'73 Bus Engine Mechanical Clatter . . .

[mylopolis]

Something just went terribly wrong. Metal on metal clatter as I pulled into work this morning.

I don't even know where to begin in diagnosing it :(

[dhoch14]

could be MANY things.

Where is the clatter coming from? Valve, exhaust, internal *hope not!

[mylopolis]

could be MANY things.

Where is the clatter coming from? Valve, exhaust, internal *hope not!

I stuck my head in shortly before turning it off. It sounded like it was coming from under my right side intake manifold.

Sorry that's not very descriptive. I'm working on towing her home right now so I can take a safer look over the weekend.

[JLT]

Don't freak before you have to. I once had something like that, and it scared the bejeezus out of me at the time. When I popped the valve cover, it turned out that the rocker arm assembly had come loose. The hardware was all there, so I put it back together, torqued the nuts down, and got many further thousands of miles on the beast before I had to take the engine out and replace a bad head ... on the other side.

[mylopolis]

Don't freak before you have to. I once had something like that, and it scared the bejeezus out of me at the time. When I popped the valve cover, it turned out that the rocker arm assembly had come loose. The hardware was all there, so I put it back together, torqued the nuts down, and got many further thousands of miles on the beast before I had to take the engine out and replace a bad head ... on the other side.

Popped the right side valve cover and everything looks completely normal. :( Going to check valve adjustments and compression tonight.

[Amskeptic]

Don't freak before you have to. I once had something like that, and it scared the bejeezus out of me at the time. When I popped the valve cover, it turned out that the rocker arm assembly had come loose. The hardware was all there, so I put it back together, torqued the nuts down, and got many further thousands of miles on the beast before I had to take the engine out and replace a bad head ... on the other side.

Popped the right side valve cover and everything looks completely normal. :( Going to check valve adjustments and compression tonight.

Check installed height of valves. If any one is sticking out further than the others with no clearance, do not start the engine, but feel free to carefully rotate it by hand to check for interference issues or clanks.

If you do start it, make little emergency notes, like how quickly the oil light went out after starting, does the noise sound mechanical/deep or surface clattery?

Fingers crossed for ya,
Colin

[mylopolis]

Check installed height of valves. If any one is sticking out further than the others with no clearance, do not start the engine, but feel free to carefully rotate it by hand to check for interference issues or clanks.

If you do start it, make little emergency notes, like how quickly the oil light went out after starting, does the noise sound mechanical/deep or surface clattery?

Fingers crossed for ya,
Colin

I left my micrometer in my other pants, but from what I can tell, the installed height is fine. Nothing looks out of the ordinary.

Did a valve adjustment. Minor tweaks (1/16th) but nothing major.

Checked compression. Unfortunately, with a different gauge than the last time, so apples:fuji apples, but every cylinder reading 10lbs lower than before, with the same variance. All in the 110-130 range.

Turning her over disconnected and everything sounds perfectly okay.

Plug her in and she fires right up, but with a horrible kerthunk kerthunk seemingly coming from cylinder 1.

No smoke. She runs. Just sounds like hell.

Any ideas? Anything else to check before I throw in the towel this weekend and start the gutting process :(

[Amskeptic]

Check installed height of valves. If any one is sticking out further than the others with no clearance, do not start the engine, but feel free to carefully rotate it by hand to check for interference issues or clanks.

If you do start it, make little emergency notes, like how quickly the oil light went out after starting, does the noise sound mechanical/deep or surface clattery?

Fingers crossed for ya,
Colin

I left my micrometer in my other pants, but from what I can tell, the installed height is fine. Nothing looks out of the ordinary.

Did a valve adjustment. Minor tweaks (1/16th) but nothing major.

Checked compression. Unfortunately, with a different gauge than the last time, so apples:fuji apples, but every cylinder reading 10lbs lower than before, with the same variance. All in the 110-130 range.

Turning her over disconnected and everything sounds perfectly okay.

Plug her in and she fires right up, but with a horrible kerthunk kerthunk seemingly coming from cylinder 1.

No smoke. She runs. Just sounds like hell.

Any ideas? Anything else to check before I throw in the towel this weekend and start the gutting process :(

You can pull the air filter and get a flashlight down in the spark plug hole and look for evidence of ingestion. You might have swallowed a nut. Bring the engine up towards TDC #1 and look as the piston comes into view (2nd gear no brake push back bumper a little while you keep checking)

Is there any possiblity that the noise is coming from the lower end? We are happier with upper end. Just pulling a head is preferable to a complete teardown. All valve guides good? Sometimes you can see a loose one under the valve springs either "swallowed or sticking up and getting rapped by the valve spring retainer. Dammit!

(I am very sorry to hear this)
Colin

[mylopolis]

You can pull the air filter and get a flashlight down in the spark plug hole and look for evidence of ingestion. You might have swallowed a nut. Bring the engine up towards TDC #1 and look as the piston comes into view (2nd gear no brake push back bumper a little while you keep checking)

Is there any possiblity that the noise is coming from the lower end? We are happier with upper end. Just pulling a head is preferable to a complete teardown. All valve guides good? Sometimes you can see a loose one under the valve springs either "swallowed or sticking up and getting rapped by the valve spring retainer. Dammit!

(I am very sorry to hear this)
Colin

I'll try poking around with a flashlight tonight.

There is certainly a possibility it's from the lower end. I have no idea how to check, however. I tried to look under the valve springs but can't really see anything. Nothing stuck out as abnormal on any cylinder when compared to others.

[Amskeptic]

There is certainly a possibility it's from the lower end. I have no idea how to check, however.

You can try to delicately spin the engine with the plugs out and listen, very little load on lower end in this scenario. Check to see if oil pressure comes up (light goes out) while the engine is spinning compression-free. This would be a helpful sign. Then try cranking engine with plugs in. If compression load may bring the noise to the fore, you may need to perform exploratory surgery.

Man, find something stupid!
Colin

[mylopolis]

Nevermind! Something stupid found and She's fixed!! *Happy dance*

I have now experienced a valuable lesson in engine noises. Kerthunk is especially the "thhhh" part, sounding like air.

Diagnostics followed:
Nasty sound
Tow home
Checked valve height and adjustment, fine
Checked compression, fine
Sound didn't occur just running on starter, only when firing.

Tonight:
Pulled plug wires. Pull wire #1 and sound (mostly) disappears. Obviously cylinder 1.
Re-torqued exhaust manifold
Re-torqued head
Pulled rocker assembly and inspected pushrods.

Went to re-torque intake, and discovered a large bolt lying on top of tin.

What bolt you ask? The "plug" inserted into the EGR hole after removing the EGR pipes.

Insert plug bolt, with extra thread locker, torqued down well.

No noise!

Yes, a seriously nasty exhaust leak makes a kerthhhunk kerthhhunk sound.

Thank you all for the diagnostic advice! I'm so happy I'm not dropping the engine tomorrow and nothing major is busted.

Now back to carb and vacuum tuning :)

[Amskeptic]

Nevermind!

Fine!
Colin
(a major exhaust leak, I know that sound!)
(very relieved over here)