Member Since: 09 Aug 2017
Location: Coventry
Posts: 25
Engine knock, i think it might be small end but which one?
Hi,
Hope someone can help with this, I just need someone to confirm or counter my thoughts below.
I've just done a bottom end re build with new bearings mains and big ends, machined and polished crank and ive got this knock that I cant work out where its coming from, see video link below.
I checked the small end play on all pistons when the crank was out by pushing and pulling the rods and couldn't feel any slop.
It does not knock if I just get the starter to turn the engine with out starting (via relay) so Im pretty sure its not valve noise.
I also think its to clunky for valve noise so then it must be a small end even though I checked for slop but maybe i missed it.
Then I marked the crank pulley up so line is vertical when pins in the cam pulleys fit into the heads and the tool in the flex plate fits which I think is 30 degrees BTDC.
Then in this slow mo video you can see the knock comes around 90 degrees after this.
So with 6 cylinders there should be a detonation every 60 degrees so that means its happening on the second detonation (30 BTDC + 60).
I searched on here for the firing order which seems to be 1-4-2-5-3-6 so that would mean tha piston number 4 that where the noise is coming from.
Does my reasoning make sense??
Thanks
Rob[/quote]
28th Apr 2019 5:40 pm
Grumpydog
Member Since: 10 Apr 2019
Location: Medway/ Mos Eisley
Posts: 153
As it doesn’t knock if the engine isn’t running have you thought about diesel knock? Could be a faulty injector.2004 Disco 3 HSE TDV6
2015 Audi Q5 S Line plus
2008 Audi A4 Avant S Line Black Edition. Gone
2005 Chrysler Grand Voyger. Gone
28th Apr 2019 7:11 pm
heresy0uk
Member Since: 09 Aug 2017
Location: Coventry
Posts: 25
I have disconnected each injector in turn and started it and the knock is always there.
Hmm, could the injector be leaking?
28th Apr 2019 7:17 pm
PROFSR G
Member Since: 06 Mar 2017
Location: Lost
Posts: 4657
Better not to run the engine with injectors unplugged. You could try a leak off test but it does sound a lot like an injector.
Can you look at injector live values via diagnostics?yµ (idµ - eAµ) ψ=mψ
28th Apr 2019 7:27 pm
Grumpydog
Member Since: 10 Apr 2019
Location: Medway/ Mos Eisley
Posts: 153
The one I’ve just brought had an injector hosing, which then ate away at the piston. I think the symptoms were just lumpy running though.
So with the diesel supply cut off there is no knock? Strange, although with no diesel there is no explosion which means less stress on the crank and associated components too.
I always find it difficult to diagnose faults without actually seeing the vehicle but you’d think that the 20 odd years of doing Diesel engines would help!2004 Disco 3 HSE TDV6
2015 Audi Q5 S Line plus
2008 Audi A4 Avant S Line Black Edition. Gone
2005 Chrysler Grand Voyger. Gone
28th Apr 2019 7:27 pm
heresy0uk
Member Since: 09 Aug 2017
Location: Coventry
Posts: 25
no I was just disconnecting the electrical connectors, Tomorrow ill make a blank for the feed pipe and take off each pipe to see.
28th Apr 2019 7:30 pm
Globetrotter448
Member Since: 21 Mar 2017
Location: Londonderry NSW
Posts: 1783
You could use the old tried and trusted technique of a long handled screwdriver up to your ear and listen for the sound by touching different area's. If you have a stethoscope that's better still. This would give you a clue to where its coming from.
29th Apr 2019 4:28 am
OvalAutos
Member Since: 28 Dec 2018
Location: Cradley Heath
Posts: 382
What was the reason for the bottom end build; big end failure?Joe
29th Apr 2019 7:17 am
heresy0uk
Member Since: 09 Aug 2017
Location: Coventry
Posts: 25
The rebuild was because of this knock but it turns out it wasn’t crank related
29th Apr 2019 7:51 am
OvalAutos
Member Since: 28 Dec 2018
Location: Cradley Heath
Posts: 382
What was the knock?
Are they the same conrods that the engine had originally or were different ones used during the build?Joe
29th Apr 2019 8:19 am
heresy0uk
Member Since: 09 Aug 2017
Location: Coventry
Posts: 25
It’s the same knock as before the strip down, same con rods, just the crank was machined and new bearings fitted. The crank only had its mains machined as it was borderline so I don’t think the knock has anything to do with the crank.
29th Apr 2019 8:22 am
OvalAutos
Member Since: 28 Dec 2018
Location: Cradley Heath
Posts: 382
OK, so now we're getting somewhere. Preexisting knock still present after bottom end rebuild. So safe to assume its not crank related. Questions....
1/ New or same oil pump
2/ Were the heads stripped down during the build
3/ When did the engine first start 'knocking', what led up to this event
4/ Did you have the injectors testedJoe
29th Apr 2019 8:32 am
heresy0uk
Member Since: 09 Aug 2017
Location: Coventry
Posts: 25
Ok so I stripped it all down again, taking out the pistons this time and the cause was bent con rods causing the pistons to slap the bores.
I didn’t mention that I bought the car as a non runner and looking at the blue gudgeon pins it must have got very hot!
19th May 2019 8:49 pm
Sloss
Member Since: 18 Aug 2013
Location: Aberdeenish
Posts: 1691
If you'd told us the full story we'd have diagnosed it ages ago!
Glad you got there though Stew,
2010 D4 gone but I really loved it
Went back to Merc - C350 AMG
20th May 2019 9:52 am
gearmuncher
Member Since: 30 Oct 2018
Location: Woodley
Posts: 143
what did the oil filter look like, was it crushed ?.
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