# Knocking engine



## Stickyfingersfrank (Feb 16, 2011)

I own a 73 lemans with a 350 2bbl,
if i drive relax, (which i ussually do, cause gas in holland costs about $2 per liter or $9 per gallon:willy there are no problems, but when i give more then half gas it starts knockin and rattling especially in higher revs.

I checked out the timing and dwell and thats ok,
What could it be?
Is it just because it's an old engine or is there something broken?
Or is my distributor busted?

Frank:seeya


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## BearGFR (Aug 25, 2008)

Stickyfingersfrank said:


> I own a 73 lemans with a 350 2bbl,
> if i drive relax, (which i ussually do, cause gas in holland costs about $2 per liter or $9 per gallon:willy there are no problems, but when i give more then half gas it starts knockin and rattling especially in higher revs.
> 
> I checked out the timing and dwell and thats ok,
> ...


Could be many things. Since it's a 73 it's a low-compression engine (or should be unless it has been modified) so I'm inclined to think it's not likely to be detonation --- but it could be. Does it seem worse if you're going up hill putting some load on it? Have you checked the ignition timing? Remove a spark plug and see what it looks like. If you can see what looks like tiny flecks of shiny metal, that's in indication of detonation.
Can you describe the sound? Is it "heavy" (like someone beating on it with a hammer) or is it more of a higher-pitched ticking sound? Does it go completely away when the engine is idling or does it just get a lot quieter?


Bear


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## Stickyfingersfrank (Feb 16, 2011)

bear it's more a rattle then a knock,
It runs smooth on idle, but when i'm accelerating it's the worst
but only when i hit the gas and then only in higher revs.
i checked out the timing long ago but at the time i had a vacuum leak so that can't be accurate, right?
i'll check out the plugs this week.
and check my ignition timing, idle and dwell also

Some guy also told me it could be a loose timing chain?
But i don't really believe him cause he never gave me tips i could work with.

Thanks for the tips anyway, i'll report back asap

:seeya Frank


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## Stickyfingersfrank (Feb 16, 2011)

Oh yeah, i run on 95 octane
With a stock engine, only headers installed


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## 66tempestGT (Nov 28, 2009)

is it an automatic? maybe cracked flexplate.


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## BearGFR (Aug 25, 2008)

Stickyfingersfrank said:


> bear it's more a rattle then a knock,
> It runs smooth on idle, but when i'm accelerating it's the worst
> but only when i hit the gas and then only in higher revs.
> i checked out the timing long ago but at the time i had a vacuum leak so that can't be accurate, right?


I'd check the timing first --- the vacuum leak is fixed right? Not intending to insult your intelligence or anything here, but do remember to disconnect and plug the hose going to the vacuum advance when checking the timing.

When it "does it", when you step on the gas --- does it start rattling right away or does it get worse/better as rpm increases?

Bear


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## Mr. P-Body (Jan 20, 2011)

"95" in Europe is similar to our "89". I agree with Bear, probably NOT detonation IF the 350 is a '73. Any verification on that? David DeRegt (RoadRageDavid on Pontiacstreetperformance.com and PY), in Schiedam, can help you. He and Clemmy are among the "leaders" in Pontiac perofrmance in Holland. "Dutch *****" is another, but I don't know him. I know David and Clemmy.

Sounds like the timing "curve" is too aggressive, to me. The "rattle" you hear is what we call "pinging". Mein Frau (Deutsch) suggests it sounds like spoons rattling in a drawer. 

Verify the year of the engine. Check the casting number of the cylinder head, visible on the center exhaust ports where they protrude from the head. Two large digits "cast in". This will tell us for certain, what you have.

Jim


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## geeteeohguy (Feb 2, 2008)

I agree with Mr. P. Sounds like too much total advance. Even if the timing is set to specs at idle, the total can be waaay off base. I checked the curves on both of my GTO's within the past two weeks, and found BOTH had total timing of about 44 degrees, which was causing surging at cruise. Both cars had the base timing and dwell right on. I put an adjustable vacuum advance on the '67 and set the total to 34 degrees, and it feels like a new car. The adjustable advance for the '65 is being shipped as we speak. Try pulling the vacuum line off of the vacuum advance, plugging it, and test drive the car. If the knocking/pinging goes away, it's too much total timing.


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## Stickyfingersfrank (Feb 16, 2011)

Thanks for the replies!!

Bear : yeah the leak i fixed and the rattling starts when i get to higher revs

Mr P-body: it does sounds like spoons in a drawer! I'll check out the cast number and engine no for verification, and post it next time!

and i'll also check timing/dwell and idle rpm

Then i'm gonna test drive without vacuum advance to see if its any better,

Thanks for the tips guys!!!


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## Mr. P-Body (Jan 20, 2011)

Frank,

I doubt the vacuum will make much difference, IF the problem is in the "curve". Either the limiter is gone or the spring/weight combination is out to lunch.

Do you know David and Clemmy? Just curious. How far from Amsterdam are you?

Jim


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## Stickyfingersfrank (Feb 16, 2011)

Last night i checked my ignition timing, it was 8 degr. advanced, so i adjusted to 12 degr advance @650rpm but it didn't change much.
I drove around the block with the vacuum plugged and it was a bit better, but still not ok.

