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PostPosted: Thu Oct 15, 2009 9:23 pm 
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drmini in aust wrote:
295 was a great head, but unless you run flat top pistons the C/R is too low because of their stupid big chambers. And if you go ripping .100" or more off, they tend to blow gaskets. .060" or so off is fine.

12G940 (and 12G1316) are the same total thickness as a 202, 295, 1456, etc.
But you can take more off without weakening them, as their deck is lots thicker than a smallbore head.
Chambers smaller too.8)


Thanks doc,

I knew someone would be brave enough to answer that little question... So I understand and knew what you wrote...

But by some chance do you know how to actually measure the meat between the gasket face and the oil galley / water jacket? I have a very accurate method for the small bore heads but with the 940's, I feel like measuring the overal thickness is only a little better than guessing because you don't know how much (if any) has been taken off the top face,, you know what I'm getting at?


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PostPosted: Thu Oct 15, 2009 9:27 pm 
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The oil gallery is a different setup to the smallbores, you can take lots off without any chance of hitting it.
No need to poke a vernier down the oil hole..

My 1360's 940 head has had about .100" off, you can take lots more.
Probably 4mm (.160")

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R. :mrgreen:


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PostPosted: Thu Oct 15, 2009 9:43 pm 
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drmini in aust wrote:
The oil gallery is a different setup to the smallbores, you can take lots off without any chance of hitting it.
No need to poke a vernier down the oil hole..

My 1360's 940 head has had about .100" off, you can take lots more.
Probably 4mm (.160")


:shock: holly crap doc... you serious? I mean I'm only guessing otherwise I wouldn't have asked... :)

But I tried the same method you described with the vernier cos thats what I do on small bore heads,,, and your right it look like I had about 4-5mm and I thought to myself,,,

""self,,, I don't think this works on this type of head,,, surely you take that much off you won't have much of a combustion chamber left"

But are you saying thats right? that you can use the same method? Just obviously not to a point where you loose your chambers?

Sorry mate I just want to be sure that I'm not misunderstanding what you wrote, if it is what it is then who am I to question right? :D


EDIT: Geeeess I'm thick some times sorry doc... I miss read what you said,,, you said don't bother with the vernier :roll:


Last edited by Phat Kat on Thu Oct 15, 2009 9:49 pm, edited 1 time in total.

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PostPosted: Thu Oct 15, 2009 9:48 pm 
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On all bigbore heads the oilway runs up the front and across the top of the head, not the bottom.
Look at front of head, you will see a small alloy plug near the top.

Oilway is nowhere near the chambers.

<edit> front meaning fan end.

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PostPosted: Thu Oct 15, 2009 9:52 pm 
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drmini in aust wrote:
On all bigbore heads the oilway runs up the front and across the top of the head, not the bottom.
Look at front of head, you will see a small alloy plug near the top.

Oilway is nowhere near the chambers.

<edit> front meaning fan end.


Great doc,

Thats all I wanted to know :D It just seemed odd, but that makes sense.. Thanks again :D :D 8)


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PostPosted: Fri Oct 16, 2009 6:37 pm 
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drmini in aust wrote:
My 1360's 940 head has had about .100" off, you can take lots more.
Probably 4mm (.160")


I'd suggest to be a bit careful here. The decks on the Turbo Heads are much thinner and they are not quickly identifiably different from the 'normal' 12G940 Heads. Same casting Number (12G940) and fairly similar from external appearances. Usually Identifiable from the exhaust valve guides (Turbo has larger ID), unless they have been changed out for standard ones. Another way is to (try) to neasure through the cooling jacket holes.


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PostPosted: Fri Oct 16, 2009 6:44 pm 
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GT mowog wrote:
drmini in aust wrote:
My 1360's 940 head has had about .100" off, you can take lots more.
Probably 4mm (.160")


I'd suggest to be a bit careful here. The decks on the Turbo Heads are much thinner and they are not quickly identifiably different from the 'normal' 12G940 Heads. Same casting Number (12G940) and fairly similar from external appearances. Usually Identifiable from the exhaust valve guides (Turbo has larger ID), unless they have been changed out for standard ones. Another way is to (try) to neasure through the cooling jacket holes.


Hey GT mowog,

Just a quick question regarding the above,, Is it only the exhaust valve guide that is different? Is it larger because of the sodium valves or something? I've got a few heads kicking big bore heads kicking around from a few different era's of 1275 and I think one of them might be a turbo head. Is there any other way of telling? Do you know how much thinner they are?

Thanks


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PostPosted: Fri Oct 16, 2009 6:46 pm 
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I was really talking about the common 12G940 used here (Morris 1100S, Cooper S, 1275 Midget) and the smog 12G1316 (1275LS etc).
These will all stand having a lot off unless corroded bad inside.

I am aware the later heads are less thick, but there are hardly any over here really.

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PostPosted: Fri Oct 16, 2009 7:01 pm 
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Phat Kat wrote:

Hey GT mowog,

Just a quick question regarding the above,, Is it only the exhaust valve guide that is different? Is it larger because of the sodium valves or something? I've got a few heads kicking big bore heads kicking around from a few different era's of 1275 and I think one of them might be a turbo head. Is there any other way of telling? Do you know how much thinner they are?

Thanks


Yeah, they had sodium filled valve stems as so need to be a bigger diameter. There are a couple of of ways to pick the turbo head from the non-turbo heads, but off hand I can't remember. I'll dig one out over the weekend and come back to you.

Hey, Doc, are all latter heads thinner or just the Turbo ones (I though it only to be the Turbo ones) ?


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PostPosted: Fri Oct 16, 2009 8:30 pm 
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MG Metro turbo head also has smaller inlet valves than the MG Metro one(1.312" not 1.401").

Somebody once told me all the later heads are less meaty in the deck than our antique 12G940 and 12G1316. Can't recall who.

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PostPosted: Fri Oct 16, 2009 8:36 pm 
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Thanks Doc.


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PostPosted: Fri Nov 06, 2009 10:01 pm 
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drmini in aust wrote:
I was really talking about the common 12G940 used here (Morris 1100S, Cooper S, 1275 Midget) and the smog 12G1316 (1275LS etc).
These will all stand having a lot off unless corroded bad inside.

I am aware the later heads are less thick, but there are hardly any over here really.



Hi Doc :) ,,

I had a couple heads out the other day picking out one for a bit of work (remember the one full of spiders :lol: ).

I started putting them away and I remember this thread and thought I'd take some photos for you.

Image

This picture shows an MG metro head..

Image

this pic shows a late model injection head
Image

this one shows an old school 12g940

Image

and this one shows an MG metro turbo head.

Image

I took photos of these ones cos I remembered that we weren't sure about deck thickness between early and late makes... I couldn't get a good photo with the verniers but you can get an idea from the photos. There wasn't much between them,, bout 0.010-0.020" and none of them had much taken off by the looks of it.

Just thought you might be interested :)

I don't rearly know how old any of these heads are though,, thats the only thing,, I'm guessing the Injection head can't be toooo old though,,,


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