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Loud Tapping Noise From Top Of Engine - Diagnosed!

PHATR32

By PHATR32,
in Engines & Forced Induction

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PHATR32 Grand Master

PHATR32

Posted
Posted (edited)

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 by PHATR32
GeeTR Grand Master

GeeTR

Posted
Posted

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 :)

dead32 Mentor

dead32

Posted
Posted

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 Grand Master

Ryanrb25

Posted
Posted

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 Grand Master

PHATR32

Posted
  • Author
Posted

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 Community Regular

Scottydoo

Posted
Posted (edited)

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 by Scottydoo
PHATR32 Grand Master

PHATR32

Posted
  • Author
Posted (edited)

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 by PHATR32
PHATR32 Grand Master

PHATR32

Posted
  • Author
Posted (edited)

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 by PHATR32
  • 2 weeks later...
PHATR32 Grand Master

PHATR32

Posted
  • Author
Posted

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 Mentor

giant

Posted
Posted

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

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