Karmann Ghia engine knock

My ghia recently started making a loud knocking sound that is only coming from the passenger side of the engine. I opened the valve cover to adjust the valves and found that one of the locking nuts had fallen off and was loose. I went ahead and adjusted all the valves and made sure the nuts were tight but when I started the car it was still making the same noise. I also took out the spark plugs and the plug from cylinder one was bent so that there was no gap on the end for the spark. But I bent it back out and tried again and it was still knocking. I just put a new transmission in and I am worried that I manhandled the engine and messed something up and caused the knock. If anyone has any ideas on what is going on, I would really appreciate it. Thanks

Can you tell if it’s a preignition/pinging knock or something else? You could try removing the spark plug wires and cranking the engine over for a few seconds to rule out pinging. The fact that one of the spark plug ground electrodes was badly bent means that there is (or was) a foreign object bouncing around in a cylinder. It could have migrated to another cylinder via one of the manifolds. Do you have good compression in all cylinders? No destroyed pistons or loose connecting rods rattling around? If the noise appeared suddenly, it doesn’t sound to me like a badly worn main bearing or piston slap, though I guess that’s still possible. Is the oil pressure good? How long have you run the engine with this knocking? If one nut came loose, I suppose others could have too (say, on a connecting rod). This is an air-cooled engine with pushrod-operated valves? Are the pushrods in tubes that you might have bent or damaged while “manhandling” the engine?

I’m assuming there was no knocking before you removed the engine, but removing and installing an air-cooled VW engine should not have any affect on the internal parts. Nor should it have caused the valve adjustment lock nut to come off. You don’t need to remove the valve covers to pull or install the engine, so the lock nut had to have been loose before.

Did all of the valves need to be adjusted, or just the one with the missing lock nut? Which way did the valves need to be adjusted, were they loose or tight? The bent spark plug electrode is worrisome, since it takes some sort of physical contact to bend it, meaning something is wrong in cylinder #1, or some foreign object got in. You didn’t have the intake manifold off, did you?

I’m afraid you may have to pull the engine and remove the cylinder head to see what’s going on.

I used to work on these all of the time but this one is bit hard to figure without having vehicle in hand.

The lock nut is assumed to be one of the valve adjuster lock nut and not a cylinder head nut I assume?
Exhaust valve lock nut?
Absolutely sure the transmission is correct for the car? They’re not all the same in spite of appearances.

Some wild guessing at this point could mean a gland nut problem, cylinder/head stud(s) pulling out of the block, or an improper fitment of the transmission/clutch assembly.
Try pushing the crankshaft pulley as far forward and as hard as you can. Now grasp the pulley and yank it backwards as hard as you can. If you hear a clunk or thunk sound you may have a problem with the engine block main bearing saddles.

On the offchance that this problem could be caused by a severe engine miss, I would advise replacing the plug (a badly bent plug should not be straightened) and inspect the plug wire resistor on the end of the plug wire. A VOM will be needed to check this and the resistor should test out at about 1000 ohms.

One of the more common pieces to end up in the cylinder is the carburator dump nozzel.These usually rattled around a bit (check and see if your nozzel is still in your carb) It was more common for the nuts that hold the rocker shaft on than the valve lash lock nut to come off.

that car with a body left intact ,is unheard of,if it does it wont last 6 months in the elements (you know out of the garage) so why waste the money on a rodknock?

omo!(for the brilliant people)one mans opinion,thats what that means.

good luck!

say good ole RUSTY JONES.

The bent spark plug is the critical clue here. The piston in #1 hit the end of the plug. Question is why? Did you change plugs? Simple answer is that cylinder has the wrong size plug in it and it extends too far into the cylinder. You didn’t say if you re-checked the plug after you straightened out the gap and put it back in. Did you? Was it bent down again? Make sure you have the correct plugs.

I think the locking nut is a red herring. A mal-adjusted valve will not affect the spacing between the top of the piston and the bottom of the spark plug.

If a head bolt nut came off, and they do, it would tend to allow the cylinder to pull away from the block, thereby increasing the spacing between the top of the piston and the plug.

If you’re lucky, you have the wrong plugs in the head. If you’re not, you have a loose connecting rod in #1 that is allowing the piston to be thrown up farther into the cylinder than it is supposed to.

Also, not likely to be related to a transmission problem.


  1. If you’ve been good, and are lucky, bad spark plug, but,
  2. If you’ve been bad, and are not lucky, you have a connecting rod problem in cylinder #1.

Do not start the engine again unless you have confirmed whether you have a spark plug problem.

ron of ron and jazz said the intate push rod is bent he found it today ordered a new set from mid america lets see jazz said the stalling is from this cylinder not working wright

I would make sure there is not an underlying reason for this push rod being bent. The odds of a push rod bending is near zero unless the push rod has been thrown from the rocker arm cup.

Oldschool mentioned a common problem with the carburetor accelerator pump discharge nozzle coming loose and being inhaled into the engine. This is not that rare a thing to happen.
If the nozzle went into that cylinder it could very well bend the spark plug tip and then possibly becomed lodged between the intake valve and valve seat. This could keep the valve open and bend a push rod on the next stroke; all happening in the blink of an eye of course.

A bent push rod will not bend the spark plug tip so examine the valve train closely.
(And remove the air cleaner, look down the throat of the carubetor, and make sure that little brazz nozzle is still there where it should be.)

I would also add that anything in the cylinder (nozzle, whatever) will become red hot during the combustion process and this can cause a knock due to severe detonation.