Hi so was driving my datsun home and when i got home i opened the bonnet to check the battery and realised a knocking/tapping noise

i revved it slightly it seemed to go away then when i let go of the speed upon slowing down its start to knocks again (on deceleration)

it will knock on idle for few seconds then go away and do it if i rev it again.

i just adjusted the valves and most where tighter than .35mm and one was loose but after adjustment it made no change if anything know the tapping stays on longer and stays when you rev it?

i have added a video so you can hear it.

thanks hope it hasnt spun a main bearing? cant see why it would just randomly do it tho? noise seems loud at the valve train area.

Check the torque on the rocker tower bolts, perhaps the shaft is bent or worn bad.

http://www.youtube.com/watch?v=a227O1rkKr4&feature=youtu.be

heres a video

dont know if you can tell but after reving it and let it idle for few seconds the tapping goes away until the next time you re it

The symptoms sound like con rod bearings my friend.

Mind you I haven't watched the video because my net is so damn slow......

I had a similar tapping noise in my A12 that would come & go that turned out to be a broken rocker shaft,it had broken where the bolt goes through the second pillar

so today i took of the rocker assembly tore it apart and found no problems so i had a spare one and put it in and it still knocks

checked compression i have 170psi on all 3 and on 4th cylinder i have 155psi

is this variation normal?

I crawled under the car the knock isnt that lound from the sump its alot louder near piston 3 and 4 near the pushrods

i also checked the pushrods there all straight

can it be something like tappets or camshaft?

Thanks!

That compression is very good,( except for the variation) but the rings and valves seem to be sealing, you might put a little oil in the cylinder with low compression to see if that temporarily seals the rings, but at 155 it is not bad. It could be a measuring error.

The knock is more of a concern. If you are up to doing it, remove the oil pan and measure clearance of rod bearings 3 and 4.

A spun main or conrod bearing will not affect compression. Use a long screwdriver like a stethoscope: With the engine running, place it at various points on the block (i.e. camshaft housing, front of block near crank pulley, rear of block near where the crank bolts to the flywheel, etc.) and place your ear on the handle. Noise travels up the shaft of the screwdriver, enabling you to pinpoint whereabouts in the engine the noise is coming from.

Oh, and for the love of God, please don't put your face into the fan and if you have long hair, tie it back!! :-O

If it is a chattering noise and it really does sound like the rocker assembly or near that area you will find it it a spun bearing.

The A-series is a small motor and I did not find the stethoscope concept useful in the diagnosis, sound advice but I find it more applicable to larger engines.

I will try and dig up my old thread, I also uploaded a video on YouTube and ill try and find it. You can tell yourself if the noise is similar.

Here you go mate.

Chattering Noise