tommo, I hope it is the cam because that would be a good excuse to remove it. The bloody thing is a 322 degree ticker, gotta get it out!

Thanks fella's I'm going round the bend trying ti figure out the issue and I only have my own skills and knowledge to diagnose. It's ruining my bloody Christmas!!

Okay, my first suspicion was the rocker assembly, changed that, no change then:

+ changed head: no change.

+ inspected distributor sprocket: looks to be fine.

+ inspected fuel pump arm: looks to be fine.

+ inspected tappet clearances: all good (have not yet checked lift).

+ inspected old head, tapped around the valve seats, tapped the guides no noise, a nice high ring when struck lightly indicating components are tight.

+ inspected valve springs: all complete all sitting well.

+ removed gearbox, started engine solo, noise still there.

+ removed engine removed sump; put a solid screwdriver on each piston and rocked the crank back and forth no noises when listening on the end of the screwdriver.

+ turned over the crank, lobes looked fine and looked to be lifting well, no bearings had slipped out etc.

+rotated crank for several revolutions, absolutely no hesitations apart from coming off or onward to flush deck height.




I did not check flywheel bolts, I thought there would have been noticeable vibrations if it were loose.

I have not yet removed timing cover to check for loose sprocket or gear failure.

I have not yet checked the gudgeon pins but there is no marking on the bores to indicate one has let loose.

The crank was spun on a balancing machine that then apprently failed, all I can think is that the crank has been bent during the machine failure but I was assured initial test were showing a balanced crank and the failure was software failure not mechanical. I also thought a bent crank would have shown a hesitation at some point in it's revolution. I also believe if the crank were bent the noise would have been audible straight away.


So I'm banking on cam (and or associated running parts) or gudgeon pin. Can people agree that that's valid reasoning or have I missed something?

To be honest the knock to me sounds like a con-rod but just a bit higher in the block and a little higher in note.

could be loosing a loab of the cam??
loab could be getting square not round?
will cause funy deap tappet noise
clearences will stay the same
u will loose lift
tommo

3 things come to mind
could be a sloppy dissy
could be a lose flywheel
if you shaved the head then could be the
rockers comming up and hitting the rocker cover

What the hell could it be?

Changed head, check ancillaries (fuel, oil pump, dizzie) up till 3am up at 6am. Engine in and out twice. Gearbox opened up and checked.

THE NOISE IS STILL THERE??!?!?!??!!!!! Aaaaagrrh!!

Not sure if it's any use to anyone, but it's looking more and more like the valve seats as ssskiwi suggested. The compression tester looks like it has a fault so my readings weren't accurate.

I'm taking the head in in the new year so I should know for sure by then.

I gotta admit I'm happy it isn't anything to do with the bottom end and I guess the pull-down was a good chance to see how everything was holding up.

Took the gearbox & motor out, pulled the head off cannot see any signs of loose seats or stems. Will get it checked.

All main caps and con-rod caps were torqued as they were, no clearance issues.

I think I just wasted my time Thanks for the input though, I swear there is still a noise but I can't seem to figure out what it is.

Hi John, yes I have noticed this before but mostly on other engines, I think the rocker assembly of the Nissan A-Series was pretty well designed as I haven;t seen nearly as much wear on the A-series as others.

Noise is still there with gearbox removed, and I am almost certain it is an internal issue. Absolutely spewing!

Removing the engine tonight and stripping it down for a look.

Thanks for the advice.

Probably a bit late in the game, but things to try for $0.00 - often the rocker 'tips' where they contact the valve stem will wear a groove. So if you use normal feeler guages, they'll sit on the 'high' spot either side of the groove, and the actual clearance when running can be 2-3 times what the feeler guages say.

So back off some rocker adjusters and lift the rocker off the valve stem and look for groove/slot wearing into the rocker tip. If this is the case, the 'ideal' solution is new or reclaimed rockers, but the cheap and workable solution is simply get a spare couple of feeler guages and carefully cut them with tin snips (you'll need to peen the edge where it was cut as it might bruise and end up thicker) so they are only around 4-5mm across, and then you can slide them directly in under the groove section and get a look at the real clearance.