14 replies to this topic

[Yams]

Purchased a 1275 engine, according to the seller its running but i'm going to strip it down and replace/refurb any parts that need doing.

 

The head is a 22g940, the block is stamped 12g1279. So i have a few questions concerning this:

 

Why would it have an 11 stud head fitted? Does it give a performance upgrade? Could it be a sign that the cylinders in the block are bored, thus giving a higher compression rate? Why were these heads made, where they stock on some engines?

 

When I start stripping it down what are signs to look for? What generally should i replace, and what is worth upgrading?

 

Many thanks

 

 

[spaulwill]

these were fitted to to cooper s models this is a different bolt to the standard head bolt. I beleive it was put in to save the head gaskets on the higher performance S engine.

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[JustSteve]

Those numbers are just standard 1275 numbers (i assumer you mean 12g940 by the way)

I think the only engine's ever originally fitted with 11 studs were the cooper 's' engines and I think some innocenti's? 


Either way, the 11 studs are only a 'just in case'. Many high powered a-series engine's have ran fine with the standard 9 studs, including the metro turbo. 


 

[JustSteve]

Probably 1300GT engine

[Yams]

Probably 1300GT engine

 

What do you mean by a 1300GT engine? I am assuming it means it has a slightly larger bore and is ripped from an austin GT? The car is was in before it was sold was a 1966 morris cooper s, but the chap restores old cars to their 'original' spec. So i know the engine isn't 50 years old. Another problem is the engine number (embossed plate riveted on) is slightly broken, so i'm missing a few characters off it. Could someone still find the spec of the engine without all of the numbers?

Edited by Yams, 07 September 2013 - 10:23 PM.

[tiger99]

Try posting the numbers you have on the plate to see if the experts on engine numbering here can make anything of it.

 

The 1300GT engine has the same bore and stroke as all other 1275 A/A+ series engines. The S should always have 11 head bolts/studs but removable tappet covers, the 1275GT (long-nosed Clubman type) has 9 bolts but a solid back on the block, no tappet covers, so possibly stronger, and later 1275 Minis were basically using A+ blocks, the best. The 1300GT would have been made well before the A+ era, and I would expect it to have the solid block, like the 1275GT Mini.

 

These days every Mini has lots of history, parts were often swapped to keep cars running when they were of little value, and as I know from my own experience, engine reconditioners often got blocks mixed up, so you could have any type of 1275 engine. Oh, and the factory sometimes fitted whatever they had in times of shortage, so possibly some 1275GTs would have had S blocks from new. After all, they fit, and work, so why not?

 

A 9 stud block can fairly easily be drilled and tapped for 11, and this used to be a very common mod. It does increase head gasket reliability on a tuned engine, and was usually done when fitting the superior head from an S.

[Yams]

Thanks for the info :) my block does have a solid back, it doesnt have the back plates. ill get as much as i can off the engine number and post it to see if anyone could help :) thanks very much guys

Edited by Yams, 07 September 2013 - 11:46 PM.

[darkrider]

South African GTS engines had 11 stud heads as well

[nicklouse]

South African GTS engines had 11 stud heads as well

Holy thread resurrection.

[Cooperman]

So did the Innocenti 1300 Cooper Export.

When the original Cooper 'S' was introduced in 1963 it was anticipated that in competition very high compression ratios would be used with 101 RON leaded petrol. The 11-stud configuration, well, 10 studs plus one bolt actually, was to allow for the gaskets of the time to still give some reliability. 

For a car running over about 11:1 CR these days it is a good idea to have the 11-stud format, even with the BK450 (TAM1521) head gasket.

[darkrider]

Well basically our GTS engines were Cooper S engines.Think about it, They took a 1275GT and modified it to Cooper specifications and called it the GT "S". Oh and they redesigned the block to strengthen it over the journals. They also put the oil filter high up like your MPI engines.

Edited by darkrider, 21 April 2020 - 09:31 PM.

[Magneto]

So did Innocenti's, at least the 1300 Exports did. 

 

One difference tho, on the Cooper S and the other factory 11 bolt/stud heads, the one on the thermostat end is a 5/16 bolt instead of a 3/8" stud. I think all the 11 stud engines are done on 9 stud blocks.

 

Edit: Cooperman beat me to it.

Edited by Magneto, 21 April 2020 - 09:29 PM.

[nicklouse]

Don’t forget the bolt had 300 stamped on the top.

[Bobbins]

Why a bolt and not an 11th stud?

[Spider]

Why a bolt and not an 11th stud?

 

Where the Bolt is fitted is just behind the Water Pump and often these go in to the cooling jacket. Because of it's location, there's little meat around and so has far less strength in the deck than all elsewhere in the deck and around the other studs. The Bolt, which only has a 5/16" UNC Thread, has a torquing up value of considerably less than the studs to prevent distortion of the block here. I think in the factory's wisdom, they fitted this bolt here of the design it is so mechanics wouldn't slip in to auto-pilot, pulling that part of the deck up through the stud hole in the head. The Torque figure of 300 in/lb (25 ft/lb) is right on the yield strength of the bolt as a 'safety valve', so that the bolt will break before any serious damage is done.

 

It is a popular modification to fit a stud here, matching the others in the head. That's fine as long as the overall clamping force used (and exerted in to the deck) is the same as that when the original bolt is used. Given that it's a larger diameter and on a finer thread, the torquing figure used here should be less than that that would be used on the bolt.

 

Personally, I don't thing the fitting of these extra 2 studs / bolts is beneficial at all. If you look at the deck of the A Series Engine, there's the 5 studs along the side (front as fitted in a Mini) and then 4 almost across the center. I can see how in design, this was arrived at, as a less (way less) than ideal arrangement, with the push rod holes to dodge around, but in engineering terms, it's far from ideal, as we have more fasteners along an edge, effectively bending the head over that way (especially given there's a soft gasket in between) and the 4 across the center working very hard, trying to pull down a far greater surface area. I feel that by adding the extra stud (and bolt to a lesser degree) only exasperates this problem, given their location closer towards the front of the deck. While the 60's Cooper S and 1300 GT engines had these from the factory, no other performance engine from the factory, including the MG Turbo, was fitted with them.

 

When you have a look at all head gasket failures, probably 50% are between cylinders with the other 50% being towards the 4 studs. I've never seen any towards the front.