oversize MGA 1500cc engine

[barrybike]

does anyone know if you can rebore a 1500 cc engine to take 1600 or 1622cc pistons ??? any help received

[Robert060379]

This may sound daft but talk to Shaun at BigCC Racing. They're bike guys but can bore anything.

[99hjhm]

Waste of time though.... get a 1622 block or engine.... 1500 heads are also rubbish.

Even beter get a 1800 MGB engine.... http://mgaguru.com/mgtech/power/pp201.htm

[Lagerlout]

The 1600's are lovely engines, much prefer them to the B engines. However, they have a fatal flaw and thats the 3 brg crank which is prone to cracking. I've been through 3 in my 1600 Mk1 but now have a steel crank. The 1600 is a lovely revvy engine, can't say the same about the 1800 B Series.

[99hjhm]

Lagerlout said:

The 1600's are lovely engines, much prefer them to the B engines. However, they have a fatal flaw and thats the 3 brg crank which is prone to cracking. I've been through 3 in my 1600 Mk1 but now have a steel crank. The 1600 is a lovely revvy engine, can't say the same about the 1800 B Series.

Never seen this problem, even in race engines... the cranks are all forged steel, not cast iron. Same revvy engine.... They use the same cam, just a smaller bore I guess.

[Lagerlout]

Well, I've personally seen over 20 cars do this, always go on no.3 big end journal and normally whilst under full load ie going up a hill at speed! I don't know if it was a batch issue (1960/61) but it's a well known problem on the cars down under (Australia). Australian cars were CKD so maybe the cranks were sourced locally but I don't think so. By steel crank, I meant aftermarket ie new not 40 yrs old. I've personally had about 10 MGA cranks magnafluxed over the years and just about all of them have some sort of issue and most have ended up in the bin half of which have never been machined. It's pretty well known that the 3brg MGB engine also had a weakness in this area hence the 5brg (amongst other reasons).

[wadgebeast]

Cheapest way might be to drop in an 1800 from the B (watch for cooling issues) and then rebuild your 1500 slow time to desired spec.

[gtr-gaz]

What do you make of this?

Seems a little harsh to me.

http://www.time.com/time/specials/2007/article/0,2...

[MG Mark]

Rather harsh - the Twin Cam was developed to go racing and required 5* fuel and an optimum state of tune for the timing and mixture to avoid burning holes in pistons. They were fine when they were set up on delivery from the factory, but for the first service and beyond it was beyond most normal service garages, that combined with using chromed piston rings which wore quickly and reduced compression. Once the problem was known, the engine was modified to rum with normal rings and a lower compression ratio (9.9:1 dropped to 8.3:1) but it was too late and the reputation had been established (a bit like MGC handling!).

As to the bore sizes of the 1487, 1588 or 1622cc engines in the MGA and the 1798 MBG engine:
MGA (1500) 73.025 mm
MGA Mk I (1588) 75.41 mm
MGA Mk II (1622) 76.2 mm
MGB Bore x Stroke - 80.30 mm
Stroke was the same at 89mm

Useful stuff here:
http://www.mgaguru.com/mgtech/engine/ch100.htm
and here
http://www.mgcars.de/seiten/mgaengine.html

My MGA Mk II coupe has its original 1622 engine (blueprinted and ported to about Stage 2, with a tubular manifold) mated up to an early MGB overdrive gearbox fitted with a close ratio gear set. The MGA engines rev more freely due to less low/mid range torque than a B, but this one pushes out more power, and the gears make sure there is no huge gap between 2nd and 3rd....flies well and cruises at 85mph at 3500rpm...

Oh and the cooling system - forget electric fans - fit a decent racing water pump with a proper curved bladed impeller, rather than the standard pump with a plastic stirring paddle, and your cooling woes disappear, as the engine and radiator get the flow around them to actually cool the coolant. Plus, make sure the gap between the bonnet and the radiator is sealed off with foam to prevent air recirculation and you have cool running.....

MG Mark

[99hjhm]

Lagerlout said:

Well, I've personally seen over 20 cars do this, always go on no.3 big end journal and normally whilst under full load ie going up a hill at speed! I don't know if it was a batch issue (1960/61) but it's a well known problem on the cars down under (Australia). Australian cars were CKD so maybe the cranks were sourced locally but I don't think so. By steel crank, I meant aftermarket ie new not 40 yrs old. I've personally had about 10 MGA cranks magnafluxed over the years and just about all of them have some sort of issue and most have ended up in the bin half of which have never been machined. It's pretty well known that the 3brg MGB engine also had a weakness in this area hence the 5brg (amongst other reasons).

What crank do you now have?? 5 main billet in a 3 main block??

[99hjhm]

I asked somebody who knows about MGA's..... His anwser was...

"Back to the question - yes, you can bore a 1500 to 1622. Yes, you can put 1622 rods in a 1500 block. 1500 heads are fine if you know what you're doing - much less fragile than a late (smog-type) MGB head. In a racecar, the 1500's small exhaust ports are really a benefit. But you frequently can't port a 1500 head for racing without hitting water. Basil"