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MG MGA - 1800 or 1500: what are the tradeoffs?

I have a 57 Roaster I bought for my wife's 2003 Christmas present. Over the winter I rebuilt the chassis and drivetraine of a 57 with a decent body, passable interior. This summer we drove it and now know it has a very worn Mmagnet1500 and a decent tranny with worn 2nd gear syncros.

My wife love it so for 2004 Christmas I'm going to freshen the motor. What should I do get another 1500 rebuild it and fix the tranny, or rebuild an 1800 and make the ranny comapabil, while I rebuild it.

I'm not interested in the car enough to ever make it a 100 point show car. What should I do?

BruceP

I would put in a 1800 5 main for the power and easier for getting parts ( $$$$) for than the 1500. The 1800 will make the car a better daily driver. I would keep the 1500 for the future to make it back to original.
JEFF BECKER

I appreciate an original car as much as the next guy, but as a driver a MGA is better with an 1800 in it. Same feel but far more power and just as reliable. I have a 3-main 1800 in my '58 A and the power is perfectly matched to the car, IMHO.

I would suggest the early 3-main 1800 over the later 5-main unit. The appearance is nearly identical to the original 1500 and you retain the mechanical tach so no instrument changes are necessary.
Steve Simmons

I am with Steve, go for a 3 main 1800 for the same reason Steve suggests, plus the MGA transmission will bolt up to it with no modifications to the backing plate. If you want to really make the car drivable, find a early MGB 3 syncro over drive transmission and trade the main shaft into your transmission, then just bolt on the O/D and adapter unit in place of the original tail piece. You will have to modify the rear mounting brackets, but I found that all the work was well worth the effort in our Magnette, which came originally with the 1500 B series engine. Good luck - Dave
David DuBois

If you use a 3 main 1800 with a MGA gearbox you have to make a decision on what flywheel and clutch to use.
Two options:
(a) Use the heavier MGA two dowel flywheel and MGA coil spring clutch with the MGA gearbox.
(b) Use the lighter MGB three dowel flywheel and MGB diaphragm clutch.
Option (a) is a simple bolt on operation, but is not the best solution.
Option (b) gives a much better result, but you have to also fit an early type MGB gearbox front cover (the one that the gearbox input shaft passes through) and a MGB clutch release lever to the MGA gearbox.

Mick
Mick Anderson

Mick is exactly right about which parts make the best combination.

I also prefer the 3 main MGB engine, as it spins a bit freer and looks right. I have reservations about the fitting of an OD unit - that works alright in a Magnette, but the OD unit fouls in the MGA at the handbrake level - I solve this on a race car by removing the handbrake, but I'd want to take a close look if I wanted to do this conversion on a street car.

A 4.88 with close ratio and OD makes a rather nice package.....

If you do it, please don't hack off the ears on the frame for the MGA trans mount - it isn't necessary!
Bill Spohn

I think everyone missed the part where Bruce wrote it has a "very worn Mmagnet1500" engine. It isn't "original" anyway...I'd expect there's no hole for the mechanical tach-drive in the block. You might offset your cost somewhat if you offer your Magnette motor to someone over on the Magnette message board. Perhaps someone will have an 1800 motor to work out a trade?
Bruce...you really might as well go with an 1800. You may want to locate a good used 3-main that has ~140psi compression fairly even in all cylinders. Lots of good tips from the others here...as usual.
Jon Bachelor

3 main engines are the best swap, but their relative scarcity can make for problems when sourcing replacement parts. Other than the tach drive, an early five main would be the next best matchup. The electric tach from the MK1 cars is the same size as the mechanical one, so that makes the tach drive arguement moot. The four synch gearbox is much better than the original 3 synch, so I'd consider that swap as well.
R. L Carleen

I hope to be swapping my 1500 for a 3 main 1800 next week. I will be keeping the original tranny as I quite like it and have just rebuilt it. The lack of first gear syncro doesn't bother me at all as mine will shift into first just before it comes to a complete stop.
Kris Sorensen

Honestly, I own both types of transmissions and I greatly prefer the 3-sync units to the later 4-sync models. I know the later ones are stronger, but the early ones "feel" stronger, and to me are easier to find the proper gear in. The later units feel more fragile and for me it's easy to select the wrong gear.

My MGA has the 3-main 1800 with the stock MGA transmission. It's a perfect matchup so long as you don't intend to spend a lot of time at high speed. If I were to change the transmission to anything, it would be a 5-speed which would give me the higher gear like the OD transmission would, and would require no extra switches to engage overdrive. It's nearly impossible to spot the modification without getting under the car.
Steve Simmons

Steve
I agree completly. I had a 74B and I much prefer the A tranny. I also have a B 3.9 diff. which gives me decent rpm's at highway speed. It will be intereting to see how they all feel together.
Kris Sorensen

Kris,

Which type of flywheel and clutch are you going to use?

Mick
Mick Anderson

I should have mentioned I have a 3.9 as well. I forget sometimes that anyone uses anything else. Other than originality I see no reason not to use higher rear end gearing.
Steve Simmons

Mike
I will be using the B flywheel and clutch but will be reusing the A pressure plate.
Kris
Kris Sorensen

David Dubois,

I will be installing a 3 main 1800 with an MGB 3 sync OD in my coupe, I don't really follow what you are saying about swapping the main shaft, keeping the MGA tranny and bolting on the MGB OD. What does this offer over the MGB 3 sync with OD? Thanks!!
David Terhune

Kris,

Sorry, I don't understand what you mean.
You say that you are using the MGB clutch, which is a diaphragm spring type, with the MGA pressure plate. I can't see how that is possible.
Do you mean the MGB clutch with the MGA 10 spline friction disk? Not the MGB 23 spline friction disk. That would make sense.
If you are using the MGB flywheel and clutch have you fitted to the MGA gearbox a front gearbox cover and clutch operating lever from a early MGB?

Mick
Mick Anderson

David Terhune - You may be able to swap the 3 syncro O/D transmission directly into the MGA. I was speaking from experience with a Magnette, which wuse a MGA transmission, but it has the clutch slave cylinder on the top of the bell housing rather than on the side as it is on the MGB transmission. I suspect that even there I could have made a straight swap if I had been willing to put in the extra plumbing for the hydraulic line to the slave cylinder. Basically, from the front of the tail piece forward the MGA and the 3 syncro MGB transmissions are the same. Cheers - Dave
David DuBois

Mick
Sorry that is what I meant. A friend of mine who has been working on MGA's for ever will be giving me a hand. Huge learning curve on my part so I apologize if I make the odd error but I am getting there. Thank goodness for this site and all the more experienced people there to help us rookies out.
Kris
Kris Sorensen

David D,

Thanks for the info.....
David Terhune

Kris,

I am interested in the second part of my question, are you going to use an early MGB gearbox front cover plate and clutch operating lever?
Just a hint, fit the MGA gearbox to the engine and turn it over a few turns before putting it in the car. This is to check that the MGB diaphragm clutch does not touch the MGA bellhousing. Not a big problem, just grind off some metal from the bellhousing.
Also, the MGB clutch operating lever can be difficult to fit through the opening in the MGA bellhousing, again just grind a bit of metal off the bellhousing.

Mick
Mick Anderson

Mick
Thanks for the advise. I know he mentioned getting the proper clutch fork which we have 2 on hold for us untill we decide which one we need. Nothing was mentioned about the front cover. I will bring this to his attention, maybe he already has one for me. We won't be removing the tranny so we will have to sort that one out before installing the new engine.
Kris
Kris Sorensen

This thread was discussed between 03/12/2004 and 05/12/2004

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