Valve knock medium throttle under load?
 

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.

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?

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.

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"

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....

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.

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 .

"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.

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

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.

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

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?

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.

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.

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?

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?

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

ahh! Thank you, that I can do

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.

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?

Thanx for chiming in. He needs some serious help .

Maybe you guys already mentioned this, but did you check your chain tensioners?

turn it over by hand and see what valve is hitting. If you can remove the rocker arm from that valve, do it and then try and turn it over again. Check your chain tensioners to see if they are too squishy or if the cam got out of timing. maybe your skipped a tooth. If you can turn over the engine without the rocker pushing the valve into the piston then you know it's a timing/cam/valve thing. If you get a bad leak down on that cylinder and it's not coming out of the intake or exhaust, then you have more serious problems like a broken ring.

I gave a quick read on you rebuild thread. Did you install the collars again on the tensioners? When my tensioner failed I had bent the exhaust valves on that side. If yours had skipped and bent the valves, you would hear the air in the exhaust, not the center of the engine.

I am curious what you mean by over spec. If the rings were worn, or the top ring land was too large it could lead to broken rings. Also, did you ever determine for sure if they were Alucil or Nikacil? Unfortunately, it looks like you will probably need to pull the heads.
How do the spark plugs look?

You say you adjusted the valves and now have big leakdown numbers. I think you might want to go back and set your valves just a little bit looser. It's free to try.

thanks all, I got busy with work for a few days.

Walt: My help has come from several sources on this board but largely from Howard Freeman. I'm going to repeat my test Saturday after opening the valve covers, checking the valve clearance and the cam timing & the head torque. I did listen at the intake and had an ear in the tailpipe and didn't hear hissing there, but I could hear it well under the engine and with an ear at the fan shroud.

Oddly it really doesn't smoke at all past the first minute or so, I keep a shiny metal pan under the engine and while there is oil on it there isn't a pronounced spot. I have some "moistness" under the engine but no real spots of an obvious drip.

E Sully: I did install the collars, the tensioners were actually rebuilt by Howard (as you may have read in that thread). I probably should have said I was told they were well over the MINIMUM specifications in his reference materials. It's been a year and a half and I've slept so now I'm having trouble remembering which pistons I had but I want to say after showing the markings under them to this board they were told to be the ones that could be refinished without destroying the coating. (I didn't do that even, just cleaned and reused).

The plugs looked really good in color on all 6. I had a questionable trace of oil on plugs 1 and 6, it didn't coat the electrode but could be seen on the base and the base of the electrode a little whereas the rest didn't have any.

____________________

Again, thank you all, I'm considering dropping the engine Saturday morning so I can check into all this easier/more thoroughly. If something's really broken I'll have to have it out and apart anyway right? I may take the covers off to have a harder look and check the head studs first but after that...?

So here is where I am:

-I opened up the valve covers, I double checked the valve adjustment on #1 & #2. I have sat and studied the springs as best I can for a good long while and don't "see" anything wrong with them.

-I realized I never went back and retorqued my head nuts, they were all needing a little tightening to get to the 23.5 ft/lb.

-I put the dial gauge on cyl #1 at TDC and set it to "0", I spun the engine 720° and it read 0.033 (which if I remember correctly was right in the middle of where it was supposed to be and is in the middle of the indicators on the gauge from last time?)

-I redid the leak-down on #1 and #2, I am now getting 24% loss on #1 and 12% loss on number 2. I can hear absolutely no hiss in the intake or the exhaust, I can FEEL the air coming out of the now exposed oil return tubes. This time I set my compressor to 80lbs and set my gauge to 50psi, I got the numbers above by doubling what I saw below 50psi on the 2nd gauge.

________________

Is there something different I need to do/read from the dial indicator to indicate the question of jumped cam tooth? Wouldn't it run really weird if that was the case?

Is what I report enough that I really do need to go ahead and drop it and at least tear open the top end to see what is faulty?

Sorry for the book, thank you for any advice offered.

Travis

If the air is coming out of crankcase then its a piston ring or cylinder problem.
If its all of them , I would hazard a guess rings installed wrong , upside dwn, or all just plain wore out.

The patient's heart is out of her body and on the stand, I'll report what I find this week as I proceed to tear it back apart :)

I've taken the left head and #1 & #3 pistons off. I've studied the head for an hour and can't find anything that looks wrong at all with it, all the valves seat well, all the springs look fine.

