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Author Subject: knocking noise
Niall

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Post #1
Well that lasted long!

Noticed today that once i warmed the car up, i get a knocking noise similar to a snapped belt tap. It only does this above 1500-2000rpm though which is odd.
My initial ideas are loose/damaged spark plug, cracked exhaust manifold/leak or bad small end bearing (not to convinced on this one as if it was, it would be there from cold and any engine speed). Any ideas?

It only does it when warmed up and above 1500-2000 rpm, is a similar noise to a tapper but does not get louder with rpm, only faster and sounds like its coming from the back or left hand side of the engine.
Posted 8th Mar 2014 at 19:16
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jeffers Forum Admin

Location: Leeds

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Post #2
Cracked exhaust mani?? Dunno

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Posted 8th Mar 2014 at 19:22
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Niall

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Post #3
Thinking if its cracked on one of the runners, it could make a bit of a noise.
Posted 8th Mar 2014 at 19:27
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jeffers Forum Admin

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Post #4
Does the engine have standard internals?

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Posted 8th Mar 2014 at 19:29
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Niall

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Post #5
Yep. Rebuilt about 300 miles ago. Refurbed head, new piston rings, big end bearings, crank bearings, thrust washers. Engine was previously a belt snapper. It snapped on idle and left 4 tiny little marks on one piston. Really wasn't that bad at all.
Posted 8th Mar 2014 at 19:37
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jeffers Forum Admin

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Post #6
Can't see it being a little end bush as you know they don't really have them in the proper sense of the word, can't see it being anything internal as you'd of had a failure by now I reckon! I'd look for like I said a cracked mani, or like you said dodgy plugs etc before panicking....

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Posted 8th Mar 2014 at 21:18
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Niall

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Post #7
Thanks Jeffers. Tbh I've never heard of a gti letting go a small end bearing but was a thought!
Posted 8th Mar 2014 at 21:45
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bigbadbowen

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Post #8
Is it a noise that seems to come from the exhaust cam side ? Ie back of the engine ?
Posted 8th Mar 2014 at 22:03
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Niall

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Post #9
It is yeah Smile
Posted 8th Mar 2014 at 22:14
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bigbadbowen

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Post #10
Had the same prob on an engine that had had a rebuild ? Never worked out what it was but I'd take the brake thing off the cam first to see if that makes a difference and maybe check the spray bar ? They have been known to get old and fall apart restricting the oil flow
Posted 8th Mar 2014 at 22:18
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jeffers Forum Admin

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Post #11
Another thought, what type of cam pulleys are fitted to it? As the earlier ones crack iirc causing a similar noise......

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Posted 8th Mar 2014 at 22:23
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Niall

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Post #12
I'm using the later type cam pullies for that reason Smile
Will take the cam cover off tomorrow and have a look.
Posted 8th Mar 2014 at 22:25
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jeffers Forum Admin

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Post #13
Hmmm let's know what you find....

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Posted 8th Mar 2014 at 22:29
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allanallen

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Post #14
Are all the bolts in the exhaust cam carrier/head heat shield? They can make a horrible rattle.

Cam belt covers worth checking to just to rule it out.

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Posted 8th Mar 2014 at 22:33
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bigbadbowen

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Post #15
Take the brake thing off the cam first as the noise is a rotating rattle metallic noise ?
Posted 8th Mar 2014 at 22:53
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stan_306gti6 Forum Admin

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Post #16
Bowen has a very point, the vacuum pumps on these can make a horrendous rattling noise if they become old and fail. Yes

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Posted 8th Mar 2014 at 23:17
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bigbadbowen

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Post #17
I'm just saving him time and hassle of getting the belt cover off for no reason ! Been there done that
Posted 8th Mar 2014 at 23:18
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allanallen

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Post #18
He can't just take the vac pump off as it'll p**s oil everywhere, you'll need to pull the drive/dog out of it or put another pump on.


If it's the cambelt covers (which can sound like a serious mechanical knock sometimes) all you'll need to do to check is bend the covers gently left and right to see if it changes the noise. It's only a 5 minute job to take the front cover off anyway if necessary.

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Posted 9th Mar 2014 at 08:09
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Niall

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Post #19


Well that's pretty conclusive!
Posted 9th Mar 2014 at 15:37
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ryangti6

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Post #20
Sorry to see this mate, been following your project with interest.

Much damage done to the crank?

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Posted 9th Mar 2014 at 16:17
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jeffers Forum Admin

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Post #21
Oh balls that is bad news.....Sad

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Posted 9th Mar 2014 at 16:23
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bigbadbowen

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Post #22
Oh dear bearing failing ?
Posted 9th Mar 2014 at 16:59
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Niall

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Post #23
Not sure whats caused it yet but number 3 is also not in great shape. Not sure if thats because of the same reason or if the metal thats flaked from this one has gotten in there.







Posted 9th Mar 2014 at 17:46
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allanallen

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Post #24
f**ks sake!

Did you plastigauge them when you built it? Look like they've not had enough clearance rather than run dry?!

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Posted 9th Mar 2014 at 18:43
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Niall

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Post #25
Nope they were all standard size bearings and the crank had never been ground before.
Posted 9th Mar 2014 at 18:47
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