Ignition Timing Issue, Phase II

[RDKeysor]

I initiated the forum's ignition timing topic on this forum that eventually triggered a debate about ignition wires, timing lights, etc. All very interesting. But I promised to report back on the result of the latest attempt to resolve my issue and herewith restart the topic. Briefly, my '60 BN7 was running badly, and I used an inductive timing light to attempt to check the timing. I think I started at about 10 degree BTD, but can't remember exactly where the timing was when I first adjusted the distributor. What I got was a car that seemed to run very nicely, tended to give a couple of carb hiccups early on, and then rather soon started to build engine temperature. My latest effort to address the problem was suggested by a reliable forum member. That involved marking the 6 1/4" pulley approximately 1 3/4" to the right of the pulley timing mark. With a warm engine and the vacuum line in place, the engine was brought to 3000 rpm and the dizzy adjusted until the timing pointer and the new pulley mark aligned. I then drove the car, getting a hiccup or two very early on. The car, which has never actually overheated, did not come to its usual 190 degree plus temperature (ambient was about 80), and only slowly came to 160 (the thermostat number) on a short drive. Satisfied, I felt brave enough to drive the the 40-plus miles to our Healey club's tech session. The car did the hiccup thing once and then ran very nicely, staying at 190 for the entire 40 miles. A Eureka moment? No. At my destination, I overshot my turn, backed around, and drove back a quarter mile or so. At that point the car was gaining temperature and running a bit off. At our tech session, a senior club member listened to my car, and did very minor adjustment on the carbs. The trip home was identical. The car ran perfectly at 190 half way home. Then the temperature started to edge up. It was getting hot and running less well until I pulled into the garage, where it remains. My temperature gun showed the radiator top at 212 degrees after shutoff. An elementary question I have is whether the temperature gain others have seen while adjusting timing relates to a dizzy position that gives a slow idle (the vacuum line disconnected and plugged) or a fast idle. Further, I'm not even certain the timing is the issue. The spark plugs look fine. ???

 

[dcarlg]

Could the fan belt be slipping?

 

[Bob_Spidell]

This is a real WAG, but I wonder if you have a blockage in your engine or cooling system somewhere, preventing coolant from circulating completely, and causing a slow heat buildup.

 

[SideShifter Tri-Carb]

What it sounds like to me is that you only checked the secondary advance at 3000 rpm. Note that the advance on the dizzy begins increasing with the RPM after around 1000 RPM. I tried to search for the advance curve for a 25D dizzy, but I couldn't find it. The numbers you gave (1.75" on a 6-1/4" pulley) equates to about 30 degrees advance. You also need to check the timing at idle as well, which should be at 15 degrees or 0.875" on a 6-1/4" pulley with the vacuum hose disconnected and plugged. You should also see that the timing is steady and not bouncing around a lot. If it is, you have some spring issues inside or the shaft bushings are worn. I say all of this to have you check the timing at multiple RPMs to ensure that the advance springs are working as they should. May not be the solution to the problem, but it's good practice to learn.

 

[glemon]

I agree with Olin, and though I said I don't generally rely on timing lights for setting final timing, they are very useful or checking to see if the mechanical and vacuum advances are working correctly. That said I also agree that timing as probably not your problem, your ride out almost sounds like normal operation--when you slowed down and turned around the radiator was getting less airflow and temperature went up. My cars, including the old Healey, always ran the warmest at low speeds or idle in traffic, and cooled off a bit at speed with good airflow on the highway. But then you state the temp holds steady at an indicated 190 (pretty normal for a Healey or most any LBC) for half the ride back, then creeps up again. Maybe an intermittent leak in the cooling system that only appears as temp or pressure goes up, the cooling system has to be under pressure to work at maximum efficiency, as it prevents the coolant from boiling on hot spots in the motor. Do you have access to a pressure testing unit for the radiator? Are you losing any coolant on long drives?

 

[RDKeysor]

I'm not aware of any coolant loss. I did fail to mention that the coolant in the radiator was below the neck before and after the trip. There was no sign of activity in my newly installed generic coolant recovery canister. I've driven this car for several years, and I do expect the temperature gauge to go up when the car comes to an idle, but this is something different. I have snugged up my water pump/generator belt. I will be checking the car at idle, but right now I am replacing the gaskets on the two rear push rod lifter panels.

 

[glemon]

You say the car "runs less well" when it starts to run hotter, what are the specifics? Rough or lower idle? Stumble on acceleration? Miss or cut out when going down the road at a steady speed? Minor rough running or afraid it's going to quit completely it's running so bad?

 

[RDKeysor]

Accompanying an unexpected engine temp rise will be a couple of carb spits and then rough running. In both the recent cases where I had driven about 40 miles, the rough running and temperature build up came just as I was getting the car home. The last run I used my laser temperature gun and recorded 212 degrees at engine shutdown, not alarming, but hotter than it had run early in the trip. I realize the heat builds for a time after shutdown. I intend to check the timing at idle with the vacuum off and plugged, as Olin suggests. I am just now reinstalling the plates over the push rod lifters. Thanks all.

 

[Roger]

Another line to pursue, and easily checked. A carburetter piston, sticking up, will give a weak mixture, temperature rise and spitting.

Just a thought.