Loud Tapping Noise From Top Of Engine - Diagnosed!

[PHATR32]

hey guys,

I pulled into the petrol station today to fill up (after a 80k freeway drive, mostly doing 110kph), and was about to shut the engine off.

It suddenly started making a real loud knocking/banging noise, and idling rough. It sounds like the noise is coming from the top of the engine, but i can feel it through the clutch pedal.

The things ive checked so far are the oil and coolant, which are in perfect condition.

The spark plugs are in mint condition.

I had a look at the pistons with torch and they look excelent too

I pulled the cam cover off the intake side(which is where the noise sounds like its coming from) and everything looked to be in order.

the only mods i have are a pair of pods, and a cam gear. car is driven daily, but not thrashed daily (although it copped a fair bit saturday). Oil changed every 6000ish k's, and its always run on ultimate 98. Its never caused any problems in the 2 years ive had it.

When you crank the engine it doesnt make the noise, only when it fires up.

im thinking the timing belt has slipped a tooth, the cam gear has loosend, or there is some serious bottom end bearing damage.

I know its hard diagnose problems over the web, but any ideas would be great.

thanks heaps,

steve

Edited December 19, 2007 by PHATR32

[GeeTR]

Big guess to say it's slipped a tooth. How olds the belt in it?

I wouldnt think a big end knock (bearing issue) would cause it do idle funny...

Could be the other way around. If the cars missing (usual AFM, AAC etc) the piston can do funny things when it goes over TDC and doesn't fire. It can knock about... thats possibly what your hearing.

Sorry I'm no real help, just some thought

[PHATR32]

the belt is about 30'000k's? and its a hks item too. i also changed the tensioner bearings too.

i suppose ill open it up tonight and see how its going.

thanks dude,

steve

[GTR-80Y]

Check afm connectors, and coilpack connections. Looks like u covered all the other usual suspencts.

[SimonR32]

rb26's are known to drop valve guides....

maybe possible

[Simon-S14]

what about a good old fashioned vac leak?

[vinnie32GTS4]

could it be your tappets?

or is it more of a clunk noise

[tek_01]

not an exhaust leak from the manifold?

i thought it was tappets but mech told me theyre hydrolic so shouldnt be them

[dead32]

try and issolate a cylinder if possible. depends how harsh the noice is, wouldnt wana cause any more damge. however by issolating the cylinder your in the general direction. could be a collapsed lifter?

[Ryanrb25]

they actually have solid lifters and naturally have fairly loud heads.

My mates GTR had simular noise, sounded like it was in the top of the head etc etc etc, turned out to be a bottom end bearing spun. worst case scenario and for your sake i hope its not.

[PHATR32]

well i took off the cam cover from the other side (exhaust) and it looks fine, also the timing belt is fine and the markings are exact. the adjustable cam gear also hasnt moved from 0.

i turned the engine over a few times by hand and found it gets stuck when cylinders 3 and 4 are at TDC (or there abouts).

it will turn over bout 2 or 3 times and id feel slight hesiation (cyl 3 and 4 TDC) then on the next turn it would get stuck to the point where id have to give it a bit of force to keep it turning.

Ive checked the belt incase theres a rock or something in one of the teeth but i found nothing.

the tapping noise is REALLY loud btw, but i havnt reved it over 1k, only idled it for a few seconds.

steve

[Scottydoo]

Im very new to skylines and this is probably wrong but thought i'd throw it out there for the hell of it

My brothers r32 (rb20) started making a really loud tapping/knocking noise a couple of days ago, would rise with revs and sounded like it was from one of the front cylinders. It actually turned out to be the clutch on the fan had given up and was making the racket. Its easy enough to test cause you can just slip the belt off and see if the noise goes.

My 2c worth

*Edit* After reading your latest post, probably not what im suggesting...

Edited December 3, 2007 by Scottydoo

[PHATR32]

thanks mate but the noise is definetly coming from inside the engine.

[MBS206]

It's not your actual clutch?

The only real way to find out is to open the engine up.

Hope you've got a good wallet when you do.

[PHATR32]

lol, i got shit in my wallet......

when i push the clutch in it still makes the noise, that said, i could definetly feel the banging through the clutch.

although, the clutch wouldnt screw up exactly when pistons 3 and 4 are TDC.

i do all the work my self, of course if the engine requires rebuilding ill have to get a pro to do it as i dont want to risk screwing it up etc.

ill do a compression test tonight to see if itll show anything?

steve

Edited December 4, 2007 by PHATR32

[PHATR32]

hey guys,

i just ran a cold compression test and all cylinders were between 135psi - 140psi except for cylinder 3 which is at 45psi!

as mensioned above when i turned the crank by hand it would get stuck when cyls 3 and 4 would hit TDC.

so i pulled the cams off and took off the lifters on cylinder 3. it all looks ok, and the valves move in when i apply force. How can i tell if a valve guide has dropped?

im gonna have to pull the engine out either ways but would anyone have any idea on what could be causing the banging and low compression?

thanks guys,

steve

Edited December 5, 2007 by PHATR32

[TurboX]

Piston hitting a dropped valve I suspect....

Maybe wrong cause I dont own a workshop...

[PHATR32]

well all the tops of the valves looked to be ok, and if the valve snapped in the middle the spring and everything above it would have come out.

[PHATR32]

well, ive been pull the engine bay apart these past few afternoons, and found the pipe that controlls the wastegate actuators had come undone!!

weird thing is i hadnt noticed any increase in boost?? that said, i do have a stock exhaust.....

engine will be out and apart this weekend hopefully.......

[giant]

i would put money on a spun big end bearing!

i know that sound well, sorry to hear that.

most the time when a big end bearing starts to go , it sounds like it's coming from the top.

russ