Sudden loud knocking from engine, Any ideas??

  • Hi guys, wondering if any one can shed any light on this.

    Bought a V6 mx3 5 days ago and up untill yesterday the engine was sweet as a nut, no knocks, rattles etc. however halfway home after work I noticed a knocking sound. After a bit of digging ive found that the auxiliary belt tensioner is worn so ill be changing that but I dont think thats the whole issue. Ive read on here that others are having problems with hla's on the rear bank and that the remedy is wynns hla treatment, couldnt find any in halfords so i put some oil treatment in (can't hurt it). Mainly whats confusing me is that the noise came from nowhere, one minute quiet, the next knocking. Could this still be the hla's? Should also mention thats it has done 140k miles but has got full service history, and the noise is only at low revs from idle (600rpm) up to 2000 rpm then it goes quiet again. Any ideas what this could be??

    Cheers lads


  • could be a belt tensioner mate. on my old alfa the noise just came out of the blue on the balancer belt, due to a pully breaking up i just cut the thing off lol. not recommended on this engine though pmsl. welcome to the forum

  • The belt tensioner gets my vote as well, makes you shit bricks when it starts to go lo

    Welcome to the madhouse…

  • Hiya Martyn, try to source the knocking noise, does it speed up with revs or does it just knock until a certain speed

    these do tend to get a knock on one of the valves at low revs with high mileage mainly at start up or if there is poor oil feed due to build up of deposits in the oil uptake pipe
    Without hearing it, you cannot really diagnose on here, the worst it could be is crank shaft shells or ends or could be valves, cams or pulleys

  • Take a video and upload it to youtube. There's so many delightful K series noises…
    HLAs / collapsed or sticky
    Friction gear spring - rear left of engine
    Rod knock - unlikely unless you're boosted
    Carbon knock/dieseling - not massively common
    Big ends or rod bearings - usually number 6 cylinder due to oil starvation
    Hydraulic Timing belt tensioner - fails and lets the pulley slap against the timing belt cover, quite clacky

  • cheers for the help lads :D next pay day ill change the timing belt and tensioner see if that helps

  • sounds like the oil is low, me and dan both had that same issue this month, pull out your dipstick, see if its below the Low mark.

  • Hey if this might help you out i have a video posted on youtube about my timing belt tentioner if you want to view it ..

    My channel is tcw691

    enjoys my loud engine lol

    hope it helps

  • Yep hydraulic cam belt tensioner, getting pretty common now.


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