Knocking/ Pinging noise- 2L Pinto

[Pazuzu]

Hi all.

Got a bugger of a knocking noise from the engine of my 2L Mk 2 Esky. This used to happen a bit, got the engine reconditioned, fixed it. The knocking noise came back after a service about a year back, took it in again & said "fix it," and 10 minutes later it was all good again. They said it was the timing back then. Then recently, got it serviced and the noise is back.
Took it back to the guys who did the service, they mucked about with the timing, couldn't eliminate it entirely but they did manage to reduce it by retarding the timing more than usual. It now knocks at about half- throttle, but foot to the floor it's fine. Unfortunately, because the timing has been retarded so severely, my car's got absolutely NO guts- feels like I'm driving with the handbrake half- on, through a sea of toffee.

Has anyone else here had this problem, or one similar? The engine recon. guys suggested it may be bad fuel, but I only ever run 98 Octane. The possibility of stale fuel was also raised, but I'd filled it up from about 2/3 empty only the day before.

Any ideas as to what the hell is going on? The Engine is less than 2 years old since reconditioning, and has only done about 11,000 km since. Am going to be annoyed if it's anything too big, as the warranty is only good for a year.

[Jimmyd]

couple of quick questions:

1. What is your oil pressure
2. What kind of "knocking" noise;
a. Deep, low pitch thumping,
b. High, light tapping noise,
c. Rapid, tinny rattle, or
d. ??
3. Any chance of getting a recording of the noise and email or post somewhere?
4. What type & grade of oil are you using,
5. what temp does she run at

Cheers

[Pazuzu]

The knocking noise is more (b) than (c), like I've got maraccas under the bonnet. It does it while accelerating, but once the speed has built up enough it stops- It's not a constant rattle. At the moment, I'm only hearing it when I've got the pedal about half- depressed to accelerate.
It was really noticeable when trying to pick up revs, like when overtaking on hills or accelerating up on- ramps. It responded O.K. for power, but the knocking was definitely there.

I'll do my best to get a recording of the rattle. The running temp is always about half- way up the gauge (except in Summer traffic); gauge works well as far as I know. Never had a problem with overheating.

I know it's been getting serviced with SAE 20W/50 SF oil, unless they've got it wrong or have changed it without informing me. Not sure about the oil pressure, will have to check.

[Jimmyd]

OK, many possibles keeping in mind at foot to the floor WOT your exhaust noise will drown out most mechanical noises (short of terminal ones...) assuming you are not running a srtandard exhaust;

1. Bigends - unlikely but possible, recommend working on eliminating all other possibles first,
2. Oil - if using thinner oil (like 5w30 or 10w30 used Fords from the 90s on) can "squeze" out of Bigends under load giving this sort of noise,
3. Oil / Fuel - what does it smell like - if smells of fuel your fuel pump diaphram may be split with fuel going straight to the sump diluting the oil giving you a bottom end knock,
4. Fuel - bad batch is possible but unlikely,
5. Fuel - did you rejet the carb when switching to 98 and then again when engine was reconditioned? *Could* be running hellishly lean which will give you a knock (and burn valves...) - retarding the Ign will help to minimise the compaints from the engine when lean.

Hard to call it without seeing/hearing it but these might give you starting point even if only for elimination purposes

Cheers

James

[Jimmyd]

Another quick one - when the engine was recoed did they rebore and fit new pistons or was it just a rering - if rering too much clearnace when rebored it could be piston slap...

Cheers

James

[JamesR]

if pinging on acceleration, wouldnt it need MORE advance?
is the vacuum advance connected, and working properly?

[Pazuzu]

The exhaust is standard, hopefuly getting that changed soon.

No rebore done, just new rings. Retained old pistons.

I reco'd the carby before the engine recon. Haven't rejetted it, but will look at doing just that. Good idea to check that out, JimmyD. Thanks for the tip. Haven't checked the oil smell yet, will do this arvo. Will also sus out the spark plugs.

The thing that's getting me is that this problem has occurred in the past & was found to be a timing issue. Then, straight after a service, it reappears. Don't know if they set the 2nd- year apprentice loose on my car or what. Am also contemplating stripping down the fuel tank & possibly look at giving the fuel lines an enema.

And to think I was going to spend my tax return on an engagement ring...

[Jimmyd]

Originally Posted by Pazuzu

No rebore done, just new rings. Retained old pistons.

Excessive clearance can lead to piston slap which will make this kind of sound - thin/contaminiated oil will make this more apparent, check the quality of the oil.

Originally Posted by Pazuzu

The thing that's getting me is that this problem has occurred in the past & was found to be a timing issue. Then, straight after a service, it reappears.

Normally the ign timing is advanced - ie sparkplug fires before the piston reaches top dead centre. If the timing is too far advanced it puts excess load on the piston as it tries to reach top dead centre - if you have excessive piston to bore clearance the piston kicks sideways and the skirt 'slaps' the bore - hence the term piston slap.

the first time was probably someone being overly abitious setting the timing, second time I'ld just about put even money on thin oil. By retarding the timing there is less load on the piston, most likely the fuel is not igniting until the piston is past TDC and on the way back down the bore so less power and less 'slap'

In very limited cases oil that is too thick can also lead to this problem - for the cost of 4lt of oil its probably worth changing to some fresh, good quality 20w50 oil even if only to eliminate that from the equation

Cheers

James

[Jimmyd]

Originally Posted by JamesR

if pinging on acceleration, wouldnt it need MORE advance?
is the vacuum advance connected, and working properly?

Pinging is pre ignition of the mixture before the piston has reached TDC and the mixture is fully compressed - the fuel ignities and the increase in volumetric pressure tries to push the rising piston back down the bore. Retarding the ignition minimises this unless you have a 'hot spot' in the cylender, the fuel charge ignites when it reaches a certain level of compression - much like a diesel engine uses a glow plug.

as an aside increasing Octane rating on fuel makes the fuel LESS volatile - you need to advance ign timing so that the fuel charge fully ignites when the piston reaches TDC.

Cheers

James