Clunking When Engine Turning Over

[blg5035]

After some fuel system troubleshooting, the engine is making a clunking noise that corresponds with cylinders 3 and 6 when spinning without spark and fuel.

The short of the fuel system issue is the fuel distributor was leaking fuel to the injectors with the air flow meter closed. Manually running the fuel pump for pressure testing caused the entire crankcase to fill with fuel and even up in to the AAR/AAV plumbing.

Not knowing this at the time, after adjusting the fuel pressures I went to crank up the engine. There was a big clunk. The starter was trying to spin the engine (could see the fan twitching), but it wasn’t turning over.

I pulled the spark plugs and found fuel spilling out of cylinder 5’s spark plug hole. With all the spark plugs removed, I bumped the starter and the engine spun with fuel shooting out of #5’s spark plug hole. I don’t think I turned the engine over any more after this.

Drained the crankcase and had probably two gallons of fluid come out with a strong fuel smell. Added 3 qts of oil to tank.

After getting the FD fixed and reinstalled, I tried to be very cautious with startup. At first, without spark plugs, I attempted to spin engine by hand via fan pulley nut. It was extremely difficult and had to use ~2 foot long cheater to get the engine spinning.

Added light liquid cutting oil direct to cylinder via spark plug hole. This made a big difference and I was able to turn the engine by hand with a 1/2" drive ratchet. Turned the engine over probably 100 times over a couple days. When I got going, I probably got to about half turn on the ratchet every second (30rpm kind of?).

With spark plugs removed, fuel pump relay disconnected and CDI plug disconnected, I bumped the starter. Did a few bumps, and then held the starter. The oil pressure light went out and the oil pressure gage went up to <1. I did this twice. There may have been a clunking noise as I was doing this, but I had never spun an engine without the spark plugs, so I wasn't sure what I was hearing

Installed new spark plugs and reconnected the fuel pump and CDI. I lifted the AFM to prime the injectors, but I may not have done it for long enough. I heard a squeal, not sure if it was all of the injectors.

Tried to crank. The clunking was much more noticeable and the shift lever would move when the clunk happened. The car itself did not move, so this is probably just the vibration moving through the system as opposed to an issue with the trans. It seemed to happen either once per revolution or once every other revolution. The sound seems to come from under the car on the driver's side. Most likely unrelated to the clunk, but as a side note, the engine didn't seem to attempt to fire. I didn't attempt to troubleshoot this because of the clunking.

I came up with three theories:
1. Crank bearing got spun
2. Piston rings broke and piston is hitting cylinder wall
3. Valve is hitting piston (doesn’t seem likely based on what happened, but a theory)

Checked intake valve lash to look for a bent/dropped valve since that is easy to access. All were on the tight side. I was assuming the lash would be bigger if the valve didn’t come all the way back up. Didn’t check exhaust, but revisited turning engine over.

Revisited turning over the engine with the starter and took videos of the distributor rotor to correlate clunk with a cylinder. Spinning the engine with the starter (no fuel or spark) and no spark plugs there is a slight clunk when distributor passes #3 & #6. (See video)

Spark plugs removed. https://youtube.com/shorts/8XWJCVWRXvw

Spark plugs removed. Video at half-speed: https://youtu.be/0j9Cw5fXHu8

Reinstalled spark plugs. Slight clunk when distributor passes #6 and big clunk that passes all the way to shifter when distributor passes #3. If you look closely at the video you can see the entire engine move at #3

Spark plugs installed. https://youtube.com/shorts/qAQjjsaNs2E

Spark plugs installed. Video at half-speed: https://youtu.be/OZUQr8MgVUE

To do an ABA test, I removed #3 spark plug and big clunk was not as prevalent and then reinstalled #3 spark plug and big clunk came back. (didn’t get good video of these)

Appreciate your thoughts.

[stownsen914]

I’m on my phone and can’t easily listen to the video, but one thing to look for with a fuel hydro lock situation is damage to a rod or piston from the attempt to turn over when its cylinder is full of fuel preventing the piston from getting to TDC.

I’d do compression and leakdown tests to rule out possible top end damage.

[stownsen914]

Actually I’d start with leakdown first to minimize turning over the engine with the starter to see if that gives you the info you need.

[snbush67]

Seems like you’ve done everything except check all of the head studs and cam tower nuts.maybe take the chain covers of and look at the tensioners and anything weird going on. Slack or metal rotating around the chain or crank.

If there is a sump plate cover pull it and look inside.

[pocv0]

I agree with stownsen914. Hydro lock from fuel filled combustion chambers could cause damage. I wouldn't continue cranking it. You could have a broken/cracked connecting rod, cracked cylinder, broken piston. JMO

[blg5035]

Thanks, good next steps here.

Further discussion on the hydro-lock line of thinking:

• The engine did, I would assume, less than one revolution before hitting the hydro-lock, since it was only spun with the starter and wasn't already running. Would that be enough force to break something?

• Assuming cylinder 5 was the one that hydro-locked based on the fuel coming out of cylinder 5 , it doesn't quite make sense that the clunking would come from the 3-6 cylinder plane.

In any case, a leakdown test seems like the first course of action.

[stownsen914]

With hydro lock, whichever cylinder is full and hits TDC on the compression stroke first is the one that will be damaged. It probably wouldn’t have even completed a single revolution. One such instance would be enough to cause damage, if that’s indeed what happened in your case.

[RobFrost]

Hydrolock. Bent rod most likely but could be any major mechanical damage, I'm sorry to say

If you're very, very lucky a cam will have slipped but caused little or no damage. The cams have a punch on the end indicating the top. Maybe you can take off your chain covers and see it.

If you're even luckier it'll be starter motor or flywheel damage, but that doesn't sound likely.

Sent from my SM-S918B using Tapatalk

['78 SC]

Just to illustrate the OP's problem, here's the result of a flow test with a failed fuel distributor (probably ruptured diaphragm). This shows how much fuel flowed through each injector in just a few seconds. The test was performed with the engine off, the fuel pump on (jumpered relay) and the air flow arm fully down. Wouldn't take long to fill a cylinder with fuel.






... and a few months later with the rebuilt fuel distributor.

[blg5035]

You show yours, I'll show mine Hopefully there isn't damage to the block

[Dpmulvan]

To do an ABA test, I removed #3 spark plug and big clunk was not as prevalent and then reinstalled #3 spark plug and big clunk came back. (didn’t get good video of these)

Appreciate your thoughts.

Broke Rings.

[icarp]

Sounds like a chain tensioner , a bad one

Ian

[safe]

No matter what the source of the noise is, it's a "tear down engine noise".
No need to further investigate, just rip out the engine and prepare the bank account.... Further cranking will only make it more expensive.