This post almost got to 10 years old without a reply. Lol

12G938 was stamped on the standard valve size 12G940 head to indicate it was for fitment on a 1275cc sprite with double valve springs. This staming was carried out after build to make sure it only went on the vehicle it was intended for.  True fact from Keith Dodd

Going with a 1380 for a few reasons, but I've driven one numerous times, had some parts already, other parts are easier to get and sometimes cheaper than other bores. Plus the knowledge on them is a bit more in depth than some other sizes. I'mve decided that 1380 is right for me. It's not going to be a monster. It's a Kent 266 cam and probably going with larger valves. Nothing too out of the ordinary. 

 

And I appreciate your comment on the heads. I understand that some work needs to be put into it. I'm just wondering if I've got a good head sitting in my lap that I'm gonna get rid of for a lesser head that's "already built". I mean, if it costs $200 more to build the 12G938, but I have a substantially better end product, I'd rather go that route. Does that make sense? Now, if we;re talking $500 difference to rebuild as opposed to buying a very similar in performance "new" head, I'd go the alternative route. 

 

I'm not overly picky on the head. I just want the best end product I can get within a reasonable budget. 

Not to confuse things but there is more to cyl heads than meets the eye. When building a race engine some years back I purchased 17 cyl heads. There is at least 5 things to look for when selecting a good head for porting. The head porter picked two and later rejected one of those. I rebuilt and sold the balance as street heads. I think if you do a little checking you will find rebuilding a stock head will cost around $500. When you figure the price of a valve job, resurface to true or remove more to adjust compression, install valve guides, install over size intakes and hardened exhaust seats, new valves and springs you are there. I'd suggest you buy a already ported head from a pro. The head and cam is where you will find the power. Why 1380?  Steve (CTR)

Hmm... well is there a "better" head out there? I know a lot of people like the aluminum heads, but I'm still liking the idea of a 5 port, and warping is always a concern on the aluminum heads.

Would you say there is a better head for a 1380? Without getting into the $1000 price range obviously. 

They (and any 940 casting) are less likely to crack than the early S heade eg AEG163. Because there is more metal between the valves and less localized hot spots there.
This is why the 12G1805 head (same 940 casting as I said above) was used on the last Mk2, and also Mk3 Cooper S.

I'm running a race prepped 12G938 (with Mk1 S sized valves in) on my 1360, and it ain't cracked yet.

Thanks for the info, Kevin.

 

So is there any truth to a "different casting" or "competition use"?  What does one of these things usually sell for? I'm trying to decide if I should sell it or keep it for the 1380.

A 12G938 is a `70s head that was used on all base model 1275 motors. It is a 12G940 casting (this is cast on top between the rocker posts).
(Main difference between it and the 12G1805 Cooper S head was the inlet valve size, the S got 1.406" ones and the 12G938 got 1.3").
These numbers were stamped in 1/8 letters near the thermostat housing, but not all 12G938s got stamped.

This common head got superseded in the 70s by the `smog' air injection head 12G1316 used on the A/A, also on Mini 1275LS in Australia.

So I have a 12G940 and a 12G938 head. Both are useable and I've been thinking about using the 12G938 on the 1380 im building. But I'm still not totally decided on whether or not I will go with a different head all together.

 

I just want to know what the REAL deal with the 12G938. I've heard that is was a special casting... and then that it's just a normal casting that had bigger valves fitted. I've read everything on it, but no one really seems to have the difinitive truth and maybe if someone has used one.

 

And if anyone is really interested in it, I could be motivated to sell it.