Welcome to our resource for MG Car Information.



MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB GT V8 Factory Originals Technical - 3.9 on carbs - power compared to FI?

I have been looking for an engine for my GT, and have a few questions about the 3.9 engine. I have been offered a 3.9 Range Rover engine from a breakers. The bloke said he was going to use it himself, but then found a 4.8 out of something else so didn't use it.

It was removed a few months ago and he siad it had no leaks, ran very well and had good compression. He is offering a 30 day warranty but I'm only just starting out so it would have well expired by the time I can get it up and running. I was a bit worried as it has done 87k miles, this is quite a high mileage for some engines, maybe not the V8 though??

He's asking £400 for it. He wants a couple of hundred extra for the injection, ECU etc but I want to run it on carbs anyway.

The other engine I have seen is a complete 4.2 V8 with 46k, again from a breakers. But they are asking £1650! (May try to haggle, it is close to Xmas!)

What sort of mileage / price should I be looking at? I know this is one of those questions that poses a million other questions - sorry!

Also, I was wondering how the power / torque output compared using a four barrel Edelbrock / Weber carb rather than the standard injection? I also plan to use the RV8 manifolds.

Any help would be much appreciated.
Many thanks. Paul.
Paul Grundy


RPI may have a few interesting bits and also on ebay
RPI site has dyno info also V8 developments


Paul G.,

Usually, the Rover V8 is fine after 100,000 miles except for the camshaft and cylinder heads. The crankshaft and bores are normally almost as good as new at that mileage, but you should definitely replace the camshaft and followers and timing chain, have the engine thoroughly cleaned internally as they get sludged up, and have the heads overhauled.

If your breaker has a complete 3.9 fuel injection set, with manifold, plenum, injectors, wiring harness and ECU, I would be interested in it. Would you consider buying it and passing it on to me? You could even charge me a little commission. E-mail me if there is any mileage in this idea.

£400 is not too bad for a running engine. £200 is cheap for the FI equipment. I bought a 100K engine that hadn't run for 10 years (but isn't seized) with a 5-speed gearbox for £250. The bottom end is perfect. The heads are not!

Mike Howlett

Paul, not directly related to your post -I hope I am not teaching you to "suck eggs". This is a long post, but I hope it may help you, or others thinking about the Rover V8 engine.

The Rover V8 is a great engines if looked after, but can be expensive if neglected; hence I would be VERY cautious about buying a used engine.

In particular the Rover V8 aluminium block is very vulnerable to corrosion if the wrong anti-freeze is used. You MUST use the correct strength of the correct anti-freeze, designed for use in aluminium engines.

Corrosion can partially block the water galleries and create a layer of "insulation" that prevents heat transfer. Corrosion of this nature can only be resolved by dismantling the engine. In bad cases the corrosion can be so severe as to make the liners porous!

The other problem is lubrication; the Rover V8 will accept a lot of abuse but is very sensitive to oil change intervals. If they are missed or if cheap oil is used a black sludge will quickly build up. This will block or constrict oil passages so some components will not get sufficient oil flow.

The first problem area will be the hydraulic followers (lifters) and then the camshaft. This is initially hard to detect but once the wear starts it can't be repaired. As the hardened surfaces wear the rate of wear accelerates.

The only symptom will probably be a slight ticking noise, accompanied by a gradual, but substantial loss of power. You won't notice this unless you are regularly driving a similar car without the problem though!

The cure is to change the cam and the followers together as the hardened surfaces work on each other; changing one without the other is a waste of time and money.

As you know the Rover V8 engine has an aluminum block with pressed in steel liners. At the factory the liners were pressed in and machined off level with the top cylinder head sealing surface.

However some engines did not have the liners pressed in far enough, or the liners were not properly retained at the bottom. In either case, the liners will eventually move up and down.

With time this movement allows coolant to leak from the waterways surrounding the liner over the top of the liner and into the cylinder. When that happens you may see steam coming out the exhaust of a warm engine, and in some cases exhaust gases may over pressurize the cooling system causing leaks and overheating.

Dropped liner failures are often related to overheating. The dropped liner may have caused the overheating, or overheating may have caused the liner to come loose.

It is vitally important that you take any potential overheating very seriously. Never drive for long periods with a clogged cooling system and the needle near the red. Never drive at all when the gauge is off the scale; not even for a few hundred yards to get to a garage. Ignore this advice at your peril!

You could fix this problem with so called "top-hat liners" and new pistons, but it will almost always be cheaper, and always better to buy a new hand build short engine from John Eales or RPI.

If you are hell bent on buying a second hand engine you should see it running, and have it pressure tested.

If this sounds like a tale of woe I should add that over the last 30 years I have had 5 cars with the Rover V8 engine; in which I have probably driven in excess of 500,000 miles and I currently own two - an RV8 and a B GT V8.

In all these cars and miles I have, of course, had engine problems, dropped liners on two engines, one at 210,000 and one at 180,000 - otherwise no serious or major problems.
Nigel J S Steward

Well thanks for that info Nigel. Very interesting. Whether my cheap engine will be OK remains to be seen. I have taken the heads off and none of the liners appears to have moved, and all the reciprocating components rotate smoothly. I was expecting to change the camshaft and followers, and to have the block properly cleaned and inspected. There's nothing like first hand experience, and you've obviously had plenty.

Be that as it may, Geoff King in Banchory used a cheapish second-hand engine in his conversion (which can be seen on the V8 register website). He used the original components, just new rings and camshaft, and by golly, it goes beautifully. Perhaps he was just lucky.

Mike Howlett

Maybe I was lucky but the engine I bought was in good condition with virtually no detectable bearing journal or bore wear, even the cam was near perfect. All bearing and bore dimensions were within spec. I can’t be sure of the mileage but the speedo read 13k miles (it had been ‘around the clock’) and it was the original engine fitted to the car.

I re-used the cam bearings, pistons and crank but fitted new rings, rocker shafts, main and big end bearings, cam, followers and a duplex chain and sprockets. The valves and guides were within spec but I fitted new Vitesse valves to help the breathing a bit and the ports were matched and the rough edges removed for the same reason.

£600 is a bargain for a 3.9 with Efi. £1,650 is probably the top end for a 4.2 but sell the fuel injection to Mike and it would not be so bad. If you go for it get the complete wiring loom, ECU and airflow meter for the Efi.

Geoff King

This thread was discussed between 29/11/2004 and 30/11/2004

MG MGB GT V8 Factory Originals Technical index

This thread is from the archive. The Live MG MGB GT V8 Factory Originals Technical BBS is active now.