Early 2TG: Pre-ignition issues

**71TA22** · 06-02-2008, 06:47 PM

Have started to encounter pre-ignition issues with my cars 2TG engine on steep hills when under 4,500 rpm in any gear. Have had to wind the static timing right back to 5 degrees BTDC to keep the car comfortably drivable. Cars a bit gutless now and does not want to rev past 6,000.

Have run through all the standard stuff: static timing, cam and valve timing, distributor, ignition cicuit, compression, carb tune and balance. Nothing out of factory specs.

First thing that springs to mind is fuel. Have tried a few varieties and octane boost but makes no difference.

Anyone else encountered this?

A solution that does not involve tossing the motor would be fantastic?

**Duk** · 06-02-2008, 07:07 PM

Sometimes carbon deposites can get hot enough to cause pre-ignition problems. I've had older engines suffer from this, possibly due to oil getting past the valve stem seals/valve guides.

**71TA22** · 06-02-2008, 07:23 PM

Checked the cylinder head chambers, valves and pistons for carbon as that was my first thought with every thing else being in spec. Everything was surprisingly clean for an old motor.

I do wonder if the engine is suffering compression ratio problems with todays lower octane fuel. I know the engine suffered a head gasket failure in the past and the block was decked at that time.

**sleeektoy** · 06-02-2008, 08:51 PM

crappy batch of fuel? i have encountered 91 octane in a 96 octane pump - they filled the wrong tank (idiots). I know mine did not run well and got bad pre-ignition from running it.

drained the tank and a fresh batch of 98 fuel solved the problem.

FYI - mine runs best on BP ultimate 98 or Caltex Vortex 95 not much else works except mobil 98 but their fuel has a bad odour and i dont use it on that principle.

[EDIT] one of the weight springs in the distributor isnt broken? Fuel filter clogged?

cheers

Mike

**jeffro ra28** · 06-02-2008, 10:08 PM

what leads you to beleive its pre-igniting?

**allencr** · 07-02-2008, 02:32 AM

It's detonation, spark-knock, pinging, not pre-ignition.
Vacuum advance connected and centrifugal/mechanical working OK or changed recently, if its got one?

The vacuum adv. retards when accelerating.

**jeffro ra28** · 07-02-2008, 07:51 AM

Originally Posted by 71TA22

Have started to encounter pre-ignition issues with my cars 2TG engine on steep hills when under 4,500 rpm in any gear. Have had to wind the static timing right back to 5 degrees BTDC to keep the car comfortably drivable. Cars a bit gutless now and does not want to rev past 6,000.

?

Allen, thats why i asked him......

Vacum advance only davances under light throttle cruise.

**71TA22** · 07-02-2008, 03:50 PM

Originally Posted by allencr

It's detonation, spark-knock, pinging, not pre-ignition.
Vacuum advance connected and centrifugal/mechanical working OK or changed recently, if its got one?

The vacuum adv. retards when accelerating.

Ok I will replace the term pre-ignition with "pinging" as that is what the symptoms sound most like.

Vacuum and mechanical advance are good. Distributor shaft is not loose.

**71TA22** · 07-02-2008, 05:44 PM

Originally Posted by sleeektoy

crappy batch of fuel? i have encountered 91 octane in a 96 octane pump - they filled the wrong tank (idiots). I know mine did not run well and got bad pre-ignition from running it.

Mike,

Thanks for that.

I've come to the conclusion that poor fuel with higher than standard compression ratio is the issue. Everything else appears to be at or close to factory spec.

Tried a new fuel filter. Distributor is good.