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MG MGA - Large bore MGA

Can the 1600 MGA engine be bored out to 1800cc by fitting MGB pistons? Or would it be better to fit a B engine? Or a 1950cc B engine , now that would be fun.
R Mcknight

I don't know the answer re boring out, but there are plenty of 1800s already out there and engineered for that additional capacity.

If you go the MGB/1800 route you will need to ask yourself some questions: Either to go for the 3-bearing earlier engine with the same MGA mechanical tachometer off-take or the later smoother running 5-bearing with the electronic tachometer. Also, the 3-bearing and early 5-bearing uses the same MGA front plate with the MGA engine bearer drillings whereas the rubber bumper 5-bearing engine has a different front plate for the round engine bearers and so would need to be swapped. I guess there are other considerations but that is for starters.

Steve
Steve Gyles

You will also need to change the backing plate and the flywheel if using the later B engine with the MGA traney. The answer really is to use one of Hi-Gear's 5- speed boxes and have them fit it to the engine you're using.
David Werblow

I tried to bore out a 1600 to 60 thou oversize (because of wear & tear) and found a mark on the bore.I got it sleeved back to original spec. Bob
B Walker

Here is an extract from my build document on how to create a 1924cc twin cam engine, which may have some relevance here:

Block Selection:
Essentially any MGB block can be used either 3 bearing or 5 bearing all the way up to the latest 18v engines.
MGB engines between 1971 and 1972 had a steel crankshaft, this is note worthy if you don’t intend to fabricate a complete crankshaft and only want to press onto the crank an extension piece. Thus if the extension piece is made of steel you must also use a steel crank and not a cast iron one.
Certain engineering companies that have produced many large bore MGB engines have indicated that blocks cast at Longbridge as indicated by an “AF” or “AF3” code will typically bore to 83.5mm without problems. Blocks cast by West Yorkshire Foundries (Part of BMC) as indicated by a “WF” code may sometimes experience problems if bored this large. The code is cast into the block just below the MGB dipstick as shown below:

Ignore the twin cam - crank extension references.

Same would apply to MGA -> 1800 cc I would think. 1600 blocks "maybe" OK but 1500 blocks from memory have different internal water way casting.

Barney’s site may have something on this.

Mark
Mark Hester

You don't want the 1489 or 1588 engines as the crankshafts are weak. The 1622 engines are rare but can be taken out to near MGB size. The factory created overbore Twin Cam engines (1588 bore but better cranks) that were 1762 cc for racing.

Best advice is to buy a 3 main MGB engine and go from there.
Bill Spohn

I have installed a 67 B five main bearing engine in one of my A's. I did this by changing the tail shaft on the transmission. The tail shafts are interchangable on the late 1600 MGA's and the 3 syncro transmissions in the 63 to 67 B transmissions. This seemed to be the easyest change over. It seems to work fine and I did not have to weld anything on the frame.
GK George

This thread was discussed between 09/07/2012 and 19/07/2012

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This thread is from the archive. The Live MG MGA BBS is active now.