Valve knock medium throttle under load?

[sobamaflyer]

As the title states, I have a very recent new knocking noise, I believe it to be coming from the valves on Cyl 2 or 3. I have a bit more than 3k miles on my complete rebuild including a valve job with new exhaust guides and all new valve springs.

At idle I hear a "knock" in this area that sounds pretty similar to that which led me to find a couple of broken valve springs before. Under medium load I hear clatter that sounds just like bad gas.

I've proven (I think) the bad gas theory false as I've now run 3 tanks of premium with some lucas fuel additive in it with no change.

*The full disclosure* My dumb a$$ got the bright idea to try and quieten an old Flowmaster I had sitting around by stuffing steel wool in it as I thought I'd read on the inter-web. Boy did it quieten it, sounded almost stock, I hated it within 5 minutes of the (1) 8 mile spin I took it on. Power was way down by the butt dyno. I got on it just once on an on-ramp, felt a big dump in power for a second then back to simply low on power (and quiet). It came off the next morning and my current magnaflow/probably was a Bursch unit went back on.

Can anyone speculate as to what I may have done/what I have going on before I pull the engine back out and open her up to find out myself? I did do an oil change a couple of weeks ago and adjusted the valves, there wasn't anything in the oil or the screen, nothing scary came out of the valve covers and I didn't see anything glaring at me as broken adjusting the valves.

[afterburn 549]

I would not think the valve train will respond with noise at different RPM....If its wrong its wrong
maybe you can post a sound bite?

[JJ 911SC]

I doubt that your "5 minutes dumb ass idea run" has anything to do with it but you are on the right track about *The full disclosure*, let some fresh eyes take a look.

Does the 3 thanks of premium all came from the same station?

If yes, try another supplier. If no try a lower grade to see if it make a difference.

[sobamaflyer]

I will try to get some sound clips, the under load knocking will be a challenge but I'll see what I can do.

She's been running fantastically since this time last year when I finished my rebuild, I feel pretty certain this started right after that botched muffler trial. You have a good point about the gas, I do tend to use the same station every time. I will try an alternate one.

Since it seems this doesn't clearly ring a bell to others I'll try and dig into this soon, don't really want to damage anything but still hoping I'm just being overly "new noise sensitive"

[pareto]

I think I just had the same issue...2k miles after rebuild a knocking noise under same conditions. I believe I have traced it to #3 rocker arm to bushing excessive clearance/wear (400k miles) along with a shaft sealing potentially related problem on same shaft and a wear scar in the rocker surface (wobbling due to clearance for both?). I am replacing the rocker tomorrow and will follow up, but it is the main suspect as the knock follows rocker frequency....Maybe you want to check the same. Good luck....

[sobamaflyer]

I tried half a dozen times for a sound clip, what I'm hearing just doesn't come through on video/audio unfortunately.

I did a leak-down yesterday and something is certainly not right. I was getting readings in the 50%-60% range on cylinders 1, 3 & 6. 15%± on the rest. The air I hear leaking seems to be coming from the middle, heard out of the fan ( breather?). I don't hear any hiss out of the intake or exhaust. I can pretty clearly hear hiss under the engine listening close to the cylinder being tested.

I'm not precisely sure what to guess at this point but I don't see any option aside from dropping the engine and opening it up to find out exactly what's going on.

[afterburn 549]

Attacking a problem with out knowing what you are attacking is ..scary
Is there anyone around you can ask for help?
How much air pressure were you using for a 100% and are you confident with a "leak dwn tester?"
(I have seen people chase their tail with these )
I would start with the stupid stuff..
are the rocker arm through studs all in place? rocker arm bushings all ok?
In the end if you verify you are off by 50% I would say you have a cam timing issue .

[sobamaflyer]

"help" only by phone unfortunately.

I was using 115-120 at the compressor to give me the 100 on the input gauge. No I wouldn't ever say I was "confident" with it. It is a decent (not HF) one I've had for a while and used several times as recommended on this board.

Is it possible cam timing could have jumped?

_________________

I didn't perform a leak-down on the stand after I rebuilt it, now I wish I had for reference point. My results make me think something didn't re-seat in the rings and/or need to check the head torque.

It seems to run well aside from the odd noises but I don't want to drive it like this and damage the engine.

