Type 4 Engine Knocking Noise at Idle - PROBABLY SOLVED

[aerosurfer]

[SGKent]

[69BahamaYellow]

Quick updates -

I purchased a set of new Kolbenschmidt cam bearings to measure the width on the thrust surface and it is 1.101". I've got a second set ordered to see if they are consistent but also to combine the 2 to make a double thrust bearing set, but I'm still pondering that one....

My first concern is that Webcam gave me their measurements on new cams as 1.110", but if that's true, I'd be starting with .009" clearance (too much). On the other hand, when they gave me the measurement, they said "one point ten" , and then clarified "one point one ten", so I took that to be 1.110"perhaps they meant 1.10". At present, my current cam measures 1.104", which would give me the perfect clearance (.003"), but I'm having my cam polished to remove the roughness, so that will open it up a bit, but hopefully not beyond .004" clearance.

My second concern is what's driving the cam back and forth in the first place, if it's not a wonky cam gear? To answer that, I was turning the crankshaft in one of my case halves, while applying resistance to the cam (as would be the case when it's lifting valves). I noticed that this would push the camshaft away from the oil pump; that makes sense with the helical drive gears. So what pushes it the other way, since the cam is always under load from the valve springs? For that, I thought about how the knocking noise only occurred at idle, and disappeared at anything above that, then I realized that when valves are closing, it loads the back sides of the cam lobes, which would tend to push the cam opposite to it's normal rotation, and the helical cam gear would cause the cam shaft to push back toward the oil pump. If you've ever replaced a timing belt on a motor with overhead cams, sometimes you have to hold the cams in place, when the belt is off, since the load from the valve springs will make them move. At higher speeds, the camshaft has too much momentum for the back loading from the valves closing to make any difference, so that's why the noise goes away (at least that's my theory)

If a wonky cam gear was driving the cam back and forth, I would think the noise would always be there. maybe it gets masked somewhat by all the other engine noises at higher speeds, but still there. When I was revving my motor, the noise was completely gone at anything above about 2000 RPM.

[lil-jinx]

Just kicking the ball around,But with the valve closing putting pressure on the back side of the cam lobe,there is also a valve opening putting pressure on the front side of the cam lobe,I would think one would cancel the other.
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https://www.thesamba.com/vw/forum/viewtopic.php?t=620186
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1974 Bay Westfalia. she likes to be called Ethel.
1968 Dune Buggy
1974 parts bus
A smart man learns from his mistakes,a very smart man learns from other's mistakes.

[SGKent]

don't know the cam grinder but is the lobe is sloped to one side or the other, that can push the cam forwards and backwards too. My webcam does not move forwards and backwards at all with the factory gear. It did with the out of round gear even though the out of round was only .0015" - more like 2 high spots where the gear was oblong.
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[mike77777]

Good discussion, I will be re camming a 77 2.0 liter soon. Has anyone had good results with the straight cut cam/crank gears? Seems like the lack of thrust of the gears would eliminate one possible difficulty.
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patience and putty

[69BahamaYellow]

[69BahamaYellow]

[raygreenwood]

[mike77777]

Points to ponder regarding cam gear choices, I thank all who contributed. The harmonic vibration information was fascinating. Do any believe Ferdinand Porsche was a genius level intellect? Flat 4 with good weights (equal) is inherently smooth. I will be splitting the case this week, took the pistons and heads off in place, been renewing/replacing worn out stuff the last 3 weeks or so. Machine shop has my re bushed conrods ready, tomorrow pickup. Great experience on here, appreciate the open sharing of what works. Mike
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patience and putty

[mike77777]

looking forward to your Video. Going with these AMC heads. Manifold is for a Weber, will have one each side.

