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MG MGA - boring out a 1500
This interesting article on Australian built A's sats that the 1500 blocks were simple bored uot to 1622cc and also bored to 3 inch. Is it possible to do this safely ? Sean
|You may have trouble with the link above if so try|
then click on "The MG Marque" and go to History.
|Australian built MGA had the same engines as the rest of the world. CKD roadsters were shipped with engines, apparently in pieces to be assembled after arrival. Any Coupe, Twin Cam or Deluxe going to Australia was be shipped as a complete car.|
In Australia they did build a "1620" engine for other applications (not MGA). This was built almost entirely from Australian fabricated parts (maybe not bearings and gaskets). The block had "1620" cast on the side, was cast to accept 3-inch pistons for 1622cc displacement. The lower end used the 1500/1600 type crankshaft, the cylinder head was equal to "15" specifications, and pistons were dished (very much like like 1500/1600 engines with larger bore).
If you are talking about over boring a standard 1500 block, then yes, they can (usually) be successfully bored out to 3.000-inches. That may have been a convenient overbore in Australia, as they had the right dished pistons to do it (1620 engine pistons that fit on 1500/1600 type con-rods).
|At the bottom of the following page are links to a couple of articles with technical details about boring out the 1500 to 1622 or even 1698. http://www.mgbmga.com/tech/index.html|
|The nice thing about the 1489 engines is that, unlike the 1588 and 1622, they are siamesed bores. In other words, there is no water passage in between cylinders 1 and 2 and between 3 and 4. The walls are hefty and you can almost always punch them out to 1622 or more.|
The catch is that they have pretty crappy crankshafts (he says, having raced with them and broken them in half on occasion). The 1622 crank is significantly stronger, but that needn't concern you on a street engine.
|I broke a 1622 crank, but that was due to a head gasket leak which let anti-freeze into the #3 cylinder. I drove 15 miles home with the crankshaft in 2 pieces !|
Question for Bill - how often does an overbore on a B-series engine encounter a water passage or other flaw ? Is this a common thing, or more rare ?
|It depends on how big you take them.|
I limit my over bores to 1950 cc or 83.5 mm. starting with a 1798 cc block. You can sometimes go bigger, but if you have a block with core shift (not unusual) you may end up with thin spots that can break through in use.
You can go to 0.080" over on just about any MG engine without risk.
|"You can go to 0.080" over on just about any MG engine without risk"|
So I could take my 1622 engine to about 1700cc couldn't I Bill? A 5% capacity gain.
On the other hand, I suspect you can gain much more than 5% by other means more cheaply.
Any comments, anyone?
|Yes, you could. There were a few Twin Cams taken out to 1762, but we think they probably had special block castings. You should be able to get out to 1700 without holing a 1622, but custom pistons aren't cheap and as you say, spending the same money on the head might get you better results.|
This thread was discussed between 16/12/2011 and 03/01/2012
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