Knock (205 gti)
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Thread: Knock (205 gti)

  1. #1
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    Default Knock (205 gti)

    I would like to say thanks to everyone who provided advice to me during the top end rebuild of my 205, i finally got it registered last week and have been enjoying every minute of driving it!

    However...

    It has developed a faint noise, when revving above about 2000 rpm (both idle or in gear) its a tapping sound that sounds like someone is tapping a tin can, i would say it coincides with the rotational speed of the engine and speeds up as the car exceeds 2000 rpm, it is quite faint but still noticable even when driving the car. Any suggestions on what it could be?

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    It is worth noting that on suggestions from the guy that reco'd the head, i did not adjust valve shims after the head was bolted down, is this what it could be? am i causing damage?

    Cheers

    Jack
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    1000+ Posts PeterT's Avatar
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    The head moves around when torqued down, so either you allow for it, knowing how much to leave from experience, or, you re-check clearances after torquing down.

    It could also be a bad lobe/bucket. Where they matching original items?

    '92 205 Mi16
    '90 Mi16x4

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    It was an SI head and GTI block, so no, I will have to recheck valve clearances then by the sounds of it!

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    I meant camshaft and bucket relationship. It's easy enough to remove the cam cover and check clearances, condition of lobes etc.

    '92 205 Mi16
    '90 Mi16x4

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    So the GTI cam was taken out of the GTI head and put in the SI head, I will have to confirm, but i am pretty sure all the buckets etc were kept from the SI head as the guy that did it seemed to think that the buckets match the head rather than the cam?

    I just measured the valve clearances, i will have to go through again and double check. But at this stage i believe they are...starting from flywheel end...

    0.40 0.17 0.155 0.385 0.38 0.14 0.09 0.33

    The 0.09 is worrying me, how much leeway from the 0.2 inlet and 0.4 exhaust is acceptable?

    Other than the tapping noise, idle wasnt great, and it would take a few extra engine rotations to turn over than i would generally expect

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    I would say it's likely these gaps are the cause of your noise. Before I took the head off mine I had a similar noise and similarly inconsistent gaps.

    I don't want to come across as an expert because I'm far from it but from what I've been told by the experts these are the ideal gap sizes; inlet 0.23 - 0.254mm (0.009 - 0.010"); exhaust 0.305 - 0.330 (0.012 - 0.013").

    So it looks like all of your exhausts apart from the 4th are a bit loose and all of your inlets, especially the 4th, a bit tight. After a couple of attempts I managed to get mine within the above ranges, it's still a bit 'tappety' when cold, but from what I've heard they're all like this, once warmed it quietens down.

    Dave

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    Thanks for the info Dave, is it possible to grind the existing shims down to spec? or do new ones need to be purchased?
    Your car is looking very tidy in the other thread! I had similar idle issues to you which i will need to address after the shims if they dont fix the problem!

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    1000+ Posts PeterT's Avatar
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    Quote Originally Posted by jack205 View Post
    i am pretty sure all the buckets etc were kept from the SI head as the guy that did it seemed to think that the buckets match the head rather than the cam?
    No, bad advice there. The lobes of the cam match the tops of the buckets. It's too late now however. Either they'll last for ever or they'll destroy themselves very quickly.

    It's possible to rub half to one thou off a shim, on a flat surface with some #60 wet & dry, but after that your fingers will be very sore.

    '92 205 Mi16
    '90 Mi16x4

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    With your idle you shouldn't need to mess with the throttle stop, the ferule thingy or the throttle switch as I've done. I think this was necessary with mine because of the modifications I've done. If you're lucky you may just need to adjust the bleed screw. Also, make sure the throttle body (particularly the entry of the bleed screw) and the breather hoses are clean and you don't have any leaks.

    You can buy new shims from Precision Shims or if you tell me what you need I can have a look through mine and we can swap, I only have 16 or so of them but might have what you need.

    Dave

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    Thanks for the offer dave, i had a donor head left over from my build so i just stole shims out of that, i also got some of the missing sizes ground down by the guy that build the head for me!

    I have done the shims, they are now all within the specs that you told me! However...It is still behaving exactly the same way! I thought that maybe it was pinging, so potentially the timing was out, I retarded the distributor quite a significant amount! (in increments) still didnt change the sound

    Any ideas?

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    From your description the noise doesn't sound like pinging, I'd put the timing back where it should be. From your description it still sounds like it's coming from the valve train/camshaft and I still think if your head has just been recoed - guides are good, valves straight - the most likely culprit is the gaps. However check first that you don't have a leak/crack in the exhaust manifold, they're notorious for this. If good, I'd be tempted to check the gaps again after a bit of a run (wait til the car's cold before checking).

    You might be able to isolate where the noise is coming from by running the engine at the place where the noise is most evident and putting your ear to the plastic handled end of a long screwdriver, placing the tip in various places on the head and base of the cam cover.

    Make sure things like the camshaft thrust plate and oil spray rail are firmly in place. If you check the gaps again and they're still good, next thing I'd do is check for consistent compression across the cylinders.

    Dave
    Last edited by DaveT; 26th July 2012 at 11:26 AM.

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    The plot thickens....

    The car is all back together with adjusted shims,

    Now I have had a chance to drive the car properly with the problem occurring...

    It occurs at idle but now only sometimes

    It speeds up and becomes much more prominent when turning right ( even a slight right)

    It's non existent when turning left

    It sometimes happens when going straight

    I ruled out cv joints as it sometimes happens at idle

    Can't be the exhaust or head as it becomes more prominent when turning

    This has completely got me stumped... Unless they are two similar sounding noises caused by different things ?

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    This may be an annoying suggestion but check the small metal (hose?) bracket that's bolted to the firewall right down at the bottom next to where the fuel lines are. When I first bought my car it quickly developed a metallic tapping that mirrors your noise pretty well. For weeks I was positive the noise was coming from the cambelt or head and it sounded expensive.

    It would start at around 1500-2k rpm and the higher the revs the more furious it sounded. Thank God I eventually found the culprit was just the bracket. It was no longer being used to hold anything and the attachment nut had backed itself off a little which allowed the bracket to resonate wildly against the firewall. It also swings from side to side which could explain the change of direction difference as from memory, it can swing further when your turning right than it can when turning left.

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    I gave up, brought it to the mechanic to diagnose! At this stage the verdict is possibly something loose within the bellhousing, i am going to drop the gearbox tonight and take a look, at the gearbox and clutch, any tips or tricks to make the job easier? the mechanic suggested removing the front subframe to make life easier, is this the best plan of attack? anything else i should replace apart from the rear main seal whilst i am at it?

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