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 Posted: Nov 16, 2017 12:59PM
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I recently used a 12G940 1275 gasket on a 998, bored to 68mm. Head is a ported 12G202.
From memory I had to plug 1 water hole and move 2 others, to suit the gasket.

Kevin G

1360 power- Morris 1300 auto block, S crank & rods, Russell Engineering RE282 sprint cam, over 125HP at crank, 86.6HP at the wheels @7000+.

 Posted: Nov 13, 2017 01:54PM
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I used to have photos hosted that compared a 12G940 (small valves) and a 12G295. The exhaust ports on the 12G295 were larger but the intake ports were the same size. Made me think of trying to use a 12G295 on a 1275 to lower compression for forced induction. I think deciding which head gasket to use is what kept me from trying.

When I was comparing different head gaskets while using a 12g940 on a 998 block and putting a small bore head gasket against a 12g940, I noticed that with very little adjustments in the fire rings that perhaps a single gasket could be designed that would work for standard bore 1275 and all 998.  But the water jackets are different sizes and is one of the concerns when using a 1275 gasket on a 998 block.

 Posted: Nov 10, 2017 02:46AM
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GB
A small bore head on a large bore block is not just uncommon, it's downright daft...

Tiny valves and a rubbish compression ratio as the smaller heads generally have bigger chambers - are you totally sure it's a 1275 block and a 202 head ?

 Posted: Nov 9, 2017 07:39PM
mur
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You know it has good compression?

 Posted: Nov 9, 2017 07:14PM
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CA
Quote:
Originally Posted by mur
If you remove the head, you might notice that the head gasket only matches the block and not the head, or vice versa. If everything matches, then you have something very uncommon.
So if I have something very uncommon will I be able to buy a replacement the head gasket? It has good compression so I might be opening a can o' worms??

 

Cool

 Posted: Nov 9, 2017 06:16AM
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US
What angle does the heater valve set at? Does it have hair pins on the valve keepers? Steve (CTR)

 Posted: Nov 8, 2017 03:40PM
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America heads had smog ports, you can tetll that without pulling the head.  You sure this isn't an MG 1100 SportSedan?  That had .the 1098.

 Posted: Nov 8, 2017 09:48AM
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CA
...it'll probably be a week or two but I'll report back..

Ron

 

Cool

 Posted: Nov 8, 2017 08:54AM
mur
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If you remove the head, you might notice that the head gasket only matches the block and not the head, or vice versa. If everything matches, then you have something very uncommon.

 Posted: Nov 7, 2017 09:43PM
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US
small bore heads are cut like hearts.

 Posted: Nov 7, 2017 08:50PM
mur
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Remove the head and determine if it is in fact a small bore 12G202. There were some anomalies at the very start of large bore mini engine production, but a quick google search did not help me find the correct links. It has been discussed here in the past, though not for years. A few minutes of work will either tell you that this is a small bore head simply stuck on a large bore engine by mistake, or if it is one of those anomalies.

 Posted: Nov 7, 2017 07:40PM
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CA
So I picked up a batch of Mini parts that included an AA 1275. The engine and casting number says 1275 but the head is a 12G202. Anyone know if there might be a good reason someone might do this? It probably would increase the compression but wouldn't breathing suffer?

Ron

 

Cool