Pining 2F (1 Viewer)

[Doug_S]

Hi,

When I run "regular" gas in my '77 desmogged 2F with an SOR two-piece header, non USA dizzy and non-USA Aisin carburator, I expereince pinging while on the freeway. It's a bit disconcerting since when I go up even a small incline the engine sounds like it's going to ping itself to death. There is no pinging while driving slower (town speeds) even if the engine is operating at high RPMs. It seems to be load RPM/load induced.

I'm currently operating with the stock heat-range Nippondenso spark plugs. Oh yeah, the timing is set at 7 degrees before top dead center and the engine has recently had a tune-up (it pinged before the tune-up as well). Any ideas? A friend of mine suggested that:

1. I run premium fuel (way too expensive)
2. I change the spark plugs to a colder value.

Thanks in advance for the advice.

 

[Pin_Head]

Maybe the compression ratio is higher than normal because someone has milled the head or accumulation of carbon. Another possibility is that the springs are weak on the centrifugal advance allowing it to advance too far at RPM.

If it is not a problem with the distributor advance, you could try backing off the timing a few degrees and see if it goes away w/o an unacceptable power loss. The other solution is to run higher octane gas.

 

[scouthead]

7 degrees BTDC taken from which mark on flywheel?...
Is it possible the motor is not pinging and the headers are popping? (valves too tight and/or mixture wrong?)

 

[bsevans]

I've owned my '78 for over 20 years and have always used premium fuel and there is no pinging under any load.
When I'm up in the White mountains and can not get anything but regular my 40 pings. The more the load the worse the pinging.

 

[Pighead]

You've got the non-USA dizzy? The one with the octane adjuster on the side? I think I'd fiddle with that octane adjuster, that's what it's there for. That's what I did...

 

[Doug_S]

I do have a non-USA dizzy. I don't know which way to turn the octain knob. Any ideas to retard the timing?

 

[brian]

Another possibility is that the springs are weak on the centrifugal advance allowing it to advance too far at RPM.

.

where would somebody get new springs?
cdan?

 

[jm599]

my nonusa dizzy also has octane adjuster, under a clear plastic top.
it has a "R" and an arrow on it. I think it stands for retard. anyway if you put a timing light on the flywheel mark and turn this knob the mark moves. one could probably figure out pretty easily where to set it for both premium and regular. good luck

 

[Doug_S]

Thanks for the advice, guys! I'll mess with the octane adjuster to see if I can retard the timing without losing too much power.

 

[Degnol]

Maybe the compression ratio is higher than normal because someone has milled the head or accumulation of carbon.
.

PH, is there any way to approximate the compression by interpereting the psi from a compression test, assuming everything is up to snuff? It would seem that regardless of the type of engine or it's displacement that numbers like say 160-165 psi would correlate with 10:1 and 145-150 psi with like 9:1 or something like that? Seems like if he did a compression test and got numbers significantly higher than factory specs it would indicate someone had, in fact, done something to raise compression.
Am I just out in left field?

Ed

 

[Fast Eddy]

PH, is there any way to approximate the compression by interpereting the psi from a compression test, assuming everything is up to snuff?

Am I just out in left field?

The problem is that it depends on temperature and base pressure, which change all the time. You could do it if you're good at figurin'.

http://en.wikipedia.org/wiki/Atmospheric_pressure

 

[Degnol]

Ed, I'm sure that all those things have some effect on compression #'s but I doubt it is significant. Boyles and Charles figured all that PV=nRT s***. But if you get compression #'s that are significantly higher than the factory, regardless of altitude or humidity or barometric pressure, I think the only conclusion is that something has raised compression. I'm also agreeing whith the carboned-up theory, too. Carbon not only raises compression, but acts like a glow plug when it gets good and hot.

.02

Ed(Slow Eddie)

 

[Degnol]

where would somebody get new springs?
cdan?

Jim C is the dizzy man. He recurved my big cap to suit my engine. Springs, weights......whatever it takes


Ed

 

[Pin_Head]

PH, is there any way to approximate the compression by interpereting the psi from a compression test, assuming everything is up to snuff?

You could make a pretty good guess about the compression ratio from the compression PSI, but you would have to assume that there is no significant blow by from the rings or leaking valves.
I would guess that the differences in air density and atmoshperic pressure would be small compared to the errors from leakage.

