The improbable task of silencing the 4bd1 county

Mine is definitely quieter when loaded up for long trips. Whether its the gear actually blocking out the noise or preventing it being created by stopping everything vibrating I'm not sure.

Doing the underside of the bonnet was the most noticeable change on mine. I've got some 25mm multi-layer engine bay insulation from a marine shop on 2/3rds of it. Unfortunately ran out and didn't have enough to finish it and haven't got around to buying another sheet.
Have the same stuff over the trans tunnel, then topped off with some heavy rubber backed carpet from Bunnings. Used the same carpet under the rubber floor mats.
Made a big difference to the heat transfer too so SWMBO can actually put her feet on the floor now without getting them burnt.

A lot of the noise in mine now is wind noise from dodgy door seals. As Flagg says, when you reduce one noise then you can hear the next distinctly.

Steve

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Originally Posted by steveG

A lot of the noise in mine now is wind noise from dodgy door seals.

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Do the window frames on your doors stick out a little? I find that mine do, even with the door latch adjusted all the way in.. it seems I may have to twist the door back into shape or work something out with spacers on one of the hinges..

When I owned my county I found that soundproofing the seatbox made a huge difference and seemed to push the noise further forward back into the engine bay.

On my series 3 I've completely changed the seatbox with soundproofing and making storage lockers and lids. I've also stuck foam under the floor plates and laid thick carpet underlay over the top of the gearbox. The difference in noise levels was very noticeable :)

A couple of pics at various stages

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Originally Posted by 110Landy86

Dougal- any info on the tight tolerance factory components? And is it possible/ ok to change these components insitu or is it best to pull the engine and carry out full rebuild?

Cheers JP

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Sure. They are factory matched piston/ring/liner kits and come in 4 grades. Either you find the factory bore size stamped on the block (probably not on the early engines) or you set to with an internal micrometer and mike up the bores to choose the appropriate grade. They are not cheap, around $NZ2k for a set of four.

I have changed pistons and liners in-situ. It can be done in a garage in a weekend if you are keen. You will need to machine up a puller plate to get the old liners out with some heavy threaded rod, some pipe and another plate across the top.
Some run a welder up the old liners to shrink them, but Cheif can tell you the reasons to not do that.:(

Regarding sound proofing. Roof flashing type is a modified bitumen layer (about 0.8mm) with an aluminium foil coating. It works just as well in a deadener application as many commerical sound proofing products at a fraction of the cost. I've put it throughout my work car, it went from terrible road noise to being able to hear rain-drops landing on the windscreen.

I'm not an acoustics engineer, but my sound proofing theories go on three layers.
First a deadener to stop the panels resonating (roof flashing tape or dynamatt). Secondly an absorber layer (I use EVA closed cell foam) and thirdly a top skin that holds it all in place (carpet etc).

I've had the most success in my rangie from plugging the holes and gaps around wires, cables, steering shafts, handbrakes etc and then layering EVA foam over the transmission tunnel. I had a noticable reduction in my work car from applying deadeners to the roof skin from inside.
Don't forget the source of noise. Balancing prop shafts etc can make a huge difference for relatively minor cost and hassle.

Quietening down vehicles is a dangerous hobby. There is no end point.

Found some websites regarding sound proofing for those that are interested...

Welcome to Sound Deadener Showdown | Sound Deadener Showdown

Sound Proofing - CSK Land Rovers

Acoustica Sound proofing

Serious Soundproofing for a 110 - Land Rover Zone

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Originally Posted by 110Landy86

Found some websites regarding sound proofing for those that are interested...

Welcome to Sound Deadener Showdown | Sound Deadener Showdown

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The above site was originally a very well put together test of sound deadening products. Unfortunately it's been sold out and is now just a marketing site.

The original content of that site I've archived and it's here: http://users.actrix.co.nz/dougal.ell...r_Showdown.pdf

I'll get back to this once I have a bit more time, however a brief summary of "quietening" a vehicle:

Noise in the cabin is the sum of:

- noise generated by the engine, drivetrain and wheels being transmitted into the cabin through the panels,
- vibration from both mechanical and aerodynamic sources transmitted into the body panels and re-radiated into the cabin as noise, and
- noise reverberating (bouncing around) inside the cabin, amplifying as it does (can add up to 4dB in a bare defender interior with only seats to absorb reverberated noise).

To effectively reduce noise in the cabin you need to reduce both modes of transmission as well as amplification.

Dynamat type products are effective at "deadening" the panels so they reduce vibration re-radiating as noise. For this to be effective you DON'T need to line the entire panel with Dynamat. It won't hurt (other than damage to the wallet and added weight in the car), but it won't really help either. Dynamat is most cost-effective when placed in patches, where each patch occupies 30% to 40% of the area generally placed in the centre of each flat panel. It is a viscoelastic material that works primarily by dissipating vibration energy into heat. It also adds some mass to the panel which shifts the panel resonant frequencies higher up the spectrum (but generally not high enough to be out of the audible range). I would use it in strips on roofs (several 10cm wide strips placed lengthwise between the stiffening ribs), with perhaps one widthwise strip across the centre, and on door sections (covering approx 40% of the centre of the flat area between the rounded section and bottom of the door). If in a wagon, a thin strip may also be placed on the rear quarter panel, below the rounded fold in the sheet.

