At wide open throttle, I have a bit of spark knocking. This happens with or without vacuum advance. Actually, I have my vacuum advance adjusted 14 turns ccw from maximum. Anyway, it's the same spark knocking either with or without the advance. This is a 351w with initial timing set at 0 degrees, and a mechanical advance of 36 degrees. This is an 88 engine [8.8 compression] with new head gaskets; could this alter compression thus causing spark knock? I am using 89 octane fuel. Maybe WOT will always have some spark knock anyway? It is working perfect with no overheating. It rarely would see WOT except for some loads of firewood uphill or something like that once in a while, and cruises on the highway at 60mph easily. Might be OK?

 

Was it a stock replacement gasket?

Are you sure the damper timing marks are correct?

Aren't you the fella that had problems some time back?

Are you sure your compression is 8.8?

Back the timing off a degree or two and see how the truck performs and whether or not it pings. Good luck

 

Yes I have been at this for awhile but gradually it has come together. I hauled about 1500 lbs. of grain today and the truck worked great. Just a little spark knock up a hill in highway traffic. Maybe this won't hurt anything. It's just that I did the work myself and I don't feel completly confident in my final tuning. To answer your questions, 1 my manual says 8.8 comp for 1988
2 it was a NAPA stock gasket set
3 I checked the damper compared to the piston top as best I could
Initial timing is now at 0-2 ATDC; will this hurt anything provided the damper is right?
If the damper was off by a few degrees could I tell thru the spark plug hole anyway?
I'm not at WOT very often so can I run the way it is and not worry about the damper if it is off a bit?
Are there any other symptoms of a bad damper?
Thank you.

 

Your timing should be bftdc not after. Your damper/harmonic balancer is there to help balance the engine and is important to the longevity of your engine, take apuller and go to a wrecker and get another , look for one that has a good rubber bond between the pieces and little or no scoring where the front seal runs, if there is too much groove the front seal will leak and/or you'll have to sleeve it.Then try the timing again. Your dist. could be adv. too fast you can bend the springs out ward on the tabs in the dist there are slots through the floor plate to do this.

 

Are you comparing it to what you think the pointer is pointing too, or what you know? My TDC is off by 1/4" to the right of the pointer. I would think if you were into the atdc range it would start like a dog, so I am thinking the same as daerhldgs2 your damper or pointer is off.

This is what I did to find top dead center.

Take the number one cylinder plug out (you facing front of vehicle left side first one).

Either get a piston stop tool that screws into the plug hole or use something that can be removed and replaced consistently.

Place someones finger in the hole rotate engine until air blows out, stop,

insert piston stop, rotate engine slowly until it rotates no more,

find a reference mark either pointer or what ever, mark the reference point with something (paint-whatever) and the damper at the same point.

take piston stop out of the plug hole

rotate engine clockwise slowly until it begins to go back down the cylinder

reinstall piston stop, be sure the piston stop goes in all the way or the same distance as before, very important.

now slowly rotate engine counter clockwise until piston hits the stop again, make a mark on the damper where the pointer mark is (pointing too)

remove piston stop

now find the half way mark on the damper, between the two marks you made, rotate engine until the halfway mark is in front of the mark you made on the pointer. Your at top dead center.

Now find top dead center on the damper, make a mark on the block or pointer where the tdc on the damper is. This mark on your block or pointer is your reference point, remove or disregard the other marks you have made up to this point.

reinstall someones finger, rotate clockwise, until they feel air coming out, insert spark plug and wire

now rotate the engine until the damper mark 8 or so degrees BTDC is in front of the last reference mark (you made on the pointer or block)

now you know for sure your at 8BTDC and that the reference mark on the pointer or block is correct in order to use a timing light.

confused yet?

If you are sure of your marks then disregard, and good luck with finding your problem, later

 

i did put the light springs in the distributor for earlier advance, but there is no problem with spark knock until well after 3500 rpm; full mechanical advance is supposed to be in by 2500 rpm.
There is no problem when I step on her and accelerate, only when I step on her at highway speeds, with a load on. The truck starts great, -10 yesterday and not even plugged in. i'll try that piston stop to get the marks isolated. So if the marks I make aren't the same as factory 0TDC then I should get a new damper, right?
Is the piston stop tool specific to each particular engine/piston combination?

 

Actually the piston stop is specific to your plug hole size. later

 

If it were me I would check to make sure the damper is good and install heavier springs. It's simply advancing too soon.

 

are you sure your vacuum adv. is good , because if it isn't the timing wont retard when the vacuum drops such as when you lug it down. try sucking on the vacuum adv.hose where you take it off the carb and see if it holds vacuum.

 

It's a new vac advance and is working well. The spark knock knocking occurs even without any vac advance. There's no spark knocking anywhere in the throttle except at full throttle at high speed. Hard acceleration from low throttle doesn't cause any spark knock. If it was advancing too soon, shouldn't it detonate all through the throttle range?

 

Yep.


Where you able to determine the condition of your damper and timing marks?

I had a similar experience as yourself, everything was good but the stupid thing knocked (one time) consistently going up a very steep hill, I bakced out the vacuum advance screw that one extra turn and finally it went away.

If you have backed the screw all the way out I would back the initial timing off just a touch (moved the distributor counter clockwise) and run it, to see if the knock goes away? Maybe your initial is just a bit too much.

Just a thought, later

 

No, I haven't had a chance to check with the piston stop yet but that's my next job . That should remove any doubt I have about the damper. I would try the base timing backed off further but I'm at 0 TDC now so I don't like to try any further in case it might do some damage. If the damper is bad I'll get a new one then turn the timing back. Thanks for that piston stop idea, shouldn't be any guess work after that.
This is an 88 engine with a 78 intake and carb. It is no longer computerized, but is there a chance that the cam was put in advanced either factory or before I bought it and that this could contribute to spark knock? I'm sorry I didn't examine the timing gear before I changed the front cover.

 

If the motor is assembled as it was from the factory or is untouched, you should be fine. There is some advance from the factory, but that would affect where the hp and tq is made in the rpm range more so than be a cause of your pinging.

Like I mentioned before my truck starts like a pile of crap at 0 tdc, and you mentioned yours fires right up, That is my first indication that your damper or pointer is off, so by backing the timing off some more, your not gonna hurt anything by giving it a shot, you can always set it back if you feel like you should wait. Just a thought

Good luck though

 

Checked my damper and it seems fine. I backed my timing way off till it lugged then just brought it ahead till it ran free. That's where I'll leave it for now. This let's me idle at 6 btdc and total timing seems to 34 btdc high throttle in park. It will still spark knock a bit if I really force it which I never do in regular driving. One question though; the carb runs quite rich, would carbon cause pinging at high rpm? Thanks for your help.

 

If you have excessive build up on the piston tops, it will increase your compression ratio, and could cause pinging. You may try a cleaner. Some people take a mister bottle full of water, have someone hold keep the rpms up on the motor and mist some water down the carb. Make sure your exhaust is pointed away from everything, because I have heard it will blow crap everywhere. Just a thought, let us know what you do or figure out, good luck once again