'74 Bus with a new spooky sounding knock...

[jimbear]

Hey folks. I went to move the bus so the kid could shoot hoops. The bus had not been started in a week as I was away with the family. I gave it three pumps of the accelerator and turned the key and it made some clunking sounds that were unfamiliar and startling. It barely caught and then died. I turned the key, checked the oil light (on) and then committed again. This time is started smoothly and stayed running, but there was an unsettling slight knock emanating from the engine. I backed it to where it needed to be and let it run for a minute. It idled fine, but the knock was still there. I shut it off, shot hoops with the kid, and tucked the fear into the back of my mind. I will head out tomorrow to assess further and really take a look and listen. My question is how should I proceed? Suggestions and insight welcome. Thanks in advance.

[luftvagon]

Was it a knock or valve chatter?

[jimbear]

I am pretty sure it was a knock and not the valves.

[Amskeptic]

I am pretty sure it was a knock and not the valves.

If that poor car has been languishing, oil may have drained out of the galleries and between the bearings.
Do you have a correct oil level with correct viscosity?
Does the oil light go out immediately at start-up?

If so, run the engine at a quick idle for five minutes and baby sit back there with ears open. Listen for knocks as you vary the rpms.
If it is a soft knock, it is likely to be loose pistons that will quiet down as the engine fully warms up.
If it only makes noise under acceleration load, it could be an exhaust leak that will diminish a bit as the engine warms up. You will hear it only under load, and the engine will sound fine when overrunning.
Go drive it and get it warm. When you get back, listen again.
The piston slap knock will be less.
If it is intermittent and hammers momentarily as you accelerate-then-release the throttle, it is a connecting rod. The connecting rod knock will be worse as the engine warms up.
A more-noticeable-still intermittent rattle knock at idle only is usually something like cam/crank gear/oil pump drive tangs.
Valve train coming apart will be less knock and more angry rattly tackity tockity like a loose valve gone rogue.

After this diagnosis, you can narrow it down by:
if valve train/exhaust leak:
rechecking the torques on the rocker shafts when the engine is cold (10 ft/lbs torque on all 11mm rocker stand nuts (mandatory valve clearance adjustment required after retorque of rocker stands!), retorquing the 12 or 13mm exhaust nuts on the cylinder heads 15 ft/lbs)

if deeper knock:
put in 20/50 oil (if you are still using winter oil) and see if that quiets things down while cold at least.
rev cold engine firmly but briefly (no more than 2,500 rpm) and listen for soft knock under cold load.
rev warm engine to 3,000 or so, and listen for a knock the instant you release the throttle.

Update us!
Colin

[jimbear]

Thanks Colin. I should be into it sometime later today.