P1V1 = P2V2 where P1 is 14.7 PSI (atmospheric pressure at sea level) and P2 is 150 PSI + 14.7 PSI (the net pressure)

V1 = cylinder volume + combustion chamber volume
V2 = combustion chamber volume.

A little simultaneous equations and you get your answer.

 

[Degnol]

You could make a pretty good guess about the compression ratio from the compression PSI, but you would have to assume that there is no significant blow by from the rings or leaking valves.
I would guess that the differences in air density and atmoshperic pressure would be small compared to the errors from leakage.

P1V1 = P2V2 where P1 is 14.7 PSI (atmospheric pressure at sea level) and P2 is 150 PSI + 14.7 PSI (the net pressure)

V1 = cylinder volume + combustion chamber volume
V2 = combustion chamber volume.

A little simultaneous equations and you get your answer.

Cool, that is what I was thinking. Thanks Charlie, you da man.

Ed

EDIT: Charlie, is there a FAQ or some other reference for the volume of the various combustion chambers? I can figure the volume of the cylinder, but I know the heads vary by model year.
Thanks, Prof.
Ed

 

[Degnol]

7 degrees BTDC taken from which mark on flywheel?...
Is it possible the motor is not pinging and the headers are popping? (valves too tight and/or mixture wrong?)

7* BTDC is the "BB" and the line is TDC

 

[65swb45]

See Doug, much better responses to a thread than a PM!

Anyhow, I see nobody has asked you about possible temperature issues. Predetonation pinging has as much [if not more] to do with heat as anything. You mention that your truck is a 77, which should mean that it has a clutch-driven fan. These often have higher running temps than the older cruisers that run direct drive fans. So here are the questions.

1. Do you know your actual running temps at the onset of pinging? Not the reading on a factory guage, but real world. You can put an air-conditioner type thermometer [cost ~$6] between the fins of your radiator and get a measurement accurate to within 1 degree. Chances are you will find that your temp is much higher than you would have thought.

2. Do you know how old your fan clutch is? They fade over time, and new aftermarket ones are often worse than old factory ones. Mark Whatley did a great tech article for TT a couple of years back on splitting the clutch open and putting new silicone in one for a fraction of the cost of a new OE one. If you're not that ambitious, you might just opt for a new clutch. If you do, GO OEM! EVERYTHING ELSE IS A WASTE OF MONEY!

3. How old is your radiator? All the same discussions as above apply. IF it's old, you might want to consider a rod out or a full replacement . If you don't have a 4 core, you should really consider getting one. They're a real necessity here in the southwest.

FWIW, here's my benchmark. My 4 core rad is now 12 years old. Just had it rodded out last month. 6 blade direct drive fan. 190 degree thermostat. At 80 degree ambient temps outside, my radiator will not hit 160 even going uphill, and cruises somewhere between 130-140.

Hth

Mark A.

 

[ken_79-fj40]

2. Do you know how old your fan clutch is? They fade over time, and new aftermarket ones are often worse than old factory ones. Mark Whatley did a great tech article for TT a couple of years back on splitting the clutch open and putting new silicone in one for a fraction of the cost of a new OE one. If you're not that ambitious, you might just opt for a new clutch. If you do, GO OEM! EVERYTHING ELSE IS A WASTE OF MONEY!

I couldn't agree more with this. My truck was pinging when it was hot after my stock fan clutch leaked all it's fluid out. I'm now on my 3rd NAPA replacement in less than 2 years. They are lifetime warranty, but it's getting ridiculous. First one locked up solid after a month. Second one didn't ever lock, and was as bad as the original worn out one. The one on the truck now has been locked since I put it on. The truck doesn't overheat, but is down on power for sure.

 

[Doug_S]

I don't know how hot the engine is getting. I'll try the AC thermometer idea. The stock gauge, which is the only temp gauge that I'm running, doesn't read any higher than it ever did. I had the radiator rodded out and re-sealed about two years ago. Thanks for all the helpful tips.

Is there a good way to check the fan clutch? If it's bad, I don't have any problem with replacing it with either a new OEM part or a good used part.

Thanks again, guys!

 

[Poser]

Is there a good way to check the fan clutch? If it's bad, I don't have any problem with replacing it with either a new OEM part or a good used part.

Spin it by hand when the engine is cold.


If it spins round and round, with little to no resistance, it is junk.

Ideally, it should only rotate one revolution when trying to spin it by hand, and there should be resistance to it rotating.



As others have stated...

If yours is junk, new OEM is the only way to go Doug man.