Next we need to do something about airborne noise transmission through the panels & into the cabin. Dynamat is a REALLY EXPENSIVE sound barrier material IMHO. Sound barrier performance at low frequencies (i.e. the hardest to block out & therefore controlling) is determined by the WEIGHT of the barrier material. "Dynamat Extreme" weighs approx 2.2kg/sqm - Barium loaded vinyls come in sheet weights of up to 8kg/sqm, and at prices comparable to, if not better than, Dynamat. If you do a search for Sorberflex on here, you should find several of my earlier posts on what I would use, why, and where to buy it. On all panels that are between an airborne noise source and the cabin (e.g. firewall, footwells, transmission tunnel, seat boxes and load area) you need to ensure full coverage and use a heavy (4 to 8kg/sqm) vinyl. I would look for an 6mm to 10mm closed cell foam backed loaded vinyl (that dampens panel vibration and decouples the vinyl from the vibrating panel). Alternatively, strategically located Dynamat strips could be used under the loaded vinyl (wouldn't be my preferred choice).

Noise absorption inside the cabin. - Any "soft" surface will provide some absorption. Seats, people, carpet, roof lining... all help absorb some of the reverberating sound. Noise that's transmitted out from the cabin (through the roof and sides) also reduces the amount of noise that's left inside. Unfortunately, closed cell foam does virtually nothing to absorb sound in our cars, especially the high density type of foam that cheap sleeping mats are made out of. It will help with heat, and may provide reasonable panel dampening if surface glued to panels, but that's about all it's useful for (that I can think of). Noise absorption would probably be the last thing I would "get to", as we can hope to gain at most a 2 to 3 dB reduction.

to give an idea of perceptive differences of the decibel scale, a reduction of:

1 dB - not noticeable by over 90% of the population
2 dB - barely noticeable
3 dB - noticeable
5 dB - clearly noticeable
10 dB - noise perceptively halved

In order for the above measures to reduce noise, we first need to ensure effective sealing of doors, windows and vent flaps. By effective sealing, I mean reasonably airtight. In addition, all firewall penetrations should either have rubber grommets in good condition, or if these have perished, or for large openings with multiple wires running through them, you can tightly pack a "ball" of fibreglass or polyester insulation wrapped in a durable cloth or similar permeable membrane to prevent it from disintegrating and spewing out fibres everywhere, but allowing air to get through. Unless the cabin is effectively sealed, any additional measures are a waste of money.

Note - I'm not convinced that a "noise barrier" type material is helpful under the bonnet - if anything, I'd use an absorptive type foam or fluff to reduce the buildup of sound within the engine bay. (EDIT: Unless driving with windows / flaps open)

Firewall is a different story - I'd use a composite material comprising a thin layer of closed cell foam, a layer of loaded vinyl, with a thick layer of open cell foam, placed closed cell foam against the firewall. A range of manufacturers make it for noise control of firewalls and engine rooms. I've posted details of products I'd use in previous posts

As for quietening the engine itself, I wouldn't have a clue where to start, but have heard that later engines are quieter than earlier ones, and some are definitely quieter than others.

Isuzu appear to have had a reasonable go at insulating the engine itself, fitting an acoustic rocker cover (the outer steel skin's only purpose is to reduce noise), as well as decoupling the oil pan from the engine by using a double rubber seal with special rubber clad studs to isolate it from the engine. I'm led to believe the pump and injectors themselves make quite a racket and, if that is the case, don't understand why they were never dressed with a cover of some sort. There may have been an operational reason - I don't know.

Lastly, fitting a turbo will also reduce exhaust noise emissions by approx 6dB from memory.

HTH

Bojan

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Originally Posted by flagg

Do the window frames on your doors stick out a little? I find that mine do, even with the door latch adjusted all the way in.. it seems I may have to twist the door back into shape or work something out with spacers on one of the hinges..

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Everything sticks out or doesn't seal on mine. I can see daylight through most of the door seals etc :angel:

FWIW - after reading Offender90's previous post, I'm thinking that the reason I got a reasonable reduction after applying the bonnet insulation is that the engine bay noise was getting in via all the holes, so stopping it getting out of the engine bay did help !!

Steve

Just want to thank those that have contributed to this thread. I'm grateful to have access to the wealth of knowledge within this forum that is attributed to its members.

Now onto the task of sound proofing :D

Cheers JP

I've had some success by doing most of what others have said above ie. Dynamat, closed cell foam, carpet everywhere and also an under-bonnnet covering I stumbled across which supposedly was for the Isuzu landies.
I still seemed to be getting annoying noise from the passenger footwell area. Not sure exactly what helped, but I stuck a couple of layers of Dynamat to the side of the heater box next to the exhaust (partly to stop the plastic casing from melting) and some self adhesive closed cell foam to the bulkhead on the engine side as well, plus filled that cavity just above the passenger sides feet with some foam stuff I had lying around, and that seemed to make a big difference.
Will also add that mine has had that door type seal around the edge of the bonnet ever since I bought it. Hasn't affected the running temperature so may be worth a try. I still have lots of holes for noise to get in around wiring and door seals but I would say it is pleasant to drive now (passengers may disagree).
But hey, part of the pleasure of having an Isuzu landy is the distinctive truck sound. If it wasn't for the family I'd have left it how it was!