Turning engine by hand, clunk

[maplesyruplover]

Hello all. I just picked up a beetle and as I turn the engine over I hear a clunk noise. The engine turns over fully but between this position it makes a noise.

[viiking]

You said the motor turns over but it doesn't! Other than about 1/8 of a turn.

The last time I heard this sort of noise was when assembling the engine and the conrod was not connected and when the crankshaft was turned it hit the loose conrod. It is a very heavy steel on steel knock. Not a steel to aluminium knock if one of the valves was in the wrong position and hit the piston when the engine was turned e.g. if camshaft has been installed incorrectly.

Has the engine ever run? Has it ever turned over more than this?

Sounds very mechanical to me so whatever you do, do NOT try and start it up until you find out. If it were me, I'd pull the engine and heads and see if there is any obvious evidence of metal to metal contact. If the heads come off and the knock is still there, then you need to split the case.

But wait for other experts to chime in. This is just my diagnosis.
_________________
1968 1500 RHD Lotus White Beetle since birth. In the hospital for major surgery
1966 Lancia Flavia Pininfarina Coupe - in the waiting room
Discharged: 1983 Vanagon, 1974 1800 Microbus,1968 Low Light,1968 Type 3

[Busstom]

Yeah, the way you've worded it is a bit confusing. When you say "fully," are you saying that it will in fact turn round and round and round several rotations, but only at that particular angle it makes that sound?

Maybe it's just the tinny speaker on my phone, but it sounds more like a screwdriver shank rapping sheet metal, not a clunk.

This is curious

[Kthomas]

Maybe something under valve cover hitting valve cover ? That’s bizarre

[maplesyruplover]

I should clarify. The engine was last run in 2003. It turns over fully without any problems and has compression. The video shows that in this position as I turn the engine it makes this clunk noise. It cannot be felt when turning the engine.
Sorry for any confusion.

[dougnlina]

I think what you are hearing is cam whip. What is happening is the pressure from one of the valve springs is putting a side load against a cam lobe by pushing on the valve train when that valve train has an open valve. This in turn causes the cam to rotate slightly against other components in the gear train and valve train. It is very subtle and sounds almost like a wet, light, tick or click you could make with your tongue. If that is what it is, it is normal and not preventable.
It is also more noticeable when engine is dry, as it is easier to hear the lash being taken up.
You normally can't feel any resistance when it happens but you can feel a very slight bump
_________________
"Olive" a '60 Ragtop Beetle
"Grover" a '87 Syncro Poptop 1.8T

[Busstom]

I like this theory ^^^

Does it make the same noise on every rotation? Or every OTHER rotation? Remember, the engine has to rotate 360° twice to run each cylinder through their full cycles, i.e. the cam needs two crank rotations to make its way around once, so it's actually doing different things with different valves through those TWO crank rotations.

[dougnlina]

What I suggest you might be hearing is a click of backlash as the pressure from the valve spring, pushing against the lifter goes over the tip of the cam lobe and causes the cam to go from loading one side of the cam gear tooth to the other side of the cam gear, this is common on opposed engines that "share" cam lobes for multiple cylinders. It is kind of tough to tell for sure that this is what it is from the video, one way to check is to pull the rocker arms off and see if it still makes the noise without the valve spring pressures....
_________________
"Olive" a '60 Ragtop Beetle
"Grover" a '87 Syncro Poptop 1.8T

[rcooled]

I've encountered something like this once before. It turned out that one of the bolts fastening the timing gear to the cam backed out slightly and was hitting a boss on the rear of the oil pump housing.
_________________
'63 Ragtop (current)
'65 Ghia coupe (totaled)
'67 Ghia convertible (current)
'69.5 Ghia convertible and
'62, '63, '65, '69 Bugs (all long gone)

[maplesyruplover]

I have gone through all the suggestions. The noise is still heard with the rockers disconnected. When cylinder 3 plug is removed, it disappears. I ran the motor and there is no knocking. Can it be the rod hitting the case.

The engine appears to be a 40hp with a vintage empi 1600 stroker kit & ram air zenith carb.

My thinking is that the case wasn't fully machined and it rubs.

[Busstom]

[splitjunkie]

[viiking]

I think you should consider the things Busstom has said re crank angle.

Does the knocking occur at the same rotation of the crankshaft?

You can get a template you can print out on the web for a VW pulley that you attach onto the pulley. Then measure the angle at which the "clunk" happens. You can then determine which valves etc are in operation from documentation on valve opening sequence, even if you think it is related to No 3 piston.
_________________
1968 1500 RHD Lotus White Beetle since birth. In the hospital for major surgery
1966 Lancia Flavia Pininfarina Coupe - in the waiting room
Discharged: 1983 Vanagon, 1974 1800 Microbus,1968 Low Light,1968 Type 3

[splitjunkie]

Don't take my word for it. Removing spark plug wires one at a time will do the same thing by eliminating the force against the crankshaft caused by the gas igniting. Removing the plug also removes all compression so you are putting the least amount of force on the crank,and thus the rod bearing.

https://www.carboncleaningusa.com/connecting-rod-bearings

How can we diagnosis the connecting rod bearing ?


Plug Wire Removal

1. One way to identify the cylinder connected with the faulty rod bearing is to open the car hood and pull out all spark plug wires one by one.
2. After removing each wire, turn on the engine and check if the knocking sound still persists.
3. If the sound is eliminated, this means that the cylinder from where the plug wire was just removed has a faulty bearing on its connecting rod.




http://corvaircenter.com/phorum/read.php?1,630718
_________________
Chris

You know, a lot of these scratches will buff right out... Jerry Seinfeld

[rcooled]

I just watched the video over again several times. That noise doesn't sound like a moving part that suddenly contacts something solid. And it doesn't seem like it's preventing the engine from turning over like you'd expect if that were the case. It sounds more like something that was sticking, then suddenly snaps back to its intended position.

It's not a rod bearing knock.

I think that it's a sticking valve...probably in the #3 cylinder. As the cam lobe starts allowing the valve to close, it sticks open a bit before contacting the seat. Then as the cam lobe continues to turn and releases pressure from the pushrod, the valve spring overcomes the sticking point and the valve snaps shut, generating that noise you're hearing. I'm not sure about the valve/piston clearances in these motors, but the piston might also be contacting the open valve and snapping it shut as it gets to the top of its stroke.

Once the motor's running, heat will quickly expand the valve guide just enough to increase the stem-to-guide clearance and eliminate the sticking point. That's why the noise disappears when the motor's running under it's own power.

You can check for a sticking valve in #3 cylinder by removing the valve cover and observing the valve movement while a helper rotates the motor to the point where it makes the noise.

I had this problem once with a Porsche 911 motor. Made noise until the motor ran for a minute or two and freed up the sticking valve. The piston was tapping the valve shut as it neared the top of its stroke, and the valve left a witness mark on the piston to prove it. I had the guides reamed out in that cylinder head and the noise disappeared.