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tips, technology, tools and techniques related to vehicle driveline components

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Kael O

(5 posts)

01/08/2017 03:05AM

Main British Car:

Coverting Rover 3.5 to 4.6 in my MGB
Posted by: Airbumps
Date: January 16, 2017 03:18AM

Hi All,

I've got a '75 MGB (converted from LHD to RHD) with a 3.5 Rover in it.

I'm in the early stages of looking at an upgrade to a 4.6 and I'm being given different details as to what's required for the conversion. The engine builder is adamant that the new engine (front over and all) will drop straight into the car inplace of the existing 3.5 with no need for relocation's or modifications.

Other people have told me (and I'm sure I've read online) that the 3.5 front cover needs to be used or that modifications need to be made to the crank of the new 4.6.

I've done a couple of searches but can't seem to find a definitive list of items that need to be changed from somebody who's been through the process.

Thanks for any advice

Dave R
Northern Virginia
(131 posts)

04/07/2016 08:29PM

Main British Car:
1979 MGB 4.6L Rover V8

Re: Coverting Rover 3.5 to 4.6 in my MGB
Posted by: RDMG
Date: January 17, 2017 07:42PM

The answer probably depends on the distance between your block and the radiator, and your oil pan and the ground. The serpentine belt system on a 4.6 has different front dimensions from the earlier v belt setup. The cast aluminum 4.6 oil pan is also very deep, presenting ground clearance problems.

I have a 2004 4.6 in my garage, but the water pump and harmonic balancer are missing, so I can't give you a precise measurement there, but the oil pan drain plug extends about 4" below the flywheel ring gear.

Oil pans, cams, and front covers are not independently interchangeable across all Rover v8s, but they can be swapped within their group. Generally it's the 3.5/4.2/3.9 style that's interchangeable with 1960s Buick v8 parts, or the more recent Rover 4.0/4.6 style which is not backward compatible.

I think there's one or two serpentine belt MGBs on here, but I'm not certain.

If you want to use a carb and distributor, it's likely best to retrofit earlier cam, cover, and pan to a 4.6.


(1 posts)

05/23/2013 06:58AM

Main British Car:

Re: Coverting Rover 3.5 to 4.6 in my MGB
Posted by: robinj66
Date: January 19, 2017 05:31PM

I can't help with the difference in physical size of the two variants of the RV8 but the blocks have the same external dimensions.
The post 1994 (in UK) engines (4.0 & 4.6) have no distributor OEM but instead use fuel injection systems.

It is possible to fit the timing covers from earlier engine to the later blocks thereby allowing the use of a distributor & carb if wished. This is a quite common mod in the UK.

As stated by RDMG the sumps are different and often need replacing for earlier items.
The earlier timing covers also have the oil pump at the bottom (driven by the distributor) . You would also have to fit the oil pick up pipe from an earlier engine - you will find that the pick up hole and mounting holes are still machined in the later blocks even though the oil pump is contained in the later front timing covers (and driven by the crank).

Use of a distributor and early timing cover means that you will need an earlier type cam with room for the gear which drives the distributor to be attached. You may also need an adaptor plate to hold the cam in place and excessive reduce end float.

There are some good photos and a bit of information here - [www.super7thheaven.co.uk] .

Also have a look at this UK forum - [www.v8forum.co.uk] and do a good search for various info and tips on using a later block/early timing cover combo.

Another good place may be the UK Cobra Club forum (have a look at the wiki's) - [www.cobraclub.com]

Look out for posts by "Sidecarbod" on both forums..

Lots more I haven't mentioned but you have to start somewhere.......



Blown v8
Bryan Phipps

(70 posts)

03/10/2013 04:52PM

Main British Car:

Re: Coverting Rover 3.5 to 4.6 in my MGB
Posted by: Blown v8
Date: January 22, 2017 08:10AM

I went from 3.5 to 4.6, I used the 3.5 front cover,distributor,oil pump,sump,cam,starter,flywheel etc,
Using the older style front cover gives you more room for a decent timing chain set,needed if you want to run a decent cam,
Externally I believe they are the same size,mine fitted on my engine mounts.
I have now changed my front cover,to a crank driven oil pump with distributor made my John Eales,not cheap

I still use the shorter P5/P6 water pump

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