I confirmed I do have Nikasil Pistons, I took my micrometer to them using the engine rebuild book's spec section as a guide and checking my #3 piston & cyl. (which I got bad #s on) I come up with it completely within the spec for "0" size. The inside of the barrel looks just as it did when I put it in there (shiny with a light cross hatch) The rings look exactly the same, none of them on #1 or #3 are broken.

I'm pretty befuddled, I'm beginning to believe my bad leak-down test numbers may be operator error of some kind or another? I still can't explain the noise that sounds like valve clatter from bad gas either.

Do I button her back up and go about my happy life and believe these things just talk to you in different ways at different times?

Leak Down - I have a cheap Home Depot compressor - I've set the hose side gauge to 100psi. I have an OTC leakage tester. Today I put it on the other side of the engine (on the stand), backed completely off the 2 rocker adjusters to ensure I was checking for just the cylinder. I set the input gauge to 80psi, this time I read a stead 76psi on the other gauge.

http://forums.pelicanparts.com/uploa...1399248076.jpg


http://forums.pelicanparts.com/uploa...1399248143.jpg


http://forums.pelicanparts.com/uploa...1399248181.jpg

Were your heads loose?
If thats a fresh engine looks like leaky heads to me. (look at cyl edge too )
and that valve looks sunk.
are the rings on upside dwn?
Where is the sealing gasket?
Pix are pix, but from here........

Heads were a tad loose yes
Valve I believe is an optical illusion in the picture (looks odd on here to me too but not in person)
Rings upside down, got me?! I never took them out the first time for fear of breaking them and lack of necessity.

could a leaking head seal cause a sound like you hear? both the head and cylinder sealing surface do not look good to me:

I had the same impression about the sealing surfaces, I put new copper gaskets on at the bases when I rebuilt but maybe I should replace them and the head gaskets too?

None were bad but I did have to tighten a bit to get them all to the 24.5lb

that would make sense because you said it only gets loud under a load bet it was the top sealing surface starting to fail..

I did/do see signs of combustion around the cylinders that shouldn't be there, makes sense what I report I could have been hearing as a "leak". Is that too much to hope for, get some new seals and properly torque and it's all good?

Last i knew 30 pounds torq with steel studs was the "right" number.
Rings can be up side dwn, not sure what the "last" guy did.
How many hours miles on this sense last taken apart ?
It does not "look" near clean enough.!
Were the ring gaps in the correct place when installed?
you say fresh overhaul right? ( how many miles or hours with this pictures"
Yes you need to use NEW sealing gaskets everywhere..no skimping !
looking the bottom pic i am sure that is a loose head for what ever reason . (so I am sure they are all headed that way)
There are a LOT of vertical FOD (scuff) marks on pistons and cyl. ( they will not seal)
you need to take rings off and measure gaps in cylinders. (wore out)
Sorry for the discrepancies .

-I had a little to go to get them to 24.5 so if 30 is right they were a good bit off.
-There is about 4k miles since I had this all shiny and clean and put together.
-I made it a point to put the gaps opposed to each other when I assembled but I forgot to note where they were when I pulled the cylinder back off.
-FWIW there isn't nearly the vertical marks evident in the light of day.
-I used new seals when putting it together, I'll order another new set today.

.The pic shows lots of vertical marks..maybe a a opticle confusion..?
You did have a huge leak dwn problem right?
Looks from pic like lots of blow by for 4K..(unless things were not clean on assembly)
oil gap up fire rings 120 apart
use NEW steel cyl studs
pour some gas or solvents in ports of vavlves and see how long it takes B4 it leaks or "shadows" out.
what cam(s) do you have?
where did you set the cam timing at ?
Hyd ten. ok?

In post #29, second pic from the top, is that a Dilivar headstud with the coating scratched off (or a painted steel stud)? I ask, because if it is Dilivar, then that is a break waiting to happen.

We all want you to succeed. so dont take anything as a flame please.
I think you need as a very min new rings, a expert to look at the cyl wall as it looks like lots of vertcle scratches to me in the pic.
The can be re chromed if necessary.
There looks like a lot of gas oil passing the fire ring .(top ring)
also pretty sure I can see damage to top rings.
Things need to be near purrfect to work.