Type 4 Engine Knocking Noise at Idle - PROBABLY SOLVED

[69BahamaYellow]

This sound just started a few weeks ago on my 1978 fuel injected 2.0Liter type 4 engine. It is completely stock with hydraulic lifters, and I wanted to see if any of the type 4 guru's out there have any ideas what this might be.


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I initially thought this could be a bad lifter, so I pulled the valve covers to check that all the rockers were tight, and they were. I then removed the valve gear to remove the lifters from cylinders 2 and 4, and they were fully pumped up, so I cleaned them, re-bled them in a jar of oil, re-installed them to the engine, adjusted valve clearance on all valves to 2 turns (completely cold), and still have the exact same knocking noise after re-starting the engine.

The hydraulic lifters are generally very quiet. They will sometimes bleed down overnight and will clatter for about 2-3 seconds after cold startup, then everything is quiet. It takes about 2 minutes of running before the random knocking noise that you hear in the video kicks in, and it does not get any worse or better after the engine is fully warmed up.

Also, I have been running 5W-30 dino oil with ZDDP additive for years and recently switched to full synthetic straight Shell Rotella T6 5W-40. The hydraulic lifters don't bleed down as quickly and pump up faster with the Rotella T6, vs previous oil, but the knocking noise started shortly after the oil change. Probably coincidence, but you never know....

[airschooled]

If you take the oil cap off, and stick a piece of breather hose in your ear to use as a "sound funnel" can you hear the sound more clearly?

You can also use a 1-foot socket extension as a mechanical stethoscope by placing on something like a valve cover and listening to it intently.

Robbie
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[timvw7476]

well, that seems timed to valvetrain,
but it could also be timed to power stroke of a cylinder with a semi-collapsed
piston skirt, -those usually tend to quiet down once the engine is fully heated.
And they can run happy til the next rebuild too.
Maybe pull plug wires one at a time, the wire that kills the noise will be
the one with a bad skirt, if the noise does not go away with any wire pulled,
it's slop in the valvetrain. Good luck.

[scubaseas]

timvw7476wrote:

[skills@eurocarsplus]

this is a hard procedure to describe, but bear with me

if you "float" the throttle between say 1200-2k and the noise goes away, but comes back on the "decel" or return to idle, my money would be on a loose cam sprocket

very long ass story short I had one that sounded like a diesel at idle. you could give it gas and it was quiet as a watch. ripped the engine down, found no smoking gun.

I went to move the cam that was sitting on the bench gear down and heard a "POP" what the hell I thought....the rivets hogged out and it was the cam gear slapping due to the play....when you would load the engine, it would slam against the rivet and be quiet. at idle, it would rack back and forth
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[aeromech]

Loose cam gear. Remove the oil pump for access
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[raygreenwood]

[69BahamaYellow]

I have a stethoscope and it sounds like the noise is coming from the area of the cam gear, but the knocking noise can be heard all over the place, so I decided to pull the exhaust, engine tin and fan shroud to get the oil pump off, but it appears the cam gear is nice and tight on the cam shaft

before I did this I tried the rubber hose in the oil filler (good tip by Asiab3), and I can hear the knock, but not as good as with the stethoscope. I also tried the cam float test that Skillz described, but anything above1500 RPM or so just makes the knock go away

Could the wear on the oil pump shaft be causing it?

I looked for any marks on the motor mount, fan shroud or any other possible external engine spots, and I can't find anything suspect. I did find a marble in one of my heat exchangers, so at least I finally found the source of 1 annoying rattle

I guess since I've come this far, I might as well pull the engine and start tearing it down to check for piston slap or rod knock. I probably should have shorted plug wires to test for that, before yanking the oil pump, but when I rebuilt the engine (about 50,000 miles ago) I replaced the cam with an aftermarket cam and gear from Webcam, so I too was betting on loose cam gear. There's a reason VW went with Rivets over bolts, but I guess I can now confirm the low profile bolts and cut washers from Webcam, installed per their specs, will hold the gear on tight without loosening up over time.

Place your bets. Piston slap or rod knock. I'm going with piston slap.

[raygreenwood]

[SGKent]

if it is not the cam gear, check the fan and hub to be sire it hasn't been walking. Check the end play too but it sounds too light to be a flywheel knock. Also have a friend crank it over with the coil wire off and see if any of the valves act jerky like a broken or collapsed spring. I would also suggest pulling the fan belt off and running it to see if removing the alternator load changes the sound. You might do that before checking the hub.

