Knocking noise in td42

[jamied]

Hi all. My mates td 42 has a knock that is only there loud at times and other times its not there. Haven't yet noticed any patterns as to when its there and not.
What we have noticed is that when it is there its only at idle and it goes away when the clutch is depressed and smoothed out when the engine revs. Trying to work out what it may be. Obviously somewhere between flywheel and gearbox

[nissannewby]

Sounds like the pressure plate of the clutch might be on its way out.

[gqmoder]

mate i really hate to be the bearer of bad news but it sounds like the big end bearings
what happens is at the bottom of each conrod (the shaft that connects the piston to the crank) is a bearing. now oil is pumped through this bearing (or you may think of it as a cup wrapped around the crank) and if it starts to wear, at idle when the oil pressure is lower you will start to hear a knock, particuarly when the engine is nice and warmed up as the oil gets abit thinner as it warms up.
also when you put your foot on the clutch it puts a slight bit of pressure on the back of that crank which may might be enough for the noise to quieten down.
also when you increase the rpm (revs) the oil pressure increases which can be enough to silence the knock.
put something heavy in the back and then drive it up a hill when the engine is warm and see if it starts to knock, if it does its probably big end bearing .... dont do to much of this tho if it is the big end ... just enought to test ......
putting really think oil in it can make it last a bit longer and quieten the knock till you can afford to fix it
a mechanic should be able to tell big end bearing noise just by listening.
dont forget that diesel work on high compression to make their bang rather then explosive fuel and a spark and are suppose to sort of knock or "tick" abit particularly when cold
if its big end bearings im afraid you will need to take the motor out and atleast turn it upside down, take the sump and so forth off and change the bearings ( not a job for the faint at heart) ... might as well do a rebuild while your at it
those td42 motors are bullet proof they should do a million km's i dont think i have ever heard of one failing like yours.
hope it turns out to be something simple for ya mate.

justo

[nissannewby]

The above is well over the top. An engine knock doesn't disappear when depressing the clutch. And at no load speeds say 4th gear around 70k and hour the noise would be present. The fact it's only audible at idle and in neutral until the clutch is depressed points straight to the clutch. The noise won't be present when driving as the clutch will have load on it and so on. Don't spook people cos of what you think you know.

[gqmoder]

if its the clutch wouldn't it get worse as the rpm increases not better? it may quiet down as you power up and put pressure on it but then when you back of and cost along it would be worst then ever and when you backed off and on it would be diabolical.
p.s it was only my guess dude, just trying to help, if i'm totally wrong i'm wrong, in fact i hope i am!!!!!!!!!!!!

[nissannewby]

Not if it's the pressure plate like I suggested in my original post. The pressure plate can lose tension after a while and cause the above symptoms. It will be noticeable when cold and when it has load on it in gear it cannot move around so there fore no knocking sounds.

[gqmoder]

wouldnt it start to slip under pressure (on a hill with load) or at very least start to feel it back thro the clutch pedal ... at very least could be a good way for him to test and see it that is the issue.
either way i feel sorry for the guy.....
clutch means either taking out the motor or dropping the HUGE gearbox.........
they weigh i ton
justo

[nissannewby]

Only under high load conditions but even then the noise can be there before the clutch shows signs of slipping. Won't feel it through the pedal due to patrols having a hydraulic clutch. He would need to put a decent load on it to test but it would be a good way to see. Doing a clutch isn't a huge job if you have someone to help and some appropriate tooling then it aint to bad.

[gqmoder]

i found things like that still come up through the pedal over the yrs even with the hydraulic clutch.
anyway don't wanna high jack this thread with some sort of debate or what ever.
i always hate dropping that big box hey even with a gearbox jack and a couple hydraulic jacks these days i have taken to putting an engine crane through the passenger door and lowering them from the top.

[Dales300exc]

Put it in 5th, handbrake on, bring the revs up let the clutch out slowly while increasing accelerator pressure and if it doesn't stall your clutch is slipping. (Would not recommend doing more than once-twice, you'll just cook your clutch)

Ive also had feedback through hydraulic clutches.

Really need to be able to hear a sound to diagnose where its coming from and where it is. Perhaps a video or sound recording to try and help.

Where abouts are you located?

EDIT: scratch that, your in canberra! I can not help to you.