Need help: noisy engine after over-rev Options

[DC_neun_vierzehn]

First, it's a '73 2.0 (2056 rebuild with about 1,000 miles on it). 123 dizzy. Car was driving great. No issues.

Then, last November, I over-rev'd my engine twice. First time due to forgetting to put the throttle body spring back on after reinstalling a new gasket under the TB. The second over-rev was immediately after because unbeknownst to me the throttle cable was tangled in at the pedal cluster due to omission of spring. Both times, I pulled the key out IMMEDIATELY, but not before I saw the tach needle shoot WELL past the red line. Both times my heart sank. Still beating myself up for the gaffes. Also frustrated that the rev limiter in my 123 dizzy settings didn't prevent the over-revving. Ed at 123 (great guy) said that rev limiter does not prevent the RPMs from going above the threshold it's set at, rather it prevents sustained RPMs beyond the limit. Ugggg.

First thing I did was look for leaks under motor, in the engine bay, check for any funny smells. Didn't see or smell anything. Next thing I did was take it for a nice and easy drive around the block. Drove fine, but I thought it sounded a little noisy. Next thing I did was take it for a slightly longer drive and slightly less nice and easy. Did not notice any loss of power or any difference it how it drove - just a little noisy. The best I can describe the sound it "loose" (thumpy ... chattery ... a little like a diesel engine).

Then winter came (snow, salty roads, etc.) and I put the car away for the winter and planned to dive in when spring came. For last several weeks, I've been diving in trying to find the culprit.

Here's what I've done so far.

1. Compression tested each cylinder. 3 were at 130. C4 was at 120.

2. Removed both valve covers. Inspected all rocker arms and springs. Everything looked fine. Checked valve lash. C1 and C2 both were in spec (.008 exhaust and .006 intake). However, C3 had .004 for both exhaust and intake, and C4 had .002 for exhaust and .009 for intake. I removed those rocker arms to inspect closer. Everything looked fine. Reinstalled the rocker arms and adjusted the valve lash to spec (matching C1 and C2).

3. Changed oil. Inspected all of the oil visually in a glass jar. Did not see any debris. I ran a magnet through each jar, no metal shavings or pieces on the magnet. I'm going to cut the oil filter open with tin snips later today to see if I see anything in there. Topped her off with 3.5 quarts of fresh oil and new filter.

4. Took a 10 mile test drive. Noises are still there. Uggggg.

5. Removed valve covers. Checked the valve lash. Everything still in spec. Nothing moved.

What could be causing the noise?

The car definitely sounds different since the over-revs. I'll try to post links to a few short vids with audio.

[DC_neun_vierzehn]

https://youtube.com/shorts/_XfSF5G5078?si=f6K6KNL_qdYOWiPh

https://youtube.com/shorts/4RIFaIZhftk?si=5N76ACgZ8PljksUg

https://youtube.com/shorts/GkzwbakjebQ?si=UeFE1I6MtK8bsKGC

https://youtube.com/shorts/SR_r3T3_5I8?si=rfGCnQOWg1rooLGF

(Ignore the smoke coming off the HE is the video under the car (that’s just oil burn off from removing the valve covers and oil dripping on top of HE).

[bdstone914]

Bent pushrod(s) ?

Pull them and roll on a flat surface

Using a stehascope or hose held to one ear can you isolate the area the noise comes from ?

[bdstone914]

https://youtube.com/shorts/_XfSF5G5078?si=f6K6KNL_qdYOWiPh

https://youtube.com/shorts/4RIFaIZhftk?si=5N76ACgZ8PljksUg

https://youtube.com/shorts/GkzwbakjebQ?si=UeFE1I6MtK8bsKGC

https://youtube.com/shorts/SR_r3T3_5I8?si=rfGCnQOWg1rooLGF

(Ignore the smoke coming off the HE is the video under the car (that’s just oil burn off from removing the valve covers and oil dripping on top of HE).

third video marked as private needing permission. I could not tell the noise you report from the video.

[Puebloswatcop]

Bent pushrod(s) ?

Pull them and roll on a flat surface

Using a stehascope or hose held to one ear can you isolate the area the noise comes from ?

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[Ishley]

I don’t hear anything loud… but it’s hard to tell precisely.

[mepstein]

I would do a leak down test.

[DC_neun_vierzehn]

https://youtube.com/shorts/_XfSF5G5078?si=f6K6KNL_qdYOWiPh

https://youtube.com/shorts/4RIFaIZhftk?si=5N76ACgZ8PljksUg

https://youtube.com/shorts/GkzwbakjebQ?si=UeFE1I6MtK8bsKGC

https://youtube.com/shorts/SR_r3T3_5I8?si=rfGCnQOWg1rooLGF

(Ignore the smoke coming off the HE is the video under the car (that’s just oil burn off from removing the valve covers and oil dripping on top of HE).

third video marked as private needing permission. I could not tell the noise you report from the video.

Sorry about that - you should be able to play it now.

[DC_neun_vierzehn]

Bent pushrod(s) ?

