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Posted by: highways Jul 12 2007, 05:44 PM

Hey guys,

So I've got my project driving again but I'm concerned about a knocking sound. It seems to come from the top center of the engine (like under the throttle body or that general area). You don't hear it very much when listening underneath the car. When the car is cold- for the first 10-20 seconds of running it sounds normal. Then the knocking starts as it heats up. It seems like it possibly gets a little worse as the engine get's hotter.

The engines history- 108,000 miles. It sat for five years. I sprayed WD40 and marvel mystery oil into the spark plug holes. It cranked over and started just fine. Drained the oil, replaced. Redid the vacuum lines. I'm 95% certain I got everythintg back on there but there is the possibility for error. Redid the fuel system. Checked the new spark plugs after 10 minutes of running- two spark plugs were found to be blackened. The other two were clean. Timing is uncertain and only 'roughed in' at this point. The engine does 'hunt' and occilate when idleing. It goes between 800-1,300 RPM's.

I need some help diagnosing this knocking sound inorder to figure out if it's something to worry about or just a normal engine sound. It's hard to tell. Any thoughts?

Posted by: rjames Jul 12 2007, 06:44 PM

Fairly similar to what mine is doing. I chalked it up to needing a valve adjustment, which I have never done in the 2 years I've owned the car- but only because I have hydraulics installed and have found only limited info on how to proceed. I'll be diving in shortly though just the same....

Posted by: rmital Jul 12 2007, 08:11 PM

My experience with knocks in that area had nothing to do with the engine warming up...just stuff knocking around.

1) The tin where the coil attached cracked. Heard the knocking, didn't really think to look at the coil...finally noticed the crack when the coil was flapping around. Ended up carefully welding the area fixing the crack. Will replace tin next time I have the motor out.

2) Replacing the vacum hoses on the air filter housing...push to hard on the housing and snapped the bracket the attaches to the intake tubes. First didn't realize, but eventually realized it was bumping around.

again nothing to do with operating temps...just stupid noises or knocks I tracked down.

Posted by: highways Jul 12 2007, 08:30 PM

Thanks for the good advice so far. Actually I forgot to mention I did the valves, twice. They seem fine except that on one valve the adjustment seems a little bit more sloppy then the rest.

Engine tin crack from the coil- yeah mine has that too. Maybe the sound is coming through the cracked tin? The knocking is very regular, and not chaotic. It follows the RPM speed going faster and slower making me think it's an internal engine problem. Either that or it's just a regular exhaust sound that's making it's way out somewhere. But I will do my dad's listening trick with a tube up to my ear to see if I can pinpoint the sounds location.

Posted by: Dave_Darling Jul 12 2007, 09:22 PM

If you disconnect one spark plug (or injector) wire, does it affect the sound? If killing one cylinder makes the noise go away, you've found that one cylinder is making the noise. Could be nearly nothing, could be a rock knock or something else that's serious.

--DD

Posted by: proto31 Jul 13 2007, 01:21 AM

seems to me Highways that you need to lay off the beans, flatulents has driven many a man crazy. The first step is accepting that you have a problem...

Posted by: highways Jul 13 2007, 04:42 PM

I admit that I have a problem. And it starts with a P and ends with a 1.

Anyway- I went ahead and did Dave Darling's spark plug process of elimination test: no change in the knock sound. Where should I go from here? How do I start to determine if it's serious or not?

How do you know if you have a dropped valve?

Posted by: proto31 Jul 13 2007, 05:03 PM

I helped Cris put the engine back into his car, everything looked solid, the engine ran fine 6 years ago when it was last fired up. We adjusted the valves (and he re-adjusted them to double check) changed the oil and cleaned everything up so it looked new again. Other than that, nothing had changed since it last ran. It doesn't seem to be an exhaust leak (no sound coming from the bottom of the engine). We know that the timing is not all that close, the dizzy was removed and reinstalled, Cris has been able to find a place for the dizzy where the timing seems to be close, but definatly not spot on. Anyone else have any ideas???

Posted by: cgnj Jul 13 2007, 05:31 PM

Had this problem, sloppy valve lash adjustment?, Dropped seat.

Posted by: proto31 Jul 13 2007, 05:55 PM

Cris had told me that as a token of good faith, he was going to hook up whoever figures out his problem with his sister. I've attached a relatively recent photo. Not to bad ehh...

Posted by: proto31 Jul 13 2007, 06:36 PM

And for you ladies who may provide the solution to Highway's engine problem he will offer up a date with his younger brother. Pictures upon request.

Posted by: highways Jul 13 2007, 06:52 PM

Well, we haven't seen my brother in a while. But when we find him... the ladies can have him.

Posted by: proto31 Jul 14 2007, 10:37 AM

You know, you'd get $50,000,000.00 if you turn your brother in. Could help you pay for some of the parts to your restoration...


proto

Posted by: SLITS Jul 14 2007, 12:27 PM

Instead of fuchin' around, time the engine correctly. If your timing is to advanced there is a possibility that the "knocking" sound is the mixture being ignited to soon making the sound. Also if to retarded.

Posted by: bottomend Jul 14 2007, 06:39 PM

Glad you finally got it "running" Cris! Wasn't about a year ago I helped you pulled the motor?

Anyway, heres my diagnosis;

First off, a dropped valve usually sounds like a bunch of small rocks ( or peanuts perhaps) being shaken in a coffee can. It's a high frequency non-cadence type sound. There wont be any sort of rhythm to the sound ( No putt, putt, putt ect).

Rod knock usually doesn't change as the engine warms up. It's usualy either there or not there. A good test is to rev the engine up to 3500 RPM and let the throttle snap to the closed position quickly. If you hear a knock upon the deceleration of the engine, it could be the rods. The timming of this sound will be in cadence with the revolutions of the engine ( i.e. "in time" with the crankshaft)

Usually a piston knock will change as the engine warms and cools. It may be present when cold but become inaudible when warm. The cadence will NOT be intime with the crank. It will sound a bit "lop-sided".

If your timming is off and you have 'pinging" it will usually only be audible from the top of the engine and will sound like fast sharp metal on metal sound. It has a cadence but it's very fast, so it might sound like just random noise.

Order of "fixes";

Adjust valves on the loose side ( a nice medium .008 perhaps) to allow for a little expansion if you do in fact have the timming set wrong and the engine starts to heat up. Tight vlaves ( a tight .006 for example) and advanced timming can heat things up FAST.

Find the timming mark/marks on your fan and make sure you understand which one is which. Some fans have different marks ect. I've spent 30 minutes in Joe Shaprs drivway looking for a mark with a bunch of guys who actually know what they are doing and we STILL couldn't find the right one!

Make sure the intake runners of the FI are tight and not allowing any leakage. Anykind of leaks make for a weirdly running engine. This will also cause heat issues.

Check fuel pressure with a guage and adjust. I watched a tiny poorly running car kick dust in the face of the big bad bully just by having this adjustment made. It's amazing the difference it can make!

Plugs, points, wires ect. All the normal stuff.

If none of this works to make your day more harmonious, then you can listen for the voice in your head that told you to rebuild the engine while you had it out of the car. ( told ya so!)