My money was on the cam gear but clearly that is not it. One thing I thought I saw during the video was that there was a slight change in pulley speed at the second the knocks occurred. If so that might indicate that the pulley is loose and rocking on the key. Catch it now if that is the case.

Wrist pins normally don't come loose or lock up because the pin floats both in the piston and rod. The only time I have see wrist pin failures is when Teflon buttons were used. Once they fracture and fall apart the pin starts hitting the cylinder wall.
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[SGKent]

2 questions -

1> Is that an A/C compressor, and if so have you put a stethoscope on it and the idler?

2> The sound seems loudest around the EGR area. Have you listened with a stethoscope in that area? How about a rubber hose?
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[hazetguy]

[busdaddy]

I'm curious what the cam does when you rotate the engine slowly with the alternator nut, does it snap forward suddenly a few degrees every 1/2 turn of the engine by any chance?
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[timvw7476]

^Yeah, what bus daddy mentioned^
that cam gear may not have the decent teeth you think it has.
Way to tackle it in a hurry!

[raygreenwood]

[MGBBob80]

Following the thread. Lots to learn here!
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[busdaddy]

[69BahamaYellow]

It was a nice afternoon, so I pulled the engine after lunch, to really figure out what is going on.

First, good catch, Hazetguy, on the recessed idle shaft on the oil pump. I totally missed that when I removed it, but that ain't right, so I'll tear it down and see what gives. Maybe I put that shaft in backwards when I re-built it last...

Second - Yes, this bus has A/C, and I triple checked everything on it. It's butter. tensioner and idle pulley running smooth as silk, so that ain't it.

I had to stop for the evening, but I did get the injector runners and cooling tin off, and with the engine on a stand, I can get a good grip on the flywheel to turn the crankshaft back and forth. When I do that, I can clearly hear the knocking sound in the area of the cam gear. Something is loose, but the cam does not appear to moving axially at all. I'll put a dial indicator on it tomorrow and pull the distributor drive gear as well.

Pictures to follow, but with the knocking noise seeming to come from inside the case, I've already decided to pull the heads and jugs (that will either confirm or eliminate the possibility of piston slap). I'll split the case if I have to.

Regarding exhaust leaks or head leaks, there were none. no carbon tracing on any of the headers and no oil seepage from head to cylinder and cylinder to case. I should share that when I rebuilt the engine 50,000 miles ago, I dipped the cylinder base gaskets and head gaskets in a mixture of Indian head Aviation case sealer and alcohol to keep them stuck in place during re-assembly. It did a really good job sealing the joints. This is the first time I tried this on an air cooled VW, but I've built several of these motors over the years with nothing on the gaskets, and they always seem to weep a little oil from the cylinder joints. I know VW's recommendation now is to delete the head gaskets entirely, but I'm still not sold on that. Regardless, the Indian Head shelack thing seems to make a leak free joint.

[69BahamaYellow]

Pulled the Heads and Cylinders today, and they look fine. The piston pins are a slopy fit in the con rods, but I did not change the small end bushings when I rebuilt it, so I'll probably re-bush them before it goes back together. Here's a few pics of the teardown. I guess one of the heads had a small leak. Didn't see it till I pulled the push rod tubes

After I got the pistons off, I could get a screwdriver on the cam shaft to check axial play. I believe this is my problem. The STP ZDDP additive I had been using with 5W-30 dino oil is thick like honey, so perhaps that was hiding the axial play on the cam shaft. The sound only started after changing to straight 5W-40 Shell Rotella T6, but maybe it would have started knocking anyway. Next step is to split the case and see what the problem is:


Link

[SGKent]

well - that is what happened to mine on my first build in 2009 using a new aftermarket Brazilian VW gear. The runout in it walked it (and the crankshaft) back and forth, opening the thrust up. Same thing happened to Colin using one of those Brazilian one size fits all cam gears too. If the cam isn't worn too bad on the thrust surfaces, I found that the kolbenschmidt cam bearings fit better than the Mahle ones as to thrust. What # cam gear came with that engine originally, do you know?

Glad you went the teardown route - it will be well worth while long term.

So we chalk this up to a cam gear.... can't ya hear me knocking.



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