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Old 12th October 2020, 14:09   #1
ianM
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Default KV6 engine rattle/grinding - *not* inlet manifold?

Hi all,


Since I bought my 75, it's had a bit of an odd rattle from the engine - in fact, it sounds more like a grinding noise than a true rattle. It's normally only when cold, it happens at bang on 1,100 revs (whether going up or down past it), and seems to all but disappear when the engine's warm. If you leave the car idling after starting the engine, it'll sound something awful as the revs come down to 1,100 with a persistent metallic grind, before going back to normal as soon as it's gone past it.


Of course, this being a KV6, I assumed it was the inlet manifold - but today I got the inlet manifold replaced with a replacement I was assured was rattle free from the trader I bought it off, only to find the dreaded rattle remains.


As far as I can tell, this only really leaves two options. Either the one I've replaced it wasn't really rattle free - or, it's something other than the inlet manifold. I'd like to assume I can write off the inlet manifold now, but if it's not that, what else could it possibly be? Is there a list of things I ought to check next that may cause a rattle, trying to figure out where it comes from?
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Old 12th October 2020, 14:36   #2
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timing belt tensioner etc would be my first point of call, when were the belts done?
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Old 12th October 2020, 14:40   #3
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Also today! Had the cam belts and water pump done, inlet manifold changed at the same time.
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Old 12th October 2020, 16:01   #4
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Also known noisey tensioner on the secondary belt that runs Power steering, Alt etc ( Spring loaded one). If i'm honest mine does it a bit
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Old 12th October 2020, 17:32   #5
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Is it possible that could make a metallic grinding noise (only at very specific revs?). Any way I can check it visually to see if that's causing the problem? Or anything else I can add to the list of things to check!
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Old 12th October 2020, 19:05   #6
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Could be the resonance frequency of a chain with a dead tensioner. Knocking against the housing it's running in.

Stops vibrating above or below this frequency.---
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Old 12th October 2020, 20:47   #7
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Quote:
Originally Posted by ianM View Post
Also today! Had the cam belts and water pump done ...
Hi Ian,

I agree with Stocktake's advice. It does sound related to a tensioner (whether timing belt or ancillary belt). It's therefore very worrying that you've had work done in this area today.

Please check that whoever renewed the timing belts (1) used the proper service tools (2) replaced the tensioner and idler pulleys if the mileage was approaching the MG Rover interval of 90,000 and (3) followed the INA instructions for adjusting the tensioner pulley (these are NOT in any MGR publication).

The noise you've reported when the engine is cold is a classic sign of incorrect belt tension (I've had this myself on the ancillary belt). Please report back.

Simon
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Old 13th October 2020, 09:14   #8
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COLVERT KV6s do not have chains.
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Old 13th October 2020, 09:27   #9
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Quote:
Originally Posted by SD1too View Post
Hi Ian,

I agree with Stocktake's advice. It does sound related to a tensioner (whether timing belt or ancillary belt). It's therefore very worrying that you've had work done in this area today.

Please check that whoever renewed the timing belts (1) used the proper service tools (2) replaced the tensioner and idler pulleys if the mileage was approaching the MG Rover interval of 90,000 and (3) followed the INA instructions for adjusting the tensioner pulley (these are NOT in any MGR publication).

The noise you've reported when the engine is cold is a classic sign of incorrect belt tension (I've had this myself on the ancillary belt). Please report back.

Simon

Hi Simon, thanks for the post. I've had the noise since I bought the car (and had the belts done twice since then), so it's nothing new, and so I don't think it's anything related to the work done. The work was done by Summit Garage, who seem to know what they're doing when it comes to these cars


I didn't realise the tensioners could make a metallic grinding sound, though. Sounds like it's worth checking out. Any tips on how best to try and figure out if they are what's causing the noise?
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Old 13th October 2020, 09:40   #10
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Hi Ian, thanks for your reply.

I've bought parts from Summit Garage and have been impressed with their service. Regarding the timing belt changes though, were you invoiced for any tensioner and/or idler pulleys at the time?

I noticed a rattle at 67,000 miles only after starting from cold. My ancillary belt had a cut across all five ribs. You can check this easily after removing the OSF wheel arch liner. But the major advance in smoothness followed later renewal of my ancillary belt tensioner and the two timing belt pulleys.

Simon
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