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What does the 12G casting mark on the block mean?

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BrianN

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Regarding the blue Bugeye we just boutht:

The serial number is missing on the top of the block and I am trying to figure out what motor this is. The side of the block has a large 12G cast into it. Does anyone know what this might indicate?

The car is an AN5 (bugeye), but the PO said the motor is a 1098. The car also has a rib case transmission with DC300 or DO300 stamped on the top of the front of the bell housing. Also disc brakes are fitted at the front. All from a donor car of some later era.

Any help is appreciated.

Thanks in advance.
 
I think (but don't know for sure) that the 12G just defines something about the mold/forms used for the casting. The MUCH later A-series cylinder heads for MG Metros were 12G940. I'm not sure a number as short as "12G" will help identify it.
 
Brian, does it have tappet covers on it, or is it a smooth sided block? If it doesn't have covers, it's a 1275.
There may be a plate attached to the lower left side of the block with 1100 stamped on it, indicating a 1098. However, there are 2 different 1098's, a big crank version, with 2" main bearing journals, and the more common small crank, with 1.750" mains. Short of tearing it down and measuring things, I don't know of any way to differentiate between the two if the ID tag is missing.
Jeff
 
Re: What does the 12G casting mark on the block me

This has tappet covers. And a bunch of other small numbers. But no 1100 that I can find. All the tags are off. Only the cast numbers remain.

BTW, it runns REALLY sweet! Even at freeway speed! The tach is indicating 5000 rpm at 65 mph indicated. Is that OK? Sounds right at home doing this. Can I drive all day like that? Are these motors really built to take it?
 
Re: What does the 12G casting mark on the block me

BrianN,

Either your tach or speedo is off. 5K should put you around 75 mph+/-. Most likely the speedo.
 
Re: What does the 12G casting mark on the block me

You can always hook up a tune-up tachometer set to high range and do a quick comparison to the tach in your car to see which is right. Alternatively, drive through a measured mile or two while a passenger keeps track of the time with a stopwatch while you hold the speed steady.

I'm not sure which early A-series block had the tappet covers. For the record, early transverse 1275s do have the covers... don't know about inline units.

Out of curiosity, which inline cars originally ran a 1098 A-series? I'm more familiar with thinking of these engines being transverse and coming from MG-1100s.
 
Re: What does the 12G casting mark on the block me

Spridgets had 1098s, so did Morris Minor 1000s.
 
Re: What does the 12G casting mark on the block me

Thanks for that. Seems odd that they'd put a 1098 in a car named Minor 1000. I always assumed something with "1000" in the name had a 998. Live and learn.
 
Re: What does the 12G casting mark on the block me

My Minor 1000 had a 948 in it, with a single carb. Of course, it was a 1960, so 1098's weren't around yet.
The Spridgets used the small crank 1098 in '63-'64, and the big crank in '65-'66.
Jeff
 
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