Timing/Pinging

[KVH]

My car starts almost the instant the key is turned. It runs great, and usually cool.

However, on any significant incline, the heat goes up and I get some pingning. Heat is never a problem since I installed an auxilliary fan, but I don't particularly like noticing that it comes on during hill climbing. The pinging is also a concern.

So, two somewhat technical questions:

a) If the extra stress of an uphill run causes pinging, would that indicate a worn distributor bushing?

b) Since it runs great otherwise, and the pinging isn't excessive, should I just leave it alone, or bump up the advance?

I ask the second question because when I "advance" the timing, I get pre-ignition on shut off, and when that happens I immediately get an unpleasant pain in my stomach.

 

[Kurtis]

The pinging is usually a symptom of too much advance. I'd retard the timing slightly and see if that helps.

 

[ObiRichKanobi]

This may be a dumb question, but are you using premium fuel?

 

[KVH]

Yes, but 91 Octane is highest I can find.

 

[KVH]

I guess I stated it wrong.

In an effort to avoid pinging, I might retard the timing a bit, and that should not contribute toward pre-ignition on shut off, though it may increase engine heat?

Sound more accurate?

 

[Kurtis]

If you retard it just enough to get rid of the pinging, you shouldn’t have any problems with the engine temperature (assuming all else is well with the car). I believe that a badly timed car will run hotter weather it’s advanced or retarded.

By “pre-ignition” at shut off, I assume you’re referring to what is commonly called dieseling or run-on. This is usually caused by many of the same things that cause pre-ignition (carbon deposits, high compression, low octane, incorrect mixture, etc.). I can’t recall off hand what effect timing has on the engine’s tendency to diesel; however, I know that many TR2/3/4 owners suffer from some degree of run-on after the engine is shut down due to the fact that these cars were designed to run on higher octane fuel than what is commonly available now.

I’d recommend that you time it so it doesn’t ping during normal driving. Severe pre-ignition can potentially do a lot more damage than running a little hot. If run-on is a problem, simply get in the habit of switching off the ignition with the car in gear and the clutch depressed, and let out on the clutch pedal as the engine dies down. This will become second nature after a while, and IMHO is much better on the engine than allowing it to diesel.

What’s the general condition of your engine? How many miles since the last rebuild?

 

[Geo Hahn]

Have you increaed the compression? I seem to recall you went with the solid copper head gasket. Higher compression with premium fuel and timing by the book = pinging under load.

As suggested, retard to relieve all but the last bit of pinging (the ping you get by trouncing it in 4th gear going uphill is okay because you're not going to drive like that). You may get run-on after all that is sorted out and you may just have to learn to live with it.

 

[dklawson]

I agree with all that's been said above. I'll add that you should not continue to drive the car in its current state if it regularly pings. This is bad. It's as bad as letting a car diesel for long periods after you switch off the key. You don't want either.

Since you're running high octane, retard the timing in 2 degree steps, test driving after each adjustment, until the pinging goes away. My experience is that dieseling (like pinging) is worse in a car with its timing advanced too far. I have my timing advanced fairly high and stop any dieseling at shut down as described above by letting out the clutch in gear as I turn off the key.

 

[vettedog72]

Do you have the gadget on the distributor that retards the timing when the motor pulls hard? It would be a white metal disk with a vacuum line attached to it. If so, you might want to check it for proper operation. If it is not retarding the spark, that could cause your problem.

 

[Geo Hahn]

I could be way off on this... but I was under the impression that the vacuum unit advances the timing on a TR4, though it retards the timing on a TR6. No wonder I get confused.

 

[vettedog72]

Geo:
I think some the "late" model TR6's had it both ways; yes, two of the little devels on the distributor. But either way, if it is not working correctly, it could have a negative effect.

 

[Kurtis]

I agree with you Geo. I'm pretty sure the vacuum advance unit on my TR4 actually advances the timing (hence the use of the term "advance" /ubbthreads/images/graemlins/smile.gif ).

 

[vettedog72]

No, it does the same function for both: retards under load and advances under lite to no load. Under WOT it will retard timming (in reference to no load) until the centrifical advance over rides it. /ubbthreads/images/graemlins/grin.gif

 

[Dugger]

The early TR6's (69 & 70) and TR250's had twin vacuum connections at the distributor.
I believe there is a centrifugal weight system within the distributor that advances the timing with increased RPM (open throttle). On my 71TR6, the vacuum connection is on the engine side of the carb damper, which means that high vacuum on throttle release will retard the timing. I believe that that would indicate a vacuum retard system.

Can you explain how that system advances the timing?

 

[AltaKnight]

Dugger.....
The distributor changed in 72 & 73 to a single vacuum retard system, in 70/71 it had a double vacuum advance/retard system.
If it only has one vacuum connection then it's for retarding the ignition when you're in an decelleration over-run condition to improve the emissions, it's also controlled by a coolant temp switch.
In the single vacuum connection case the only advance you have is the centrifugal weight type internal to the distributor.

 

[Dugger]

Thanks Graham,

That is exactly what I thought.

One problem is that many of these cars don't have the correct year gear. For instance, I think the ZS's I have are from a later model car probably added/changed by the DPO, and since my car was assembled in August of '71 (90th from the last) it had the '72 year distributor, i.e. single vacuum retard connection.

 

[Stinky]

My 71' also has just the Vacum Retard too. This sort of thing sure makes it hard to tell what's original and what's not.