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MG MGA - Thinking of an 1800

I've been semi-seriously thinking about redoing an early 1800 engine, flywheel, and perhaps clutch for my MGA. It's a 1956 car with the low-mount starter and a 1600 block fitted by a PO back in the 80's. The engine runs fine, but I'm thinking I'd like the extra power, etc of an 1800. Since the car already doesn't have the original engine, maintaining originality isn't so much of an issue.

I know this has been discussed many times in the past, but some of the info in the archives is a bit confusing, what with all the engine, flywheel, clutch, and transmission options available. I figured I'd bring the topic up yet again, but this time seek advice specific to my application. I have local sources for both an 18G (3 main) or an 18GB (5 main) engine. I don't know the exact state of either, but both are reasonably priced and I expect either would require some amount of rebuilding.

My car has a five speed gearbox (Ford Sierra conversion) which I'd obviously keep. Either engine would require a rear plate swap for the low-mount starter. For the 18GB engine, the rear plate would have to be machined for a rear oil seal. According to info on the Moss Motors website, the 18GB would require a different spigot bush adapter to mate with the Sierra gearbox, while the 18G could use the the same spigot bush adapter that came with my conversion kit (and is currently on my 1600).

I could use my existing mechanical tach with the 18G, where as the 18GB would mean sourcing an early MGB electric tach.

OK, now we're getting into areas I'm not sure about. Flywheel, clutch, etc. Would I be wise to use the MGB clutch? Is retaining the MGA clutch even an option with either the 18G or 18GB engine? Given that the bell housing on my gearbox is sized for an MGA clutch, would there be any fitment issues with an MGB clutch?

So far, it's sounding to me like the 18G (3 main) engine would be a more economical approach than the 18GB (5 main). In terms of rebuilding, are parts for these two engines priced similarly? Are there other factors that would overwhelmingly tilt the scales in favour of one engine over the other?

Lastly (perhaps this should be the first question), to those who have done such an engine replacment, does an 1800 provide a noticable difference over a 1600 in terms of power, acceleration, drivability, etc, etc?
Andy Bounsall

Andy.
I would opt for the 3 main umit. I have had many npeople state that produces much more power that the 1800.Others will know more about that.
Sandy
Sandy Sanders

I would use the B clutch. It works in my A gbx housing, which is also a low-starter one. The issue will be the clutch lever arm, which I think will need to be an early B one - check the guy selling the engine, he may have one.

Likewise I would use the B flywheel as it is lighter than the A pne. You need a complete set in other words - from flywheel, pressure plate, and actuator arm /release bearing.

You could also use the A clutch, but as they are a bit more fragile, a lot more expensive, and don't seem to last as long as the B one, I switched to the B one and have been happy with it.

for either clutch system, you need the friction plate that has the correct number of splines for the gearbox input shaft. Otherwise they are identical in dimension and construction.

The other option (if you can find it in Canada) is a 1622 engine, which is an A engine, puts out c 98HP, and requires none of the stuff with water pump etc. Same clutch rules apply, but you don't need to machine the rear plate for an oil seal.

If you find a B clutch arm, could you see if the guy has a second one, plus the front cover for an early B gbx, I know someone who wants to do the B clutch conversion,and is looking for the bits.
dominic clancy

Dominic - the 1622 did not put out 98 BHP, nor was it just in Canada - they came in all Mk 2 MGAs and produced in the region of 93 BHP.

The 3 main MGB is the best swap - you retain the mechanical tach drive, and need only swap over the MGA rear engine plate that suits the conversion transmission.

He will not be able to use an early MGB release fork in a Sierra transmission - you'll have to research the differences between them, but the diaphragm clutch is worthwile if it isn't too much hassle. If it is, you could always retain the MGA clutch and flywheel (the dowels on the MGB 3 main flywheel for the diaphragm are in slightly different spots) and perhaps have the MGA pressure plate rebuilt with heavier springs to accomodate the higher torque. We used to do that sort of thing alll the time.

You will notice a very significant increase in power with the MGB engine.
Bill Spohn

The Sierra supplier, Hi-Gear Engineering can supply clutch fork adapters for the 'B clutch fork. I have an 1800 GB five main engine with a low starter backing plate machined for the rear main seal. My flywheel was from an earlier "crash" starter MGB. The late Butch White put together the complete bolt in package for my specific combination. I'd be surprised if Moss couldn't do the same.
Doug
D Sjostrom

Thanks for the feedback thus far. Doug/Bill, I checked a bit further and Hi-Gear does have a part that adapts the early B clutch release lever to my bell housing, and yes, it is also available through Moss.

