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Whats this noise?

Postby Paul Cornell » 16 Jan 2017 16:08

Hoping someone might be able to point me in the right direction to investigate an odd noise, although its difficult from just a description but here goes. My car starts without problem, however, there is an odd (what I can only describe as a 'chuff chuff') sound coming somewhere (i think) from the rear offside of the engine. The 'chuff chuff' increases in volume and frequency as you accelerate but once you are cruising the sound disappears. The performance of the car is good and at cruising runs normally. If for any reason you decelerate and accelerate the noise comes back again increasing in volume and frequency again until you cruise. I can find no evidence that the manifold or exhaust is blowing so I don't think its that. The sound appears to be coming from within the engine but a bit like the 'pot of gold' at the end of the rainbow the sound appears to come from different places depending from where you listen. Very difficult to say exactly where it originates. Any ideas?
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Re: Whats this noise?

Postby Philip Irving » 16 Jan 2017 18:54

The manifold bolts are a well known weak point - they back-off and this creates a lack of seal for the exhaust gases. My guess is that you haven't had yours tightened up for at least a couple of years? Also funnily enough, bolts at the back of the engine are the biggest bugger to reach. Hope this helps !
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Re: Whats this noise?

Postby Paul Cornell » 16 Jan 2017 23:01

Yes I was aware that the manifold bolts could be a problem. I did tighten them all when I purchased the car 3 years ago. Maybe I should revisit them as a starting point. I do remember the rear bolts being a devil to tighten.
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Re: Whats this noise?

Postby Bill Cole » 31 Jan 2017 18:56

I had a hairline crack in the exhaust manifold a number of years ago. A right pig of a job to remove the manifold and get it rewelded.
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Re: Whats this noise?

Postby Nic Houslip » 07 Feb 2017 19:02

The V8 manifold bolts are a problem, they do work loose, but the reason is obscure unless you understand fastener technology. For a bolt to stay tight it must stretch when torqued, the bolt should also be elastic enough to maintain tightness after the manifold has heated up and cooled down. The problem here is that the bolts are not really long enough to accommodate the amount of stretch needed and after some heating / cooling cycles they stretch beyond their elastic limit and loosen. Tony Lake made a suggestion to me that a longer bolt with a spacer under the bolt head may be a solution and I have made some 3/4" long spacers and fitted them to the manifold bolts my RV8 on the LH bank. After half a season's hill climb, sprint and track days the one with the spacers under their heads have not required tightening, but the others have. This isn't a total solution because on the RV8 there are some bolts that do not have clearance between the tubes or adjacent parts. I haven't been able to check a BGTV8 with Cast iron manifolds yet.
I'm currently investigating other solutions, but have not had time to delve deeply. IMORTANT!!!!! Do not overtighten the manifold bolts, they are steel threaded into an aluminium head and cannot stand too much torque. If you do you risk scrapping the head, because there isn't enough metal between the bolt hole lands and the water passages. The recommended Torque for B GT V8 is 13 lbs Ft [1.80 Kg M] and RV8 40 Nm [29 lbs ft.] This seems a little high, but the RV8 has a fabricated manifold rather cast iron.
If the manifold has been loose for some time it might be worth checking that the gaskets are not burned through. If they are replace them as soon as you can to avoid damaging the head, Clive Wheatley has them.
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Re: Whats this noise?

Postby Jim Gibson » 08 Feb 2017 21:35

Has anybody tried these ?

Rover Part Number 90613659 aka LandRover ERC 7321
Attachments
ERC7321.jpg
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Re: Whats this noise?

Postby Tony Lake » 08 Feb 2017 23:24

Jim,
The problem with tab washers is that they have to be soft in order to bend the tab over. That in turn means the torque that should go into bolt stretch disappears as friction between the bolt head and the soft washer. In the case of the exhaust manifold and aluminium cylinder head; clamping force is quite low because aluminium thread strength, even with coarse threads is lower than a cast iron female thread. Bolt stretch is about .0025" with 13 lbft of torque, easy to lose half of that in compressing a soft washer, net effect is that everything looks tight but after a few thermal cycles clamping force is largely lost and eventually a leak will occur. The long bolt/tubular spacer arrangement works because it stretches more for the same torque, doubling bolt length gives about .005" stretch which provides a bigger margin to deal with hot and cold cycles.
Tony Lake
 
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Re: Whats this noise?

Postby Dave Morris » 13 Feb 2017 12:54

Has anyone tried replacing the bolts with studs and brass nuts?
This is recommended on some Rover V8 sites...
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Re: Whats this noise?

Postby Bob Owen » 14 Feb 2017 09:00

Brass nuts were traditional on MOWOG manifolds and exhaust unions and have the great advantage of not rusting. However, I can't see any material advantage in terms of staying tight in this particular case. I have never had any problem on my V8 but I still have the cast iron manifolds. Stainless steel typically has a coefficient of thermal expansion more than 50% greater than cast iron so will stretch the bolts at least 50% more than the cast manifolds. People have not mentioned the manifold material but I wonder if this is a factor - for the fixing bolts it''s the same as having a more than 50% increase in operating temperature range.

Others with more knowledge could point out the fallacy but I wonder if Belleville washers might offer a solution to maintaining tightness?
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Re: Whats this noise?

Postby Bob Owen » 14 Feb 2017 09:07

Immediately you post a reply you see another aspect! The bolts have a thermal coefficient of expansion too and high tensile steel has a coefficient closer to cast iron than to stainless. The ideal is presumably if bolt and material being fixed have the same coefficient so that they expand and contract together so again the cast manifold is advantageous.
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