So whats my best option for changing my advance curve, changing springs/weight or a adjustable vacuum? And how can i check my total advance? 

Mr. P-body : No i dont know David and Clemmy but i think i need to get to 
know them, i live about 100 miles from Amsterdam, in the south of Holland.


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## Stickyfingersfrank (Feb 16, 2011)

Oh and the numbers on my heads are 46...


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## Mr. P-Body (Jan 20, 2011)

Frank,

46 is a 350 "large chamber" head. Detonation from excess compression is NOT an issue here. I'm still thinking the advance curve is too aggressive. Or perhaps total timing is simply too high.

David has a company called "American Muscle". Clemmy is a tuner/builder that's more familiar with Pontiacs and Chevys than most other European mechanics. He's a friend of David.

Jim


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## BearGFR (Aug 25, 2008)

Stickyfingersfrank said:


> Last night i checked my ignition timing, it was 8 degr. advanced, so i adjusted to 12 degr advance @650rpm but it didn't change much.


Hi Frank,
Advancing it more, from 8 to 12, would have made it worse - not better. Try it at 6 degrees initial with the vacuum plugged and see how it does.



> So whats my best option for changing my advance curve, changing springs/weight or a adjustable vacuum?


Neither, actually. If your problem is too much total advance, then changing the springs/weights will alter how quickly the advance "comes in" but won't limit the total amount (at least not unless you go with springs that are so strong, or weights so light, that the distrubutor never gets to "full advance" - but I don't recommend that because it's too hard to control accurately.)

If you're comfortable removing and reinstalling your distributor and know how to do it properly... remove it, drive out the drift pin that holds the drive gear on, and remove the shaft. Turn it over and you'll see that the "T"-shaped part on top has a pin underneath that inserts into a slot in the piece that contains the cam that actuates the points. There should be a rubber grommet on this pin that takes up some of the space in the slot, thereby limiting the amount of total advance. If this grommet is gone or badly deteriorated, this could be the cause of you getting "too much" total advance. Many of the aftermarket advance tailoring "kits" contain, in addition to springs and weights, different sized bushings that can be pressed onto this pin to limit the amount of movement, thereby limiting the amount of centrifugal advance.



> And how can i check my total advance?


Either use a timing light that has the ability to check total advance, such as one like this, or install a timing tape on your harmonic balancer, similar to this one. If you go the timing tape route, make sure you get one that matches exactly the circumference of your balancer otherwise it won't read correctly.

Also, if your balancer is "old" it's possible that the outer ring may have slipped and no longer is indexed to accurately indicated Top Dead Center (TDC). If you've got the slightest doubt about that, it's worth going through the procedure to make sure the mark is correct --- otherwise you'll never know for sure how your timing is really set.
I've seen brand new balancers that had the TDC marks "wrong" and needed a timing tape put on them to correct the alignment. In your situation, sounding more and more like you've got an advance "problem", I'd double and triple check everything just to make sure you know where you're "at". 

If everything is correct as far as your balancer and marks go, then you may wind up needing a combination using a different limiter bushing and different weights/springs to control both the amount of total advance and how quickly it comes in to solve the problem - if indeed it's an advance curve problem. I know it's a pain, but it's worth the effort to get it right.

Bear


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## Eric Animal (Oct 28, 2007)

Put the timing back to 6BTDC and try a higher octane gas or booster....Do you live near The Hague' ??????:cheers


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## Stickyfingersfrank (Feb 16, 2011)

Hm, a lot of good tips! if i have a day off then i'll check out my distributor, i also ordered an advance curve kit so i can install that too

My friend has a digital timing light so i hope i can borrow it..

I really floored it last sunday and when i hit higher revs it goes like "tak tak tak":confused (try to write down something you hear...)

Is it a good idea to make a soundclip or movie to let you guys hear it cause it could be something else?

Frank:seeya

Eric : nope, i live in the south of Holland about 110 miles away, it might be close for American standards but for Dutch it;s the other side of the country..


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## Stickyfingersfrank (Feb 16, 2011)

Hi guys!

First of al i want to thank you for the good advices!!

I've been away for a while from this thread because my hobby has been paused for a bit.. lets call it a money issue.. damn you recession!!
But i'm pickin it up again!!

I'm going to remove my engine because it leakes a lot of oil from the oil pan and it really needs a paintjob and front crank seal is busted too.

So when the engine is out i am gonna take a good look at the distributor and the bushing and springs etc as bear described.

i have ordered a distibutor kit with bushings springs and weights and a timing tape to get it right!!

I also ordered a full gasket kit so i have all the gaskets if i need them because it's not so easy here to buy parts.
Autopartstores here only have parts for european cars and the most shops for us parts mostly have chevy parts so thats a bit of a problem..
It takes a few weeks to get them.
I'm fixing it at my friends shop because i dont have the space myself so i cant leave it there for weeks.
Can you guys give me some advice about whats important to have before i pull the engine out so i can fix it all in a few days? 


Thanks in advance!!

Frank

Ps sorry for the bad english i'm a bit rusty, just like my engine...


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