307 tapping thoughts?

[classic gbody]

OK found it.

I inspected the pushrods while blowing them out and found a bent one.

I also found some small junk inside some of the lifters, likely leftover from the last build - I didnt disassemble the lifters when I overhauled the engine. Lesson learned.

My theory is that one of the small loose "bits" inside a lifter jammed it up long enough to bend the pushrod.

Anyhow I found the bent pushrod which provides a definitive answer to the question of what was wrong.

The lifters are all cleaned up and move smoothly.

The bent pushrod - well I dont know if I will just hammer it "straight" or replace it......

I will reassemble the engine then update the thread with a final outcome.

You will not be able to hammer it straight. Replace it, they are cheap. I had a similar issue with my 80 Cutlass when I did the cam, lifter and heads. I ended up having to file the rocker arm bridges to adjust them since they don't adjust. It worked perfectly.

 

[techg8]

I got it put back together last night and fired it up.

I had some rocker clatter until the oil warmed up, then it quieted right down. had to move some air out of the lifters I guess.

however, The "tapping" noise is still there at part throttle. Imagine my surprise!

I dropped a bunch of timing just to see the effect, and it "seemed" to help. I need to spend some more time on it.

I am now considering two possible causes, and I will have to investigate each.

one - as mentioned above - a hot bit of carbon in the chamber that is preigniting the mix.

two - headgasket leak of water into a combustion chamber, causing the clatter

I am going to pull and check the plugs, try grounding a plug at a time while running at the rpm where it occurs to see if it kills the problem, do the water trickle to try to break up some carbon, pressure test the cooling system, and work on the timing to try to reduce the symptom.

I think the headgasket failure is unlikely but worth checking.
I also think the timing is probably not the issue because it was fine for a long time prior to this issue popping up.

I may drop the oil and replace to see what it looks like. Its got a bunch of carbon cleaner and ATF in it right now anyhow so it should be dropped..

 

[techg8]

well....

I have isolated the rattle to the #8cylinder by pulling and grounding plug wires, one at a time, while the rattle was occurring. #8 eliminated the noise when grounded. No spark, no knock.

I dropped the engine oil and drained it thru cheesecloth to see if there was a lot of metal indicating a spun bearing or anything. The oil was brown but clean and relatively clear. No silverish haze or suspended particulate. I found a few small silver flakes but nothing abnormal. This is the 1st oil change since the overhaul. SO I am thinking its not a spun or worn bearing.

Also, In Park, the rattle occurs only on slow throttle increase. not on any speed of throttle closing/decelleration, and not at all on heavy accelleration. When driving, it occurs only at lean cruise.

I checked the plug in #8 and it looks fine if a little black, but dry. So no headgasket leak.

I am down to spark knock from too much timing and or A/F mix leanness.....OR some carbon bit in there preigniting the mix.

I sucked a bunch of seafoam into the intake there, let it sit and ran the engine hard till the exhaust cleared of the smoke. No change.
I tried sipping some water in there to shock the carbon free - but no change.

I guess all I have left to try would be retiming the engine and retuning the carb. I really thought I had it when I found that bent pushrod......

any thoughts?

 

[pontiacgp]

it could be piston slap

 

[techg8]

hm yea that would suck. but it is possible.

I will have to take a look at that.

to test it I would pull all the plugs but #8 and crank til compression stroke on 8 right? then rock the crank and listen for the piston rattling around?

 

[pontiacgp]

we had a piston slap on a race engine and it never blew up even with the abuse we gave it

 

[Bonnewagon]

I only had a case of piston slap once, and it quieted down when the motor warmed up. This motor was rebuilt? Same or new pistons? Pins? (could be a sloppy piston pin) Any machine work? Looking at the first post I still lean to Peter's question, could it be pinging from a malfunctioning EGR. When the timing is set for EGR, it is advanced way more than a non-EGR motor. take away the EGR and you now have an extreme case of too much timing and it will ping at light part throttle. Try backing off the timing to pre-EGR specs and test.

 

[sergio]

Have the same problem with my 86 Olds 442 62,000 org miles and the motor taps. I had all 16 lifters replaced than it stopped 3 months later back. when the engine heats up it gets louder. But oil pressure never drops. Some Olds mechanic told me it was a wrist pin. I give up ,,,,,Im putting in a 350 olds these cars should have came with them. So I have a 307 for sale Vin 9 its still in the car if anyone is intrested

 

[techg8]

I only had a case of piston slap once, and it quieted down when the motor warmed up. This motor was rebuilt? Same or new pistons? Pins? (could be a sloppy piston pin) Any machine work? Looking at the first post I still lean to Peter's question, could it be pinging from a malfunctioning EGR. When the timing is set for EGR, it is advanced way more than a non-EGR motor. take away the EGR and you now have an extreme case of too much timing and it will ping at light part throttle. Try backing off the timing to pre-EGR specs and test.

yes piston slap "should" quiet some as things get up to heat. My knock does not, but its worth checking out.

This motor was "overhauled" - cleaned up honed reringed, bearings, no machining all original used parts.

EGR is a good possibility too - I should have looked at it sooner, but its such a loud knocking that I discounted detonation early on. It was running great and all of a sudden developed this issue. So my thinking is something had to change to create the tapping. EGR malfunction is something to check. I will pull the valve today and have a look.

thanks everyone for your input

 

[techg8]

I tried a little more stuff this morning.

if I turn the distributor waay back I can eliminate the knocking. However it takes so much timing out that I cannot idle.

I checked the EGR valve it looks to be in good shape (was new on overhaul), but I am not certain how to test it. Hand vacuum pump wont hold vacuum on it, but If I remember, EGR valves can be like that. Ive got a warranty replacement on the way - should have it later today.

I pulled the #8 spark wire and did another SeaFoam treatment, hoping to maybe dislodge anything in 8 that might be glowing hot.

I am getting tired of chasing this, but I will persevere. I miss driving my Cutlass!