I'm quite surprised that no one has stepped forward yet with a compelling argument in favour of the 5 main bearing engine.
Andy Bounsall

Retrospectively, I wished I had the low starter postion on my 1800 5 bearing conversion. With the high position and the right hand drive steering shaft I am unable to remove the starter motor without first removing the spin on oil filter!

Steve
Steve Gyles

Steve (and others), what was your reasoning for choosing a 5 main engine?
Andy Bounsall

Andy

Availability and smoother running. Lovely engine.

Steve
Steve Gyles

Steve

Even with the low starter, the spin-on has to be removed before the starter motor comes out
dominic clancy

Dominic

Oh, ok. I did not know that. I did not have any recollection of a problem with the old 1500 engine. There again, memory fades.

Steve
Steve Gyles

OK, I've decided to go with the 3 main 18G engine, provided it's in reasonable shape. I intend to strip it down and do some work on it, but hoping not to have to do a complete rebuild. Seller says the engine came out of a running car, although I'm not sure how long ago that was. He's well known though and has a good reputation with our club members so I don't expect the engine to be junk.

I'll have to arrange to go and have a look at it before handing over any cash. What should I be looking for that would indicate potential trouble? One thing that worries me a bit is whether it has a serious leak from the rear crank. Is there any way to tell from a visual inspection if this is likely to be a problem?
Andy Bounsall

Andy,
I would remove the head (check the manual for the proper method) so you can check for cracks in the combustion chambers, take a look at the cylinder walls for scoring and determine what size pistons it has. Make sure that the tach drive is not missing. It would be a plus if you could look at one of the main and rod bearings to determine if the crank has been machined. Good luck and have a good day!

John
John Progess

I have a spin on conversion and didn't remove the filter to change the starter. It was a squeeze, but doable.
D Sjostrom

The problem with the starter motor is with RHD cars. The steering shaft limits the lateral movement of the motor. It has to be pulled straight forward and fouls the filter.

Steve
Steve Gyles

I use a 1800 GB 5 bearing unit with the MGB flywheel and clutch cover and the MGA plate. Front cover and lever are from an early MGB. I use the MGA gearbox. It is a straightforward swop.

I have a Maniflow exhaust header and 1.75 carbs, Peter Burgess "Fastroad head" and a Fastroad camshaft (Piper)and 123Ignition.

The result is very pleasing - fast and responsive and well-mannered
A highly recommendend combination.

I kept all the original items so there is always a way back!

Goodluck!

Huib

Huib Berger

Went to check out the engine today. The 3 main turned out to be a bit of a mystery. The ID tag on the side of the block said "18G.....", however the head was from a later engine with smog ports. There was also no mechanical tach drive. I mean there wasn't even a hole in the block were the drive should've been. It seemed to be a later 5 main egine that someone had changed the ID tag on at some point. Not knowing what other surprises I might find inside, I opted instead for an 18GB engine that had recently been removed from a running '66 B. I also picked up decent looking early B clutch and a clutch release arm. All for a very reasonable price.

So now I'm all set with a new project for next winter...if I can wait that long before I start to tear into it.
Andy Bounsall

When my 1600 thru a rod and caused other damage, I had it replaced with a 1800 3-main. Great power, love the get up and go. Only problem is the oil leaks. I've been told thats the life of a 3-main. If I had to do it over, I would go with the 5-main.
Robert Peate

Robert, a 3 main shouldn't have any more oil leaks than a 5 main.

IF it coming from the rear of the engine, the crank oil return scroll may be worn. See Barney's site for an interesting way of retrofitting a conventional oil seal to a 3 main crank.
Bill Spohn

I do have a 3-main with a nasty oil leak. Bill, I queried once about the oil scroll wearing and was told it never actually makes contact with anything, so it should never wear. More likely the cause of severe oil leakage is blowby forcing the oil out. On the other hand, my 5-main doesn't drip a drop.
Mark J Michalak

You are correct - the scroll had better not touch anything.

What happens is that the clearance between the scroll and the crank gets enlarged and they start sucking, or rather pushing oil past it.

This usually happens in one of two ways. Either an inept machinist polishes that surface on the crank when the crank is turned down and he is polishing the adjoining journal, or someone has the block align bored, which can change the clearance as well as the scroll depth.

Like many things mechanical, the scroll system works admirably as long as you leave it alone. Mess with it and of course you cause problems.
Bill Spohn

This thread was discussed between 26/05/2008 and 05/06/2008

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