[afterburn 549]

There has to be Porsche capable people around you !
As far as timing jumped...all i know once you do a Compression check and come up with low number again ...go from there ( Not likely unless engine was turned backwards a LOT)
You can call me by phone if i am the only smartest person willing to help you. (PM me)
I am pretty savvy,......but over the phone sucks LOL
I still say the kiss method..a noise indicates a problem if a rocker shaft is 1/2 out you will have noise.
KISS method.....step by step

[sobamaflyer]

Thank you for the offer :-)

I live in the great state of Alabamy, by trial and error I've found people that actually KNOW more than I've figured out myself through this great resource, local to me must be in hiding. There is a gentleman a couple hours north of me that is a 911 encyclopedia and has provided me gobs of help, he's at least a bit responsible for the fact I've taken this from a barely operational machine to a quite nicely running one that [now] starts instantly.

That said..... I think I'll take your advice and do a little more digging with the valve covers off before I drop it.

[afterburn 549]

How were the guides?
How were the rocker bushings?
New rings gaped right?

[sobamaflyer]

Had the heads done by a recommended local machinist when I rebuilt it. New guides all around, I put new rocker bushings in during reassembly. Pistons and Cylinders all were in good shape so I reused them all including the existing rings all back in the original order.

I haven't seen evidence of ring fragments in the oil when I changed it a few weeks ago but?

[afterburn 549]

the local machinist answer scares the heil out of me. Unless he did a LOT of reading or does Porsche on a reg basis.......there might be the answer.
I have done chevy heads and all kinds of heads. Porsche is NOT like anything they have ever done !
Its complicated by 10 fold.

[sobamaflyer]

He was recommended by the master mechanic from MS and has done work for the folks in the Porsche club to the west of me. I question everything, my own work (albeit slow, methodical as precise as possible) his work, my testing methods, etc.

That said, I have felt that I found with this car as with several VW rebuilds before it that I trusted myself to do stuff right (or go back and fix what I learned I did wrong) more than any other unknown quantity.

[afterburn 549]

OK, good to know.
If the sound is only under load, and you have low compression numbers..I would guess recheck came timing.
you can do that with out pulling the engine and will give you a base line to go from.
were cams changes?

[sobamaflyer]

The cams were unscored and so were cleaned and put back in. The only things I really replaced during my rebuild were the outer bearings, valve springs, 1 valve, guides & rocker bushings. I got the impression this engine saw a full rebuild or had pretty low miles after disassembling all the way to the crank.

It was running strong, but I had 2 broken valve springs that I mistook for rod knock, and had an unknown quantity of an engine and wanted to know what was in there. So I mostly tore it apart, cleaned everything, replaced all seals and put it back together. It's seen ~3500 miles in the last year and a half since that. It doesn't use a full quart of oil in somewhere north of 1,000 miles.

I can dig out the rebuild manual but would you mind elaborating on how I'd check cam timing in situ?

[afterburn 549]

As in " time it" with dial indicator like on your rebuild.

[sobamaflyer]

ahh! Thank you, that I can do

[afterburn 549]

Your over all low compression would indicate valve timing.
The noise is a concern too, Maybe when you pop all the covers it will all jump at you..in a good way i hope.

[Walt Fricke]

15% leakdown is not good, but 50% is just horrible, so something is drastically wrong.

You listen for ring leakage by pulling the crank vent hose (you could do this at the oil tank, or maybe just listen in the tank) and listening for the noise. A plastic or rubber hose you can stuff in an ear makes a perfectly adequate stethoscope for localizing noise. Also helps when you listen at the tailpipe. For intakes, you could easily take off the rubber boot, hold the throttle wide open, and listen in at the throttle body.

No hissing from either the exhaust or intake is a good sign for the heads, and rules out valve timing as well.

You really should be able to find where this air is escaping with the leakdown. In fact, you might skip the tester part, and just hook up your air, as once you know the numbers are lousy, listening is where you will learn something. Or leave the tester on, so you know you are still at a high percentage of leak when listening.

If your rings are so shot you are getting 50% leakage past them, I'd think you'd see much worse oil consumption, lots of smoke under deceleration, and similar signs of bad rings.

I am interested in your thinking that you hear air escaping under the engine cover. The only way I can think of that happening is if your heads are loose. Did you check the torque on the head nuts? Can you see oil or discoloration on the head/cylinder mating surface when you have the car up in the air some and can look under there?

Is your encyclopedic source named Jim?