Thread: The improbable task of silencing the 4bd1 county

jp, if you remove the plastic covers the bulkhead isn't even cut out, like a puma!

jc

If you want to really cut noise. Fit the later graded piston and liner kits.

A cheap (and nasty) way of acheiving the same noise reduction is to press in cast iron liners an have them bored to your existing pistons.

Please explain more Dougal how are the late ones quieter ? I'm rebuilding one now

Hi JP,

I've found that it is 1000 little changes that make the difference. Make sure there are no holes anywhere. I had a hole drilled behind the instrument binnacle for Maxi-Drive vacuume lines and a lot of engine noise (and dust etc) was getting in there. Also your heater will allow more noise if the rubber duckbill thing is perished.

I have very heavy marine engine insulation under my bonnet. It has a thick rubber side, an inch of close cell foam and then a silver reflective coating. This made a very large difference. I've also got the whole firewall covered in dynamat, then vinyl loaded rubber sheets (4kg/m) then carpet. (although it isn't in at the moment while I do some other interior things). Dynamat throughout the rear as well, and then vinyl loaded rubber sheets (4kg/m again) then carpet. Then get hold of some of the Puma style door seals. My door seals are letting me down right now, and are my next focus once I've sorted out some mechanical stuff.

As you mute one noise you will find others. When I insulated the bonnet I suddenly discovered the driveline noise.

Originally Posted by Adrian18

Please explain more Dougal how are the late ones quieter ? I'm rebuilding one now

Tightening up the piston/bore clearance to the minimum possible (which the factory matched piston/ring/liner kits do) greatly reduces engine noise and blowby.

My engine was rebuilt once with cast liners bored to the pistons. It was spookily quiet at idle and low load. I'm currently running generic liners of the loosest grade which are about 200tdi noise level but will go back to the factory close clearance sets when I get the engine back apart.

The factory piston/liner/ring kits come in four different grades which you match to each bore to get the best result. Aftermarket tend to be all the loosest grade.

I'm hoping to use more boost to quieten down the engine under load too. Boost is the best way to silence diesel combustion clatter as it encourages the fuel to burn cleanly as soon as it is injected. Without boost you get an ignition delay between the fuel being injected and combusting. This is the diesel clatter we all know well.
I need to see if a GT2256V can provide a few psi boost at idle for noise suppression and warm-up.

Don't forget the geatbox tunnel. Remove teh carpet and the rubber boot over the gearstick and you are left with a large, un-insulated hole. 25mm thick foam makes a big difference here.
The noisiest part of my car is the maxxis bighorn mud terrain tyres. I rotate them every 5000km, but they still hum.

Hi all thanks for your comments - all very helpful!!!

Flagg- I've been reading through MLD's thread "sound insulation in a defender" where you have commented. I understand that the Dynamat Xtreme is the product of choice to use, as such, I ordered myself two bulk packs- this should get me started. This stuff isn't cheap so must be ok?!

If the Dynamat xtreme product works as well as I'm led to believe, I'll probably replace/ redo all the interior (where I previously placed the closed-cell foam) with the Dynamat.

I also came across Dynaplate product. do you or anyone else have experience in this product (basically thin aluminium sheeting to further increase rigidity of the steel plates)????

To this point, I've used an 18 mm thick, close-cell foam with aluminium surfacing (for heat insulation) and have lined the following:

>bonnet underside,
>areas of the bulkhead within the engine bay that can be easily accessed,
>the transmission tunnel (interior and exterior),
>every flat section that is exposed on the underside of the vehicle,
>The middle floor and cargo area (including wheel arches),
>I also plan to do the doors and line the roof.

With all the above I'm still hitting ~90 dB at 80-100 km. Wouldn't go to this effort if I didn't love my Landy to bits but my ears do pay the price after long drives.

Obviously the more layers of sound insulation product the greater the damping affect. So i haven't ruled out multiple layers!!

Flagg did you go to the extent of removing the entire dashboard and lining the interior bulkhead?? I am seriously considering this.

I'm interested in this vinyl inserted rubber you speak of - where can I get this? I understand this type of product may have replaced the more effective, yet harmful, lead-lined rubber products.

ScottW- thanks! Gearbox tunnel done and dusted.

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

Originally Posted by 110Landy86

Hi all thanks for your comments - all very helpful!!!

Flagg- I've been reading through MLD's thread "sound insulation in a defender" where you have commented. I understand that the Dynamat Xtreme is the product of choice to use, as such, I ordered myself two bulk packs- this should get me started. This stuff isn't cheap so must be ok?!

If the Dynamat xtreme product works as well as I'm led to believe, I'll probably replace/ redo all the interior (where I previously placed the closed-cell foam) with the Dynamat.

I also came across Dynaplate product. do you or anyone else have experience in this product (basically thin aluminium sheeting to further increase rigidity of the steel plates)????

To this point, I've used an 18 mm thick, close-cell foam with aluminium surfacing (for heat insulation) and have lined the following:

>bonnet underside,
>areas of the bulkhead within the engine bay that can be easily accessed,
>the transmission tunnel (interior and exterior),
>every flat section that is exposed on the underside of the vehicle,
>The middle floor and cargo area (including wheel arches),
>I also plan to do the doors and line the roof.

With all the above I'm still hitting ~90 dB at 80-100 km. Wouldn't go to this effort if I didn't love my Landy to bits but my ears do pay the price after long drives.

Obviously the more layers of sound insulation product the greater the damping affect. So i haven't ruled out multiple layers!!

Flagg did you go to the extent of removing the entire dashboard and lining the interior bulkhead?? I am seriously considering this.

I'm interested in this vinyl inserted rubber you speak of - where can I get this? I understand this type of product may have replaced the more effective, yet harmful, lead-lined rubber products.

ScottW- thanks! Gearbox tunnel done and dusted.

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

Dynamat certainly isn't cheap, but it made a big difference to mine. I went a bit overboard as I got 4 packs from a local car audio place that was closing down - you don't need 100% coverage to get good results.

I've not tried dynaplate..

If the foam you are using isn't heavy then I'd say there are two problems - you need mass to absorb sound waves and you may have air leaks (any gaps).

My firewall was rusty, so I replaced it completely and that gave me a good time to seal it all up and fit the dynamat. The whole firewall is done, including behind the dash. I also used a tube of sealant when I put it all back together so all the panels are sealed between them as well.

The matting I used was the 4kgm/2 "sonicbar" from Sonicbar

I've not tested how loud mine is, and I have to finish installing the vinyl matting and sealing the doors but it is a lot better than it used to be. You have have a conversation up until about 100km/h then you have to strain your voice.

I already have hearing damage so even though I've put all the time and effort into sealing it up I still use ear plus for long drives.. but the above made a massive difference.