Knocking V8, advice please

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S

Spee

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My V8i has started knocking, not too bad but concerning.

It doesn't knock at all when you rev it out of gear, sounds nice and quiet, however, under load in gear it makes a knocking noise that increases with engine speed, again, not bad, but you can hear it clearly, or I can now!

Could it just be detonation with it only knocking under load, or something more serious??

Oil level is good by the way. Oh, and it's an Auto.

Thanks

Gareth
 
could be a bit of big end knock starting im not friendly with the v8 engine myself more of a diesel man! but had a similar problem a few years back with a tvr i looked after that had a rangerover v8 in dont no if they are the same or not! but the problem just got worse and then a full rebuild was in order.
hope this is not the case with yours
 
Impossable to diagnose a sound without listening to it but if it's a 3.5 then it could be camshaft wear although the 3.9 suffer also it's not as bad.

There's no mistaking big end rumble you would not want to drive the vehicle.

Detonation (pinking) would disappear as soon as you eased off the throttle

Could be a worn alternator bearing.

You need to say what area of the engine the sound is coming from.
 
It's hard to say where it's coming from as I need to drive it to get the noise. However, it only makes it under load, ie. foot on the gas and accelerating, take your foot off the gas (and hence take the loading away) it sounds normal, this is why I thought about detonation. On idle from cold, no hint of it, rev it on idle, again, no hint of it.

I'm going to change all the leads, Dizzy cap etc this weekend then take it down for a check over fueling wise, if this doesn't clear the noise, it's time to start worrying me thinks.

Gareth
 
If it knocks worse when cold but fades to a barely perceptable knock when hot it could be 'piston slap'.

Worn camshaft bearings (which are pressed into the block) can cause a camshaft to wobble and oscillate, causing a knock.

Try doing an oil change and put a thicker grade of oil in the engine - if the knock lessens then the thicker oil is certainly taking up some of the slack somewhere.

There is a flexplate linking the flywheel to the torque converter, these can start to crack and that will cause a rattly noise as well.

My V8 knocks abit, has done for ages, still goes well, it has regular oil changes and I'm not abit bothered by it - still sounds better than a diesel ;)

Good luck.
 
BoomerV8 said:
If it knocks worse when cold but fades to a barely perceptable knock when hot it could be 'piston slap'.

Worn camshaft bearings (which are pressed into the block) can cause a camshaft to wobble and oscillate, causing a knock.

Try doing an oil change and put a thicker grade of oil in the engine - if the knock lessens then the thicker oil is certainly taking up some of the slack somewhere.

There is a flexplate linking the flywheel to the torque converter, these can start to crack and that will cause a rattly noise as well.

My V8 knocks abit, has done for ages, still goes well, it has regular oil changes and I'm not abit bothered by it - still sounds better than a diesel ;)

Good luck.
Click to expand...


Thanks.

Well, as far as my ears can tell, the noise is the same regardless of engine temp. Tone wise, it's more of a hard tap than a knock.

As for transmission, UJ's etc, I can get the noise by loading the car in drive and keeping the brakes on, just loading the engine up to the point of moving the car in gear, so can't be anything back from the auto box.

Baffling, I'm going to pop down to the local LR specialist in the next couple of days, I was going to do this anyway but not knowing what the noise was concerned me a little, I don't want them telling me it's something it's not and taking the p*ss!

Thanks so far guys.

Gareth
 
If i remember correctly - Knocking noises - Big end knock occurs under load, little end knock occurs under no-load (i.e. over-run).

sounds like you have run a big end bearing. It IS possible that you might just, if you are quick, get away with dropping the sump and replacing all main crank bearings and big end bearings. But you will need to drop the sump and remove at least one set to determine what size they are.
 
the hit man talks sense big end knock occurs under load! so they always told me at college in the tvr icase turned out to be true! that was the 3.9 v8 dont no what yours is!
 
Well, today it died! Cut out on me 500 yards from home. Managed to get it started to get it back but its clattering like mad under load now, and not running at all right.

Anyone know of a good engine place in the Accrington area that don't charge the earth?

Gareth
 
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