Sounds like a top end tick which is better than a bottom end rap. I don't think you need to remove spark plug wires as I suggested above. I suspect a rocker arm or shaft issue since the sound goes away when you rev (i.e oil pressure increases with increased engine speed) the engine. I'd concentrate on the right bank where you say the sound is coming from and the oil spray is 1/2 the height of the other side. Can you move (i.e with your fingers or maybe a screw driver to give you some leverage )the rocker arm perpendicular to the rocker shaft axis (i.e. with both valves closed) to check for wear in the rocker arm or shaft? You may want to remove rocker arms on cylinders 5 and 6 to inspect them for wear or scoring due an oil restriction on that side of the engine.

Hope this helps
Bill
90C2

 

ok on the noise if you think it is oil related then rev slightly to 1500 rpm or what ever rpm while acceleration to when the noise stops. if you rev it to that rmp and holt it there is the noise gone??

on the vidie you just rev and let it return to idle so its hard to tell.


i think you have piston slap because of the sound. i think the reason the sound goes away when you rev it , is because you are fire that cylinder faster and the piston is more center in the bore because of the even combustion in the cylinder.

i may not be saying this right in the best terms, but if you rev it to bring the oil pressure up and hold it and there is the noise present or not.


i guess what i am trying to say is that the piston has more pressure on it while revving and will be more true in the bore and not slighty canting, meaning leaning on the skirt of the piston. so lets say something fell down the intake it would be on the bottom of the bore and maybe while the load is better distibuted on the piston while reving the noise goes away till you either hold it steady or let it idlle.





thank god i no technical writer as i would have everyone confused


if it were a bent valve you would hear back fire or popping whitch you do not.


need to know about the sound at raised rpm and hold whether its there or not

 

After listening to the sound file, I would agree that it sounds more like valve train / top-end related. Had the rapping sound remain with varying throttle, but increase in frequency to RPM, I would suspect loose valves. I have heard similar sound before cured by valve adjustments. Unfortunately, that is not what we have here and I am very curious to learn of the findings.

 

One more thing... does the rapping sound change as the engine warms up? In other words, is the rapping sound pretty much the same when 1st started from cold to when engine is warm/hot?

 

The rapping sound dissapears on the acceleration curve but once the rpm levels off no matter how high the rapping reappears.

The sound does not change whether the engine is cold or warm.

I have not run the engine more than 10 min so I do not believe the oil thermostat has opened.

 

tall02, take out 1 set of plugs on all cylinder maybe just the lower ones, and turn over by hand and see if you can feel a binding spot, should rotate smooth thru out the entire rotation

 

I had a quick look at the sound clip you posted. As you can see the period of the primary noise ticks is about 8Hz. If your idle is 960 RPM the pistons go up and down at 16Hz and the valves half that or 8Hz. So you can rule out the piston hitting the head or piston slap and concentrate on a valve problem.

Greg

 

 

migrated valve seat ?????

 

Dear gfunk

Your graph and analysis is great. This is exactly the feedback I needed. It has at least narrowed down my options to the valve train rather than the piston option.

I spoke to my Porsche engine head machinist and asked if he had any problems rebuilding my heads. He said no. He did not machine the heads. I had purchased and requested him to install new valves, seals, guides and retainers. He said the seats were warped but he was able to recondition grind them and use them. I was wondering if one came loose why would I have 190# compression?

Anyone have any ideas if I can confirm this problem before pulling the engine?

Thanks gfunk and I appreciate everyones helpful responses

 

hello Tall02, you have all the data, i would email Nine Meister or steve weiner and have them look at the sound clip and the info that gfunk posted and i am sure they can help. everyone has contributed good info but i think a specialist that rebuids engine day in and day out can take this info and pin point it right away.

 

"He said the seats were warped but he was able to recondition grind them and use them."
"warped" ?

 

"If your idle is 960 RPM the pistons go up and down at 16Hz and the valves half that or 8Hz. "
Does this take in to account that its a four stroke and only fires on half the up and downs ?
That the piston gets more forcefully pushed over to the other side when the cylinder fires off ?

 

I believe so. The camshafts rotate at half the rate of the crankshaft and the spark fires in time with the camshafts.

If you wanted to isolate which cylinder was causing the problem (although there could be more than one) you would need to record 2 channels: the audio and the ignition signal from one of the cylinders. You could then measure the time between the ignition signal and the noise and determine which cylinder(s) were making noise.

Greg

 

The fire in the cylinders "run" at the same speed as the cams . 1/2 crank speed .

The rap could still be other than the heads because of this .