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Old 11th July 2018, 10:44 PM   #1
Plunky
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Default Exhaust knock

I've been having an issue where I am getting a bad vibration/knock from the exhaust hitting something. I'm fairly sure it is fowling on the 2 central cross members, one of which has the rubber mounts attached.

I have since had the central rubber mounts replaced, as they were completely shot, and now I've also fitted Hack engineering rear mounts as 2 out for the 3 were torn.

With all the new mounts fitted the noise has got even worse?!

Any ideas?

I have thought about adjusting the exhaust, as I would have thought with the new mounts it would probably want to pull itself back into place, however I cannot work out how I would do this as the joints are all flanges...
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Old 12th July 2018, 10:37 AM   #2
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The closest point my exhaust gets to anything is here

It is very close!
Loads of room between the support cross pieces. The pipes barely drop down if just the cross support with the rubber mounts is unbolted and I have two box hangers stuffed.
Fitting the more rigid Hack hangers probably amplifies the vibration if there is contact somewhere.
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Old 12th July 2018, 11:32 AM   #3
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Quote:
Originally Posted by crockett View Post
The closest point my exhaust gets to anything is here

It is very close!
Loads of room between the support cross pieces. The pipes barely drop down if just the cross support with the rubber mounts is unbolted and I have two box hangers stuffed.
Fitting the more rigid Hack hangers probably amplifies the vibration if there is contact somewhere.
Thanks!
Where am I going wrong then?
Judging by what youíve said, my exhaust is far too low!
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Old 12th July 2018, 12:04 PM   #4
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Probably not likely with the hack mounts (I don't personally think they're a good idea, Exhaust system will grow over it's length as it heats up so restraining it more seems like a bad idea to me - and NVH worse) anyway

But you can 'time' the exhaust centre section and backbox, I know because I've tightened up the clamps before with the centre/backbox join lower than it should be, and that puts it really close to the V brace under the car (and sounds bloody horrible) - maybe yours is a touch close and knocking?
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Old 12th July 2018, 02:14 PM   #5
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I donít see much scope for adjustment in height without putting a strain on connections. The cross supports have elongated bolt holes for lateral movement of about 4mm but thatís just so you can let it find itís natural position without straining anything.. You need to get under and inspect
Not related to your problem but like Jimbo25, Iím comfortable with a bit of pipe wobble.
For £83 for 3 OEM hangers, itís not worth also changing the engine and/or gearbox mounts to polyurethane ones which is what Hack Engineering recommend and are not exactly cheap.
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Old 15th July 2018, 07:59 PM   #6
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The hack mounts do still allow a small amount of movement as they are built using a poly bush.
What do you mean by time the exhaust?
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Old 16th July 2018, 01:04 PM   #7
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Quote:
Originally Posted by Plunky View Post
The hack mounts do still allow a small amount of movement as they are built using a poly bush.
What do you mean by time the exhaust?
If you imagine looking side on at the car, and the two exhaust pieces are joined in a straight line (centre to backbox) - it's possible to have this join above or below the centre line, effectively timing the two parts at an angle to each other. In theory impossible if you do the clamps up evenly, but in reality very possible, as I found out. My join was below the centre line of the pipes, and therefore the centre rested on the V brace. I've got a supersprint centre pipe so could be closer to the V brace than a standard centre, but I can confirm it's quite easy when you're rushing to tighten it up with the centre section resting on the V brace
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Old 17th July 2018, 08:04 AM   #8
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So is the only real adjustment where the backbox joins?
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