MGA MGB engine in an MGA

[Monark192]

How well does it fit? How about the transmission? Any major surgery required that couldn't be undone? Is it a bad idea? Just wondering out loud......

 

[Steve_S]

It depends on which MGB engine you'r talking about. If you can find an early 3-main 1800 from a '62-'64 MGB, it will be a direct bolt-in. The block is essentially a bored out 1622 MGA unit. Later MGB engines also basically bolt in but there will be some slight modifications necessary.

The 3-main 1800 will also allow the use of your current tachometer, as it has a mechanical drive on the block just like the MGA engine does. Later MGBs have electronic tachs so you would need to change that out.

I have an early 1800 in my MGA. I have retained the MGA carburetors, air filters, intake and exhaust manifolds, generator, etc. Only the block and head are MGB and unless you really know what you're looking for you will never be able to tell the difference. I also have the stock MGA transmission in the car.

 

[Hap Waldrop]

The MGB engine I'm building now has been in a MGA for like 20 years, it's already been rebuilt once when originally installed. Now I can't tell you much about the fit of the MGB engine in the MGA, other than it must not be that big of a deal, lots of folks have done and are doing this. The engine I'm rebuilding for the MGA is a 18GB 5 main with the MGA backing plate and a pre-1968 MGB flywheel, no tach on the back of the cam, so I'm assuming they have switch tachs.

 

[Hap Waldrop]

The MGB engine I'm building now has been in a MGA for like 20 years, it's already been rebuilt once when originally installed. Now I can't tell you much about the fit of the MGB engine in the MGA (this engine was shipped to me from a shop in Florida), other than it must not be that big of a deal, lots of folks have done and are doing this. The engine I'm rebuilding for the MGA is a 18GB 5 main with the MGA backing plate and a pre-1968 MGB flywheel, no tach on the back of the cam, so I'm assuming they have switch tachs.
Hope this helps.

 

[MGADerek]

You'll find good info here:-

https://www.mgbmga.com/tech/index.html

 

[Billm]

To use a 5-main MGB engine in the A you will need that special "conversion" pilot bushing since the input shaft from the trans is small on the 3-main engines but much bigger on the 5-main engines. The bushing is avail from VB or Moss (can't remember which)
Bill

 

[1965_MGB]

I had to install one of the conversion pilot bushings in my B. The Moss part number is 330-570, and runs about $25.00.

 

[Monark192]

Will the MGB trans fit as well? I have a complete running 1974.5 mgb engine and trans vs. nothing for the 'A.

 

[Steve_S]

MGA transmissions are pretty cheap and easy to find. It would be easier to fit this than the later, larger unit. It has a nice vintage "mechanical" feel to it also which the MGB unit will not have.