a bit of trial-and-error that's involved in getting the teeth lined up so the tang sits at 11:25.  Took me a couple of tries.

It's pretty easy to pull the distributor and recheck the angle of the tang if you're concerned about it.

[ensys]

Thanx for your replies.

Turns out that the shaft's drive gear is a press fit, so that given sufficient shock (say, from a sudden ignition anomaly at speed like those that I experienced during a period of spasms (for lack of a better word) not long ago), the gear can move on the shaft.

This phenomenon is documented in older forum posts and can be the only logical conclusion for the obvious change in rotor position (and drastic timing change) in an otherwise undisturbed oil pump/shaft.

[Zed Head]

I recall reading about that but the gear also moved up the shaft.  A comparison of shafts or a measurement should show something.  Without that it's just a guess.

[ensys]

Mr.BU:

Of course, the distributor has been removed for verification, several times in multiple exhaustive TDC checks of system alignments (including that of the crank pulley) that showed that the rotor position is about 10deg (at the rotor, 20deg. at the crank) retarded.

These included timing light checks that showed (much to my confusion when first done) that maximum possible advance rotation of the dist. body could only pull the pulley notch out of retardation to just shy of 0deg at the crank.

By the by, the probable diagnosis of this problem is further reinforced by the very poor vacuum in a verified leak-free system that would rise with the rate of ignition advance (such that it was). Note that the number of in.Hg is always in proper proportion to the fuel pressure psi.

Pulling the pump/shaft is a job of work currently in process, but I don't do so in the expectation of revealing relevant information, given the fact that there is no benchmark (beyond vertical positioning... provided one knows what the normal distance is...) for establishing rotation; there is only the tang angle to tell the tale. And that tells me "something" down that hole is wonky.

But hey; I'm not the sharpest knife in the drawer, and this chase began with an effort to cure the "spasms" without any inkling that there was some collateral problem with an issue I did not know could exist. I mean, who'da thunk that the Factory would not require the Sub to pin the gear.

You know, German cars don't have these kind of cost-driven engineering decisions, and the Brits have always been very construction-detail conscious....

Edited August 13, 2022 by ensys

[Zed Head]

The reason to verify is so that you can fix it. 

https://forums.hybridz.org/topic/106792-slop-in-the-distributor-drive/

https://forums.hybridz.org/topic/115353-l28et-issues-oil-pump-shaft-gear-spun/

[ensys]

Mr.Head:

My thanks for your reinforcements of the Theory at hand.

Now, the issue is what is a proper (and doable) lasting "fix". Since there is little chance of returning the gear to its original orientation, it would lead to the inevitable solution of replacement as the only viable cure for the problem.

This coincides with my own prognosis, but more importantly (and entertaining), this discussion item may serve to inform a wider audience that this problem exists.

Fortunately for me, there are still a few choices in shaft (and gear) replacement at the present. At best, the purpose of this discussion is less about "what's going on here?" than in providing an awareness of an issue that may not be recognized by fellow Z owners.

I thank you for your attention.

Edited August 13, 2022 by ensys

[Zed Head]

Actually, most people "fix" it so that they can go racing or making large amounts of high RPM power, as described in those Hybridz threads.  Most of the people that have problems are exceeding the design limits of the engine.

Your situation is interesting because you had the common engine problems that many people have.  No high RPM dyno runs or race miles.

But, anyway, you've accomplished your mission.  Another thread about the slipping oil pump shaft drive gear.  Plus it has links to two others now.  It would be cool to see a good one and a slipped one side-by-side though.  If you ever get the chance.

[ensys]

Of course, your good links are not the only ones available, but the point is the same; as you have aptly noted, this could be anyone's tale of woe from a direction that few could, or should, have any reason to expect.

As for comparos, the telling shot would be end to end, to see the difference in clocking gear to drive tang. But of course, one can tell that from the dist. end with the shaft still in place, when you know what to look for.