Pull them and roll on a flat surface

Using a stehascope or hose held to one ear can you isolate the area the noise comes from ?

Thanks for the suggestion.

@bdstone914 when I was inspecting the rocker arms on C4, I was able to pull the push rod out below the exhaust valve to have a look (looked fine, but I didn't know about the rolling on a flat table trick). I wasn't able to pull the push rod out for the intake because it was hitting the HE. Seemed like the same challenge for C3.

Same to assume I need to remove the HE to pull all the push rods out for C3 & C4?

And what about C1 and C2 - does the HE need to come off to have room for the push rods to come all the way out?

[JamesM]

I would do a leak down test.

(IMG:style_emoticons/default/agree.gif)

Now that you have the valves adjusted back to speck, leakdown to see if one bent.

Hope the difference in compression could have just been the miss adjusted valves, but could also be due to a slightly bent valve.

[stownsen914]

If you have rev limiter set (and it's actually working), it can shoot past the limit a bit due to momentum of the rotating mass even after the ignition cuts out. It shouldn't shoot THAT much past though. A few hundred RPM?

Hopefully it's something minor. A mechanic's stethoscope can help localize the noise, in case you are not sure where it's coming from.

[IronHillRestorations]

Have you checked the alternator and impeller? Does the engine have single or double valve springs?

[GregAmy]

Now that you have the valves adjusted back to speck, leakdown to see if one bent.

That's where I'd go. I "money shifted" the 2L racer engine at Lime Rock a few years ago and that was the culprit. I'm thinking it hit around 10k. It was bad enough to where the engine would not even start, not enough compression...

I don't know if that was a factor in the crankshaft failure a couple years later...

[DC_neun_vierzehn]

If you have rev limiter set (and it's actually working), it can shoot past the limit a bit due to momentum of the rotating mass even after the ignition cuts out. It shouldn't shoot THAT much past though. A few hundred RPM?

I didn't think it would either, but it did. Like I said, I talked to Ed at 123 about the rev limiter in his product ... he said it would not stop the revs from exceeding the setting, only prevent it from prolonged/sustained over-rev. Thus, I guess it's not like a rev limiting rotor, which I had in my OG Bosch dizzy. As you can see in my 123 app, the curve setting I'm using has the rev limit set to 5700.

Good suggestion on the mechanic stethoscope. I need to look into those.

[DC_neun_vierzehn]

Have you checked the alternator and impeller? Does the engine have single or double valve springs?

@IronHillRestorations

Perry - can you define "checked' for a non-mechanic like me?

The things I'm able to do on my 914 are mostly due to Ian Karr's vids, stuff I've read on 914 World since buying a 914 a few years back, and reading Pelican Forums.

I reached back and felt around in the impeller. I found a couple of plastic plugs (the ones that hold the insulation/pad into the firewall in the engine bay). Made no difference after getting those out of there.

Can you walk me through checking the impeller and alternator?

[DC_neun_vierzehn]

I would do a leak down test.

Ok. Never done one of those and do not have the equipment. I have not found an air-cooled dub or Porsche shop within an 100 miles of Rehoboth, DE.

Probably need to buy the equipment to do it ... or find someone semi-local who could assist.

[Shivers]

@DC_neun_vierzehn

A broken valve spring can make a racket, and not necessarily show in a visual. Some can still function, for a while. I have this tool that looks like a stethoscope but it has a skinny rod that goes to a sound chamber and that goes to the ears. You just stick the rod around the engine until the noise is the loudest. And dig in there. Sorry about the engine.

[mepstein]

I would do a leak down test.

Ok. Never done one of those and do not have the equipment. I have not found an air-cooled dub or Porsche shop within an 100 miles of Rehoboth, DE.

Probably need to buy the equipment to do it ... or find someone semi-local who could assist.

A leak down gauge isn’t just for air cooled cars. Ask your local mechanic or see if the auto parts store has a loaner.

[914sgofast2]

Harbor Freight sells leak down gauges, as well as compression test gauges. Every 914 owner needs one of each.

[Dave_Darling]

... I was able to pull the push rod out below the exhaust valve to have a look (looked fine, but I didn't know about the rolling on a flat table trick). I wasn't able to pull the push rod out for the intake because it was hitting the HE.

The pushrods should not hit the heat exchangers at all. Ever. Are you talking about the pushrod tubes? Those are not what we're talking about; the pushrods are the rods that actually push the valves open.

You have to remove the rocker arms for a cylinder to get the pushrods for that cylinder out. Remove them and roll them on a clean table top to see if any are bent. Installation can be a bit annoying, but it's easiest to put that cylinder at TDC so the valve springs aren't exerting any force on the rocker arms when you bolt the arms back onto the head. (Because 11 lb-ft isn't enough to seat the rocker arm shaft against the head when working against an open valve's spring!!) Convincing the inner end of the pushrod to stay in the lifter cup can also be annoying; I have been able to push an L-shaped Allen wrench down the pushrod tube and use the short end of the L as a fulcrum to move the inboard end of the rod up into the cup. It fell out, so I had to re-do it a few times, but eventually I got it to stay...

--DD