Timing question

[Anonymous]

Refering to this post:
http://fordsix.com/forum/viewtopic.php?t=24328

What would cause excessive knocking? It was severe enough to have to reduce the timing to about 5-0º BTDC.
Is this a carb problem or a distributor/vacuum advance problem? The carb (autolite 1100) has been rebuilt within the last one and a half to two years and the dist. was replaced about three years ago.

Any and all help/suggestions appreciated!

Scott B

 

[HorsesNHogs]

Scott,
I had plenty of timing problems for months, of course that was before I found this forum
My issue was the harmonic balancer was slipping. Who knew this could happen?, Now while the slipping itself does not cause the bad timing, the timing marks are no longer accurate.
so you think your setting at 12 BDC, but you may be much higher/lower
So the knocking 'might' not be occuring at 12 BDC at all.
just my thoughts for this morning, there are many smarter men than me here who will be able to help more.
gjt

 

[CZLN6]

Howdy Scott:

I've given that situation a lot of thought. It seems to me that pre-ignition or detonation could not likely have caused the head gasket to fail. More likely it was a combination of factors such as an imperfect mating surface, a flawed gasket, carbon buildup which becomes a hot spot.

Pre-ignition and/or detonation can be the result of simple things like too much initial ignition advance, too lean an air/fuel mixture, poor combustion characteristics caused by large bore, poor chamber design, poor quench characteristics, poor gas, lugging an engine, etc.....

Pre-ignition is caused by a hot spot/glow plug that ignites the mixture before the spark plug does, causing two flame fronts to collide causing the knock sound and the damage. It can also be caused by detonation which is a maverick ignition of a non-spark plug flame front caused by ambient heat and compression. This second scene is more likely to occur in a higher compression engine with a large bore.

Knock is less likely to happen in a smaller bore engine like ours so, if you have it you have to look at all the factors to assess what is the root cause.

Certainly, the wider quench margin caused by aftermarket head gaskets reduces combustion efficiency, but it also lower CR. Ignition timing is also a factor. Make sure all reference marks are accurate

Another is carbon build up. It can raise CR and become the source for hot spots.

Adios, David

 

[Anonymous]

Thanks for the responses.
HorsesNHogs, it definately isn't the balancer. The timing mark is dead on, I checked a couple of weeks ago.

David, I don't think I can follow your explaination! I don't know what "quench characteristics" are or what "lugging an engine" means, sorry. It is a stock 200 motor taken from a 66 Fairlane? and dropped into my 65 Mustang. The block and head/valves were rebuilt about 7 years ago. It was basically refurbished to stock spec if I remember correctly.

The head was just resurfaced/machined and the head gasket replaced. But the timing had to be retarded to keep it from knocking. I was just living with the knock before the head gasket change. It only knocked audibly while under hard-ish excelleration.

If you don't think the knocking and the blown head gasket are related, what do you think could be the cause of the knocking? (my appologies if the answer to this question is your answer above and I'm too dense to understand it! )

Scott

 

[ludwig]

If the tech solutions don't do the job, try a higher grade of gas. I can't use regular with my otherwise stock setup without extreme clatter on acceleration. I run mid-grade all the time now. Works just fine.

 

[LEROY POLL]

HELLO SCOTT B


.....HOW DOES IT RUN IF YOU UNHOOK THE VACCUM ADVANCE? WILL IT STILL KNOCK ? DOSE ADVANCE HAVE ANYTHING TO DO WITH YOUR PROBLEM?

.....WHAT GAS WERE YOU RUNNING WHEN IT STARTED KNOCKING? HAVE YOU CHANGED STATIONS? HOW MUCH DID YOU TAKE OFF THE HEAD WHEN YOU RESURFACED THE HEAD? WHAT WERE THE OTHER THINGS THAT THE SHOP DID TO THE HEAD?

.....WITH MORE INFO IT MAKES IT EASIER TO SEE WHAT IS GOING ON.

LOTS OF LUCK....LOL

LIVE IN GRACE

LEROY POLL