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patience and putty

[SGKent]

like the lady said, it's just a Volkswagen.
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[mike77777]

Just a Volkswagen. good point there, this is not a religious movement, just a bunch of gearheads working on 40 and 50 year old machinery. The owner serviced vehicle concept was discouraged by car manufctureres, cuts down on sales volume if you can keep em going after the car loan is paid off. Connecting rods back in the shop, excellent job on the Sunnen honing machine (1950's vintage00) by Gary at 730 SE 9th Street in Portland. The machine shop recommended by the guys at Halsey Automotive is operating at reduced capacity, owner illness. Gary charged 85 bucks to renew the pin bushings, drill for the oil holes, and precision hone the pin fit. Excellent workmanship, fast turnaround, shop floor was immaculate. Anyhow, making gaskets for the little metal covers that go over the aluminum flappers in the big air chamber near the back of the Vehicle. Get that hot air on my windshield, instead of leaking it out to the street. May drop the short block if the weather gives a letup on rain. Mike
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patience and putty

[69BahamaYellow]

Just fired up my engine today, after a multi-months long hiatus, and I can confirm the engine knocking noise is gone, so I can officially say the cam thrust bearing was the source of the noise.

I'm running a double thrust cam bearing set now, so time will tell how much longer it lasts, but I believe what started this whole mess was the thrust surface on my aftermarket Webcam having .002" run out and being too rough (probably from it leaving the factory without a final machining step). I believe the run out on the cam thrust surface caused the cam to move back & forth axially, just ever so slightly, as the high spot on the thrust surface encountered the single thrust bearing and wore it out over the last 50,000 miles. Perhaps if I had used a double thrust cam bearing set to begin with, the high spot on the cam would have never had a low spot to fall into. That's pure speculation, but it's right now. I'll post a new video (post rebuild) soon

[69BahamaYellow]

Link


Running at last. Replaced the old muffler with a new $130 Pacesetter. Looks exactly like my old one, but oddly, it's louder. I'd love to replace it with OEM, but way too many obsolete parts are missing, so it would be cost prohibitive....

Mechanically, the engine is very quiet now.

[/youtube]

[white74westy]

You should be pumped! That sounds great!

[Spike0180]

Well done. Congrats on the fix, and your engine sounds great.
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Brutis Patches Izabich: 1970 VW Transporter - 1776cc DP
Current State: Projects never truly end...
Location: Grosse Pointe, Michigan
Other cars: 2003 F150, 2003 Jetta GLI vr6-6sp

Sambastic: adj; the quality of being nit picky, elitist, expecting everyone to do things the way they believe is best with no regard to situation, "sambastic"

[69BahamaYellow]

Yep, you've got to love Fuel injection. Those parts were sitting on my garage bench for 2 months, while I waited on machine work, and after bolting everything back together, I just turned the key and it fired right up.

The only extra thing I did was to remove the oil pressure switch, before startup, and hook up a manual oil pump to refill the oil cooler and purge all the air out of the oil galleys. Those were dry after the engine rebuild, and I never like to rely on assembly lube alone. After that, just replace the pressure switch and fire it up.

The first drive was just like it was before, less the knocking noise at idle. Feels good to be back on the road; just have to break it in properly, then it's all back to normal again

[orwell84]

I was curious about your oil pump as your pics show the idler gear shaft deeply recessed in the pump boss. Someone mentioned that it should be flush. I have always wondered about that as I have come across oil pumps that show it in both ways. In one of the pumps I disassembled, it took a lot of force with a press to remove the shaft even though it was deeply recessed. In reassembling the pump, the person helping me made sure to put the shaft in the position he found it in. Since it was so deeply recessed I thought, great. I can remove a lot of material from that boss to make sure aftermarket cam bolts have plenty of clearance. I am also running a webcam, but not using the low profile bolts. when assembling the engine there seemed to be ample clearance between the oil pump and the cam bolts. I am currently running a CB performance pump, but plan on switching back to the stock pump so this is something I will have to check carefully. Thanks. BTW, your engine sounds great. Super quiet.

[69BahamaYellow]

Forgot about the oil pump question, so thanks for the reminder. I too have seen some type 4 oil pumps with the idle shaft flush with the end of the boss, and others where it was recessed, like mine. I first thought the recessed shaft might be a problem, but then I examined how it fits into a recess in the pump housing side, and realized this is OK. I should also add that my father bought this bus brand new in 1978, so I know the oil pump has never been messed with. That was how it left the factory, so I put it back together that way and will run with it.